NEET-PG 2012

1213 Questions — Page 22 of 122

Anatomy

1 questions

Q211

All are lateral branches of the abdominal aorta, EXCEPT which of the following?

Biochemistry

6 questions

Q211

Neonatal tyrosinemia is due to deficiency of which enzyme?

Q212

Lipogenesis is stimulated by?

Q213

The Central Dogma of molecular biology includes all except?

Q214

DNA microarrays allow detection of gene mutations through which process?

Q215

Enzymes that move a molecular group from one molecule to another are known as -

Q216

What is the net number of ATP molecules and NADH formed in glycolysis per glucose molecule?

NEET-PG 2012 - Biochemistry NEET-PG Practice Questions and MCQs

Question 211: Neonatal tyrosinemia is due to deficiency of which enzyme?

A. Tyrosine transaminase
B. Hydroxyphenyl pyruvate hydroxylase (Correct Answer)
C. Fumarylacetoacetate hydroxylase
D. Tyrosinase

Explanation: ***Hydroxyphenyl pyruvate hydroxylase*** - **Neonatal (transient) tyrosinemia** is caused by delayed maturation or deficiency of **hydroxyphenylpyruvate hydroxylase** (also called 4-hydroxyphenylpyruvate dioxygenase or HPPD). - This enzyme converts 4-hydroxyphenylpyruvate to homogentisic acid in tyrosine catabolism. - Common in **premature infants** and newborns, leading to elevated tyrosine levels in blood. - The condition is **benign and self-limiting**, usually resolving with **vitamin C supplementation** or as the enzyme matures. - Note: Severe hereditary deficiency of this enzyme causes **tyrosinemia type III**, a distinct and rare disorder. *Fumarylacetoacetate hydroxylase* - Deficiency of **fumarylacetoacetate hydroxylase (FAH)** causes **tyrosinemia type I** (hepatorenal tyrosinemia), NOT neonatal tyrosinemia. - This is a severe hereditary disorder with liver failure, renal tubular dysfunction, and accumulation of toxic metabolites like succinylacetone. - Distinct from the benign transient neonatal form. *Tyrosine transaminase* - Deficiency of **tyrosine transaminase** (tyrosine aminotransferase) causes **tyrosinemia type II** (Richner-Hanhart syndrome). - Presents with corneal ulcers, palmoplantar hyperkeratosis, and sometimes intellectual disability. *Tyrosinase* - Deficiency of **tyrosinase** causes **albinism**, characterized by lack of melanin pigment in skin, hair, and eyes. - Not involved in tyrosine catabolism but in melanin synthesis.

Question 212: Lipogenesis is stimulated by?

A. Insulin (Correct Answer)
B. Glucagon
C. Epinephrine
D. Corticosteroids

Explanation: ***Insulin*** - **Insulin** is a key anabolic hormone that promotes the synthesis and storage of fat (lipogenesis) by increasing the uptake of glucose into adipose tissue and stimulating enzymes involved in fatty acid synthesis. - It enhances the conversion of excess carbohydrates into **triglycerides** for storage. *Glucagon* - **Glucagon** is a catabolic hormone that primarily promotes the breakdown of glycogen (glycogenolysis) and fat (lipolysis) to release glucose and fatty acids into the bloodstream, especially during fasting. - It generally **inhibits** lipogenesis and stimulates **gluconeogenesis**. *Epinephrine* - **Epinephrine** (adrenaline) is a stress hormone that promotes the breakdown of fat (lipolysis) to provide energy during acute stress or exercise. - It would **inhibit** lipogenesis, as its primary role is to mobilize energy stores. *Corticosteroids* - While **corticosteroids** can influence fat metabolism, their effect on lipogenesis is complex and often indirect. High levels can lead to fat redistribution (e.g., central obesity) rather than direct stimulation of overall lipogenesis. - Corticosteroids generally promote **lipolysis** in the extremities and can contribute to insulin resistance, which would hinder lipogenesis in some tissues.

Question 213: The Central Dogma of molecular biology includes all except?

A. Reverse transcription (Correct Answer)
B. Transcription
C. RNA replication
D. Translation

Explanation: ***Reverse transcription*** - The **original Central Dogma** as proposed by Francis Crick described the unidirectional flow of genetic information: **DNA → RNA → Protein**. - **Reverse transcription** (RNA → DNA) was **not part of the original Central Dogma** and was only discovered later with the identification of **reverse transcriptase enzyme** in retroviruses by Baltimore and Temin (1970). - While reverse transcription is now recognized as an important biological process, it represents an **exception to the classical Central Dogma** rather than a core component. *Transcription* - **Transcription** (DNA → RNA) is a **fundamental process** within the Central Dogma. - It involves synthesis of RNA from a DNA template and is the first step in gene expression in all living organisms. *Translation* - **Translation** (RNA → Protein) is the **second major step** of the Central Dogma. - This process occurs on ribosomes where mRNA is decoded into a specific sequence of amino acids to form proteins. *RNA replication* - **RNA replication** (RNA → RNA), while primarily seen in RNA viruses, is considered part of the **expanded Central Dogma**. - It represents one of the possible flows of genetic information in biological systems, though not universal to all organisms.

Question 214: DNA microarrays allow detection of gene mutations through which process?

A. Polymerase Chain Reaction
B. Cloning
C. Southern Blotting
D. Hybridization (Correct Answer)

Explanation: ***Hybridization*** - DNA microarrays detect mutations by **hybridizing labeled patient DNA** to **thousands of oligonucleotide probes** containing known DNA sequences immobilized on a solid surface. - A mismatch between the patient's DNA and the probe results in **reduced or absent hybridization**, indicating a **mutation or genetic variation**. - This principle allows **high-throughput screening** of multiple genes simultaneously. *Polymerase Chain Reaction* - PCR is used to **amplify specific DNA sequences exponentially**, creating millions of copies from minimal starting material. - While PCR may be used to **prepare DNA samples** before microarray analysis, it is **not the detection mechanism** on the chip itself. *Cloning* - Cloning involves creating **identical copies of DNA fragments, cells, or organisms** using vectors and host cells. - It's a method for **producing large quantities** of specific DNA sequences but **not a detection technique** for mutations on microarrays. *Southern Blotting* - Southern blotting detects specific DNA sequences through **gel electrophoresis, membrane transfer, and probe hybridization**. - While it also uses hybridization, it is a **low-throughput technique** analyzing one sample at a time, unlike the **high-throughput parallel analysis** of DNA microarrays.

Question 215: Enzymes that move a molecular group from one molecule to another are known as -

A. Transferases (Correct Answer)
B. Ligases
C. Dipeptidases
D. Oxido-reductases

Explanation: ***Transferases*** - **Transferases** are a class of enzymes that catalyze the transfer of a specific functional group (e.g., methyl, acetyl, phosphate) from one molecule (the donor) to another (the acceptor). - This broad category includes enzymes vital for many metabolic pathways, such as **kinases** (transferring phosphate groups) and **transaminases** (transferring amino groups). *Ligases* - **Ligases** are enzymes responsible for joining two large molecules together, typically by forming a new chemical bond. - This process usually involves the concomitant hydrolysis of a small, energy-rich molecule such as **ATP**, to provide the necessary energy for bond formation. *Dipeptidases* - **Dipeptidases** are a type of hydrolase enzyme that specifically cleaves the peptide bond within a **dipeptide**, releasing two free amino acids. - They are crucial for the final stages of protein digestion, breaking down small peptides into absorbable **amino acid units**. *Oxido-reductases* - **Oxido-reductases** are enzymes that catalyze **oxidation-reduction reactions** (redox reactions), where electrons are transferred from one molecule to another. - This class includes enzymes like **dehydrogenases** and **oxidases**, which play critical roles in cellular respiration and energy production.

Question 216: What is the net number of ATP molecules and NADH formed in glycolysis per glucose molecule?

A. 4 ATP, 2 NADH
B. 4 ATP, 4 NADH
C. 2 ATP, 4 NADH
D. 2 ATP, 2 NADH (Correct Answer)

Explanation: **2 ATP, 2 NADH** - Glycolysis has a net yield of **2 molecules of ATP** because 4 ATP molecules are produced, but 2 ATP molecules are consumed during the initial energy investment phase. - **2 molecules of NADH** are also produced during the energy generation phase when glyceraldehyde-3-phosphate is oxidized. *4 ATP, 2 NADH* - While 4 ATP molecules are indeed produced during glycolysis, this option does not account for the **2 ATP molecules consumed** in the initial steps, leading to an incorrect net value. - The production of **2 NADH** is correct, but the ATP count is the gross rather than the net. *4 ATP, 4 NADH* - This option overstates the production of both ATP and NADH. While **4 ATP are produced (gross)**, the net is 2 ATP. - Only **2 NADH** molecules are formed per glucose molecule in glycolysis, not 4. *2 ATP, 4 NADH* - This option accurately reflects the **net ATP yield of 2 molecules**. - However, it exaggerates the production of NADH, as only **2 molecules of NADH** are formed during glycolysis, not 4.

Physiology

3 questions

Q211

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%.

Q212

Which of the following factors increases stroke volume?

Q213

Tetanic contraction is due to accumulation of?

NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs

Question 211: 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%.

A. 40%
B. 50%
C. 55%
D. 60% (Correct Answer)

Explanation: ***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'.

Question 212: Which of the following factors increases stroke volume?

A. Increased end-diastolic and end-systolic volumes
B. Decreased end-diastolic and end-systolic volumes
C. Increased end-diastolic volume and decreased end-systolic volume (Correct Answer)
D. Decreased end-diastolic volume and increased end-systolic volume

Explanation: ***Increased end-diastolic volume and decreased end-systolic volume*** - **Stroke volume (SV)** is calculated as **End-Diastolic Volume (EDV)** minus **End-Systolic Volume (ESV)**. Therefore, increasing the volume before contraction while decreasing the volume after contraction will maximize the ejected blood. - A higher **EDV** signifies greater **preload** (more blood filling the ventricle), and a lower **ESV** indicates more complete ejection of blood, often due to increased **contractility** or decreased **afterload**. *Increased end-diastolic and end-systolic volumes* - While an **increased EDV** would tend to increase stroke volume, an **increased ESV** suggests that the heart is ejecting less blood per beat, which would decrease stroke volume. - The combined effect makes it less likely to unequivocally increase stroke volume, as the increase in ESV might offset or even surpass the effect of increased EDV. *Decreased end-diastolic and end-systolic volumes* - Both a **decreased EDV** (less filling) and a **decreased ESV** (more complete ejection) work against each other in terms of stroke volume calculation. - If **EDV** decreases, there's less blood to eject, and if the decrease in **EDV** is proportionally larger than the decrease in **ESV**, stroke volume will decrease. *Decreased end-diastolic volume and increased end-systolic volume* - A **decreased EDV** means less blood is available for ejection, reducing preload and the amount of blood the heart can pump. - An **increased ESV** means the heart is ejecting less blood with each beat, indicating reduced contractility or increased afterload, both of which would decrease stroke volume.

Question 213: Tetanic contraction is due to accumulation of?

A. Na+
B. K+
C. Ca2+ (Correct Answer)
D. Cl-

Explanation: ***Ca2+*** - **Tetanic contraction** results from a rapid succession of muscle stimulations, leading to the sustained elevation of **intracellular calcium (Ca2+)** levels. - This persistent high Ca2+ concentration in the sarcoplasm allows for continuous binding to **troponin**, maintaining the activation of cross-bridge cycling. *Na+* - **Sodium (Na+)** influx is primarily responsible for the **depolarization** of the muscle cell membrane, leading to an **action potential**. - While essential for initiating the contraction, Na+ accumulation itself does not directly cause the sustained high Ca2+ levels characteristic of tetany. *K+* - **Potassium (K+)** efflux is crucial for the **repolarization** of the muscle cell membrane after an action potential. - Accumulation of K+ in the extracellular space can contribute to muscle fatigue and reduce excitability, but it does not directly lead to tetanic contraction. *Cl-* - **Chloride (Cl-)** ions play a significant role in stabilizing the resting membrane potential and contributing to muscle **repolarization**, particularly in skeletal muscle. - While important for muscle function, changes in Cl- concentration do not directly cause the sustained Ca2+ release required for tetanic contraction.