NEET-PG 2012 Practice Questions

Q: Which of the following statements about protein denaturation is correct?

The primary structure of the protein is unaffected.. ***The primary structure of the protein is unaffected.*** - Denaturation refers to the disruption of a protein's **secondary, tertiary, and quaternary structures**, while the **covalent peptide bonds** that form the primary structure remain intact. - The sequence of amino acids, which defines the primary structure, is not typically altered by denaturing agents such as heat, pH changes, or chemicals. *Biological properties are retained after denaturation.* - Denaturation typically leads to the **loss of a protein's specific three-dimensional shape**, which is essential for its biological function. - Therefore, the biological properties and **activity of the protein are usually lost** or significantly impaired upon denaturation. *Denaturation is always irreversible.* - While many cases of denaturation are irreversible (e.g., cooking an egg), some proteins can **renature** if the denaturing conditions are removed, restoring their original structure and function. - This reversibility depends on the **severity and duration of the denaturing agent**, as well as the protein's inherent stability. *Denaturation never results in proteins becoming insoluble.* - Denaturation often exposes **hydrophobic regions** of a protein that were previously buried within its folded structure, leading to aggregation and **precipitation**, thereby making the protein insoluble. - This insolubility is a common consequence of denaturation, particularly with significant structural disruption.

Q: Acute intermittent porphyria is due to deficiency of?

Porphobilinogen deaminase. ***Porphobilinogen deaminase*** - **Acute intermittent porphyria (AIP)** results from a deficiency in **porphobilinogen deaminase** (also known as hydroxymethylbilane synthase). - This enzyme deficiency leads to the accumulation of **aminolevulinic acid (ALA)** and **porphobilinogen (PBG)**, which are neurotoxic and cause the characteristic symptoms of AIP. *Uroporphyrinogen III synthase* - A deficiency in **uroporphyrinogen III synthase** causes **congenital erythropoietic porphyria (Günther disease)**, which is characterized by severe photosensitivity and hemolytic anemia. - This enzyme defect leads to the accumulation of uroporphyrinogen I and coproporphyrinogen I, not the ALA and PBG associated with AIP. *Ferrochelatase* - Deficiency in **ferrochelatase** causes **erythropoietic protoporphyria (EPP)**, which presents with photosensitivity and chronic liver disease due to the accumulation of **protoporphyrin**. - This condition does not cause the acute neurological attacks seen in AIP. *ALA synthase* - **ALA synthase** is the **rate-limiting enzyme** in heme synthesis; while its activity is crucial, a congenital *deficiency* is not the cause of AIP. - Instead, the *upregulation* of ALA synthase activity in AIP (due to the PBG deaminase block) contributes to the accumulation of ALA and PBG.

Q: The primary site of lipogenesis is:

Liver. ***Liver*** - The **liver** is the principal organ for **de novo lipogenesis**, converting excess carbohydrates into fatty acids and triglycerides. - This process is highly active in response to a high-carbohydrate diet, with the synthesized lipids packaged into **VLDL** for transport. *Skeletal muscles* - **Skeletal muscles** primarily utilize fatty acids for **energy production** rather than synthesizing large amounts of new lipids. - While they can store some triglycerides, their capacity for de novo lipogenesis is significantly lower compared to the liver. *Myocardium* - The **myocardium** (heart muscle) primarily relies on fatty acids for its continuous **energy demands** and has limited capacity for de novo lipogenesis. - Its metabolic focus is on efficient **ATP generation** to maintain cardiac function. *Lungs* - The **lungs** are not a primary site for general lipogenesis, though they are involved in the synthesis of specific lipids like **surfactant**. - Surfactant synthesis is a specialized process crucial for lung function, distinct from general energy storage lipogenesis.

Q: Which amino acid among the following has significant UV absorption at 280 nm used in protein quantification?

Tyrosine. ***Correct Option: Tyrosine*** - Tyrosine contains a **phenol functional group** (aromatic ring with hydroxyl group), giving it **significant UV absorption at 280 nm** (specifically ~274 nm) - Along with **tryptophan** and **phenylalanine**, tyrosine is one of the three aromatic amino acids used for **protein quantification via UV spectroscopy** - The aromatic side chain with conjugated double bonds enables strong UV light absorption *Incorrect Option: Alanine* - Alanine has a **methyl group** as its side chain (non-polar, aliphatic) - **Lacks aromatic rings** or conjugated systems - Does **not absorb UV light** at 280 nm *Incorrect Option: Histidine* - Histidine has an **imidazole ring** (heterocyclic aromatic) in its side chain - While technically aromatic, it has **minimal UV absorption at 280 nm** (weak absorption around 210-230 nm) - **Not used for protein quantification** at 280 nm due to insignificant absorption at this wavelength *Incorrect Option: Arginine* - Arginine contains a **guanidinium group** (highly basic, polar) - **Non-aromatic structure** without conjugated double bonds - Does **not exhibit UV absorption** at wavelengths used for protein analysis

Q: What does Chargaff's rule state regarding the base pairing in DNA?

A=T, G=C. ***A=T, G=C*** - **Chargaff's rules** state that in any double-stranded DNA, the amount of **adenine (A)** is approximately equal to the amount of **thymine (T)**, and the amount of **guanine (G)** is approximately equal to the amount of **cytosine (C)**. - This equivalency reflects the specific **base pairing** in the DNA double helix, where A always pairs with T, and G always pairs with C. *A=G, T=C* - This statement is incorrect as it proposes an atypical and biologically inaccurate pairing between a **purine (A)** and another **purine (G)**, and a **pyrimidine (T)** with a **pyrimidine (C)**. - This combination would disrupt the uniform diameter of the DNA double helix required for its structural stability. *A=C, G=T* - This option is incorrect because it suggests pairing a purine (A) with a pyrimidine (C) and a purine (G) with a pyrimidine (T) in a way that is not observed in natural DNA. - Such pairings would also lead to an irregular width of the DNA molecule, destabilizing its structure. *Any combination possible* - This statement is false; base pairing in DNA is **highly specific** and not random due to chemical and structural constraints. - The specific pairing rules (**A with T, G with C**) are crucial for maintaining the consistent structure of the DNA double helix and for accurate DNA replication and transcription.

Q: Which of the following is most important in sodium and water retention ?

Renin angiotensin system. ***Renin angiotensin system*** - The **renin-angiotensin-aldosterone system (RAAS)** is the most important mechanism for **both sodium AND water retention**, which is what the question specifically asks about. - **Aldosterone** directly promotes **sodium reabsorption** in the principal cells of the collecting duct by increasing apical ENaC channels and basolateral Na-K-ATPase pumps. - **Angiotensin II** stimulates sodium reabsorption in the proximal tubule and also stimulates ADH release, contributing to water retention. - When sodium is retained, **water follows passively** due to the osmotic gradient, resulting in effective volume expansion. - RAAS is the primary system activated in states of volume depletion and is most important for combined sodium and water retention. *Vasopressin* - **Vasopressin (ADH)** primarily controls **water retention only** by increasing aquaporin-2 channels in the collecting duct. - While crucial for water balance, it has minimal direct effect on sodium reabsorption. - It causes retention of **free water**, which can actually dilute plasma sodium concentration. - ADH is the answer if the question asked about water retention alone, but not for combined sodium and water retention. *ANP* - **Atrial natriuretic peptide (ANP)** promotes **sodium and water excretion** (natriuresis and diuresis). - Released in response to atrial stretch from volume expansion. - Acts to *oppose* retention mechanisms, making it incorrect for this question. *BNP* - **Brain natriuretic peptide (BNP)** similarly promotes **natriuresis and diuresis**. - Released from ventricular myocytes in response to volume overload. - Like ANP, it acts to *excrete* sodium and water, not retain them.

Q: From the given pressure-volume curve, identify the end-diastolic volume (EDV) and end-systolic volume (ESV), then calculate the ejection fraction using the formula EF = (EDV - ESV)/EDV × 100%.

60%. ***60%*** - From the pressure-volume loop, the **end-diastolic volume (EDV)** is the volume at point 'a', which is **130 mL**. - The **end-systolic volume (ESV)** is the volume at point 'd', which is **50 mL**. - Using the formula EF = (EDV - ESV) / EDV × 100% = (130 mL - 50 mL) / 130 mL × 100% = 80 mL / 130 mL × 100% = **61.5%**, which rounds to **60%** (the closest option). *40%* - To obtain an ejection fraction of 40%, the ESV would need to be higher, or the EDV lower, than what is indicated by the points 'a' and 'd' on the graph. - (130 - ESV) / 130 = 0.40 => 130 - ESV = 52 => ESV = 78 mL. This isn't consistent with the graph. *50%* - An ejection fraction of 50% would mean that the heart ejected half of its EDV. - (130 - ESV) / 130 = 0.50 => 130 - ESV = 65 => ESV = 65 mL. This value for ESV is not depicted at point 'd'. *55%* - For an ejection fraction of 55%, the calculation would yield a different ESV than what is presented in the curve. - (130 - ESV) / 130 = 0.55 => 130 - ESV = 71.5 => ESV = 58.5 mL. This is not the ESV at point 'd'.

Q: What is the process by which water moves from the extracellular space to the intracellular space?

Osmosis. ***Osmosis*** - **Osmosis** is the movement of water across a **semipermeable membrane** from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration). - In the context of fluid shifts, if the **extracellular fluid** becomes hypotonic relative to the **intracellular fluid**, water will move into the cells to equalize the solute concentration. *Diffusion* - **Diffusion** refers to the net movement of particles from an area of higher concentration to an area of lower concentration, down their **concentration gradient**. - While water molecules can diffuse, **osmosis** specifically describes the net movement of water across a membrane due to **solute concentration differences**, which is the precise mechanism for water moving between fluid compartments. *Filtration* - **Filtration** is the process by which water and solutes move across a membrane due to a **pressure gradient**, typically a **hydrostatic pressure gradient**. - This process is crucial in the kidneys for forming filtrate, but it is not the primary mechanism for water movement between the intra- and extracellular spaces based on solute concentration. *Active transport* - **Active transport** involves the movement of molecules across a membrane against their **concentration gradient**, requiring **energy expenditure** (e.g., ATP). - Water movement between fluid compartments is generally a passive process, relying on **osmotic gradients** rather than direct energy input to pump water molecules.

Question 1

Which statement accurately describes a characteristic of synovial joints?

Accepted Answer

Hyaline cartilage covers the articular surfaces of synovial joints.

Answer

The metacarpo-phalangeal joint is a condyloid joint.

Answer

Cartilage can sometimes divide the joint into two cavities.

Answer

Stability is inversely proportional to mobility in synovial joints.

Question 2

Which of the following statements about protein denaturation is correct?

Accepted Answer

The primary structure of the protein is unaffected.

Answer

Biological properties are retained after denaturation.

Answer

Denaturation is always irreversible.

Answer

Denaturation never results in proteins becoming insoluble.

Question 3

Acute intermittent porphyria is due to deficiency of?

Accepted Answer

Porphobilinogen deaminase

Answer

Uroporphyrinogen III synthase

Answer

Ferrochelatase

Answer

ALA synthase

Question 4

The primary site of lipogenesis is:

Accepted Answer

Liver

Answer

Skeletal muscles

Answer

Myocardium

Answer

Lungs

Question 5

Which amino acid among the following has significant UV absorption at 280 nm used in protein quantification?

Accepted Answer

Tyrosine

Answer

Alanine

Answer

Histidine

Answer

Arginine

Question 6

What does Chargaff's rule state regarding the base pairing in DNA?

Accepted Answer

A=T, G=C

Answer

A=G, T=C

Answer

A=C, G=T

Answer

Any combination possible

Question 7

Which of the following is most important in sodium and water retention ?

Accepted Answer

Renin angiotensin system

Answer

ANP

Answer

BNP

Answer

Vasopressin

Question 8

From the given pressure-volume curve, identify the end-diastolic volume (EDV) and end-systolic volume (ESV), then calculate the ejection fraction using the formula EF = (EDV - ESV)/EDV × 100%.

Accepted Answer

60%

Answer

40%

Answer

50%

Answer

55%

Question 9

What is the process by which water moves from the extracellular space to the intracellular space?

Accepted Answer

Osmosis

Answer

Diffusion

Answer

Filtration

Answer

Active transport

Question 10

The plateau phase of this graph is due to:

Accepted Answer

The calcium channels remaining open longer than the sodium channels

Answer

Increased membrane permeability to potassium ions

Answer

A decrease in calcium diffusion across the membrane

Answer

The movement of fewer sodium ions across the cell membrane

NEET-PG 2012

Anatomy

Biochemistry

Physiology