- DNA consists of two polynucleotide strands coiled around each other to form a right-handed double helix.
- The two strands run in opposite directions, one from 5′ to 3′ and the other from 3′ to 5′, making them antiparallel.
- The sugar–phosphate backbone forms the outer framework of the helix, while nitrogenous bases lie inside.
- The two strands are held together by hydrogen bonds between complementary bases.
- Adenine pairs with thymine through two hydrogen bonds, and guanine pairs with cytosine through three hydrogen bonds, making A–T and C–G complementary base pairs.
Definitions [46]
Define carbohydrates.
Carbohydrates are optically active polyhydroxy aldehydes or polyhydroxy ketones or compounds that can be hydrolysed to polyhydroxy aldehydes or polyhydroxy ketones.
Define α-amino acids.
α-Amino acids are carboxylic acids having an amino (–NH2) group bonded to the α-carbon, that is, the carbon next to the carboxyl (–COOH) group.
Define peptide bond.
The bond that connects α-amino acids to each other is called a peptide bond.
Define the term Protein.
Chemically proteins are polyamides which are high molecular weight polymers of the monomer units, i.e., α-amino acids. OR It can also be defined as proteins are the biopolymers of a large number of α-amino acids and they are naturally occurring polymeric nitrogenous organic compounds containing 16% nitrogen and peptide linkages (-CO-NH-)
Define enzymes.
Enzymes are biological catalysts that speed up chemical reactions in living cells without being consumed in the process.
Definition: Peptides
The compounds obtained by condensation of two or more α-amino acids are called peptides.
Definition: Polypeptide
The peptide formed by condensation of many α-amino acids is called a polypeptide.
Definition: Proteins
The long polymers of amino acids linked together by peptide bonds and having high molecular mass are called proteins.
Definition: Mutation
A chemical change in a DNA molecule which leads to the synthesis of proteins with a different amino acid sequence is called a mutation.
Definition: Apoenzyme
The protein part of an enzyme without its cofactor is called an apoenzyme.
Definition: Nucleotide
The monomer unit of a nucleic acid is called a nucleotide.
Definition: Biomolecules
The complex lifeless organic substances which form the basis of life and are responsible for the growth and maintenance of living systems are called biomolecules.
Definition: Metabolism
The sum total of all chemical reactions occurring in a living organism is called metabolism.
Definition: Metabolic pathway
The sequence of enzyme-catalysed reactions by which food is converted into body parts is called a metabolic pathway.
Definition: Carbohydrates
Polyhydroxy aldehydes or polyhydroxy ketones, or substances which on hydrolysis yield such compounds, are called carbohydrates.
Definition: Monosaccharides
Carbohydrates which cannot be hydrolysed to give simpler carbohydrates are called monosaccharides.
Definition: Oligosaccharides
Carbohydrates which on hydrolysis give a definite number (2–10) of monosaccharide units are called oligosaccharides.
Definition: Disaccharides
Carbohydrates which on hydrolysis give two monosaccharide units are called disaccharides.
Definition: Trisaccharides
Carbohydrates which on hydrolysis give three monosaccharide units are called trisaccharides.
Definition: Tetrasaccharides
Carbohydrates which on hydrolysis give four monosaccharide units are called tetrasaccharides.
Definition: Polysaccharides
Carbohydrates which on hydrolysis give a large number of monosaccharide units are called polysaccharides.
Definition: Reducing sugars
Carbohydrates capable of reducing Tollens’ reagent and Fehling’s solution are called reducing sugars.
Definition: Aldoses
Monosaccharides containing an aldehyde (–CHO) group are called aldoses.
Definition: Ketoses
Monosaccharides containing a keto (>C=O) group are called ketoses.
Definition: Heptoses
Monosaccharides containing seven carbon atoms are called heptoses.
Definition: Enantiomers
Two stereoisomers which are mirror images of each other and are non-superimposable are called enantiomers.
Definition: Mutarotation
The spontaneous change in optical rotation of an optically active compound in aqueous solution until equilibrium is reached is called mutarotation.
Definition: Anomers
A pair of stereoisomers which differ in configuration around the anomeric carbon atom are called anomers.
Definition: Glycosidic linkage
The linkage formed between two monosaccharide units through an oxygen atom by condensation is called a glycosidic linkage.
Definition: Starch
The principal storage polysaccharide of plants composed of α-glucose units is called starch.
Definition: Amylose
The linear water-soluble component of starch composed of α-1,4-glycosidic linked glucose units is called amylose.
Definition: Amylopectin
The branched water-insoluble component of starch composed of α-1,4 and α-1,6-glycosidic linked glucose units is called amylopectin.
Definition: Cellulose
The structural polysaccharide of plants composed of β-1,4-glycosidic linked glucose units is called cellulose.
Definition: Glycogen
The storage polysaccharide of animals found in liver and muscles is called glycogen.
Definition: Zwitter ion
The internal salt formed due to transfer of a proton from —COOH group to —NH₂ group in aqueous solution is called a zwitter ion.
Definition: Isoelectric point
The pH at which an amino acid exists as a neutral dipolar ion and does not migrate in an electric field is called the isoelectric point.
Definition: Peptide linkage
The —CO—NH— bond formed by condensation of two amino acid molecules is called a peptide bond or peptide linkage.
Definition: Enzymes
Globular proteins which act as biological catalysts in living systems and are produced by living cells are called enzymes.
Definition: Holoenzyme
The complete catalytically active enzyme consisting of apoenzyme and cofactor is called a holoenzyme.
Definition: Hormones
Chemical substances secreted by ductless glands which regulate development and control activities of the body are called hormones.
Definition: Nucleic Acids
Biomolecules present in the nuclei of living cells which are responsible for storage and transmission of genetic information are called nucleic acids.
Definition: Nucleoside
The base-sugar unit present in a nucleic acid chain is called a nucleoside.
Definition: Phosphodiester linkage
The linkage formed between nucleotides through phosphate group between 5′ and 3′ carbon atoms is called a phosphodiester linkage.
Definition: Chargaff’s rule
The rule stating that in DNA the amount of adenine equals thymine and the amount of cytosine equals guanine is called Chargaff’s rule.
Definition: Gene
The sequence of DNA that codes for a specific protein or polypeptide is called a gene.
Definition: Mutant gene
The defective form of a gene resulting from mutation and capable of causing genetic disorders is called a mutant gene.
Key Points
Key Points: Structure of Proteins
| Feature | Primary Structure | Secondary Structure | Tertiary Structure | Quaternary Structure |
|---|---|---|---|---|
| Meaning | The linear sequence of amino acid residues linked by peptide bonds is called primary structure of protein. | The regular local folding of the polypeptide chain into specific patterns is called secondary structure of protein. | The overall three-dimensional folding of a single polypeptide chain is called tertiary structure of protein. | The spatial arrangement formed by association of two or more polypeptide chains is called quaternary structure of protein. |
| Structural Description | Specific order of amino acids from N-terminal to C-terminal. | Organized into α-helix or β-pleated sheet patterns. | Compact globular or fibrous three-dimensional form. | Multiple folded subunits assembled into one functional unit. |
| Main Bonds / Forces Involved | Peptide bonds (–CO–NH–). | Hydrogen bonding between C=O and N–H groups. | Hydrogen bonds, ionic bonds, disulfide bonds, dipole interactions and London forces. | Same intermolecular forces acting between different subunits. |
| Stability Features | Determines identity and properties of protein. | Provides backbone stabilization. | Stabilized by side-chain interactions. | Necessary for functional activity of certain proteins. |
| Example | Amino acid sequence notation. | α-helix in keratin; β-sheet in silk. | Many enzymes and globular proteins. | Haemoglobin (four subunits). |
Key Points: DNA double helix
Key Points: Functions of Carbohydrates
- Carbohydrates are the main source of energy for living organisms and act as body fuels.
- Carbohydrates are stored as reserve food in plants as starch and in animals as glycogen.
- It provide structural support in plants by forming the cell wall (cellulose).
- Glucose formed from carbohydrates is oxidised in the body to release energy required for life processes.
Key Points: Properties of Enzymes
- The property by which an enzyme acts only on a specific substrate and catalyses only a particular type of reaction is called specificity of enzymes.
- The ability of enzymes to increase the rate of a reaction by many times compared to uncatalysed reactions is called catalytic efficiency of enzymes.
- The property by which a very small amount of enzyme is sufficient to catalyse a large amount of substrate because the enzyme is regenerated is called high catalytic power of enzymes.
- The condition at which the activity of an enzyme is maximum at a particular temperature and pH is called the optimum temperature and optimum pH of an enzyme.
Key Points: Classification of Hormones
| Type of Hormone | Description | Examples | Main Function |
|---|---|---|---|
| Steroid Hormones | Hormones which possess a steroid nucleus (four fused rings) and are derived from cholesterol. | Testosterone, Estrogen, Progesterone, Cortisone, Aldosterone | Control development of sex organs, metabolism, water and mineral balance. |
| Peptide Hormones | Hormones which consist of one or more polypeptide chains. | Insulin, Oxytocin, Vasopressin, Angiotensin II | Regulate blood glucose, control childbirth, water balance and blood pressure. |
| Amine Hormones | Hormones which are water-soluble amine compounds derived from amino acids. | Adrenaline, Thyroxine | Prepare body for emergency (adrenaline); control metabolism of carbohydrates, proteins and lipids (thyroxine). |
Key Points: Physiological Functions of Vitamins
- Vitamins are biological catalysts required in very small amounts to regulate various metabolic reactions in the body.
- Deficiency of one or more vitamins causes specific deficiency diseases, and this condition is called avitaminosis.
- Vitamins help in growth, metabolism, immunity, maintenance of tissues, blood formation and proper functioning of organs.
- Different vitamins have specific functions and sources, and their deficiency leads to characteristic diseases such as night blindness (Vitamin A), beriberi (Vitamin B₁), scurvy (Vitamin C) and rickets (Vitamin D).
