PGMEE Biochemistry MCQs 11-20

Q-11. In chromatography mass movements of the substances in due to:
a) Diffusion
b) Electrophoresis
c) Osmosis
d) Paper chromatography

Answer: Diffusion
Chromatography is a method by which a mixture is separated by distributing its components between two phases. The stationary phase remains fixed in place while the mobile phase carries the components of the mixture through the medium being used.
Diffusion is the process whereby solute is transferred in a fluid from a point of high concentration to a point of lower concentration. Diffusion is a concentration driven mass transfer process.
Solute diffusivity affects the quality of a chromatographic separation in two ways. If the diffusivity of the solute is high in the two phases of a chromatographic system, solute exchange is rapid.

Q-12. Vitamin K is needed for which of these post translational modification processes:
a) Methylation
b) Carboxylation
c) Hydroxylation
d) Transketolation

Answer: Carboxylation
Gamma-glutamyl carboxylase is an enzyme that catalyzes the posttranslational modification of vitamin K-dependent proteins.
Many of these vitamin K-dependent proteins are involved in coagulation so the function of the encoded enzyme is essential for hemostasis.
The posttranslational modifications of proteins that depend upon vitamin C as a cofactor include proline and lysine hydroxylations and carboxy terminal amidation. The hydroxylating enzymes are identified as prolyl hydroxylase and lysyl hydroxylase.
The donor of the amide for C-terminal amidation is glycine.
The most important hydroxylated proteins are the collagens.
Several peptide hormones such as oxytocin and vasopressin have C-terminal amidation.

Q- 13. Which end product of citric acid cycle is used in detoxification of ammonia in brain?
a) Citrate
b) Succinate
c) Alfa-keto glutarate
d) Oxalo-acetate

Answer: Alfa-keto glutarate
Glutamine is an amide of Glutamic acid which is formed from alfa-keto glutarate.
Glutamine is the sole form of transport of ammonia in brain.
Glutamine provides non-toxic storage and transport form of ammonia.
The formation of glutamine occurs primarily in the muscles, liver but also important in the nervous system, where it is the major mechanism for the removal of ammonia in the brain.

Q-14. Dietary triglycerides are transported by
a) Chylomicrons
c) LDL
d) HDL

Answer: Chylomicrons
Dietary triglycerides are transported as part of lipoprotein particles called chylomicrons.
Triglycerides synthesized in the liver are transported as part of lipoprotein particles called very low density lipoproteins or VLDLs.

Q-15. Thiamine is not used in which of the following reactions
a) Glucose to pentose
b) Lactate to Pyruvate
c) Oxidative decarboxylation of Alfa-keto amino acids
d) Alfa-keto glutarate to succinyl Co-A

Answer: Lactate to Pyruvate
Thiamine pyrophosphate, or thiamine di-phosphate, is a thiamine (vitamin B1) derivative which is produced by the enzyme thiamine pyrophosphatase.
Thiamine pyrophosphate is a cofactor catalyzes several biochemical reactions.
TPP works as a coenzyme in many enzymatic reactions, such as:
Pyruvate dehydrogenase complex
Pyruvate decarboxylase in ethanol fermentation
Alpha-keto-glutarate dehydrogenase complex
Branched-chain amino acid dehydrogenase complex
2-hydroxyphytanoyl-CoA lyase
Lactate dehydrogenase: It catalyzes the inter-conversion of pyruvate and lactate with concomitant inter-conversion of NADH and NAD+. Co-enzyme is niacin.

Q-16. In which type of chromatography, the proteins are bound to another substance?
a) Gel Chromatography
b) Paper Chromatography
c) Hydrophobic Chromatography
d) Affinity Chromatography

Answer: Affinity Chromatography
Affinity Chromatography is a separation technique based upon molecular conformation, which frequently utilizes application specific resins.
These resins have ligands attached to their surfaces which are specific for the compounds to be separated.
Many membrane proteins are glyco-proteins and can be purified by lectin affinity chromatography.
Detergent-solubilized proteins can be allowed to bind to a chromatography resin that has been modified to have a covalently attached lectin.
Proteins that do not bind to the lectin are washed away and then specifically bound glyco-proteins can be eluted by adding a high concentration of a sugar that competes with the bound glyco-proteins at the lectin binding site.

Q-17. Dietary fibres are degraded by colonic bacteria to form which of the following?
a) Butyrate
b) Glycerol
c) Sucrose
d) Free Radicals

Answer: Butyrate
Some non-absorbed carbohydrates are fermented to short-chain fatty acids (chiefly acetic, propionic and n-butyric), and carbon dioxide, hydrogen and methane. Almost all of these short-chain fatty acids will be absorbed from the colon.
The production of short-chain fatty acids has several possible actions on the gut mucosa.
All of the short-chain fatty acids are readily absorbed by the colonic mucosa, but only acetic acid reaches the systemic circulation in appreciable amounts.
Butyric acid appears to be used as a fuel by the colonic mucosa as the preferred energy source for colonic cells.

Q-18. A child presents with hepatomegaly and bi-lateral lenticular opacities. Deficiency of which of the following enzymes will not cause such features?
a) Galacto-kinase
b) Galactose-1- phosphate uridyl transferase
c) UDP Galactose 4 Epimerase
d) Lactase

Answer: Lactase
Child is suffering from Galactosemia.
Lactase deficiency doesn’t cause Galactosemia.
Defect in the following enzymes can cause Galactosemia:
Galactose-1- phosphate uridyl transferase- Classical type
Galacto-kinase- Minor type
UDP Galactose 4 Epimerase-Rarely seen

Q-19. What is the possible cause of hyper-uricemia and gout in a patient who has a glucose-6-phosphatase deficiency?
a) More formation of pentose
b) Increased accumulation of sorbitol
c) Increased synthesis of glycerol
d) Impaired degradation of free radicals

Answer: More formation of pentose
Cause of hyper-uricemia and gout in glucose-6-phosphatase deficiency:
Increased production of uric acid:
G-6-phosphatase deficiency> Increased G-6-phosphate> Increased pentose formation (HMP shunt) > Increased purine synthesis> Increased uric acid formation
Decreased renal excretion of uric acid:
G-6-phosphatase deficiency> Decreased conversion of G-6-phosphate to Glucose> Hypoglycemia> Increased catecholamines> Increased glycogenolysis in muscles> Increased lactic acidosis> It competes with urate for excretion> Decreased uric acid excretion

Q-20. Cancer cells derive nutrition from
a) Glycolysis
b) Oxidative phosphorylation
c) Increase in mitochondria
d) From a fast food joint

Answer: Glycolysis
Most cancer cells exhibit increased glycolysis and use this metabolic pathway for generation of ATP as a main source of their energy supply.
The paradox is that cancer cells rely on glycolysis even if oxygen is available. This phenomenon is called aerobic glycolysis or the Warburg effect.
Warburg effect is considered as one of the most fundamental metabolic alterations during malignant transformation.