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Can Galactose be synthesized with photosynthesis?

Can Galactose be synthesized with photosynthesis?


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I know that galactose can be found in sugar beets and some gums so I thought plants could synthesize galactose but in my book the answer to the question "Which of these can be synthesized with photosynthesis in plants" was only fructose and glucose. Is that correct?


Galactose

Galactose ( / ɡ ə ˈ l æ k t oʊ s / , galacto- + -ose, "milk sugar") sometimes abbreviated Gal, is a monosaccharide sugar that is about as sweet as glucose, and about 65% as sweet as sucrose. [2] It is an aldohexose and a C-4 epimer of glucose. [3] A galactose molecule linked with a glucose molecule forms a lactose molecule.

  • 59-23-4 N
  • CHEBI:28061 Y
  • ChEMBL300520 N
  • 388480 Y
  • D04291 N
  • X2RN3Q8DNE Y
InChI=1S/C6H12O6/c7-1-2-3(8)4(9)5(10)6(11)12-2/h2-11H,1H2/t2−,3+,4+,5−,6+/m1/s1 Y Key: WQZGKKKJIJFFOK-PHYPRBDBSA-N Y

Galactan is a polymeric form of galactose found in hemicellulose, and forming the core of the galactans, a class of natural polymeric carbohydrates. [4]


Galactosemia☆

Introduction

Galactose is an energy-providing nutrient and also a necessary basic substrate for the biosynthesis of many macromolecules in the body. Galactose is an important constituent of the complex polysaccharides, which are part of cell glycoconjugates, key elements of immunological determinants, hormones, cell membrane structures, endogenous lectins, and numerous other glycoproteins. In addition, galactose is incorporated into galactolipids, which are important structural elements of the central nervous system.

Metabolic pathways for galactose are important not only for the provision of these macromolecules but also to prevent the accumulation of galactose and galactose metabolites. Problems with galactose metabolism that result in galactosemia can cause a variety of clinical manifestations in humans.


Difference Between Glucose and Galactose

Although the molecular formula of glucose and galactose are identical, they have distinct structural formulas.

Glucose is a simple sugar (monosaccharide) and also termed as blood sugar, grape sugar or corn sugar. It is a vital carbohydrate in biology. It is a premium source of energy for the living cells and also acts as a metabolic intermediate. It is among the chief products extorted from the process of photosynthesis. On the other hand, galactose also comes under the family of monosaccharide and it is a type of sugar that is less sweet in comparison to glucose. It consists of food energy (expressed in calories or joules) and termed as nutritive sweetener.

There are only two stereoisomers actually known as glucose in the category of aldohexose sugars. In these two stereoisomers, only dextrose monohydrate (commonly known as D-glucose) is organically active. In contrast, there is polymer of sugar galactose called galactan. It exists in the body to maintain the supply of galactose. It is stored inside the body in bulk form at a place called hemicellulose. Whenever there will be an additional requirement of galactose than the process of hydrolysis takes place and galactan is eventually converted into galactose.

Coming back to glucose, besides D-glucose there is one more glucose, which is biologically inactive. The inactive form of glucose is termed as L-glucose. It is not possible to metabolize the molecules of L-glucose by the process called glycolysis.

Glucose and galactose are also synthesized by the body. However, the external sources will vary from each other. Glucose can be divided into two types: simple carbohydrate and complex carbohydrate. Simple carbohydrates easily get to digest and their main sources include fruits and their juices, alcoholic beverages, sweets and table sugar. Complex carbohydrates get digested slowly. Their major sources include beans and legumes, whole grains, breads, cereals and nuts.

The major sources of galactose include sugar beets, dairy products and different gums & mucilages. Galactose is also synthesized by the body. It forms a part of glycoproteins and glycolipids in various tissues.

Glucose and galactose can also be differentiated on the basis of their melting point. The standard melting point of galactose is 167°C and the melting point for α-D-glucose is 146 °C and β-D-glucose is 150 °C.


What is the Difference Between Glucose Galactose and Mannose?

Galactose and mannose are epimers of the glucose molecule. The key difference between glucose galactose and mannose is that glucose is a six-carbon structure and galactose is the C4 epimer of glucose whereas mannose is the C2 epimer of glucose. Moreover, glucose is naturally produced through photosynthesis in plants. Galactose is produced through the hydrolysis of lactose that is catalyzed by the lactase enzyme while mannose is produced through the oxidation of mannitol or from glucose through the Lory-de Bruyn-van Ekenstein transformation route.

Below infographic tabulates the differences between glucose galactose and mannose in detail.


Stages of Photosynthesis

The Light Reactions

The light reactions happen in the thylakoid membranes of the chloroplasts of plant cells. The thylakoids have densely packed protein and enzyme clusters known as photosystems. There are two of these systems, which work in conjunction with each other to remove electrons and hydrogens from water and transfer them to the cofactors ADP and NADP + . These photosystems were named in the order of which they were discovered, which is opposite of how electrons flow through them. As seen in the image below, electrons excited by light energy flow first through photosystem II (PSII), and then through photosystem I (PSI) as they create NADPH. ATP is created by the protein ATP synthase, which uses the build-up of hydrogen atoms to drive the addition of phosphate groups to ADP.

The entire system works as follows. A photosystem is comprised of various proteins that surround and connect a series of pigment molecules. Pigments are molecules that absorb various photons, allowing their electrons to become excited. Chlorophyll a is the main pigment used in these systems, and collects the final energy transfer before releasing an electron. Photosystem II starts this process of electrons by using the light energy to split a water molecule, which releases the hydrogen while siphoning off the electrons. The electrons are then passed through plastoquinone, an enzyme complex that releases more hydrogens into the thylakoid space. The electrons then flow through a cytochrome complex and plastocyanin to reach photosystem I. These three complexes form an electron transport chain, much like the one seen in mitochondria. Photosystem I then uses these electrons to drive the reduction of NADP + to NADPH. The additional ATP made during the light reactions comes from ATP synthase, which uses the large gradient of hydrogen molecules to drive the formation of ATP.

The Calvin Cycle

With its electron carriers NADPH and ATP all loaded up with electrons, the plant is now ready to create storable energy. This happens during the Calvin Cycle, which is very similar to the citric acid cycle seen in mitochondria. However, the citric acid cycle creates ATP other electron carriers from 3-carbon molecules, while the Calvin cycle produces these products with the use of NADPH and ATP. The cycle has 3 phases, as seen in the graphic below.


Coupling biology to synthetic nanomaterials for semi-artificial photosynthesis

Biohybrid artificial photosynthesis aims to combine the advantages of biological specificity with a range of synthetic nanomaterials to create innovative semi-synthetic systems for solar-to-chemical conversion. Biological systems utilize highly efficient molecular catalysts for reduction-oxidation reactions. They can operate with minimal overpotentials while selectively channeling reductant energy into specific transformation chemistries and product forming pathways. Nanomaterials can be synthesized to have efficient light-absorption capacity and tuneability of charge separation by manipulation of surface chemistries and bulk compositions. These complementary aspects have been combined in a variety of ways, for example, where biological light-harvesting complexes function as antenna for nanoparticle catalysts or where nanoparticles function as light capture, charge separation components for coupling to chemical conversion by redox enzymes and whole cells. The synthetic diversity that is possible with biohybrids is still being explored. The progress arising from creative approaches is generating new model systems to inspire scale-up technologies and generate understanding of the fundamental mechanisms that control energy conversion at the molecular scale. These efforts are leading to discoveries of essential design principles that can enable the development of scalable artificial photosynthesis systems.

Keywords: Artificial photosynthesis Biohybrid Solar fuels.


Biomolecules Important Extra Questions Very Short Answer Type

Question 1.
What is hydrolysis?
Answer:
During the digestion of carbohydrates, the glycosidic bond between sugar residues is broken by the addition of water and this is called hydrolysis.

Question 2.
Define fatty acid.
Answer:
Fatty acids are organic acids with a hydrocarbon chain ending in a carboxyl group.

Question 3.
What are iso-enzymes?
Answer:
The enzymes possessing slightly different molecular structures but similar in their bio-catalytic action.

Question 4.
Give the names of 2 non-polar organic solvents that are used for lipid extraction from cells.
Answer:
Chloroform, Ether.

Question 5.
Name one monosaccharide sugar that is found in the blood plasma of human beings.
Answer:
Glucose.

Question 6.
What is the function of calcium in the human body?
Answer:
Calcium in bones and teeth provides strength and rigidity to them.

Question 7.
Name the bonds uniting the monosaccharide subunits.
Answer:
Monosaccharide sub-units are joined together by glycoside bonds.

Question 8.
What are lygases?
Answer:
Lygases are the enzymes that join two substrate molecules.

Question 9.
Name the ending group of fatty acids which are organic acids with a hydrocarbon chain.
Answer:
Carboxyl.

Question 10.
Which is the most common form of sugar in fruits?
Answer:
Fructose.

Question 11.
How can we overcome the deficiency of iodine?
Answer:
By using iodized common salt.

Question 12.
Names the important food storage of carbohydrates.
Answer:
Starch and Glycogen.

Question 13.
Define allosteric modulation.
Answer:
It regulates the activity of some enzymes internally.

Question 14.
Mention two functions of the sodium and potassium ions in the body.
Answer:
Functions of the sodium and potassium ions in the body are:

  1. To maintain the volumes of extracellular and intracellular fluids.
  2. Transmission of nerve impulses.

Question 15.
Name the small molecules of the cell.
Answer:
The small molecules of the cell are:

  1. Minerals
  2. Water
  3. Amino acids
  4. Sugars
  5. Lipids
  6. Nucleotides.

Biomolecules Important Extra Questions Short Answer Type

Question 1.
What are monosaccharides? Give few examples.
Answer:
Monosaccharides are the simplest carbohydrates that cannot be hydrolyzed into still smaller carbohydrates. The general formula is Cn H2n On e.g. Ribose, Glucose, Fructose.

Question 2.
What is a disaccharide?
Answer:
A disaccharide is a sugar molecule composed of two monosaccharide sub-units e.g. a molecule of sucrose is formed from a molecule of glucose and a molecule of fructose by dehydration.

Question 3.
Why do fats release more energy than carbohydrates on oxidation?
Answer:
Like carbohydrates, fats are made up of C, H, and O but they contain fewer oxygen molecules than carbohydrates. On oxidation they consume more oxygen releasing more energy.

Question 4.
What is the function of calcium in our body? In what form is calcium deposited in the middle lamella?
Answer:
Calcium is impregnated in bones and teeth. It provides them with strength and rigidity.
Calcium is deposited in the middle lamella in the form of calcium pectate.

Question 5.
Define cellular pool. What are the characteristics of a small molecule in the cellular pool?
Answer:
The collection of various types of molecules in a cell is termed a cellular pool.

The characteristics of small molecules in the cellular pool are

Question 6.
What are lipids or fats? State their characteristic. What are the functions of subcutaneous fat in our body?
Answer:
Fat or lipids are esters of glycerol and fatty acids. They are made up of C, H, and O but include proportionately less oxygen as compared to carbohydrates. They are insoluble in water and soluble in non-polar organic solvents.

Functions of subcutaneous fat are

Question 7.
How are amino acids linked to form a peptide chain?
Answer:
Amino acids are condensed together to form a peptide chain. The bond is formed between the carboxyl group of one amino acid and the amino group of adjacent amino acid. This is called a peptide bond and it is formed by dehydration.

Question 8.
What are phospholipids?
Answer:
Phospholipids are lipids containing phosphate groups e.g. phosphoglyceride. They have a hydrophilic polar head and a hydrophobic non-polar tail.

Question 9.
What are macromolecules? Give examples.
Answer:
Simple molecules assemble and form large and complex molecules called macromolecules e.g. proteins, lipids, nucleic acid, and carbohydrates.

Question 10.
Give two examples of storage polysaccharides.
Answer:
Two advantages of storing carbohydrates in the form of polysaccharides:

  1. Food storage polysaccharides are starch and glycogen. Starch is found in rice, wheat, etc. Glycogen is stored in the liver. During their formation, many molecules of water are removed from monosaccharides.
  2. If necessary, polysaccharides are broken down by enzymes for the release of energy.

Question 11.
What is chitin?
Answer:
Chitin: Chitin is similar to cellulose in many ways except its basic units are not glucose, but a similar molecule that contains nitrogen (N-acetyl glucosamine) and is soft as well as leathery.

Question 12.
Explain how glycosidic bonds are formed?
Answer:
Formation of Glycosidic Bonds: The aldehyde or ketone group of a monosaccharide can react and bind with an alcoholic group of another

Glycosidic bond

organic compound to join the two compounds together. This bond is known as a glycosidic bond. This bond may be hydrolyzed to give the original compounds. Monosaccharides by uniting together through glycosidic bonds give rise to compound carbohydrates.

Question 13.
Describe functions of polysaccharides in living organisms.
Answer:
Food storage polysaccharides: As the name suggests saccharides which perform the function of storing food. Examples are starch, glycogen.

Starch: It is formed as a result of photosynthesis. It is found in large quantities in rice, wheat, cereals, legumes, potato, tapioca, and bananas. It is an energy-giving substance as it stores energy.

Glycogen: It is found in the muscles and liver of mammals and stores energy. There are distinct advantages of storing carbohydrates in the form of polysaccharides

  1. During the formation, many molecules of water get removed and bulk reduced
  2. Polysaccharides are relatively easy to store and get broken down easily by enzymes to release energy.

Structural Polysaccharides: Examples of these are cellulose and chitin. These take part in the formation of the organism.

Cellulose: It is a plant product. It is perhaps the most abundant material found in the living world. If forms cell walls. It is a fibrous polysaccharide that has high tensile strength. Wood and cotton have large quantities of cellulose.

Chitin: Chitin is similar to cellulose in many ways except that its basic unit is not glucose, but a similar molecule that contains nitrogen (N-acetyl glucosamine). Chitin is soft and leathery, it becomes hard when it gets impregnated with calcium carbonate or certain proteins. The insolubility of these polysaccharides in water helps in retaining the particular form it also helps in strengthening the structure of organisms.

Question 14.
What is meant by the tertiary structure of proteins?
Answer:
The tertiary structure of proteins: Many amino acid units form polypeptides. The peptide bonds holding the amino acids together in a particular way constitute the primary structure of the protein. A functional protein contains one or more polypeptide chains.

Through the formation of hydrogen bonds, peptide chains assume a secondary structure. Secondary protein may be in the form of a twisted helix or pleated sheet.

When the individual peptide chains of the secondary structure of the protein are further extensively coiled and folded into sphere-like shapes with the hydrogen bonds between the amino and carboxyl group and various other kinds of bonds cross-linking on-chain to another they form tertiary structure.

The ability of proteins to carry out specific reactions is the result of their primary, secondary, and tertiary structure.

The tertiary structure (myoglobin)

Question 15.
Explain the composition of triglycerides.
Answer:
Fat is esters of fatty acids with glycerol. Each molecule of glycerol can react with 3molecules of fatty acid. On the basis of fatty acids that are attached to the glycerol molecule, the esters are called either mono, di, or triglycerides.

Triglyceride-Tripalmitin

Question 16.
Mention the difference between saturated and unsaturated fat?
Answer:
Differences between saturated and unsaturated fat:

Saturated fat Unsaturated fat
(i) They have higher melting points (i) lower melting points
(ii) Carbon align in the chain (ii) Double or triple banded
(iii) Remain in solid form at 20°c but on heating become liquids (iii) Remain in liquid form at 20°c even in water

Question 17.
Describe the structure of phospholipid. How are they arranged in the cell membrane?
Answer:
Structure of phospholipids: Phospholipids are a class of lipids that serve as the structural component of the cell membrane. Phospholipids have only 2 fatty acids attached to the glycerol while the 3rd glycerol binding site holds a phosphate group. This phosphate is bound to alcohol.

These lipids have both hydrophilic and hydrophobic pans due to a charge on the phosphoric acid/alcohol head of a molecule and lack a charge of the long tail of the molecule (made by fatty acids). When exposed to an aqueous solution the charged heads are attracted to the water phase and the non-polar tails are repelled from the water phase.

Phospholipids
When two layers of polar lipids come together to make a double layer, the outer hydrophilic face of every single layer will orient itself towards the solution, and the hydrophobic part will become immersed in the core of the bilayer.

Water acts as a solvent for polar molecules and the arrangement of phospholipids in the lipid bilayer of membranes is dependent on water.

Question 18.
Write short notes on
(i) Steroids
Answer:
Steroids: Steroids are complex compounds mostly found in animal hormones and cell membranes. The best example of steroids is cholesterol. The cell membrane of fungi contains ergosterol. The prostaglandins are fatty acid derivatives. They occur in minute amounts and function in blood clotting, smooth muscle contraction, and allergic reactions, etc.

(ii) Wax.
Answer:
Wax: Waxes are lipids. They are esters formed by the combination of a saturated long-chain fatty acid with long-chain alcohol. They play an important role in protection as tires form a water-proof covering over the root hairs and parts of the body in some organisms. Wax is soft and pliable. The paraffin is hard when cold. Fruits, feathers, leaves, the skin of man, and the exoskeleton of insects are waterproofed by the coating of wax. The bacteria causing TB and leprosy produce wax (Wax D.).

Question 19.
Describe the structure and function of ATP.
Answer:
ATP: It is a primary and universal carrier of chemical energy in the cell. Living cells capture, store and transport energy in a chemical form, largely as ATP and it is the ATP that is the carrier and intermediate source of chemical energy to those reactions in the cell which do not occur simultaneously.

These reactions can take place only if the chemical energy is released. It was Fritze Lipmann in 1941 who postulated this unifying concept and proposed the ATP cycle as given in the figure below.

Adenosine triphosphate

Question 20.
How are amino acids bonded together? Describe how these bonds are formed?
Answer:
Proteins are also formed from amino acids but they have small peptides. The two amino acids are linked by the formation of a peptide bond. Successive amino acids can be linked by peptide bonds to form a linear chain of many amino acids.

When a few amino acids are joined together, the molecule is called a peptide. Proteins are macromolecules formed from a large number of amino acids.

Peptide band

Question 21.
Draw the structure of amino acid.

(A) Acidic amino acid
Answer:
Amino acids: These are small molecules made of carbon, hydrogen, oxygen, and nitrogen, in certain cases sulfur is also found. Amino acids may be monocarboxylic or dicarboxylic acids bearing one or two amino groups.

The a-carbon is next to the carboxyl – C. The four valencies of the a-carbon of an amino acid hold respectively an amino (NH2) group, a carboxyl (COOH) group, a hydrogen atom, and side-chain fig (B) which may be polar or non-polar.

A free amino group is basic, a free carboxyl group is acidic. Lysine and alanine are basic amino acids because they have two amino groups and one carboxyl group. Glutamic acid and aspartic acid contain one amino and two carboxyl groups each is classified as acidic amino acids.

Alanine, glycine, valine, and phenylalanine are neutral amino acids because these contain one carboxyl group. Two amino acids can be linked by the formation Of a bond called a peptide bond. With the help of peptide bonds, many amino acids form a linear chain of many amino acids.

(B) Non-polar-side chain

Question 22.
Describe the primary structure of the protein.
Answer:
Primary Structure of Protein: Proteins are made of amino acids which have carboxyl group (COOH) and amino (group) (-NH2). The COOH end of an amino acid is joined to the -NH2 end of the other amino acid. Many amino acids are joined by peptide bonds which held them together in a particular sequence and constitute the primary structure of proteins. The structure does not make a protein functional.

It is a linear sequence of amino acids.

Question 23.
Name different types of RNA.
Answer:
There are three types of RNA.

Question 24.
List the differences between DNA and RNA.
Answer:
Differences between DNA and RNA:

DNA RNA
(1) It consists of double-helical two polynucleotide chains. (1) It consists of only one helical of a single polynucleotide chain.
(2) Deoxyribose sugar is present in the nucleotides. (2) Rihose sugar is present in the nucleotides.
(3) Pyrimidine bases are thymine and cytosine. (3) Uracil base is present instead of thymine-Cytosine is the second pyrimidine base.
(4) DNA synthesizes RNA to regulate cell metabolism. (4) RNA is synthesized by DNA and carries information from DNA to regulate cell metabolism.
(5) DNA from the main genetic material of eukaryotes. (5) It is the genetic material of plant viruses.
(6) DNA occurs in one form only. (6) It is the genetic material of plant viruses.
(7) It controls the transmission of hereditary characters. (7) It controls the synthesis of proteins in the cell.

Question 25.
Distinguish between prosthetic group and co-factors.
Answer:
Differences between coenzyme, cofactor, and prosthetic groups:

Cofactor Coenzyme Prosthetic group
1. It is a non-protein substance or group that gets attached to an enzyme. 1. It is a non-protein group that is loosely attached to the open enzyme in a functional enzyme. 1. It is a non-protein part or group which gets attached to an open enzyme.
2. It is essential for functioning. It may be organic or inorganic or metallic co-factor 2. NAD is a coenzyme for dehydrogenases. 2. Some prosthetic groups have metals e.g. iron porphyrin of the cytochromes.

Question 26.
Explain the structure of an enzyme.
Answer:
Structure of an Enzyme: The enzymes are chemical substances. They catalyze the chemical reactions in the cells. They are secreted and synthesized by living cells. Most all the enzymes are proteinous in nature. Some enzymes contain a nonprotein part called the prosthetic group. Some p esthetic groups are metal compounds. NAD is a coenzyme. All enzymes have active sites.

1. the First carbon forms a part of the aldehyde group. 1. Second carbon forms a part of the keto group.
2. Aldoses are most commonly found in nature i.e. glucose, ribose. 2. Ketoses are less common in nature, e.g., ribulose, fructose.

Question 27.
Distinguish between Unsaturated fatty acids and Saturated fatty acid
Answer:

Unsaturated fatty acid Saturated fatty acid
(i) Don’t have a double band between the carbon atoms. (i) Have one or more double bonds.
(ii) High melting points (ii) Low melting points
(iii) Can’t be synthesized in an animal body. (iii) Can be synthesized in the animal body
(iv) Don’t cause cardiovascular diseases. (iv) Can cause cardiovascular disease

Question 28.
Distinguish between aldose sugar and Ketose sugar
Answer:

Aldose sugar Ketose sugar
(i) First carbon forms a part of the aldehyde group (i) Second carbon forms a part of the Keto group
(ii) Commonly found in nature e.g. glucose, ribose. (ii) Less common in nature, eg. ribulose, fructose.

Question 29.
Distinguish between Oil and Fat.
Answer:

Oils Fats
1. Rich in unsaturated fats. 1. Rich in saturated fats.
2. Liquid at ordinary temperature. 2. Solid or semisolid at ordinary temperature.
3. Contains essential fatty acids. 3. Do not contain essential fatty acids.
4. Do not cause cardiovascular disorders e.g., vegetable oils. 4. Can cause cardio-vascular disorders e.g., Ghee, hydrogenated vegetable oils like Dalda.

Biomolecules Important Extra Questions Long Answer Type

Question 1.
Enlist the functions of small carbohydrates?
Answer:

  1. Monosaccharides are formed during the photosynthetic pathway. They are stored in plants and are utilized by other living organisms depending on them.
  2. Glucose is the blood sugar of many animals and on oxidation, it provides energy for all vital activities.
  3. Nucleotides and nucleosides contain pentose sugar in the form of ribose and deoxyribose sugars. They form a part of nucleic acids.
  4. Lactose of milk is formed from glucose and galactose and mammary glands of mammals.
  5. Glucose is used for the synthesis of fats and amino acids.
  6. Structural polysaccharides like cellulose and oligosaccharides are derived from mono-saccharides.
  7. Food storage polysaccharides like starch and glycogen are derived from monosaccharides.

Question 2.
Enumerate the functions of Lipids.
Answer:

  1. Lipids are storage products in plants as well as animals.
    (a) In plants, fats are stored in cotyledons or endosperm to provide nourishment to the developing embryo.
    (b) In animals fats are stored in adipocytes to be used whenever required by the body.
  2. In animals, subcutaneous fats act as an insulation layer and shock absorber.
  3. They form structural components of membranes, phospholipids, glycolipids, and sterols.
  4. They take part in the synthesis of steroid hormones, vitamin D, and bile salts.
  5. Act as a solvent for fat-soluble vitamins i.e., vitamin A, D, E, and K.
  6. The neutral fats form a concentrated fuel producing more than twice as much energy per gram as do the carbohydrates. They thus, represent an economical food reserve in the body.
  7. The wax lipids form a waterproof protective coating on animal furs, plant stem, leaves, and fruits.

Question 3.
How does water help in maintaining the constancy of the internal environment of an organism?
Answer:
Some substances, capable of neutralizing acids or bases, remain in solution in the cytoplasm as extracellular fluids, e.g., bicarbonate (HCO3), carbonic acid, dibasic phosphate (HPO4 -2 ). Acids and bases mix in the body fluids with these substances and are neutralized by them. Because of its solvent action water aids in keeping a constant pH.

Water also helps in maintaining constant body temperature by eliminating excess heat through the evaporation of sweat. Elimination of waste products through urine also helps in maintaining the constancy of the internal environment of an organism.

Question 4.
What are peroxisomes and phagosomes?
Answer:
Peroxisomes: These were for the first time observed in the kidney of rodents. They are found both in plants and animals. Their size varies from 0.5 to lp in diameter. They are delimited by a single membrane and contain a finely granular matrix. They often possess a central core called nucleoid which may consist of parallel tubules or twisted with strands. Peroxisomes are generally observed in close association with the endoplas¬mic reticulum.

Peroxisomes in different plant and animal cells differ con¬siderably in their enzymatic make-up, but they contain some peroxide-producing enzymes like urate, oxidase, D-amino acid oxidase, B-hydroxy acid oxidase, and catalase. Peroxisomes are somehow associated with some metabolic processes like photorespiration and lipid metabolism in animal cells.

Sphaerosomes: There are cell organelles bounded by a single membrane. They contain enzymes and are visible under the light microscope. These show some affinities for fat stains, including Sudan stain and sodium tetroxide.

These organelles originate from E.R. by budding. They contain enzymatic proteins which help in synthesizing oils and fats. Further devel¬opment of phagosomes takes place through an increase in the lipid content with a concomitant decrease in protein.

Question 5.
Enumerate the importance of Energy carriers.
Answer:
Energy carriers consist of nucleotides having one or two additional phosphate groups linked up at their phosphate end forming diphosphates and triphosphates. Linkage of additional phosphate groups occurs at the cost of a large amount of energy. This energy is provided by the oxidation of food mainly glucose and by photosynthesis.

Separation of the additional phosphate groups from the nucleotides by enzymatic hydrolysis releases a correspondingly large amount of energy.

Thus, ADP and ATP provide ready energy for biological activities.

The bonds joining the additional phosphate groups to the nucleotides are called high energy or energy-rich bonds, as they carry a great deal of energy. The nucleotides having more than one phosphate group are called higher nucleotides.

The energy of energy carriers, when set free is utilized for driving energy-dependent reactions in the cell and is biologically useful energy. ATP is the most common energy carrier in cells and is often called the energy currency of the cell.

Question 6.
Explain the functions of amino acids.
Answer:

  1. Amino acids are the building blocks for proteins.
  2. The amino acid Tyrosine takes part in the formation of the skin pigment melanin as well as hormones thyroxine and adrenaline.
  3. Glycine is important for the formation of heme.
  4. Tryptophan takes part in the formation of the vitamin nicotinamide.
  5. In plants, tryptophan forms the growth hormone indole-3- acetic acid.
  6. Amino acids are converted into glucose by deamination.
  7. Histamine and other biogenic amines are formed by the removal of carboxyl groups from amino acids.

Question 7.
Give reasons for following
(i) Salts dissolve in water but oil does not
Answer:
Water molecules are hydrogen-bonded to form short-lived macromolecular aggregates. To dissolve in water, a solute molecule must form hydrogen bonds with water molecules. Salts are polar compounds, their hydrophilic polar groups form hydrogen bonds with water molecules. So they dissolve oils having hydrophobic non-polar groups that cannot join the lattice structure of water. Thus non-polar molecules of oil do not dissolve in water.

(ii) Amino acid can be basic
Answer:
A free amino group is basic and a free carboxyl group is acidic. Amino acids can be basic because they may carry two amino groups and one carboxyl group e.g., Arginine. One free amino group causes amino acids to be basic.

(iii) Phospholipids form a thin layer on the surface of an aqueous medium.
Answer:
Phospholipids form a thin layer on the surface of an aqueous medium due to the simultaneous presence of both polar and non-polar groups in the molecule. As a result, the phospholipid molecules may arrange themselves in a double-layered membrane in aqueous media.

Question 8.
Illustrate lock and key hypothesis of enzyme action?
Answer:
Mechanism of Enzyme action: The working of enzymes is a complex one. All enzymes first of all combine with the reactions they catalyze. In other words, enzymes with substrates form an intermediate complex before decomposition of the substrate can occur.

This two-way reaction can be represented as follows.
1st step: Enzyme substrate complex = Enzyme + Product.
Formation of the enzyme-substrate complex during enzyme action.

From the above, it is clear that the enzymes must combine first with substrate molecules in order to act. In order to explain the mode of action of an enzyme. Fischer proposed a lock and key theory. According to him if the right key fits in the right lock. The lock can be opened, otherwise not.

Model of enzyme activity

To explain the above in context with the enzyme action it is believed that molecules have specific configurations into which other molecules can fit. The molecules which are acted upon by the enzymes are called substrates of the enzymes. Under the above assumption, only those substrate molecules with the proper geometric shape can fit into the active site of the enzymes.

If this happens, the above molecules may compete with the substrate, and the reaction may either slow down or stop. Substances are called competitive inhibitors because they act to prevent the production of a substance.

An induced-fit model of enzyme action was given by Koshland (1959). Buttressing and catalytic are two groups of the active site of the enzyme. Their site when the substrate attaches to its bonds is broken.

Question 9.
What is the structure of DNA?
Answer:
The nucleic acids are among the largest of all molecules found in living beings. They contain three types of molecules (a) 5 carbon sugar, (b) Phosphoric acid (usually called phosphates when in chemical combi¬nation), and nitrogen-containing bases (Purines and Pyrimidines). The three join together to form a nucleotide i.e., sugar+ base + phosphate = Nucleotide. Only a few nucleotides are possible. They differ only in the kind of purines or pyrimidine (nitrogen-containing bases).

In 1953 J.D. Watson and F.H.C. Crick working in Cambridge Uni¬versity, England prepared a model of DNA molecule elucidating the struc¬ture of DNA molecule. They were awarded the Nobel Prize for this outstanding work.

Structure of DNA

Watson and Crick model of DNA: According to Watson and Crick, the DNA molecule consisted of two strands twisted around each other in the form of a helix. Each strand is made of polynucleotides, each polynucleotide consisting of many nucleotides which remain united with its complimentary’ chain with the help of bases.

Adenine always unites with thymine and cytosine with guanine. It means that one polynucleotide chain of DNA molecule is complementary to the other.

The distance between two chains of the helix is about 20 A and the helix turns over every 34 A. Each mm of the chain consists of about 10 nucleotides.

Structure of DNA

Question 10.
How does the substrate concentration affect the velocity of enzyme reaction?
Answer:
Michaelis constant or more appropriately Michaelis-Menten constant (Km) is a mathematical derivation given by Leonor Michaelis and Monde Menten in 1913 with the help of which velocity of reaction can be calculated for any substrate concentration.

Effect of substrate concentration on enzyme action

Km or Michaelis constant is the substrate concentration at which the chemical reaction attains half its maximum velocity. The constant is an inverse measure of the affinity of an enzyme for its substrate, that is the smaller the Km the greater the substrate affinity and vice versa. The value usually lies between 10 4 – 10 5 M


Which statement about water is correct?

A. The atoms within a molecule of water are held together by hydrogen bonds.
B. Water has a low heat capacity allowing enzymatic reactions to happen at a wide range of temperatures.
C. Water molecules are polar, therefore fatty acids do not dissolve.
D. Ice has a higher density than liquid water, therefore some organisms can live under the ice.

Which statements correctly explain properties of water?

I. Water is a useful medium for metabolic reactions as many substances dissolve in water.
II. Water is useful as a coolant as it takes a small amount of heat energy to change its temperature.
III. Water molecules are cohesive which helps water transport in the roots and stems of plants.

A. I and II only
B. I and III only
C. II and III only
D. I, II and III

What is involved during oxidation?

A. The loss of electrons
B. The gain of electrons
C. The gain of hydrogen
D. The loss of oxygen

What property of water makes it suitable as a coolant?
A. It takes a lot of energy to increase the temperature of water.
B. It takes a lot of energy for water to evaporate.
C. Water molecules are cohesive and stick to the skin.
D. Water is a good solvent so it can transport heat from the body.

What is formed from glucose during anaerobic cell respiration?

A. Lactate and ATP in cytoplasm
B. Carbon dioxide and water in mitochondria
C. Lactate and carbon dioxide in mitochondria
D. Carbon dioxide and water in cytoplasm

Why is light important in photosynthesis?

A. To produce ATP and split water molecules
B. To produce ADP needed to fix carbon dioxide
C. To activate the enzymes that fix carbon dioxide
D. To activate carbon dioxide molecules

Which molecules are monosaccharides?

A. starch, glycogen, cellulose
B. sucrose, maltose, lactose
C. fructose, glucose, galactose
D. glucose, lactose, cellulose

What is light energy used for during photosynthesis?

A. To produce carbon dioxide
B. To produce water molecules
C. To produce ATP
D. To break down sugar molecules

Which sugars are examples of a monosaccharide and disaccharide?

Which of the following statements is/are correct for DNA replication?

I. It occurs during interphase.
II. It is semi-conservative.
III. It is a stage in protein synthesis.

A. I only
B. II only
C. I and II only
D. I, II and III

What happens during the pathway of glycolysis?

A. Glucose is broken down into pyruvate.
B. Carbon dioxide is produced.
C. More ATP is consumed than is produced.
D. Lactic acid is produced.

If 15 % of a sample of DNA is thymine, what percentage of the DNA is guanine?

A. 15 %
B. 30 %
C. 35 %
D. It cannot be determined from the information given.

Which of the following processes uses DNA ligase?

A. Unwinding DNA
B. Gene transfer using plasmids
C. Adding primers
D. Complementary base pairing

Which type of molecule is shown in the diagram below?

What is the energy absorbed by chlorophyll used directly for in plants?

I. To produce ATP
II. To split water
III. To fix CO2

A. I only
B. III only
C. I and II only
D. II and III only

What happens during translation?
A. Copying of DNA to produce DNA
B. Copying of DNA to produce mRNA
C. Copying of DNA to produce tRNA
D. Polypeptide synthesis

Which molecule is a polysaccharide?

A. Glucagon
B. Glucose
C. Glycerol
D. Glycogen

Why does exposure to high temperatures cause an enzyme to lose its biological properties?
A. The substrate blocks the active site at high temperatures.
B. The three dimensional structure of the enzyme becomes changed.
C. Chemical reactions cannot take place at high temperatures.
D. High temperatures increase the activation energy of reactions.

On which molecule is a codon found?

Blood is a water-based transport medium. Which property of water makes it a good transport medium?

A. High specific heat
B. Transparency
C. Versatility as a solvent
D. It has its greatest density at 4°C

Glucose is absorbed through protein channels in the plasma membrane of epithelium cells in the small intestine. Which characteristics of glucose prevent its diffusion through the phospholipid bilayer?

A. It is non-polar and therefore hydrophobic.

B. Its hydrogen bonds link with amino acids in the protein channel.

C. It is polar and therefore hydrophilic.

D. Its covalent bonds interact with the phospholipids.

What occurs during DNA replication?

A. DNA polymerase separates the two DNA strands.
B. DNA molecules containing nucleotides from the original molecule are produced.
C. Adenine forms a base pair with either thymine or uracil.
D. New bases attach to the original sugar-phosphate backbone.

Which carbohydrates are used to provide energy storage in plants and animals?

Which of the following statements is true about enzymes?

A. They are used up in the reactions they catalyse.
B. Allosteric inhibitors bind to the active site.
C. They lower the energy of activation for a reaction.
D. They supply the energy of activation for a reaction.

What are the most frequently occurring elements in living organisms?

A. calcium, phosphorus, iron and sodium
B. calcium, sodium, nitrogen and phosphorus
C. carbon, phosphorus, oxygen and nitrogen
D. nitrogen, carbon, oxygen and hydrogen

Which sugars are both disaccharides?

A. maltose and lactose
B. lactose and fructose
C. fructose and galactose
D. galactose and maltose

Which is the activation energy of a reaction when it is catalysed by an enzyme?

The base sequence of a fragment of DNA is:
ACC GTG CAG GAT

What is the base sequence on the messenger RNA (mRNA) molecule transcribed from it?

A. TGG CAC GTC CTA
B. TGG CUC GTC CTU
C. UGG CTC GUC CUT
D. UGG CAC GUC CUA

Which diagram represents the polarity of a water molecule?

This question refers to the following DNA diagram.

Which points to the 3&prime end of a strand of DNA?

Why is sweat a good coolant for the body?

A. The arterioles that transfer water to sweat move closer to the skin surface when it is hot.
B. Breaking H bonds between water molecules in sweat requires energy from body heat.
C. Sweat contains minerals such as sodium chloride.
D. Sweat is non-polar.

A channel protein is used to transport ions across a membrane. What would you expect to find lining the inside of the channel?

A. Phospholipids
B. Non-polar amino acids
C. Fatty acids
D. Polar amino acids

What is phosphorus used for in plant cells?

A. Structure of hemoglobin
B. Composition of long-term energy storage
C. Positive charge of membranes
D. Composition of nucleic acids

Organisms can be genetically modified to produce the human blood clotting factor IX. What characteristic of the genetic code makes this possible?

A. It is conservative.
B. It is degenerate.
C. It is complementary.
D. It is universal

Which of the following is true about a polar amino acid and cellulose?

A. Both are polysaccharides.
B. Both contain nitrogen.
C. Both are hydrophobic.
D. Both contain hydrogen atoms.

Which can be explained by the solvent properties of water?

A. Sodium chloride is transported as Na + and Cl &ndash in blood.

B. Movement of water occurs under tension in the xylem.

C. Water is the coolant in sweat.

D. Ice floats on liquid water.

What principle is necessary to prevent mutation of DNA during replication?
A. Base pairing is complementary.
B. One gene codes for one polypeptide.
C. Substrates are specific to enzymes.
D. The genetic code is universal.

How is oxygen produced during photosynthesis?

A. Water molecules are split with energy from ATP.
B. Water molecules are split with energy from light.
C. Carbon dioxide molecules are split with energy from ATP.
D. Carbon dioxide molecules are split with energy from light.

What is decreased when lactase is added to milk?

In cell respiration, what is the name of the process where glucose is broken down into pyruvate?

A. Electron transport chain
B. Krebs cycle
C. Link reaction
D. Glycolysis

A base substitution in a gene has changed a codon. Which of these consequences could result from a base substitution in a codon?

I. Another amino acid will be incorporated in the protein
II. A stop codon is generated
III. The same protein will be synthesized

A. I only
B. I and II only
C. I and III only
D. I, II and III

What is produced when the enzyme lactase is added to milk?

A. Glucose and galactose
B. Lactose
C. Glucose and fructose
D. Lactic acid

It is possible to attach &beta-galactosidase to alginate beads for use in the production of lactose-free milk. What are enzymes that have been attached in this way called?

A. Inhibited
B. Immobilized
C. Catalysed
D. Activated

What happens in both respiration and photosynthesis?

A. Triose phosphates are decarboxylated.
B. NADPH is produced.
C. ATP is produced.
D. Electrons pass through ATP synthase.

For what purpose is the enzyme lactase useful?

A. Production of lactose-free milk so that more people can consume dairy products
B. As a dietary supplement to aid in protein digestion of milk
C. For use in coagulating milk protein to make cheese
D. To improve protein consumption in developing countries that lack milk

Which of the following are involved in both replication and transcription?

A. DNA only
B. DNA and RNA
C. DNA and ribosomes
D. DNA, RNA and ribosomes

The percentage of thymine in the DNA of an organism is approximately 30 %. What is the percentage of guanine?

The diagrams show three representations of the structure of the same chemical substance.

Which graph shows the effect of increasing the substrate concentration on enzyme activity?

What is required to replicate DNA?

B. Free nucleotides carrying A, C, G and T bases

Which structure represents a fatty acid?

Where are proteins synthesized by free ribosomes used?

A. Outside the cell after secretion
B. Within the nucleus
C. Within the lysosomes
D. Within the cytoplasm

What is the source of the oxygen released into the air as a product of photosynthesis?

A. Chlorophyll
B. Carbon dioxide only
C. Water only
D. Both water and carbon dioxide

Which gas produces most of the bubbles in bread dough?

A. Oxygen
B. Methane
C. Carbon dioxide
D. Water vapour

This reaction is a step in anaerobic cell respiration in a yeast cell.

Which molecular structure correctly illustrates two amino acids linked by a peptide bond?

Olive oil may reduce the risk of coronary heart disease. What is/are the compound(s) responsible for the health benefits of olive oil?

I. Cis unsaturated fatty acids
II. Trans unsaturated fatty acids
III. Saturated fatty acids

A. I only
B. I and II only
C. II and III only
D. I, II and III

What is the relationship between enzymes and DNA?

A. Enzymes contain the code for DNA.
B. Enzymes act on DNA during translation.
C. Both enzymes and DNA have similar shapes.
D. The structure of enzymes is determined by DNA.

Which statement describes glycogen?

A. It is a hormone involved in the control of blood glucose.
B. It is a component of the cell wall in plants.
C. It is a monosaccharide converted to pyruvate during cell respiration.
D. It is a polysaccharide found in animals.

What substance is represented by this structure?

A. Glycerol
B. Fatty acid
C. Cellulose
D. Glycogen

How can the rate of photosynthesis be measured?

I. By the amount of oxygen produced

II. By the increase in biomass

III. By the amount of carbon dioxide produced

A. I only
B. I and II only
C. I and III only
D. I, II and III

What usually distinguishes DNA from RNA?

Which always contains carbon, hydrogen and oxygen?

What type of bond is labelled X?

What happens during glycolysis for one molecule of glucose?

A. Two pyruvates are formed.
B. There is a net gain of two NADPH + H + .
C. There is a net loss of two ATP.
D. Two acetyl CoA are formed.

This question refers to the following DNA diagram.

What type of bond does Z represent?

A. Covalent bond
B. Hydrogen bond
C. Peptide bond
D. Semi-conservative bond

What characteristic shows that this steroid molecule is a lipid?

A. It is made of carbon rings.

B. It has a very low proportion of oxygen to carbon.

C. It contains OH groups as do fatty acids.

D. It is made only of nitrogen, oxygen and hydrogen.

Which sequence represents the order of events in protein synthesis?

What conclusion can be drawn from examining the action spectrum for a green plant shown below?

Which graph shows the effect of increasing substrate concentration on enzyme activity?

What is a consequence of the specific heat capacity for liquid water, ice and water vapour?

A. Less energy is needed to warm water vapour than liquid water.
B. Salt dissolves more readily in liquid water than in ice.
C. Small insects can walk on liquid water.
D. Ice floats on liquid water.

What type of molecule is shown in this diagram?

The table below shows the codons that determine different amino acids in protein translation.

A. Met-Pro-Arg-Ile-Thr
B. Met-Cys-Ser-Tyr-Trp
C. Met-Gly-Ala-Tyr-Trp
D. Met-Gly-Tyr-Ala-Thr

Which chemical is shown in the diagram below?

Which of the following graphs represents the effect of changing light intensity on the rate of oxygen production by a green plant?

Which model represents transcription?

The diagram below represents part of the DNA molecule.

In the model of the DNA molecule shown below, which arrows point to covalent bonds?

A cricket was placed in a respirometer at constant temperature for ten minutes. The soap bubble moved along the pipette.

[Source: © International Baccalaureate Organization 2017]

What was measured by the movement of the soap bubble?

A. Production of carbon dioxide

B. Volume of excretory products

Which molecules show a monosaccharide and a fatty acid?

What is correct for the DNA double helix?

A strand of mRNA consists of the following nucleotides:

Which of the following represents the non-transcribed (sense) strand of the DNA?

Which molecule is a sugar?

Which of the molecules contain peptide bonds or are sugar molecules?

The diagram shows the translation of a mRNA molecule.

A tRNA molecule with anticodon CAG carries the amino acid phenylalanine. Which codon of mRNA will the tRNA join?

Which equation shows a chemical reaction that occurs during anaerobic cell respiration?


Difference Between Glucose and Galactose

Although the molecular formula of glucose and galactose are identical, they have distinct structural formulas.

Glucose is a simple sugar (monosaccharide) and also termed as blood sugar, grape sugar or corn sugar. It is a vital carbohydrate in biology. It is a premium source of energy for the living cells and also acts as a metabolic intermediate. It is among the chief products extorted from the process of photosynthesis. On the other hand, galactose also comes under the family of monosaccharide and it is a type of sugar that is less sweet in comparison to glucose. It consists of food energy (expressed in calories or joules) and termed as nutritive sweetener.

There are only two stereoisomers actually known as glucose in the category of aldohexose sugars. In these two stereoisomers, only dextrose monohydrate (commonly known as D-glucose) is organically active. In contrast, there is polymer of sugar galactose called galactan. It exists in the body to maintain the supply of galactose. It is stored inside the body in bulk form at a place called hemicellulose. Whenever there will be an additional requirement of galactose than the process of hydrolysis takes place and galactan is eventually converted into galactose.

Coming back to glucose, besides D-glucose there is one more glucose, which is biologically inactive. The inactive form of glucose is termed as L-glucose. It is not possible to metabolize the molecules of L-glucose by the process called glycolysis.

Glucose and galactose are also synthesized by the body. However, the external sources will vary from each other. Glucose can be divided into two types: simple carbohydrate and complex carbohydrate. Simple carbohydrates easily get to digest and their main sources include fruits and their juices, alcoholic beverages, sweets and table sugar. Complex carbohydrates get digested slowly. Their major sources include beans and legumes, whole grains, breads, cereals and nuts.

The major sources of galactose include sugar beets, dairy products and different gums & mucilages. Galactose is also synthesized by the body. It forms a part of glycoproteins and glycolipids in various tissues.

Glucose and galactose can also be differentiated on the basis of their melting point. The standard melting point of galactose is 167. C and the melting point for . -D-glucose is. 146 . C and . -D-glucose is 150 . C.


Glucose Vs. Galactose

Although the formula of glucose molecule and galactose are very alike yet they have a different structural formula.

Glucose is a simple sugar (monosaccharide) and also called blood sugar, glucose or corn sugar. It is important carbohydrate in biology. It is considered as the most essential energy source amongst living organisms and actively behaves like an intermediate of metabolic processes. It is among the main products derived from photosynthesis. On the other hand, a galactose is a part of the monosaccharide family and it is a type of sugar which is less sweet than glucose. It consists of Food energy (calories or joules), referred to as nutritive sweeteners.

There are only two stereoisomers actually called as glucose in the aldohexose class. In the two stereo Somers only dextrose monohydrate (generally known as D-glucose) is in an organically active state. Sugar polymers of galactose are termed as galactan. It is found in the body to maintain the availability of galactose. It is maintained in the body in a bulk form at Hemicellulose. When there is a need for additional galactose then hydrolysis occurs and galactan is converted to galactose.

Coming back on glucose, except for D-glucose there is no other glucose, in the biologically inactive state. The inactive form of glucose is called L-glucose. Breaking the molecules of L-glucose is impossible by glycolysis.

Glucose as well as galactose is integrated within the body. However, various external sources will cause the difference from each other. Glucose can be sub divided into two: simple carbohydrates and complex carbohydrates. Simple carbohydrates are easy to digest and the main sources are fruits and juices, alcoholic drinks, sweets and sugar. Complex carbohydrates involve slow digestion. The main sources are beans and legumes, whole grains, breads, grains and nuts.

The main sources of galactose are sugarbeets, milk and other dairy products and various gums and mucilages. Galactose is also synthesized in the body. It is a component of glycoproteins and glycolipids of the different tissues.

Glucose and galactose have different melting points. This standard melting galactose is 167a ° C and the melting point of the ±-D-glucose ISA 146 ° C and I ²-D-glucose is 150 ° C.


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Comments:

  1. Tuzragore

    It is reserve

  2. Gajora

    Sorry, but this option was not suitable for me.



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