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.
Folate: Folic Acid, Folacin Folate, also known as folic acid or folacin, aids in protein metabolism, promoting red blood cell formation, and lowering the risk for neural tube birth defects. Folate may also play a role in controlling homocysteine levels, thus reducing the risk for coronary heart disease.
RDA for folate is 400 mcg/day for adult males and females. Pregnancy will increase the RDA for folate to 600 mcg/day.
Folate Deficiency
Folate deficiency affects cell growth and protein production, which can lead to overall impaired growth. Deficiency symptoms also include anemia and diarrhea.
A folate deficiency in women who are pregnant or of child bearing age may result in the delivery of a baby with neural tube defects such as spina bifida.
| Enzyme | Clinical Use | Indicates |
|---|---|---|
| CK (Total) | Muscle injury, rhabdomyolysis | Trauma, statin-induced myopathy |
| CK-MM | Skeletal muscle-specific | Muscular dystrophies |
| AST | Also elevated in muscle damage | Used alongside CK |
| LDH | Non-specific marker | Muscle, liver, or cardiac damage |
FACTORS AFFECTING ENZYME ACTIVITY
Velocity or rate of enzymatic reaction is assessed by the rate of change in concentration of substrate or product at a given time duration. Various factors which affect the activity of enzymes include:
1. Substrate concentration
2. Enzyme concentration
3. Product concentration
4. Temperature 5. Hydrogen ion concentration (pH)
6. Presence of activators
7. Presence of inhibitor
Effect of substrate Concentration : Reaction velocity of an enzymatic process increases with constant enzyme concentration and increase in substrate concentration.
Effect of enzyme Concentration: As there is optimal substrate concentration, rate of an enzymatic reaction or velocity (V) is directly proportional to the enzyme concentration.
Effect of product concentration In case of a reversible reaction catalyzed by a enzyme, as per the law of mass action the rate of reaction is slowed down with equilibrium. So, rate of reaction is slowed, stopped or even reversed with increase in product concentration
Effect of temperature: Velocity of enzymatic reaction increases with temperature of the medium which they are most efficient and the same is termed as optimum temperature.
Effect of pH: Many enzymes are most efficient in the region of pH 6-7, which is the pH of the cell. Outside this range, enzyme activity drops off very rapidly. Reduction in efficiency caused by changes in the pH is due to changes in the degree of ionization of the substrate and enzyme.
Highly acidic or alkaline conditions bring about a denaturation and subsequent loss of enzymatic activity
Exceptions such as pepsin (with optimum pH 1-2), alkaline phosphatase (with optimum pH 9-10) and acid phosphatase (with optimum pH 4-5)
Presence of activators Presence of certain inorganic ions increases the activity of enzymes. The best examples are chloride ions activated salivary amylase and calcium activated lipases.
Effect of Inhibitors The catalytic enzymatic reaction may be inhibited by substances which prevent the formation of a normal enzyme-substrate complex. The level of inhibition then depends entirely upon the relative concentrations of the true substrate and the inhibitor
Glycogen Storage Diseases are genetic enzyme deficiencies associated with excessive glycogen accumulation within cells.
- When an enzyme defect affects mainly glycogen storage in liver, a common symptom is hypoglycemia (low blood glucose), relating to impaired mobilization of glucose for release to the blood during fasting.
- When the defect is in muscle tissue, weakness and difficulty with exercise result from inability to increase glucose entry into Glycolysis during exercise.
Various type of Glycogen storage disease are
|
Type |
Name |
Enzyme Deficient |
|
I |
Von Geirke’s Disease |
Glucose -6-phosphate |
|
II |
Pompe’s Disease |
(1, 4)glucosidase |
|
III |
Cori’s Disease |
Debranching Enzymes |
|
IV |
Andersen’s Disease |
Branching Enzymes |
|
V |
McArdle’s Disease |
Muscles Glycogen Phosphorylase |
Cori Cycle
The Cori Cycle operates during exercise, when aerobic metabolism in muscle cannot keep up with energy needs.
For a brief burst of ATP utilization, muscle cells utilize ~P stored as phosphocreatine. For more extended exercise, ATP is mainly provided by Glycolysis.
Lactate, produced from pyruvate, passes via the blood to the liver where it is converted to glucose. The glucose may travel back to the muscle to fuel Glycolysis.
The Cori Cycle costs 6 P in liver for every 2P made available in muscle. The net cost is 4 P Although costly in terms of "high energy" bonds, the Cori Cycle allows the organism to accommodate to large fluctuations in energy needs of skeletal muscle between rest and exercise.
Weak Acids and pKa
• The strength of an acid can be determined by its dissociation constant, Ka.
• Acids that do not dissociate significantly in water are weak acids.
• The dissociation of an acid is expressed by the following reaction: HA = H+ + A- and the dissociation constant Ka = [H+ ][A- ] / [HA]
• When Ka < 1, [HA] > [H+ ][A- ] and HA is not significantly dissociated. Thus, HA is a weak acid when ka < 1.
• The lesser the value of Ka, the weaker the acid.
• Similar to pH, the value of Ka can also be represented as pKa.
• pKa = -log Ka.
• The larger the pKa, the weaker the acid.
• pKa is a constant for each conjugate acid and its conjugate base pair.
• Most biological compounds are weak acids or weak bases.