Karnataka 1st PUC Biology Question Bank Chapter 9 Biomolecules

1st PUC Biology Biomolecules One Marks Questions and Answers

Question 1.
Give two examples for monosaccharides.
Answer:
Glucose and fructose.

Question 2.
Give two examples for oligosaccharides.
Answer:
Maltose and lactose.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Question 3.
What are monosaccharides?
Answer:
These are simple carbohydrates which cannot be hydrolysed further into subunits.

Question 4.
What are amino acids?
Answer:
Amino acids are organic compounds having an amino group (-NH2) and acidic group (-COOH).

Question 5.
What are metabolites?
Answer:
Metabolites are organic compounds that are formed in living beings as a result of their metabolic activity.

Question 6.
What is holoenzyme?
Answer:
The complete conjugate enzyme (apoenzyme + cofactor) is called a holoenzyme.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Question 7.
What are biomolecules?
Answer:
All the carbon compounds present in living tissues are called biomolecules.

Question 8.
What are saturated fatty acids?
Answer:
Fatty acids without double bonds are called saturated fatty acids.

Question 9.
What are unsaturated fetty acids?
Answer:
Fatty acids with one or more double bonds are called unsaturated fatty acids.

Question 10.
What is a nucleoside?
Answer:
When a nitrogen base is linked to a pentose sugar, the molecule formed is called a nucleoside.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Question 11.
How a nucleotide is formed?
Answer:
A nucleotide is formed by the joining of a nucleoside with phosphate group.

Question 12.
Which are the building blocks of proteins?
Answer:
Amino acids.

Question 13.
How many types of amino acids are present in a protein?
Answer:
Twenty types of amino acids are present in a protein.

Question 14.
What are non-essential amino acids?
Answer:
The amino acids which synthesise in the human body are called non-essential amino acids.

Question 15.
How can a human get essential amino acids?
Answer:
A human get the essential amino acids through food intake.

Question 16.
Name the polysaccharide form of the exoskeleton of arthropods.
Answer:
Chitin.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Question 17.
Which are the buildings blocks of nucleic acids?
Answer:
Nucleotides.

Question 18.
Name the pentose sugar present in DNA.
Answer:
Deoxy ribose sugar.

Question 19.
Name the pentose sugar present in RNA.
Answer:
Ribose sugar.

Question 20.
By which bond are the amino acids linked in a protein?
Answer:
Peptide bond.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Question 21.
In polysaccharides, by which bond are the mono saccharides linked?
Answer:
Glycosidic bond.

1st PUC Biology Biomolecules Two Marks Questions and Answers

Question 1.
What are homopolysaccharides? Give two examples.
Answer:
Homopolysaccharides : When a polysaccharide is made up of only a single type of monosaccharides, it is called homopolysaccharide. eg. Starch, Glycogen, Cellulose.

Question 2.
What are polysaccharides? Give two examples.
Answer:
polysaccharides
Carbohydrates made up of 10 or more monosaccharides, linked by glycosidic bonds are called polysaccharides or Glycans. They are also called insoluble polymérs made up of many units of called mõnomers. e.g. Starch, Glycogen, Cellulose , Chitin etc.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Question 3.
What are simple lipids? Give two examples.
Answer:
Simple Lipids :
Thése are esters of fatty acids with alcohols. Simple lipids include natural fats,’ oils and waxes. They are generally referred to as triglycerides.

Neutral fats are the triglycerides present in animals. They are solids at room temperature. They are esters of saturated fatty acids and glycerol. e.g. Butter, Ghee etc.

Oil are the triglycerides present in plants and animals. They are liquids at room temperature. They are esters of unsaturated fatty acids and glycerol.  e.g. Groundnut oil, Sunflower oil etc.

Waxes are esters of long chain flitty acids with long chain alcohols, instead of glycerol. They have a high molecular weight. They have high melting points. They are soft when warm and hard when cold. e.g. Cutin present in cuticles of leaves, Suberin in roots, Cermen in human ear, Beewax etc.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Question 4.
What are macromolecules? Give examples.
Answer:
Biomolecules whose molecular weight is less than thousand Daltons, are referred to as micromolecules while those with molecular weight more than thousand, Daltons are called as biomacromolecules.
Micromolecules include one
(i) amino acids
(ii) sugars
(iii) nucleotides and
(iv) lipids

Biomacromolecules include
(i) polysaccharides
(ii) nucleic acids and
(iii) proteins.

Question 5.
Illustrate a glycosidic, peptide and phospho-diester bond.
Answer:
(1) Peptide Bonds : They are also called amide bonds : A peptide bond is Iormel by me reacuui. between an amino group (- NH2) of one amino acid with the carboxylic group (- COOH) of the other amino acid with the loss of one molecule of Water (dehydration synthesis). The bond formed is – CO  – NH – Peptide bonds develop during the formation of oligopeptides and polypeptides.

1st PUC Biology Question Bank Chapter 9 Biomolecules

(2) Glycosidic Bonds : They are found in carbohydrates. The bonds occur between carbon atoms of adjacent monomers through any type of group (e.g.,  – COOH, –  CNH, – CNH2)which can provide hydroxyl (- OH) and hydrogen ( – H) for synthesis of water (1-120). Glycosidic bonds are generally  – C.O.C. –  or –  C. N. C –

(3) Phosphodiester Bonds : Two ester bonds are established between one phosphate radical and two adjacent pentose sugars of nucleotides. A molecule of water is released (dehydration synthesis). Phosphodieaster bonds (0-HPO2-O) help in polymerisation of nucleotides to form polynucleotide.

Question 6.
What is meant by ternary structure of proteins?
Answer:
Tertiary structure of protein: The’ helix of protein is further folded into specific loops and bends to produce specific three dimensional configurations to carry out specialised functions. This is called tertiary structure of the protein. The tertiary structure is stabilized by four kinds of bonds.

  • Hydrogen bonds.
  • Hydrophobic bonds.
  • Ionic or electrostatic bonds.
  • Disulfide bonds.

Question 7.
Explain the composition of triglyceride.
Answer:
They contain esters of saturated fatty acids and glycerol.

Question 8.
Draw the structure of the amino acid, alanine.
Answer:
1st PUC Biology Question Bank Chapter 9 Biomolecules 5

Question 9.
What are compound lipids? Give two examples.
Answer:
compound Lipids : These are lipids containing organic or inorganic group in addition to fatty acids and glycerol. They are of the following types.
(a) Phospholipids: These are lipids containing a phosphate group. Phospholipids are constituents of membranes of cells. eg: Lecithin and Cephalin.

1st PUC Biology Question Bank Chapter 9 Biomolecules

(b) Glycolipids: These are lipids containing a carbohydratë group, usually galactose.

  • Glycolipids present in the mycin sheath of nerve cells are cerebrosides.
  • Glycolipids containing sphingosine (amino alcohol) backbone are called sphingolipids.

(c) Lipoproteins: They are lipids which contain a protein molecule. They are found in milk and egg.

Question 10.
Write a brief note on mRNA?
Answer:
The anticodon arm: It is opposite to acceptor arm. It has 5 base pairs in its stem and 7 unpaired base pairs. Three unpaired bases of the loop forming anticodon or NODOC which is responsible for recognizing and binding to the codon of mRNA.

Question 11.
Write a brief note on rRNA?
Answer:
Ribosomal RNA (rRNA), molecule in cells that forms part of the protein-synthesizing organelle known as a ribosome and that is exported to the cytoplasm to help translate the information in messenger RNA (mRNA) into protein. The three major types of RNA that occur in cells are rRNA, mRNA, and transfer RNA (tRNA).

1st PUC Biology Biomolecules Plants Three Marks Questions and Answers

Question 1.
Find out a qualitative test for proteins, fats and oils, amino acids and test any fruit juIces saliva, sweat and urine for them.
Answer:
Test for protein : Biuret’s test.
Test for Amino acid : Ninhydrin test.
Test for fais and oils : Sudan test.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Question 2.
Select the appropriate chemical bond among ester bond, glycosidic bond, and peptide bond and write against each of the following:
(a) Polysaccharide (b) Protein (c) Fat (d) Water.
Answer:
(a) Polysaccharide : Glycosidic bond.
(b) Protein : Peptide bond.
(c) Fat : Ester bond.

Question 3.
Write the name of any one amino acid, nucleotide and fatty acid.
Answer:
Amino acid …. Valine
Nucleotide …. Adenylic acid (Adenosine monophosphate)
Fatty acid … Palmitic acid.

1st PUC Biology Biomolecules Five Marks Questions and Answers

Question 1.
Describe the Watson and Crick model of DNA structure with a diagram.
Answer:
Structure of DNA or Watson and Crick model of DNA:
• James D. Watson and Frances H.C.Crick in 1953 proposed a model to explain the structure of DNA. Based on x-ray diffraction structure by Wilkins. According to this model DNA has the following features.

1st PUC Biology Question Bank Chapter 9 Biomolecules

1. DNA molecule is composed of two polynucleotide strands, which are twisted right-handedly like a spiral staircase.
1st PUC Biology Question Bank Chapter 9 Biomolecules.2
2. Each polynucleotide strand consists of number of deoxy-ribonucleotides attached to one another by phosphodiester bonds.

3. The two polynucleotide strands are joined by the specific base pairing i.e purines with pyrimidines and viceversa.

4. The base pairing is specific among purines and pyrimidines. Adenine of one strand always pairs with thymine of another strand. Guanine always pairs with cytosine.

5. The adenine and thymine are joined by two hydrogen bonds. The guanine and cytosine are joined by three hydrogen bonds.

6. In these two strands, the sugars and phosphates form the backbone, and nitrogen bases that are projected towards the inner side forms axis of the molecule.

7. The two strands of the DNA are antiparallel and complementary. i.e One strand with 51 to 31 pairs with the other strand, in an opposite manner (31 to 51 man nerl

8. Thus, in one strand, the phosphate is present in the 5th carbon of sugar and at the opposite end OH is present at the 3rdcarbon of the sugar. In the other strand the ends are reversed.

9. In a DNA molecule the amount of purines is always equal to the amount of pyrimidine i.eA+GT + C orAT and G = C This is called ChargoWs law or Equivalent base rule.

10. Each turn in the DNA molecule consists often nucleotide pairs. The length of each turn is 34 A°, the distance between each nucleotide in a strand is 3.4 A° and the distance between the two strands is 20 A°.

Question 2.
Describe the important properties of enzymes.
Answer:
Properties of enzymes.:
Enzymes possess the following properties:
1. Catalytic activity : Their large catalytic activity is high since minute quantity of enzyme can bring about a change in a large amount of substrate.

1st PUC Biology Question Bank Chapter 9 Biomolecules

2. Specificity : They exhibit specificity in their reactions i.e., only a specific enzyme can act on a particular substrate.

3. Thermosensitivity : They are sensitive to temperature changes. The temperature at which an enzyme works at its best is called optimum temperature. For several enzymes, it lies between 25° – 45°C. At low temperatures the enzyme is ineffective. At high temperatures i.e. above 65 C they are destroyed. Hence enzymes are said to be thermolabile (sensitive to heat).

4. pH sensitivity : They are highly sensitive to pH changes. They are active at a particular range of pH only (between 6 & 7.5).

5. Reversibility of enzyme’s reaction : They catalyse reactions in both ways i.e. they act in either directions. It may catalyse the splitting of 1 molecule into 2 or unites 2 molecules into one.

6. Team activity : They usually work in co-ordination with each other i.e., as a team.

7. Enzymes can be destroyed or inactivated by a number of substances like cyanide, iodoacetic acid, malonic acid etc. These substances which are capable of hampering enzymatic reactions, are called as enzyme inhibitors.

8. Enzyme’s substrate complex : Each enzyme bears active sites, that bind the substrate molecular to form enzyme substrate complex. As a result, the substrate is converted into a simpler product and enzyme remains unchanged. This can be shown by the following reaction.
E + S – ES → E + P.

9. Substrate concentration : Enzyme molecule is larger in size and bears several active sites over its surface. Increase in substrate enhances the rate of reaction as more molecules will collide with enzyme to fill more active sites so at constant enzyme concentration. Increase in substrate concentration increases the rate of reaction. Further increase in substrate concentration does not increase the rate of reaction.

10. Enzymes are mostly endoenzymes (act within same cell) eg. Respiratory enzymes. But some enzymes are  excenzymes also eg. Digestive enzymes.

  1. When the products of fraction accumulate, the enzyme’s action slows down (feed back  Inhibitions).

12. Activation of enzymes: Most of the enzymes are often produced in their inactive state (such enzymes are called zymogens), which are activated by activators, e.g. Pepsin is secreted in its in active form as pepsinogen. Pepsinogen is activated by the activator HCl to active pepsin.

  1. Almost all the enzymes known are functional proteins.
  2. Enzymes are generally soluble in water, salt solution, dilute alcohol and glycerol.
  3. Enzymes can be precipitated by absolute alcohol.
  4. These are biological in origin/produced in living cells.
    1st PUC Biology Question Bank Chapter 9 Biomolecules 2

Question 3.
Describe the various forms of lipids with a few examples.
Answer:
Lipids:
Lipids are organic compounds containing carbon, hydrogen and oxygen like carbohydrates but in varying ratio. Some lipids may contain phosphorus or nitrogen. Lipids are defined as esters of fatty acids and glycerol. They are insoluble in water but are soluble in organic solvents like alcohol, chloroform, benzene, ether, carbon disuiphide etc.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Classification of lipids:
Lipids are classified into three categories namely
(i) Simple lipids.
(ii) Compound lipids.
(iii) Derived lipids.

(i) Simple Lipids : These are esters of fatty acids with alcohols. Simple lipids include natural fats, oils and waxes. They are generally referred to as triglycerides. Neutral fats are the triglycerides present in animals. They are solids at room temperature.
They are esters of saturated fatty acids and glycerol. e.g. Butter, Ghee etc.

Oil are the triglycerides present in plants and animals. They are liquids at room temperature. They are esters of unsaturated fatty acids and glycerol. e.g. Groundnut oil, Sunflower oil etc.

Waxes are esters of long chain fatty acids with long chain alcohols, instead of glycerol. They have a high molecular weight. They have high melting points. They are soft when warm and hard when cold. e.g. Cutin present in cuticles of leaves, Suberin in roots, Cermen in human ear, Beewax etc.

(2) Compound Lipids : These are lipids containing organic or inorganic group in addition to fatty acids and glycerol. They are of the following types.
(a) Phospholipids.: These are lipids containing a phosphate group. Phospholipids are constitueñts of membranes of cells. . eg: Lecithin and Cephalin.

(b) Glycolipids: These are lipids containing a carbohydrate group, usually galactose.

  • Glycolipids present in the mycin sheath of nerve cells are cerebrosides.
  • Glycolipids containing sphingosine (amino alcohol) backbone are called sphingolipids.

(c) Lipoproteins : They are lipids which contain a protein molecule. They are found in milk and egg.

(3) Derived Lipids : They are the products that the compound lipids yield on hydrolysis. They
cannot form esters withTatty acids. The derived lipids include steroids, sterols and prostaglandins.
Biomacromolecules:

1st PUC Biology Question Bank Chapter 9 Biomolecules

Polysaccharides:
Carbohydrates made up of 10 or more monosaccharides, linked by glycosidic bonds are called polysaccharides or Glycans. They are also called insoluble polymers made up of many units of called monomers. e.g. Starch, Glycogen, Cellulose , Chitin etc.

They are of two types:
(i) Homopolysaccharides and
(ii) Hetcropolysaccharides.
Homopolysaccharides : When a polysaccharide is made up of only a single type of monosaccharides, it is called homopolysaccharide. Eg. Starch, Glycogen, Cellulose.
Heteropolysaccharides : When a polysaccharide is made up of different types of monosaccharides, it is called heteropolysaccharide. Eg. Pectin, Agar agar, Hyaluronic acid, Heparin.

1st PUC Biology Biomolecules Text Book Questions and Answers

Biological Molecules:

The protoplasm consists of both organic and inorganic compounds. Inorganic substances are those which do not have carbon-hydrogen bonds. The in organic components of protoplasm mostly occur in the form of H2O dissolved gases like oxygen and CO2, minerals and salts. The chemical substances which contain carbon in combination with one or more other elements such as hydrogen, nitrogen, sulphur etc., are called as organic compounds. The organic compound usually contains large molecules which are formed by similar or dissimilar unit. structure, known as monomers or building blocks. A monomer is the simplest unit of the organic molecule which can exist freely.

Biomolecules whose molecular weight is less than thousand Daltons, are referred to as micromolecules; while those with molecular weight more than thousand, Daltons are called as biomacro molecules. Micromolecules include one
(i) amino acids
(ii) sugars
(iii) nucleotides and
(iv) lipids

Biomacromolecules include
(i) polysaccharides
(ii) nucleic acids and
(iii) proteins.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Amino acids:
Amino acids are the building block of proteins. Proteins are the polymers of aminoacids. Aminoacid is an organic compound containing one or more amino groups and one or more carboxyl groups (-COOH and NH2). General structural formula of an amino acid.
1st PUC Biology Question Bank Chapter 9 Biomolecules.1
R may be H, CH3, etc.
There are about 20 amino acids present in the body naturally. The human body can synthesize about 12 of them. Such amino acids are called non-essential amino acids. e.g.Alanine, asparitic. acid, arginine, glutamic acid, glycine, serine, tyrosine etc.

Amino acids which the cells cannot synthesise are obtained as a part of food. These amino acids are called essential amino acids. e.g: valine, lysine, isoleucine, tryptophan, phenylalanine and methionine etc.

Sugars:
Sugars are the simplest carbohydrates which are sweet to taste and are soluble in cold water. Based, on the number of monomeric units present, they are further classified into two types namely:
(1) Monosaccharides.
(2) Oligosaccharides.

Monosaccharides:

The simple sugars like glucose, fructose etc., which cannot be further split by hydrolysis, are called monosaccharides.
Based on the number of carbon atoms present in them, the monosaccharides can be classified as follows:

  • Trisoses : Three carbon atoms in a chain (C3H6O3) g. Glyceraldehydes. These are formed in the body during metabolic breakdown of hexoses.
  • Tetrasoses : Four carbon atoms in a chain (C4H8O4). g. Erythrose.
  • Pentoses : Five carbon atoms in’a chain (C5H10O5). g. Ribose sugar in RNA, Deoxy ribose sugar in DNA.
  • Hexoses : Six carbon atoms in a chain (C6H12O6). g. Glucose, Fructose and Galactose. They are physiologically more important monosaccharides, serving the cells as a major metabolic fuel

1st PUC Biology Question Bank Chapter 9 Biomolecules

Oligosaccharides: 

The sugars with 2-10 monosaccharides linked by glycosydic bonds are called oligosaccha­rides. On hydrolysis they give rise to monosaccharides.

Disaccharides : The carbohydrates, which are made up of two monosaccharides are called disaccharides. e.g. Maltose, Sucrose and Lactose.

Trisaccharides : The carbohydrates, which are made up of three monosaccharides are called trisaccharides. e.g. Rabinose, Raffinose.

Tetrasaccharides : The carbohydrates which are made up of four monosaccharides, are called tetrasaccharides. e.g. Stachyose.

Pentasaccharides : The carbohydrates which are made up of five monosaccharides, are called pentasaccharides. e.g. Verbascose.

Nucleotides:
Nucleotides are organic compounds with heterocyclic rings. A nucleotide consists of a nitrogen base, a pentose sugar and a phosphate group
(or)
Nucleotide is a union of a nucleoside and a phosphate group, e.g. Adenylic acid, guanylic acid, thymidylic acid, cytidilic acid and uridylic acid.

A nucleoside is made up of nitrogen base and a molecule of pentose sugar.
e.g. Adenosine, guanosine, thymidine, cytidine and uridine.

Nitrogen bases, are cyclic nitrogen containing compounds. They occur in two forms, namely purines and pyramidines.

Purines :

They have double ringed structures, hence are larger than pyrimidine molecules. These are two types of purines namely adenine (A) and guanine (G).

Pyramidines : They have single ring structure, hence are smaller than purines. There are three types of pyrimidines, namely cytosine (C), thymine (T) and uracil (U).

Lipids:        

Lipids are organic compounds containing carbon, hydrogen and oxygen like carbohydrates but in varying ratio. Some lipids may contain phosphorus or nitrogen.

Lipids are defined as esters of fatty acids and glycerol. They are insoluble in water but are soluble in organic solvents like alcohol, chloroform, benzene, ether, carbon disulphide etc.

Classification of lipids:

Lipids are classified into three categories namely,

  • Simple lipids.
  • Compound lipids.
  • Derived lipids.

(1) Simple Lipids : These are esters of fatty acids with alcohols. Simple lipids include natural fats, oils and waxes. They are generally referred to as triglycerides.

Neutral fats are the triglycerides present in animals. They are solids at room temperature. They are esters of saturated fatty acids and glycerol. e.g. Butter, Ghee etc.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Oil are the triglycerides present in plants and animals. They are liquids at room temperature. They are esters of unsaturated fatty acids and glycerol. e.g. Groundnut oil, Sunflower oil etc.

Waxes are esters of long chain fatty acids with long chain alcohols, instead of glycerol. They have a high molecular weight. They have high melting points. They are soft when warm and hard when cold.

e.g. Cutin present in cuticles of leaves, Suberin in roots, Cermen in human ear, Beewax etc. Note:

(1) Saturated fatty acid : When a fatty acid has no double bonds between the carbon atoms of the hydrocarbon chain, it is called a saturated fatty acid. They are solids at room temperature. e,g. Palmitic acid and Stearic acid.

(2) Unsaturatedfatty acid : When a fatty acid has double bonds existing between the carbon atoms of the hydrogen chain, it is called unsaturated fatty acid. They are liquids at room temperature. e.g. Oleic acid.

(2) Compound Lipids : These are lipids containing organic or inorganic group in addition to fatty acids and glycerol. They are of die following types.

  • Phospholipids : These are lipids containing a phosphate group. Phospholipids are constituents of membranes of cells. eg: Lecithin and Cephalin.
  • Glycolipids : These are lipids containing a carbohydrate group, usually galactose.
  • Glycolipids present in the mycin sheath of nerve cells are cerebrosides.
  • Glycolipids containing sphingosine (amino alcohol) backbone are called sphingolipids.
  • Lipoproteins : They are lipids which contain a protein molecule. They are found in milk and egg.

(3) Derived Lipids : They are the products that the compound lipids yield on hydrolysis. They cannot form esters with’fatty acids. The derived lipids include steroids, sterols and prostaglandins.Polysaccharides:
Carbohydrates made up of 10 or more monosaccharides, linked by glycosidic bonds are called polysaccharides or Glycans. They are also called insoluble polymers made up of many units of called monomers, e.g. Starch, Glycogen, Cellulose , Chitin etc.

They are of two types:
(i) Homopolysaccharides and
(ii) Heteropolysaccharides.
Homopolysaccharides : When a polysaccharide is made up of only a single type of monosaccharides, it is called homopolysaccharide, eg. Starch, Glycogen, Cellulose.

Heteropolysaccharides : When a polysaccharide made up of different types of monosaccharides, it is called heteropolysaccharide. Eg. Pectin, Agar agar, Hyaluronic acid, Heparin.

Nucleic Acids:

Nucleic acids are large biological macromolecules found in all living organisms. They are found in the nucleus and also in the cytoplasm of the cell. They carry the genetic information from one generation to the next. They were first discovered by Friedrick Miescher and the term nucleic acid was coined by Altmann,
In eukaryotes, the nucleic acids are associated with histone protein to form nucleoprotein and in prokaryotes, they are not associated with histone proteins.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Deoxyribonucleic acid (DNA):
Occurrence: The DNA is present in all plants, animals” prokaryotes and in some viruses. In eukaryotes, they are present in the nucleus, chloroplasts and mitochondria. In prokaryotes, they are present in the cytoplasm.

Chemical composition of DNA:
DNA is a macrqjnolecule and is made up of monomeric units [structural and functional units] called nucleotides. Chemically each deoxy-ribonueleotide consists of 3 components namely.

  • A pentose sugar
  • A nitrogen base
  • A phosphate group.

Structure of DNA or Watson and Crick inodel of DNA:

James D. Watson and Frances H.C.Crick in 1953 proposed a model to explain the structure of DNA. Based on x-ray diffraction structure by Wilkins. According to this model DNA has the following features.
1. DNA molecule is composed of two polynucleotide strands, which are twisted right-handedlylike a spiral staircase.

2. Each polynucleotide strand consists of number of deoxy-ribonucleotides attached to one another by phosphodiester bonds.

3. The two polynucleotide strands are joined by the specific base pairing i.e purines with pyrimidines and viceversa.

4. The base pairing is specific among purines and pyrimidines. Adenine of one strand always pairs with thymine of another strand. Guanine always pairs with cytosine.

5. The adenine and thymine are joined by two hydrogen bonds. The guanine and cytosine are joined by three hydrogen bonds.

6. In these two strands, the sugars and phosphates form the backbone, and nitrogen bases that are projected towards the inner side forms axis of the molecule.

7. The two strands of the DNA are antiparallel and complementary, i. e One strand with 51 to 3′ pairs with the other strand, in an opposite manner [3′ to 51 manner]

8. Thus, in one strand, the phosphate is present in the 5th carbon of sugar and at the opposite end OH is present at the 3rd carbon of the sugar. In the other strand the ends are reversed.

9. In a DNA molecule the amount of purines is always equal to the amount of pyrimidine i.e A+G = T + C or A = T and G = C This is called ChargofFs law or Equivalent base rule.

10. Each turn in the DNA molecule consists of ten nucleotide pairs.

The length of each turn is 34 A0, the distance between each nucleotide in a strand is 3.4 A° and the distance between the two strands is 20 A0.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Functions of DNA:
1. DNA stores and transmits genetic information from parents to off springs.
2. It controls all the cellular activities of the cell.
3. It has the capacity to undergo mutation leading to variations.
4. It acts as a template for the synthesis of different types of RNAs.
5. It directs the synthesis of. proteins and helps in the growth and development.
6. It directs the synthesis of specific enzymes of RNA.

Ribonucleic acid (RNA): 
Occurrence: It is a type of nucleic acid present in both the prokaryotes and eukaryotes. It is mainly found in the cytoplasm and a little in nucleus of eukaryotes. It is made up of a single polynucleotide strand.
Chemical composition: RNA is a biological macrotnolecule made up of four types of ribonucleotides. Each ribonucleotide consists of a pentose sugar, a nitrogen base and a phosphate group.

Types of RNA:
There are two categories of RNAs namely genetic RNA and non-genetic RNA.
1. Genetic RNA:- It is the RNA which acts as the genetic material and carries hereditary characters from one generation to the next. It is found in viruses like TMV, [ssRNA], Wound tumour virus [dsRNA] HIV, Poliomyelitis, [ssRNA] Reo virus [ds RNA].

2. Non-genetic RNA:- It is the RNA involved in protein synthesis. It is of three types namely r-RNA, m-RNA and t-RNA. All these 3 types of RNAs are synthesized by DNA.

(a) Ribosomal RNA or r-RNA:
It is the ribosomal RNA. It forms the structural component of ribosomes and it accounts for 80% of the total RNA of the cell. It is a single polynucleotide strand with a number of curves and coiling at some regions. It is rich with guanine and cytosine. This r-RNA combines with specific type of proteins, forming ribosome.

Functions:
1. It helps in the binding of mRNA and tRNA to the ribosome during protein synthesis.
2. It is involved in the formation of ribosome.
3. It acts as an enzyme, ribozyme in peptide bond formation between aminoacids.

(b) Messenger RNA or Informational RNA or mRNA:
It is the messenger RNA, synthesized by DNA on its templates. It is the largest RNA [900-1500 nucleotide] of all the types. It accounts for about 5% of the total RNA in the cell. It was discovered by Volkin and the term mRNA was coined by Jacob and Monad. The life span of mRNA is 2 minutes [1 to 4 hours in Eucaryotes]

Functions:
It carries message from DNA to cytoplasm in the form of triplet codons for the synthesis of proteins.

1st PUC Biology Question Bank Chapter 9 Biomolecules

(c) Soluble RNA or transfer RNA [tRNA]: –
It is the transfer RNA synthesized by the DNA. It is the smallest RNA with 80 nucleotides. It accounts for about 15% of the total RNA of a cell. It is primarily a single stranded molecule but the nucleotides at certain regions pair with one another to form double stranded stems. It looks like a clover leaf and forms a secondary structure. This secondary structure was first discovered and described by Robert Holley who got Nobel prize for the same.

Secondary structure of tRNA consists of four arms namely acceptor arm, DHU arm, anticodon, arm and TTC arm. Each arm has a stem and a loop but the acceptor arm is loopless. The stem has paired bases and the loop has unpaired bases.

The four arms are as follows:
(1) The acceptor arm: This is formed by 7 base pairings between nucleotides at the 5’ and 3’ aids of tRNA. Beyond the base pairings there extends three unpaired nucleotides CCA at the 3 end. The aminoacid gets attached to the OH group of last adenine nucleotide. Hence this 3’ end is called aminoacid binding site.

(2) DHU or Dihydrouridine arm: It is towards 5’ end of the molecule after the acceptor arm. It has 4 base pairs at its stem and 10 unpaired nucleotides at its loop. It has an unusual pyrimidine called Dihydrouridine. This arm has a specific charging enzyme that catalyses union of specific amino acid to tRNA molecule. Hence it is also called aminoacid activating site [enzyme site].

(3) The anticodon arm: It is opposite to acceptor arm. It has 5 base pairs in its stem and 7 unpaired base pairs. Three unpaired bases of the loop forming anticodon or NODOC which is responsible for recognizing and binding to the codon of mRNA.

(4) T Ψ C or pseudo uridine arm: It is opposite to DHU arm. It has 5 base pairs in its stem and 7 unpaired nucleotides in the loop. It contains unusual nucleotides like pseudouridine, dimethyl guanosine and inosine. This arm is responsible for the recognition of ribosomes during protein synthesis. Hence is called ribosome recognition arm or site.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Variable arm: It is small extra arm present in between the anticodon arm and TTC arm in some tRNAs. Its function is not yet known.

Functions:
1. It transfers a specific aminoacid to the site of protein synthesis.
2. Protein synthesis makes use of about 20 types aminoacids. So there are 20 different tRNAs in a cell to cariy 20 types of aminoacids.
3. It carries information at its anticodon.

Proteins:
Definition: Proteins are the building block is of the living body, and make up the structure and functional component of the living system. They are polymers made up of monomers called amino acids, linked by peptide bonds.

Protein structure :
The protein structure is referred to as a three dimensional structure or conformation, which determines the biological function. Four basic structural levels are assigned to proteins^ They dre primary structure, secondary structure, tertiary structure and quaternary structure.

(a) Primary structure of protein : The primary structure of protein refers to the linear sequence of amino acids in the polypeptide chain. The amino acids are linked by polypeptide bonds only.

(b) Secondary structure of protein : The folding of polypeptide chain into specific coiled three-dimensional structure like a helix or p sheet is called the secondary structure. The coiled configuration is produced by hydrogen bonding between carboxyl and amino groups of individual aminoacids.

(c) Tertiary structure of protein : The- helix of protein is further folded into specific loops and bends to produce specific three dimensional configurations to carry out specialised functions. This is called tertiary structure of the protein.

1st PUC Biology Question Bank Chapter 9 Biomolecules

The tertiary structure is stabilized by four kinds of bonds.
(i) Hydrogen bonds.
(ii) Hydrophobic bonds.
(iii) Ionic or electrostatic bonds.
(iv) Disulfide bonds.
(d) Quaternary structure of protein: When a protein is made up of 2 or more polypeptide chains as in haemoglobin, it is known to possess quaternary structure. The polypeptide chains are held together by hydrogen bonds and electrostatic or salt bonds, formed between amino acids.

Enzymes:
Definition : An enzyme is defined as a specialised protein produced within an organism, which is capable of catalyzing a specific chemical reaction without itself undergoing any change. They are referred to as biocatalysts.
or
An enzyme is a protein, that enhances the rate of biochemical reactions but does not affect the nature of the final product.

Properties Of Enzymes :
Enzymes possess the following properties:
1. Catalytic activity : Their large catalytic activity is high since minute quantity of enzyme can bring about a change in a large amount of substrate.

2. Specificity : They exhibit specificity in their reactions i.e., only a specific enzyme can act on a particular substrate.

3. Thermosensitivity : They are sensitive to temperature changes. The temperature at which an enzyme works at its best is called optimum temperature. For several enzymes, it lies between 25° – 45°C. At low temperatures the enzyme is ineffective. At high temperatures i.e. above 65 C they are destroyed. Hence enzymes are said to be thermolabile (sensitive to heat).

4. pH sensitivity : They are highly sensitive to pH changes. They are active at a particular • range of pH only (between 6 & 7.5).

5. Reversibility of enzyme’s reaction : They catalyse reactions in both ways i.e. they act in either directions. It may catalyse the splitting of 1 molecule into 2 or unites 2 molecules into one.

6. Team activity : They usually work in co-ordination with each other i.e., as a team.

1st PUC Biology Question Bank Chapter 9 Biomolecules

7. Enzymes can be destroyed or inactivated by a number of substances like cyanide, iodoacetic acid, malonic acid etc. These substances which are capable of hampering enzymatic reactions, are called as enzyme inhibitors.

8. Enzyme’s substrate complex : Each enzyme bears active sites, that bind the substrate molecular to form enzyme substrate complex. As a result, substrate is converted into a simpler product and enzyme remains unchanged. This can be shown by the following reaction.
E + S – ES → E + P

9. Substrate concentration : Enzyme molecule is larger in size and bears several active sites over its surface. Increase in substrate enhances the rate of reaction as more molecules will collide with enzyme to fill more active sites so at constant enzyme concentration. Increase in substrate concentratin increases the rate of reaction. Further increase in substrate concentration does not increase the rate of reaction.

10. Enzymes are mostly endoenzymes (act within same cell) eg. Respiratory enzymes. But some enzymes are excenzymes also eg. Digestive enzymes.

11. When the products of fraction accumulate, the enzyme’s action slows down (feed back Inhibitions).

12. Activation of enzymes: Most of the enzymes are often produced in their inactive state (such enzymes are called zymogens), which are activated by activators, e.g. Pepsin is secreted in its in active form as pepsinogen. Pepsinogen is activated by the activator HCl to active pepsin.

1st PUC Biology Question Bank Chapter 9 Biomolecules

13. Almost all the enzymes known are functional proteins.

14. Enzymes are generally soluble in water, salt solution, dilute alcohol and glycerol.

15. Enzymes can be precipitated by absolute alcohol.

16. These are biological in origin/produced in living cells.
1st PUC Biology Question Bank Chapter 9 Biomolecules 2

Enzyme nomenclature:

Generally, the enzymes are named after their substrate molecules with a suffix ‘ase’, maltase is an enzyme, which works on maltose. In the same way lipase acts on lipids, protease acts on proteins and so on.

Sometimes, the suffix-lytic is used to identify the activity on different substances, e.g. proteolytic enzyme cuts the proteins. Lipolytic enzyme acts on lipids, and those acting on carbohydrates are known as the amylolytic or sucrolytic enzymes. However, in certain enzymes such as ptyalin, pepsin and trypsin no.suffix is used. They are just the original and popular names of some enzymes.

Classification of enzymes:
Oxidoreductases – Act on many chemical groupings to add or remove hydrogen atoms.
Transferases – Transfer functional groups between donorand acceptor molecules.
Kinases are specialised transferases that regulate metabolism by transferring phosphate from ATP to other molecules.
Hydrolases – Add water across a bond, hydrolyzing it.
Lyases – Add water, ammonia or carbon dioxide across double bonds, or remove these elements to produce double bonds.
isorne rases – Carry out many kinds of isomerization : L to D isomerizations. Mutase reactions (shifts of chemical groups) and others.
Ligases – Catalyze reactions in which two chemical groups are joined (or ligated) with the use of energy from ATP.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Enzymes are specific in their substrate molecules.
When enzyme (E) and its substrate (S) come together, they make an intermediary complex called the E-S complex, like a key coming with a lock and making a complex. This is the primary step for enzyme action.
So the enzymes are highly specific for the type of reaction they catalyse.
Over a fraction of a time the enzyme cleaves the substate into its product.
Since the product is different from the substrate, it cannot remain in contact with the enzyme, the enzyme becomes free.

The free enzyme can take up another substrate molecule.
E + S = ES → E + P

1st PUC Biology Question Bank Chapter 9 Biomolecules.3

Coenzyme and apoenzyme:
Enzymes can consist of only proteins or can have a non-protein component also. The protein part in the combination is called the apoenzyme and non-protein part may be coenzyme, cofactor or a prosthetic group. An apoenzyme joining with any of these factors would become a complete enzyme called the holoenzyme.

Allosteric action:
The activity of some enzymes is controlled by certain molecules binding to a specific regulatory (or allosteric) site on the enzyme, distinct from the active site. Different molecules can inhibit or activate the enzyme, allowing sophisticated control of the rate. Only a few enzymes can do this, and they are often at the starting of a long biochemical pathway. They are generally activated by the substate of the pathway and are inhibited by the product of the pathway, thus only turning the pathway on when it is needed.

1st PUC Biology Question Bank Chapter 9 Biomolecules

Concept of Metabolism:

  • Turn over of biomolecules means that they are constantly being changed into some other biomolecules and are also made of other biomolecules.
  • All the chemical reactions that occur in a living cell/organism constitute metabolism.
  • No metabolic reaction occurs in isolation; always metabolic reactions are linked to other reactions.
  • These metabolic pathways are either linear or circular and they may criss-cross each other.
  • The metabolic flow through a pathway has a rate and direction.
  • This metabolic flow is called the dynamic state of body constituents.
  • All the metabolic reactions are catalysed reactions – catalysed by enzymes.

Metabolism is of two types:

  • Anabolism : Where more complex compounds / structures are formed from simple ones. e.g. protein synthesis.
  • Catabolism : Where a complex substance is broken into two or more smaller substance/ compounds. e.g. Digestion of proteins by peptidases.
  • Energy for the metabolic reactions is liberated from a compound called Adenosine Triphosphate (ATP) which is also known as the energy currency of cells.

Co-factors:
Enzymes are composed of one or several polypeptide chains. However, there are a number of cases in which non-protein constituents called co-factors are bound to the enzyme to make the enzyme catalytically active.

Nature of bond linking monomers in a polymer :
Three different types of bonds occur in the formation of polymeric biomolecules – peptide, glycosidic and phosphodiester.

1st PUC Biology Question Bank Chapter 9 Biomolecules

  • Peptide Bonds : They are also called amide bonds : A peptide bond is formed by the reaction between an amino group (-NH2) of one amino acid with the carboxylic group (-COOH) of the other amino acid with the loss of one molecule of water (dehydration synthesis). The bond formed is -CO- NH-. Peptide bonds develop during the formation of oligopeptides and polypeptides.
  • Glycosidic Bonds : They are found in carbohydrates. The bonds occur between carbon atoms of adjacent monomers through any type of group (e.g., -COOH, – CNH, -CNH2) which can provide hydroxyl (-OH) and hydrogen (-H) for synthesis of water (H2O). Glycosidic bonds are generally -C.O.C. – or – C. N. C-
  • Phosphodiester Bonds : Two ester bonds are established between one phosphate radical

and two adjacent pentose sugars of nucleotides. A molecule of water is released (dehydration synthesis). Phosphodieaster bonds (0-HPO2 -O) help in polymerisation of nucleotides to form polynucleotide.

1st PUC Biology Question Bank with Answers

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