FMGE 2019 - Biochemistry Practice Questions

Q: Gluconeogenesis is inhibited by?

Insulin. ***Insulin*** - **Insulin** is a key hormone released in response to high blood glucose, promoting glucose uptake and storage, and **inhibiting hepatic glucose production** through gluconeogenesis and glycogenolysis. - It achieves this by decreasing the transcription and activity of key gluconeogenic enzymes like **phosphoenolpyruvate carboxykinase (PEPCK)** and **glucose-6-phosphatase**. *Cholecystokinin* - **Cholecystokinin (CCK)** is a gastrointestinal hormone primarily involved in digestion, stimulating bile release and pancreatic enzyme secretion. - It does not directly regulate gluconeogenesis; its main role is related to **fat and protein digestion**. *5-alpha reductase* - **5-alpha reductase** is an enzyme involved in steroid metabolism, converting testosterone to the more potent androgen, dihydrotestosterone (DHT). - This enzyme has no direct role in the regulation of **gluconeogenesis**. *Glucagon* - **Glucagon** is a hormone that has the opposite effect of insulin, stimulating gluconeogenesis and glycogenolysis to increase blood glucose levels during fasting or hypoglycemia. - Its primary action is to **promote** hepatic glucose output, not inhibit it.

Q: Which of the following interfere with iron absorption?

Phytates. ***Phytates*** - **Phytates** (phytic acid), found in plant-based foods like whole grains, legumes, nuts, and seeds, are **potent inhibitors of non-heme iron absorption**. - They **chelate non-heme iron** and form insoluble complexes in the gastrointestinal tract, making it unavailable for absorption. - Phytates are considered **the most significant dietary inhibitor** of iron absorption among the options listed. *Myoglobin* - **Myoglobin is a heme-containing protein** found in muscle tissue and serves as an excellent dietary source of readily absorbable **heme iron**. - It does **not interfere** with iron absorption; instead, it provides bioavailable heme iron. *Vitamin C* - **Vitamin C** (ascorbic acid) significantly **enhances the absorption of non-heme iron** by reducing ferric iron (Fe³⁺) to ferrous iron (Fe²⁺), which is more soluble and bioavailable. - It counteracts the inhibitory effects of phytates and other dietary inhibitors. - This is an **absorption enhancer, not an inhibitor**. *Oxalate* - **Oxalate** (oxalic acid), found in foods like spinach, rhubarb, and beet greens, can also **interfere with iron absorption** by forming insoluble complexes with iron and other minerals. - However, oxalate is a **less potent inhibitor** compared to phytates, and its primary effect is on calcium absorption. - While it does reduce iron bioavailability, **phytates remain the more clinically significant inhibitor** of iron absorption.

Q: Synovial fluid contains-

Hyaluronic acid. ***Hyaluronic acid*** - **Hyaluronic acid** is a major component of **synovial fluid**, providing **viscosity** and **lubrication** to joints, which is crucial for reducing friction between articular cartilages. - It's a **glycosaminoglycan** (GAG) responsible for the fluid's unique rheological properties, maintaining joint health and function. *Keratan sulphate* - **Keratan sulphate** is primarily found in **cartilage**, **cornea**, and **bone**, contributing to their structural integrity. - It is not a significant component of **synovial fluid** itself; rather, it is part of the extracellular matrix of surrounding tissues. *Dermatan sulphate* - **Dermatan sulphate** is typically found in **skin**, **blood vessels**, and **heart valves**, where it plays a role in tissue organization and repair. - It is not a characteristic or primary component of **synovial fluid**. *Chondroitin sulphate* - **Chondroitin sulphate** is a GAG abundant in **cartilage**, contributing to its **compressive strength** and elasticity. - While essential for **joint health**, it is found within the cartilage matrix, not freely in high concentrations within the **synovial fluid**.

Q: Which enzyme level is tested in thiamine deficiency?

Transketolase. ***Transketolase*** - The activity of **transketolase** in red blood cells is a reliable biochemical indicator of **thiamine deficiency (vitamin B1)**. - Thiamine pyrophosphate (TPP), the active form of thiamine, is a critical coenzyme for transketolase in the **pentose phosphate pathway**. *PDH* - **Pyruvate dehydrogenase (PDH)** is an enzyme complex that uses thiamine pyrophosphate as a cofactor, but its activity is not typically measured directly for diagnosing thiamine deficiency. - While PDH function is impaired in thiamine deficiency, direct assessment of transketolase activity is the standard diagnostic test. *Kinase* - **Kinase** is a general term for an enzyme that catalyzes the transfer of a phosphate group from a high-energy phosphate-donating molecule (like ATP) to a specific substrate. - This general class of enzymes is not specifically tested for thiamine deficiency. *Pyruvate kinase* - **Pyruvate kinase** is a key enzyme in **glycolysis** that catalyzes the final step of the pathway, converting phosphoenolpyruvate to pyruvate. - Its activity is not directly related to thiamine metabolism or deficiency.

Q: Which of the following is present in skeletal muscle?

GLUT 4. ***GLUT 4*** - **GLUT 4** is the primary glucose transporter found in **skeletal muscle** and adipose tissue. - Its translocation to the cell membrane is **insulin-dependent** and also stimulated by muscle contraction, allowing increased glucose uptake. *GLUT 2* - **GLUT 2** is predominantly found in the liver, pancreas (beta cells), intestine, and kidney. - It has a **low affinity (high Km)** for glucose, allowing it to transport glucose efficiently only at high blood glucose concentrations. *GLUT 7* - **GLUT 7** is a glucose transporter located in the **endoplasmic reticulum** membrane of the liver and other gluconeogenic tissues. - It plays a role in the flux of glucose within the ER lumen, particularly in **hepatic glucose production**. *GLUT 5* - **GLUT 5** is primarily responsible for **fructose transport** in the small intestine, testes, and kidneys. - It does not transport glucose and has a specific affinity for fructose.

Q: Which of the following is cardio protective?

HDL. ***HDL*** - **High-density lipoprotein (HDL)** is known as "good cholesterol" because it helps remove **excess cholesterol** from the body and transport it back to the liver for excretion. - This process, called **reverse cholesterol transport**, helps prevent the buildup of plaque in arteries, thereby reducing the risk of **atherosclerosis** and cardiovascular disease. *CHYLOMICRON* - **Chylomicrons** are responsible for transporting **dietary triglycerides** from the intestines to various tissues. - While essential for nutrient absorption, elevated chylomicron levels can contribute to **hypertriglyceridemia**, which is a risk factor for cardiovascular disease and pancreatitis. *VLDL* - **Very low-density lipoprotein (VLDL)** primarily transports **endogenously synthesized triglycerides** from the liver to peripheral tissues. - High levels of VLDL are considered a **risk factor for atherosclerosis** as they can be metabolized into LDL, contributing to plaque formation. *LDL* - **Low-density lipoprotein (LDL)** is often referred to as "bad cholesterol" because it deposits cholesterol in the walls of arteries. - This deposition leads to the formation of **atherosclerotic plaque**, which can narrow arteries and increase the risk of heart attacks and strokes.

Q: Most potent lipid phase antioxidant:

Vitamin E. ***Vitamin E*** - **Vitamin E** (primarily alpha-tocopherol) is a **fat-soluble antioxidant** that is highly effective at neutralizing **lipid peroxyl radicals** within cell membranes and lipoproteins, making it the most potent lipid-phase antioxidant. - It protects against **oxidative damage** to **polyunsaturated fatty acids** in lipid bilayers, which is crucial for maintaining cell membrane integrity. *Vitamin A* - **Vitamin A** (retinol and its derivatives) has antioxidant properties, particularly **beta-carotene**, which can scavenge **single oxygen radicals**. - However, its primary role is not as potent a lipid-phase chain-breaking antioxidant compared to vitamin E. *Vitamin C* - **Vitamin C** (ascorbic acid) is a **water-soluble antioxidant** that works primarily in aqueous environments, such as the cytosol and plasma. - It regenerates expended vitamin E by reducing the **tocopheroxyl radical**, but it doesn't directly act in the lipid phase. *Vitamin K* - **Vitamin K** is essential for **blood coagulation** and **bone metabolism**, serving as a cofactor for gamma-glutamyl carboxylase. - While it has some very limited antioxidant activity in specific contexts, it is not considered a significant or potent antioxidant, especially in the lipid phase.

Q: Ammonia formed in the brain is converted into

Glutamine. ***Glutamine*** - **Ammonia** is detoxified in the brain by combining with **glutamate** to form **glutamine** via the enzyme **glutamine synthetase**. - This conversion is crucial because **glutamine** is non-toxic and can be safely transported out of the brain to the liver for further processing. *Glycine* - **Glycine** is an amino acid that can function as a neurotransmitter, but it is not the primary product of ammonia detoxification in the brain. - While it can be synthesized in the brain, it does not serve as the molecule to which toxic ammonia is directly converted for transport. *Urea* - **Urea** is the primary end-product of ammonia detoxification in the **liver** through the **urea cycle**. - The brain lacks the complete set of enzymes required for the **urea cycle**, so it cannot convert ammonia into urea. *Cysteine* - **Cysteine** is a sulfur-containing amino acid involved in protein synthesis and antioxidant defense, but it is not directly involved in the detoxification pathway of ammonia in the brain. - Its synthesis and metabolism are distinct from the process of ammonia sequestration.

Question 1

Gluconeogenesis is inhibited by?

Accepted Answer

Insulin

Answer

Cholecystokinin

Answer

5-alpha reductase

Answer

Glucagon

Question 2

Which of the following interfere with iron absorption?

Accepted Answer

Phytates

Answer

Myoglobin

Answer

Vitamin C

Answer

Oxalate

Question 3

Synovial fluid contains-

Accepted Answer

Hyaluronic acid

Answer

Keratan sulphate

Answer

Dermatan sulphate

Answer

Chondroitin sulphate

Question 4

Which enzyme level is tested in thiamine deficiency?

Accepted Answer

Transketolase

Answer

PDH

Answer

Kinase

Answer

Pyruvate kinase

Question 5

Which of the following is present in skeletal muscle?

Accepted Answer

GLUT 4

Answer

GLUT 2

Answer

GLUT 7

Answer

GLUT 5

Question 6

Which of the following is cardio protective?

Accepted Answer

HDL

Answer

Chylomicron

Answer

VLDL

Answer

LDL

Question 7

Most potent lipid phase antioxidant:

Accepted Answer

Vitamin E

Answer

Vitamin A

Answer

Vitamin C

Answer

Vitamin K

Question 8

Ammonia formed in the brain is converted into

Accepted Answer

Glutamine

Answer

Glycine

Answer

Urea

Answer

Cysteine

FMGE 2019 — Biochemistry