NEET-PG 2013 - Biochemistry Practice Questions

Q: Which type of DNA polymerase is responsible for the replication of mitochondrial DNA?

DNA polymerase gamma. ***DNA polymerase gamma*** - **DNA polymerase gamma** is the sole DNA polymerase responsible for replicating and repairing the mitochondrial DNA in eukaryotic cells. - It consists of a large catalytic subunit and two smaller accessory subunits that provide **proofreading** and processivity functions. *DNA polymerase alpha* - **DNA polymerase alpha** is primarily involved in initiating DNA replication on both the leading and lagging strands of nuclear DNA. - It forms a complex with **primase** to synthesize short RNA primers followed by a short stretch of DNA. *DNA polymerase delta* - **DNA polymerase delta** is a key enzyme in nuclear DNA replication, primarily responsible for the **elongation of the lagging strand**. - It also plays a significant role in various DNA repair pathways, including **nucleotide excision repair**. *DNA polymerase beta* - **DNA polymerase beta** is mainly involved in **DNA repair processes**, specifically **base excision repair (BER)** in the nucleus. - It has a low processivity and lacks **proofreading activity**, making it unsuitable for bulk DNA replication.

Q: Which of the following statements about chaperones is false?

Are lipid in nature. ***Are lipid in nature*** - Chaperones are **proteins** (typically **heat shock proteins** or **chaperonins**), not lipids. - Their function involves assisting in the proper **folding and assembly of other proteins**, and they are composed of amino acids. *Cause folding of proteins* - Chaperones **do not cause** proteins to fold; rather, they **assist in proper folding** and refolding by preventing aggregation or misfolding. - They bind to nascent or partially unfolded proteins to guide them towards their correct three-dimensional structure. *May have ATPase activity* - Many chaperones, especially **Hsp70** and **chaperonins** like GroEL/GroES, utilize **ATP hydrolysis** for their function. - This **ATPase activity** drives conformational changes essential for binding, release, and refolding of their client proteins. *Include heat shock proteins* - The **heat shock protein (Hsp)** families (e.g., Hsp70, Hsp90, Hsp60) are a major class of chaperones. - Hsps are upregulated in response to stress (like heat) to help refold damaged proteins and prevent aggregation.

Q: Which of the following is NOT a characteristic of the genetic code?

Overlapping. ***Overlapping*** - The genetic code is generally **non-overlapping**, meaning each nucleotide is part of only one codon, and codons are read sequentially. - An overlapping code would mean that a single nucleotide could be part of multiple codons, which is not how protein synthesis typically occurs. *Nonambiguous* - This statement IS a characteristic; each codon specifies **only one amino acid**, meaning there is no ambiguity about which amino acid will be added. - While multiple codons can specify the same amino acid, a single codon never specifies more than one different amino acid. *Universal* - This statement IS a characteristic; the genetic code is largely **universal** across almost all organisms, from bacteria to humans. - The same codons typically specify the same amino acids in different species, which supports the idea of common ancestry. *Degeneracy* - This statement IS a characteristic; the genetic code is **degenerate**, meaning that most amino acids are specified by more than one codon. - This redundancy helps protect against the effects of single-nucleotide mutations.

Q: Which type of RNA is primarily involved in gene silencing?

miRNA. ***miRNA*** - **miRNA** (microRNA) is a small non-coding RNA molecule that plays a crucial role in **post-transcriptional regulation of gene expression**. - It functions by binding to complementary messenger RNA (mRNA) molecules, leading to **mRNA degradation** or **inhibition of translation**, thereby silencing genes. - miRNA is the primary RNA type involved in **gene silencing** through the RNA interference (RNAi) pathway. *rRNA* - **rRNA** (ribosomal RNA) is a primary component of **ribosomes**, the cellular machinery responsible for protein synthesis. - Its main function is to **catalyze peptide bond formation** and provide structural integrity to the ribosome, not gene silencing. *tRNA* - **tRNA** (transfer RNA) is responsible for carrying specific **amino acids** to the ribosome during protein synthesis. - It acts as an adapter molecule, translating the **genetic code** in mRNA into an amino acid sequence. *mRNA* - **mRNA** (messenger RNA) carries genetic information from **DNA to ribosomes** for protein synthesis. - While mRNA can be targeted by gene silencing mechanisms (like miRNA), it is not the RNA type that performs the silencing function itself.

Q: What is a physiological uncoupler?

Thermogenin. ***Correct: Thermogenin*** - **Thermogenin (uncoupling protein 1, UCP1)** is the primary physiological uncoupler found in brown adipose tissue - It directly facilitates the **leak of protons** back into the mitochondrial matrix, bypassing ATP synthase - This dissipates the **proton-motive force as heat** rather than producing ATP, making it the classic example of non-shivering thermogenesis - Essential for **temperature regulation** in neonates and cold adaptation in adults *Incorrect: Free fatty acids* - While free fatty acids can activate UCP1 and act as weak protonophores in some contexts, they are primarily **substrates for β-oxidation** and **activators** of thermogenin - They are not considered the primary physiological uncoupler, though they support uncoupling activity *Incorrect: Thyroxine* - **Thyroid hormone** increases metabolic rate and can upregulate the **expression of uncoupling proteins** - However, it does **not directly uncouple** oxidative phosphorylation - It acts as a metabolic regulator rather than a true uncoupler *Incorrect: All of the options* - Only thermogenin is the true physiological uncoupler by definition - The other substances play supportive or regulatory roles but are not direct uncouplers

Q: Which of the following tests is most commonly used to detect glucose in urine?

c) Glucose-oxidase test. ***Glucose-oxidase test*** - The **glucose-oxidase test** is a highly specific and sensitive enzymatic test used to detect **glucose** in urine. - It uses the enzyme glucose oxidase which specifically catalyzes the oxidation of glucose to gluconic acid and hydrogen peroxide, which then produces a color change. - This is the **most commonly used method** in modern clinical practice for detecting glucosuria due to its **high specificity for glucose** and ease of use (dipstick method). - It is the preferred test for **monitoring diabetes** and screening for hyperglycemia. *Benedict's test* - **Benedict's test** is a general chemical test for **all reducing sugars** (glucose, fructose, galactose, lactose, maltose), not specifically glucose. - It works by reducing copper sulfate (Cu²⁺) to copper oxide (Cu⁺) in an alkaline solution, forming a colored precipitate (green, yellow, orange, or brick-red depending on sugar concentration). - While it can detect glucose, it **lacks specificity** and can give false positives with other reducing substances (vitamin C, certain drugs), making it less suitable for routine clinical testing. *Fehling's solution* - **Fehling's solution** is also a general chemical test for **reducing sugars** based on copper reduction, similar to Benedict's test. - It consists of two solutions mixed before use and detects various reducing sugars, not just glucose. - It is **not commonly used in clinical urine analysis** due to lack of specificity and the need for heating and mixing two solutions, making it impractical compared to the simple glucose-oxidase dipstick. *None of the above* - This option is incorrect because the **glucose-oxidase test** is indeed the most commonly used test for detecting glucose in urine in modern clinical practice.

Q: Hay's sulfur test is used to detect which of the following?

Bile salts in urine. ***Bile salts in urine*** - Hay's sulfur test is a classic qualitative test used to detect the presence of **bile salts** in a urine sample. - Bile salts reduce the **surface tension** of urine, causing sulfur powder to sink when sprinkled on the surface. *Reducing sugar in urine* - Reducing sugars (like glucose) are typically detected using tests such as **Benedict's test** or glucose oxidase strips, not Hay's sulfur test. - These tests rely on color changes due to the **reduction of copper ions** or enzymatic reactions, respectively. *Ketone bodies in urine* - Ketone bodies (acetoacetate, beta-hydroxybutyrate, acetone) are detected using tests like the **Rothera's test** or dipsticks, which react with acetoacetate. - These reactions produce color changes in the presence of ketones, unrelated to surface tension. *Urobilinogen in urine* - Urobilinogen in urine is commonly detected using **Ehrlich's reagent** (e.g., in a dipstick test) which forms a red color. - Elevated urobilinogen indicates issues with liver function or hemolysis, and its detection does not involve surface tension.

Q: Apolipoprotein E is rich in

Arginine. ***Arginine*** - **Apolipoprotein E (apoE)** is notably rich in **basic amino acids**, with **arginine** being particularly abundant. - The high content of **positively charged arginine residues** is critical for apoE's ability to bind to negatively charged lipid surfaces and interact with receptors such as the **LDL receptor** and **LDL receptor-related protein (LRP)**. - This arginine-rich composition is a defining characteristic of apoE and is essential for its role in **lipid metabolism** and **receptor-mediated lipoprotein uptake**. *Lysine* - While apoE does contain **lysine** (another basic amino acid), it is **arginine** that is particularly abundant and functionally emphasized. - Both lysine and arginine contribute positive charges, but **arginine residues** are specifically highlighted in apoE's **receptor binding domains** and are more characteristic of this apolipoprotein. *Histidine* - **Histidine** is also a **basic amino acid**, but it is not present in the same high proportions as **arginine** in apoE. - Its pKa (~6.0) is closer to physiological pH, meaning its charge state can vary, making it less consistently positive than arginine or lysine in biological contexts. - Histidine is not a defining feature of apoE's amino acid composition. *Methionine* - **Methionine** is a **sulfur-containing, nonpolar amino acid**, not a basic amino acid. - It does not contribute to the positive charge characteristic of apoE. - Its role in proteins is typically structural or as the initiator of protein synthesis (as the first amino acid), but it is not relevant to apoE's receptor-binding properties.

Q: Which transporter is responsible for the transport of glucose in the pancreas?

GLUT 2. ***GLUT 2*** - **GLUT2** is a **low-affinity, high-capacity** glucose transporter primarily found in the **pancreatic beta cells**, liver, small intestine, and kidneys. - In pancreatic beta cells, GLUT2 allows rapid entry of glucose for metabolism, leading to **insulin secretion** in response to elevated blood glucose levels. *GLUT 1* - **GLUT1** is a **ubiquitous glucose transporter** found in most tissues, including red blood cells and the blood-brain barrier. - It has a high affinity for glucose, ensuring **basal glucose uptake** even at low concentrations. *GLUT 3* - **GLUT3** is a **high-affinity glucose transporter** concentrated in **neurons** and the brain. - Its efficient glucose uptake is critical for the constant and high energy demands of the central nervous system. *GLUT 4* - **GLUT4** is an **insulin-dependent glucose transporter** primarily found in **adipose tissue** and **striated muscle (skeletal and cardiac muscle)**. - Insulin stimulates the translocation of GLUT4 to the cell membrane, facilitating glucose uptake from the blood after a meal.

Q: Which of the following plant components is not fermented by gastrointestinal microorganisms?

Lignin. ***Lignin*** - **Lignin** is a complex polymer found in plant cell walls that is highly resistant to degradation by digestive enzymes and microbial fermentation in the gastrointestinal tract. - Its complex, cross-linked structure makes it **non-fermentable** by the microorganisms typically present in the human gut. *Cellulose* - **Cellulose** is a major component of plant cell walls and is a type of dietary fiber that can be fermented by certain gut bacteria. - While humans lack the enzymes to digest cellulose, colonic microorganisms possess cellulases that break it down into **short-chain fatty acids (SCFAs)**. *Hemicellulose* - **Hemicellulose** is a diverse group of plant polysaccharides that are a significant source of fermentable fiber for gut microbiota. - It is readily broken down by gastrointestinal bacteria into **SCFAs** and gases, contributing to colonic health. *Pectin* - **Pectin** is a soluble dietary fiber found in fruits and vegetables, known for its gel-forming properties. - It is highly fermentable by gut microorganisms, leading to the production of **SCFAs** like butyrate, propionate, and acetate.

Question 1

Which type of DNA polymerase is responsible for the replication of mitochondrial DNA?

Accepted Answer

DNA polymerase gamma

Answer

DNA polymerase delta

Answer

DNA polymerase alpha

Answer

DNA polymerase beta

Question 2

Which of the following statements about chaperones is false?

Accepted Answer

Are lipid in nature

Answer

Cause folding of proteins

Answer

Include heat shock proteins

Answer

May have ATPase activity

Question 3

Which of the following is NOT a characteristic of the genetic code?

Accepted Answer

Overlapping

Answer

Universal

Answer

Degeneracy

Answer

Nonambiguous

Question 4

Which type of RNA is primarily involved in gene silencing?

Accepted Answer

miRNA

Answer

rRNA

Answer

tRNA

Answer

mRNA

Question 5

What is a physiological uncoupler?

Accepted Answer

Thermogenin

Answer

Thyroxine

Answer

Free fatty acids

Answer

All of the options

Question 6

Which of the following tests is most commonly used to detect glucose in urine?

Accepted Answer

c) Glucose-oxidase test

Answer

a) Benedicts test

Answer

b) Fehling solution

Answer

d) None of the above

Question 7

Hay's sulfur test is used to detect which of the following?

Accepted Answer

Bile salts in urine

Answer

Reducing sugar in urine

Answer

Ketone bodies in urine

Answer

Urobilinogen in urine

Question 8

Apolipoprotein E is rich in

Accepted Answer

Arginine

Answer

Methionine

Answer

Lysine

Answer

Histidine

Question 9

Which transporter is responsible for the transport of glucose in the pancreas?

Accepted Answer

GLUT 2

Answer

GLUT 1

Answer

GLUT 3

Answer

GLUT 4

Question 10

Which of the following plant components is not fermented by gastrointestinal microorganisms?

Accepted Answer

Lignin

Answer

Cellulose

Answer

Hemicellulose

Answer

Pectin

NEET-PG 2013 — Biochemistry