NEET MDS Lessons
Biochemistry
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
Regulation of PTH secretion
Secretion of parathyroid hormone is controlled chiefly by serum [Ca2+] through negative feedback. Calcium-sensing receptors located on parathyroid cells are activated when [Ca2+] is low.
Hypomagnesemia inhibits PTH secretion and also causes resistance to PTH, leading to a form of hypoparathyroidism that is reversible.
Hypermagnesemia also results in inhibition of PTH secretion.
Stimulators of PTH includes decreased serum [Ca2+], mild decreases in serum [Mg2+], and an increase in serum phosphate.
Inhibitors include increased serum [Ca2+], severe decreases in serum [Mg2+], which also produces symptoms of hypoparathyroidism (such as hypocalcemia), and calcitriol.
|
|
b Oxidation Pathway |
Fatty Acid Synthesis |
|
pathway location |
mitochondrial matrix |
cytosol |
|
acyl carriers (thiols) |
Coenzyme-A |
phosphopantetheine (ACP) & cysteine |
|
electron acceptors/donor |
FAD & NAD+ |
NADPH |
|
hydroxyl intermediate |
L |
D |
|
2-C product/donor |
acetyl-CoA |
malonyl-CoA (& acetyl-CoA) |
VITAMIN C: ASCORBIC ACID, ASCORBATE
Vitamin C benefits the body by holding cells together through collagen synthesis; collagen is a connective tissue that holds muscles, bones, and other tissues together. Vitamin C also aids in wound healing, bone and tooth formation, strengthening blood vessel walls, improving immune system function, increasing absorption and utilization of iron, and acting as an antioxidant.
RDA The Recommended Dietary Allowance (RDA) for Vitamin C is 90 mg/day for adult males and 75 mg/day for adult females
Vitamin C Deficiency
Severe vitamin C deficiency result in the disease known as scurvy, causing a loss of collagen strength throughout the body. Loss of collagen results in loose teeth, bleeding and swollen gums, and improper wound healing.
The Bicarbonate Buffer System
This is the main extracellular buffer system which (also) provides a means for the necessary removal of the CO2 produced by tissue metabolism. The bicarbonate buffer system is the main buffer in blood plasma and consists of carbonic acid as proton donor and bicarbonate as proton acceptor :
H2CO3 = H+ + HCO3–
If there is a change in the ratio in favour of H2CO3, acidosis results.
This change can result from a decrease in [HCO3 − ] or from an increase in [H2CO3 ]
Most common forms of acidosis are metabolic or respiratory
Metabolic acidosis is caused by a decrease in [HCO3 − ] and occurs, for example, in uncontrolled diabetes with ketosis or as a result of starvation.
Respiratory acidosis is brought about when there is an obstruction to respiration (emphysema, asthma or pneumonia) or depression of respiration (toxic doses of morphine or other respiratory depressants)
Alkalosis results when [HCO3 − ] becomes favoured in the bicarbonate/carbonic acid ratio
Metabolic alkalosis occurs when the HCO3 − fraction increases with little or no concomitant change in H2CO3
Severe vomiting (loss of H+ as HCl) or ingestion of excessive amounts of sodium bicarbonate (bicarbonate of soda) can produce this condition
Respiratory alkalosis is induced by hyperventilation because an excessive removal of CO2 from the blood results in a decrease in [H2CO3 ]
Alkalosis can produce convulsive seizures in children and tetany, hysteria, prolonged hot baths or lack of O2 as high altitudes.
The pH of blood is maintained at 7.4 when the buffer ratio [HCO3 − ] / [ H2CO3] becomes 20
Polyprotic Acids
• Some acids are polyprotic acids; they can lose more than one proton.
• In this case, the conjugate base is also a weak acid.
• For example: Carbonic acid (H2CO3 ) can lose two protons sequentially.
• Each dissociation has a unique Ka and pKa value.
Ka1 = [H+ ][HCO3 - ] / [H2CO3]
Ka2 = [H+ ][CO3 -2 ] / [HCO3- ]
Note: (The difference between a weak acid and its conjugate base differ is one hydrogen)
CALCIUM
Total calcium in the human body is 1 to 1.5kg, out of which 99% is seen in bone and 1% in extracellular fluid. The main source of calcium is milk.
The daily requirement of calcium for child is 1200mg/day and for adult it is 500mg/day. During pregnancy /lactation the calcium requirement is 1500mg/day.
The absorption of calcium takes place in 1st and 2nd part of deuodenum. Calcium absorption requires carrier protein, helped by Ca2+ - dependent ATpase.
Factors responsible for increase in calcium absorption include Vitamin D, Parathyroid hormone, acidity and amino acids. Factors such as phytic acid,oxalates, malabsorption syndromes and Phosphates decreases calcium absorption. The normal calcium level in blood is 9-11mg/dl.