Molecular weight: 18 to 800 Dalton (Da).
- Acidic amino acids: e.g. Glutamic acid, Aspartic acid.
- Basic amino acids: e.g. Lysine, Arginine.
- Neutral amino acids: e.g. Valine.
E.g. Fatty acids (R-COOH).
- Saturated fatty acids: No double bond b/w carbon atoms. E.g. Palmitic acid (CH3 - (CH2)14 - COOH), Stearic acid.
- Unsaturated Fatty acids: One or more C=C bonds. E.g. Oleic acid, Arachidonic acid (20 C).
Fatty acids are esterified with glycerol → monoglycerides, diglycerides & triglycerides.
- Purines: Adenine (A) & Guanine (G).
- Pyrimidines: Cytosine (C), Thymine (T) & Uracil (U).
E.g. Adenosine, Guanosine, Cytidine, Thymidine, Uridine.
Nitrogen base + Sugar + Phosphate → Nucleotide.
E.g. Adenylic acid, Guanylic acid, Cytidylic acid, Thymidylic acid, Uridylic acid.
They are heteropolymer of amino acids to form polypeptides. i.e., amino acids linked by peptide bonds.
Structural levels of protein:
- Primary structure: Sequence of amino acids, i.e. the positional information in a protein.
- Secondary structure: Polypeptide folded as helix.
- Tertiary structure: Helical polypeptide chain is further folded giving 3-D view.
- Quaternary structure: Assembly of 2 or more polypeptide or subunits. E.g. Haemoglobin. It has 4 subunits (2 α subunits and 2 β subunits).
Functions of proteins:
- For growth and tissue repair.
- Transport nutrients across cell membranes. E.g. GLUT-4.
- Acts as intercellular ground substance. E.g. collagen.
- Acts as antibodies, receptors, hormones (e.g. Insulin), enzymes (e.g. trypsin), pigments (e.g. hemoglobin) etc.
Most abundant protein in biosphere: RuBisCO
Polymers of sugars (monosaccharides). E.g.
- Starch, Cellulose, Glycogen: Homopolymers of glucose
- Inulin: Homopolymer of fructose.
- Chitin: Homopolymer of N-acetyl glucosamine.
Diagrammatic representation of glycogen:
Heteropolymer of nucleotides. i.e. polynucleotide.
Structure of DNA (Watson - Crick Double Helix Model)
Steps are formed of Nitrogen base pairs.
A pairs with T (A=T) by 2 hydrogen bonds. G pairs with C (G≡C) by 3 hydrogen bonds.
Bond b/w sugar (deoxyribose) and phosphate is phosphodiester bond.
Anabolic (Biosynthetic) pathway
Simple molecules form complex structures.
Complex molecules become simple structures.
It consumes energy.
It releases energy (stored as ATP - energy currency)
E.g. acetic acid → cholesterol, amino acids → protein.
E.g. glycolysis, respiration etc.
Metabolites (intermediate products of metabolism):
- Primary metabolites: Have identifiable functions in physiological processes. E.g. amino acids, sugars, nucleic acids, lipids, vitamins etc.
- Secondary metabolites: They are not directly involved in growth, development or reproduction. E.g. Pigments (Carotenoids, Anthocyanins etc), Alkaloids (Morphine, Codeine), Terpenoids, Essential oils (Lemongrass oil etc.), Drugs (Vinblastine, curcumin etc.), Polymers (Rubber, gums, cellulose etc.).
Almost all enzymes are proteins.
Ribozymes: Nucleic acids (RNA) that behave like enzymes.
Nature of enzyme action (catalytic cycle):
- The substrate binds to the active site of enzyme (E+S).
- Formation of enzyme- substrate complex (ES).
- Formation of enzyme- product complex (EP).
- Release of the products from enzyme (E+P).
Factors affecting enzyme activity:
- Temperature & pH: Enzymes show highest activity at optimum temperature & pH. Activity declines below and above optimum value.
- Concentration of substrate: With the increase in substrate concentration, the velocity of enzyme action rises at first and reaches a maximum velocity (Vmax). This is not exceeded by further rise in concentration because enzyme molecules are fewer than the substrate molecules.
- Presence of Inhibitor: Binding of inhibitor shuts off enzyme activity. The inhibitor closely similar to the substrate is called competitive inhibitor. It competes with substrate for the binding site of the enzyme. E.g. Malonate is similar to the substrate succinate. So, it inhibits succinic dehydrogenase.
- Oxido-reductases / Dehydrogenases: Catalyze oxido-reduction b/w two substrates.
- Transferases: Catalyze transfer of a group.
- Hydrolases: Catalyze hydrolysis of ester, ether, peptide, glycosidic, C-C, C-halide or P-N bonds.
- Lyases: Catalyze removal of groups leaving double bonds.
- Isomerases: Catalyze inter-conversion of optical geometric or positional isomers.
- Ligases: Catalyze the linking of 2 compounds together (joining of bonds like C-O, C-S, C-N, P-O etc.).
Non-protein component bound to enzyme to make the enzyme catalytically active.
Apo-enzyme: Protein portion of enzyme.
Co-factor + Apoenzyme = Holoenzyme.
Co-factors are 3 types:
- Prosthetic group: Organic. Tightly bound to apoenzyme. E.g. Haem.
- Co-enzymes: Organic. Transient binding to apoenzyme. Many co-enzymes contain vitamins. E.g. nicotinamide adenine dinucleotide (NAD) and NADP contain niacin.
- Metal ions: E.g. Zn is a cofactor for Carboxypeptidase.