Medical Biochemistry
Question 1
Which disease would occur if there was a deficiency in the enzyme necessary for the conversion of phenylalanine to tyrosine:
A. maple syrup urine disease
B. phenylketonuria
C. tyrosemia
D. galactosemia
Correct Answer: B - Phenylketonuria
Explanation:
Phenylketonuria (PKU)(Choice A) is the disease caused by the impaired conversion of phenylalanine to tyrosine due to the absence of breaking down enzyme. Hence it will be build up excessively in the body and results in various medical problems including brain damage. The common symptom of PKU is “mousy” smell in urine and also in the body. The occurrence of PKU can be predicted in a baby in very earlier stages, even when it is in the mother’s womb.
Maple Syrup disease (Choice A) is an uncommon medical condition usually trailed from one of the parent’s. It is often confused with the PKU due to the similarities in the clinical symptoms. But there are similarities in the basis of the disorder. The urine is often characterized by sweet smell like the maple syrup.
Tyrosinemia (Choice C)is also an uncommon medical condition due to absence of tyrosine breaking substances/enzymes. This result in an increase in acidic tyrosine in the blood stream and hence cause health problems. This disorder is often characterized by nervous system problems and stomach related symptoms. Though most of the features are similar to PKU and other disorders, the distinct feature to identify tyrosinemia is the “rotten/boiled cabbage” smelled urine which is absent in PKU and other similar problems.
Galactosemia (Choice D)is a rare disorder that affects the individuals’ right from the birth, due to the absence of breaking substances the complex form of biological substances (sugars) is not converted to simpler substances. Like PKU, it is also caused by the enzyme deficiency. This medical condition can be identified by number of medical laboratory tests.
Question 2
The molecule that enzymes act upon is known as:
A. product
B. proteins
C. amino acids
D. substrate
Correct Answer: D - Substrate
Explanation:
(Choice D) The molecule that enzyme act upon is known as substrate. In a chemical reaction, substrate can be any biological substance to which the enzyme binds/reacts and the chemical reaction proceeds to form one or more products.
(Choice A) The formation of the product is the final step in a chemical reaction. The product(s) is/are the final end product(s) that form after the enzyme reacts with the substrate.
(Choice B) All enzymes are proteins that act up on the substrate to form a product. But the final product will not be a protein or protein complex.
(Choice C) Amino acids are also biological molecules that present mostly in the enzyme binding sites (active sites). In these active sites, the substrates bind to the active sites, and then the chemical reaction will proceed.
Question 3
Which of the following is a product of pyruvate that can enter the TCA cycle
A. acetyl CoA
B. CO2
C. isocitrate
D. oxaloacetic acid
Correct Answer: A – AcetylCoA
Explanation:
(Choice A) The pyruvate enters the TCA cycle through an intermediate/product called acetyl CoA by means of oxidative process (oxidation). By the mediation of enzyme pyruvate dehydrogenase, acetyl CoA is produced.
(Choice B) CO2 is a by-product of the pyruvate to acetyl CoA reaction. The main product of this reaction is the Acetyl CoA and the additional products that are formed during this reaction are NADH and CO2.
(Choice C) Isocitrate is produced after the formation of intermediary product called citrate. This step proceeds after the formation of acetyl CoA from the pyruvate.
(Choice D) In the Krebs cycle, the oxaloacetate is produced as a terminal product in the citric acid cycle pathway with acetyl CoA as a precursor.
