Which of the following is false?
Answer: D
Correct answer: Heterotropic allosteric enzymes have the substrate and modulator same
That is the wrong way round. In a homotropic enzyme the substrate is itself the modulator - which is what produces cooperative binding and the sigmoid curve. In a heterotropic enzyme the modulator is a different molecule, typically the end product of the pathway.
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The total blood volume of an individual is approximately
Answer: D
Correct answer: 80 ml/Kg body weight
Blood volume is roughly 80 ml per kilogram in an adult, so a 70 kg person has about 5.6 litres - some 7-8% of body weight. Infants have proportionately more, about 85-90 ml/kg. The figure matters in judging how much blood loss a patient can tolerate.
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Enzymes are
Answer: A
Correct answer: organic compounds produced by living organism
Enzymes are organic catalysts - proteins, with a few catalytic RNAs - made by living cells. Their being protein is what gives them their specificity and their sensitivity to heat and pH. Inorganic catalysts exist, but they are not enzymes.
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The control and regulation of biological processes involve some enzymes. They are known as
Answer: C
Correct answer: allosteric enzymes
Allosteric enzymes are the control points of metabolism. Because a modulator binding at a regulatory site can change the activity of the catalytic site, such an enzyme responds to signals other than its own substrate - which is what lets a pathway be regulated by conditions elsewhere in the cell.
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How does a noncompetitive inhibitor affect an enzyme?
Answer: C
Correct answer: Lowers the maximum rate of the enzymatic reaction
A noncompetitive inhibitor binds at a separate site and disables whatever enzyme molecules it occupies, whatever the substrate concentration. In effect it removes enzyme from the pool, so \(V_{max}\) falls while \(K_m\) stays the same - the molecules still working have the same affinity as before.
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Main function of an enzyme is to
Answer: B
Correct answer: decrease the activation energy
An enzyme lowers the activation energy by binding the substrate in a strained arrangement that resembles the transition state, so a far greater fraction of molecules have enough energy to react. What it does not change is the equilibrium or the overall free energy change - it makes the reaction faster, not more favourable, and it speeds both directions equally.
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Normal range of MCHC is
Answer: C
Correct answer: 35 ±3 gm%
MCHC normally runs at about 32-38 g/dL, that is 35 ± 3. It cannot rise much above that, because the red cell is already close to saturated with haemoglobin - which is why a value below the range (hypochromia, as in iron deficiency) is common while a high one usually means spherocytosis or an artefact.
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Number of iron atoms in one haemoglobin molecule are
Answer: C
Correct answer: 4
A haemoglobin molecule has four globin chains - two alpha and two beta - each with one haem group holding one iron atom. So one molecule binds four O2, and the binding is cooperative: each one bound makes the next easier, which is what gives the oxygen dissociation curve its sigmoid shape.
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Which of the following is a proenzyme?
Answer: A
Correct answer: Pepsinogen
A proenzyme (zymogen) is an inactive precursor activated by cleavage. Pepsinogen becomes pepsin in stomach acid; trypsinogen becomes trypsin, and chymotrypsinogen chymotrypsin. Trypsin and chymotrypsin as listed are the active forms, so they are not proenzymes.
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Increased synthesis of an enzyme is known as
Answer: B
Correct answer: Induction
Induction is an increase in the rate at which an enzyme is synthesised, usually because a substrate or signal molecule has relieved the repression of its gene. The lac operon is the standard example: lactose induces the enzymes that digest it.
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