INI-CET 2024 - Biochemistry PYQs Practice Questions

Q: Select the correct sequence of events in the cAMP signaling pathway.

Adenylyl cyclase converts ATP to cAMP, which activates PKA.. ***Adenylyl cyclase converts ATP to cAMP, which activates PKA.*** - **Adenylyl cyclase** is an enzyme that catalyzes the conversion of **ATP (adenosine triphosphate)** into **cyclic AMP (cAMP)**, a crucial second messenger. - Subsequently, **cAMP** binds to and activates **Protein Kinase A (PKA)**, which then phosphorylates various target proteins to mediate cellular responses. *PKA is activated before cAMP is formed.* - **cAMP formation** is a prerequisite for **PKA activation**; PKA cannot be activated independently before cAMP is produced. - The binding of **cAMP** to the regulatory subunits of **PKA** is what causes the dissociation and activation of its catalytic subunits. *Adenylyl cyclase activates PKA before producing cAMP.* - **Adenylyl cyclase's** sole function in this pathway is to synthesize **cAMP** from ATP; it does not directly activate PKA. - **PKA activation** is mediated by **cAMP**, not directly by adenylyl cyclase. *cAMP directly activates adenylyl cyclase to produce more cAMP.* - While **cAMP** is a critical messenger, it does not directly activate **adenylyl cyclase** to produce more of itself in a positive feedback loop. - **Adenylyl cyclase** is typically activated by **G-protein coupled receptors (GPCRs)** binding to their ligands, which then stimulate G proteins to activate adenylyl cyclase. [Practice more Biochemistry PYQs on OnCourse]

Q: Which of the following is not an amino acid-derived neurotransmitter?

Creatine. ***Creatine*** - **Creatine** is an organic compound that helps supply energy to cells, primarily muscle cells, but it does **not** function as a neurotransmitter. - It is synthesized from **amino acids** like arginine, glycine, and methionine, but it is not itself an amino acid-derived neurotransmitter. *Dopamine* - **Dopamine** is a **catecholamine neurotransmitter** derived from the amino acid **tyrosine**. - It plays crucial roles in **motivation**, reward, motor control, and various other brain functions. *GABA* - **GABA** (gamma-aminobutyric acid) is the **primary inhibitory neurotransmitter** in the central nervous system, derived from the amino acid **glutamate**. - It works to reduce neuronal excitability throughout the nervous system. *Serotonin* - **Serotonin** (5-hydroxytryptamine or 5-HT) is a **monoamine neurotransmitter** derived from the amino acid **tryptophan**. - It regulates mood, appetite, sleep, and numerous other physiological processes. [Practice more Biochemistry PYQs on OnCourse]

Q: Which is not a product of heme catabolism?

Aminolevulinic acid. ***Aminolevulinic acid*** - **Aminolevulinic acid (ALA)** is a precursor in the **heme biosynthetic pathway**, not a product of its degradation. - The formation of ALA is the **rate-limiting step** in heme synthesis, catalyzed by ALA synthase. *Ferrous ion* - During heme catabolism, the **iron atom (Fe2+)** is released from the porphyrin ring. - This **ferrous ion** is then recycled or stored, as it is a product of heme degradation. *Biliverdin* - **Biliverdin** is the first green-colored product formed when heme oxygenase cleaves the **porphyrin ring** of heme. - It is an intermediate in the conversion of heme to **bilirubin**, making it a direct product of heme catabolism. *Carbon monoxide* - The oxidative cleavage of the heme ring by **heme oxygenase** liberates one molecule of **carbon monoxide (CO)**. - This CO is an important signaling molecule and has vasodilatory effects, making it a product of heme degradation. [Practice more Biochemistry PYQs on OnCourse]

Q: Which of the following minerals is needed for fertility?

Zinc. ***Zinc*** - Zinc is crucial for **reproductive health** in both men and women, impacting **testosterone synthesis**, **spermatogenesis**, egg quality, and **hormone regulation**. - Essential for **gonadal development** and function in both sexes. - Deficiency leads to **hypogonadism**, reduced fertility, impaired sperm production, and increased risk of **miscarriage**. - Most commonly deficient mineral affecting fertility globally. *Selenium* - Selenium is also **essential for male fertility**, being a critical component of **glutathione peroxidase** in sperm mitochondria. - Required for **sperm motility**, morphology, and structural integrity of the sperm midpiece. - Deficiency can cause male infertility due to impaired sperm function. - However, zinc deficiency is more prevalent and has broader effects across both male and female reproductive systems. *Iron* - Iron is vital for **red blood cell formation** and preventing **anemia**. - Severe iron deficiency anemia can **impair ovulation** and indirectly affect fertility in women. - Not directly involved in reproductive processes at the cellular level like zinc. *Copper* - Essential for various enzymatic functions but not primarily associated with fertility. - **Excessive copper** can negatively impact fertility and cause hormonal imbalances. - Deficiency is rare and not a primary cause of infertility. [Practice more Biochemistry PYQs on OnCourse]

Q: Which nutrient deficiency directly impairs hydroxylation during collagen synthesis?

D. Vitamin C. ***Vitamin C*** - **Vitamin C** (ascorbic acid) is a crucial **cofactor** for the enzymes **prolyl hydroxylase** and **lysyl hydroxylase**, which are essential for **collagen cross-linking and stability**. - Its deficiency leads to **scurvy**, characterized by weakened connective tissue, impaired wound healing, and fragile blood vessels due to **defective collagen synthesis**. *Vitamin D* - **Vitamin D** is primarily involved in **calcium and phosphate homeostasis**, which are vital for bone mineralization. - Its deficiency can lead to **rickets** in children and **osteomalacia** in adults, conditions of weakened bones, but not directly to collagen defects. *Copper* - **Copper** is a cofactor for **lysyl oxidase**, an enzyme that cross-links collagen and elastin, contributing to the tensile strength of connective tissues. - While copper deficiency can affect collagen structure, **Vitamin C deficiency** has a more direct and severe impact on the initial synthesis and hydroxylation steps of collagen, making it the primary answer for collagen defects. *Vitamin E* - **Vitamin E** is a fat-soluble antioxidant that protects cell membranes from **oxidative damage**. - Its deficiency is associated with neurological symptoms and hemolytic anemia but does not directly cause defects in **collagen synthesis or structure**. [Practice more Biochemistry PYQs on OnCourse]

Question 1

Select the correct sequence of events in the cAMP signaling pathway.

Accepted Answer

Adenylyl cyclase converts ATP to cAMP, which activates PKA.

Answer

PKA is activated before cAMP is formed.

Answer

Adenylyl cyclase activates PKA before producing cAMP.

Answer

cAMP directly activates adenylyl cyclase to produce more cAMP.

Question 2

Which of the following is not an amino acid-derived neurotransmitter?

Accepted Answer

Creatine

Answer

Dopamine

Answer

GABA

Answer

Serotonin

Question 3

Which is not a product of heme catabolism?

Accepted Answer

Aminolevulinic acid

Answer

Ferrous ion

Answer

Biliverdin

Answer

Carbon monoxide

Question 4

Which of the following minerals is needed for fertility?

Accepted Answer

Zinc

Answer

Copper

Answer

Iron

Answer

Selenium

Question 5

Which nutrient deficiency directly impairs hydroxylation during collagen synthesis?

Accepted Answer

D. Vitamin C

Answer

A. Vitamin D

Answer

B. Copper

Answer

C. Vitamin E

Question 6

Congenital lactic acidosis is due to the defect of:

Accepted Answer

Pyruvate dehydrogenase

Answer

Transaldolase

Answer

Alpha-ketoglutarate dehydrogenase

Answer

Branched chain alpha-ketoacid dehydrogenase

Question 7

Which gene defect causes familial hypercholesterolemia?

Accepted Answer

LDL Receptor

Answer

Apo E

Answer

Apo CII

Answer

Apo B48

Question 8

In an infant presenting with doll-like facies, which enzyme is deficient in Von Gierke disease?

Accepted Answer

Glucose 6 phosphatase

Answer

Fructose 1,6 bisphosphatase

Answer

Debranching enzyme

Answer

Phosphorylase

Question 9

A male with hyperpigmentation tanner stage 5 presents with hypertension & precocious puberty. The causative defect is:

Accepted Answer

11 beta hydroxylase deficiency

Answer

17 alpha hydroxylase deficiency

Answer

17 beta hydroxylase deficiency

Answer

21 beta hydroxylase deficiency

Question 10

Which type of mutation can act as a suppressor to restore the wild-type phenotype in organisms carrying a mutant gene?

Accepted Answer

Mutation of tRNA

Answer

Frameshift mutation of coding gene

Answer

Deletion of mutant gene

Answer

Addition of another normal gene

INI-CET 2024 — Biochemistry