NEET MDS Lessons
Biochemistry
FATTY ACIDS
Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end.
• are usually in esterified form as major components of other lipids
• are often complexed in triacylglycerols (TAGs)
• most have an even number of carbon atoms (usually 14 to 24)
• are synthesized by concatenation of C2 units.
• C16 & C18 FAs are the most common FAs in higher plants and animals
• Are either:
—saturated (all C-C bonds are single bonds) or
—unsaturated (with one or more double bonds in the chain)
—monounsaturated (a single double bond)
1.Example of monounsaturated FA: Oleic acid 18:1(9) (the number in unsaturated FA parentheses indicates that the double bond is between carbons 9 & 10)
2. Double bonds are almost all in the cis conformation
—polyunsaturated (more then one double bond)
Polyunsaturated fatty acids contain 2 or more double bonds. They usually occur at every third carbon atom towards the methyl terminus (-CH3 ) of the molecule. Example of polyunsaturated FA: Linoleic acid 18:2(9,12)
• the number of double bonds in FAs varies from 1 to 4 (usually), but in most bacteria it is rarely more than 1
Saturated FAs are highly flexible molecules that can assume a wide range of conformations because there is relatively free rotation about their C-C bonds.
CLASSIFICATION OF ENZYMES
1. Oxidoreductases : Act on many chemical groupings to add or remove hydrogen atoms. e.g. Lactate dehydrogenase
2. Transferases Transfer functional groups between donor and acceptor molecules. Kinases are specialized transferases that regulate metabolism by transferring phosphate from ATP to other molecules. e.g. Aminotransferase.
3. Hydrolases Add water across a bond, hydrolyzing it. E.g. Acetyl choline esterase
4. Lyases Add water, ammonia or carbon dioxide across double bonds, or remove these elements to produce double bonds. e.g. Aldolase.
5. Isomerases Carry out many kinds of isomerization: L to D isomerizations, mutase reactions (shifts of chemical groups) and others. e.g. Triose phosphate isomerase
6. Ligases Catalyze reactions in which two chemical groups are joined (or ligated) with the use of energy from ATP. e.g. Acetyl CoA carboxylase
Enzyme Kinetics
Enzymes are protein catalysts that, like all catalysts, speed up the rate of a chemical reaction without being used up in the process. They achieve their effect by temporarily binding to the substrate and, in doing so, lowering the activation energy needed to convert it to a product.
The rate at which an enzyme works is influenced by several factors, e.g.,
- the concentration of substrate molecules (the more of them available, the quicker the enzyme molecules collide and bind with them). The concentration of substrate is designated [S] and is expressed in unit of molarity.
- the temperature. As the temperature rises, molecular motion - and hence collisions between enzyme and substrate - speed up. But as enzymes are proteins, there is an upper limit beyond which the enzyme becomes denatured and ineffective.
- the presence of inhibitors.
- competitive inhibitors are molecules that bind to the same site as the substrate - preventing the substrate from binding as they do so - but are not changed by the enzyme.
- noncompetitive inhibitors are molecules that bind to some other site on the enzyme reducing its catalytic power.
- pH. The conformation of a protein is influenced by pH and as enzyme activity is crucially dependent on its conformation, its activity is likewise affected.
The study of the rate at which an enzyme works is called enzyme kinetics.
ESSENTIAL FATTY ACIDS (EFAs) Polyunsaturated FAs,such as Linoleic acid and g(gamma)- Linolenic acid, are ESSENTIAL FATTY ACIDS — we cannot make them, and we need them, so we must get them in our diets mostly from plant sources.