FMGE 2018 - Biochemistry PYQs Practice Questions

Q: Muscles cannot release free glucose from glycogen stores because of a deficiency of:

Glucose-6-phosphatase. ***Glucose-6-phosphatase*** - **Glucose-6-phosphatase** is the enzyme that dephosphorylates glucose-6-phosphate to free glucose, allowing its release into the bloodstream. - This enzyme is **physiologically absent in muscle tissue** (present only in liver and kidneys), meaning muscles can break down glycogen for their own energy needs but cannot release free glucose into circulation. - This ensures that muscle glycogen stores are reserved exclusively for muscle's own metabolic needs during contraction. *Glycogen phosphorylase* - **Glycogen phosphorylase** is present in muscle and catalyzes the breakdown of glycogen by cleaving α-1,4 glycosidic bonds to release glucose-1-phosphate. - Muscles have this enzyme and can normally break down glycogen for energy; deficiency causes **McArdle disease** (glycogen storage disease type V) with exercise intolerance. *Hexokinase* - **Hexokinase** is abundant in muscle tissue and phosphorylates free glucose to glucose-6-phosphate for entry into glycolysis. - This enzyme is necessary for utilizing both blood glucose and glycogen-derived glucose-6-phosphate. *Phosphoglucomutase* - **Phosphoglucomutase** is present in muscle and converts glucose-1-phosphate (from glycogen breakdown) to glucose-6-phosphate. - This enzyme is essential for channeling glycogen-derived glucose into glycolysis. [Practice more Biochemistry PYQs on OnCourse]

Q: Km increases, but Vmax remains same. This is which type of inhibition?

Competitive. ***Competitive*** - In **competitive inhibition**, the inhibitor **reversibly binds** to the **active site** of the enzyme, competing with the substrate. - This competition means that a higher substrate concentration is required to achieve half-maximal velocity, thus **increasing the Km**, while the maximum velocity (**Vmax**) remains unchanged if sufficient substrate is present. *Uncompetitive* - **Uncompetitive inhibition** involves the inhibitor binding only to the **enzyme-substrate complex**. - This type of inhibition typically leads to a **decrease in both Km and Vmax**. *Non-competitive* - In **non-competitive inhibition**, the inhibitor binds to a site other than the active site (allosteric site) on either the free enzyme or the enzyme-substrate complex. - This binding usually **decreases the Vmax** (due to reduced enzyme efficiency) but does not affect the Km (as substrate binding is not directly hindered). *Irreversible* - **Irreversible inhibition** involves the formation of a strong, often covalent, bond between the inhibitor and the enzyme, permanently inactivating it. - This type of inhibition effectively **reduces the concentration of active enzyme**, leading to a **decrease in Vmax** (as fewer enzyme molecules are available to catalyze the reaction) with varying effects on Km depending on the mechanism. [Practice more Biochemistry PYQs on OnCourse]

Q: Apoprotein for chylomicron remnants:

Apo E. ***Apo E*** - **Apolipoprotein E** (**Apo E**) is crucial for the uptake of **chylomicron remnants** and **VLDL remnants** (IDL) by the liver via the **LDL receptor-related protein 1 (LRP1)**. - It acts as a **ligand** for this receptor, facilitating the clearance of dietary fats from the circulation. *Apo A2* - **Apo A2** is a primary apolipoprotein of **high-density lipoprotein (HDL)**, not chylomicron remnants. - Its exact function is not fully understood, but it may modulate the activity of **hepatic lipase**. *Apo C1* - **Apo C1** is found on **chylomicrons**, **VLDL**, and **HDL**, but it is not the primary apoprotein responsible for the uptake of chylomicron remnants by the liver. - It is known to **activate lecithin-cholesterol acyltransferase (LCAT)** and may inhibit **cholesterol ester transfer protein (CETP)**. *Apo A1* - **Apo A1** is the most abundant apolipoprotein in **HDL** and is essential for its structure and function. - It is a potent **activator of LCAT**, an enzyme that esterifies cholesterol in HDL, which is key for **reverse cholesterol transport**. [Practice more Biochemistry PYQs on OnCourse]

Q: Low glycemic index food is:

Has slower absorption. ***Has slower absorption*** - **Low glycemic index (GI)** foods are digested and absorbed more slowly, leading to a gradual rise in blood glucose and insulin levels. - This characteristic is beneficial for managing **blood sugar** and providing sustained energy. *Easily digestible* - **Easily digestible** foods often have a **high glycemic index** because their carbohydrates are rapidly broken down and absorbed. - Low GI foods, by contrast, contain more complex carbohydrates and fiber, making them slower to digest. *Increase glycogen deposits* - While all carbohydrates are eventually converted to **glucose** and can contribute to **glycogen synthesis**, low GI foods do not uniquely or preferentially increase glycogen deposits compared to high GI foods. - Glycogen synthesis is primarily influenced by insulin levels and the total amount of carbohydrates consumed, irrespective of GI. *Increases plasma glucose* - All carbohydrate-containing foods will eventually increase **plasma glucose**, but low GI foods cause a **slower and smaller rise** in blood glucose compared to high GI foods. - They prevent the sharp spikes in blood sugar that are associated with high GI foods. [Practice more Biochemistry PYQs on OnCourse]

Q: Which is branching enzyme?

Amylo-1, 4-1, 6-transglycolase. ***Amylo-1, 4-1, 6-transglycolase*** - This enzyme is also known as **glycogen branching enzyme**. - It catalyzes the formation of **α-1,6-glycosidic bonds** by transferring a segment of four to six glucosyl residues from the non-reducing end of a growing glycogen chain to another chain. *Glycogen synthase* - This enzyme is responsible for the **elongation of glycogen chains** by forming **α-1,4-glycosidic bonds**. - It adds glucose units to the non-reducing end of a pre-existing glycogen primer. *Glycogen Phosphorylase* - This enzyme is involved in **glycogen degradation**. - It catalyzes the **phosphorolytic cleavage** of α-1,4-glycosidic bonds, releasing glucose-1-phosphate. *Glucose-6 phosphatase* - This enzyme is primarily found in the **liver** and kidneys and is crucial for **gluconeogenesis** and **glycogenolysis**. - It dephosphorylates glucose-6-phosphate to **free glucose**, allowing its release into the bloodstream. [Practice more Biochemistry PYQs on OnCourse]

Question 1

Muscles cannot release free glucose from glycogen stores because of a deficiency of:

Accepted Answer

Glucose-6-phosphatase

Answer

Hexokinase

Answer

Phosphoglucomutase

Answer

Glycogen phosphorylase

Question 2

Km increases, but Vmax remains same. This is which type of inhibition?

Accepted Answer

Competitive

Answer

Uncompetitive

Answer

Non-competitive

Answer

Irreversible

Question 3

Apoprotein for chylomicron remnants:

Accepted Answer

Apo E

Answer

Apo A2

Answer

Apo C1

Answer

Apo A1

Question 4

Low glycemic index food is:

Accepted Answer

Has slower absorption

Answer

Easily digestible

Answer

Increase glycogen deposits

Answer

Increases plasma glucose

Question 5

Which is branching enzyme?

Accepted Answer

Amylo-1, 4-1, 6-transglycolase

Answer

Glycogen synthase

Answer

Glycogen Phosphorylase

Answer

Glucose-6 phosphatase

Question 6

Preferred biochemical marker(s) in patients presenting with myocardial infarction:

Accepted Answer

Cardiac specific Troponins

Answer

All of the options

Answer

Myoglobin

Answer

CK-MB

Question 7

Most Common enzyme deficient in galactosemics:

Accepted Answer

Galactose-1-phosphate uridyl transferase/GALT

Answer

Galactosidase

Answer

UDP galactose epimerase

Answer

Galactokinase

Question 8

Chaperones are:

Accepted Answer

Mediators of post-translational assembly of protein complexes

Answer

Antigen presenting cells

Answer

Purine metabolism mediators

Answer

None of the above

Question 9

Which organelle contains its own DNA apart from the nucleus?

Accepted Answer

Mitochondria

Answer

RER

Answer

Golgi complex

Answer

SER

Question 10

Western blot is done for:

Accepted Answer

Protein

Answer

RNA

Answer

Lipid

Answer

DNA

FMGE 2018 — Biochemistry