Metabolic Integration Practice Questions

Q: All are actions of insulin except :

Gluconeogenesis. ***Gluconeogenesis*** - Insulin's primary role is to **lower blood glucose levels**, and it does so by suppressing processes that produce glucose, such as **gluconeogenesis**. - **Gluconeogenesis** is the synthesis of glucose from non-carbohydrate precursors, and insulin inhibits the key enzymes involved in this pathway. *Glycolysis* - Insulin **promotes glycolysis** by stimulating the activity of key glycolytic enzymes like **glucokinase** and **phosphofructokinase-1**. - This action helps to **increase glucose utilization** within cells, thereby reducing blood glucose levels. *Lipogenesis* - Insulin **promotes lipogenesis**, the synthesis of fatty acids and triglycerides, especially in the liver and adipose tissue. - This is a key mechanism for **storing excess energy** when glucose levels are high. *Glycogenesis* - Insulin **stimulates glycogenesis**, which is the synthesis of **glycogen** from glucose, primarily in the liver and muscle cells. - This process helps to **store excess glucose** for later use, thus lowering blood glucose.

Q: Not done by insulin:

Ketogenesis. ***Ketogenesis*** - **Ketogenesis** is primarily a catabolic process stimulated by low insulin levels or insulin resistance, particularly during prolonged fasting or uncontrolled diabetes. - Insulin's main role is to promote anabolic processes and energy storage, thus it **inhibits ketogenesis** rather than performing it. *Glycolysis* - **Insulin** promotes **glycolysis** by increasing the expression and activity of key glycolytic enzymes, facilitating glucose breakdown for energy. - It enhances the uptake of **glucose into cells**, where it can then be metabolized via glycolysis. *Lipogenesis* - **Insulin** is a potent stimulator of **lipogenesis**, promoting the synthesis of fatty acids and triglycerides from excess glucose. - This process helps store excess energy in adipose tissue, converting carbohydrates into **fat**. *Glycogen synthesis* - **Insulin** directly stimulates **glycogen synthesis** (glycogenesis) in the liver and muscle cells. - It promotes the uptake of **glucose** and activates enzymes like **glycogen synthase**, leading to storage of glucose as glycogen.

Q: Primary link between citric acid cycle and urea cycle is:

Fumarate. ***Fumarate*** - **Fumarate** is the primary link between the urea cycle and the citric acid cycle, forming what is known as the **"Krebs bicycle"** or **"Krebs-Henseleit bicycle"**. - **Fumarate** is produced in the **cytosol** during the urea cycle when argininosuccinate is cleaved by argininosuccinate lyase to form arginine and fumarate. - This cytosolic fumarate can be converted to **malate** by cytosolic fumarase, which is then transported into the mitochondria to join the citric acid cycle. - This link allows the urea cycle to contribute intermediates to the TCA cycle and provides metabolic integration between amino acid catabolism and energy production. *Malate* - While **malate** is an intermediate in both pathways, it is **fumarate** that serves as the primary and direct link from the urea cycle. - Malate is formed from fumarate in the cytosol and then transported into the mitochondria, acting as a carrier but not the primary connecting molecule itself. *Succinate* - **Succinate** is an intermediate of the citric acid cycle but does not directly link to the urea cycle. - It is formed from succinyl CoA in the TCA cycle and typically remains within the **mitochondria**, with no role in the urea cycle. *Citrate* - **Citrate** is the first intermediate formed in the citric acid cycle and does not have a direct linkage to the urea cycle for substrate exchange. - While citrate can be transported out of mitochondria for fatty acid synthesis, it has no connection to the urea cycle.

Q: Gout results due to defective function of the following enzyme:

Glucose 6 phosphatase. ***Glucose 6 phosphatase*** - Deficiency of **glucose-6-phosphatase** causes **glycogen storage disease type I** (von Gierke disease), which leads to **secondary hyperuricemia** and recurrent **gout attacks**. - The mechanism involves impaired **gluconeogenesis** and **glycogenolysis**, causing increased production of **lactate** (which competes with uric acid for renal excretion) and accelerated **purine nucleotide degradation** to uric acid. - This is the **most common enzyme deficiency** among the options that results in gout as a clinical manifestation. *Glucose 6 phosphate dehydrogenase* - Deficiency of **G6PD** primarily causes **hemolytic anemia** due to oxidative stress on red blood cells, not gout. - It is crucial for the **pentose phosphate pathway** generating NADPH, but does not directly affect purine or uric acid metabolism. *PRPP synthetase* - **Overactivity** (gain-of-function mutation) of **PRPP synthetase** leads to gout through increased purine synthesis. - However, **defective function** (as stated in the question) would actually **decrease** purine synthesis and **lower** uric acid levels, not cause gout. - This is not the correct answer since the question specifically asks for "defective function." *Purine nucleotide phosphorylase* - Deficiency of **purine nucleoside phosphorylase** (PNP) causes severe **T-cell immunodeficiency**, not gout. - While it affects purine metabolism, the accumulated metabolites are immunotoxic rather than causing hyperuricemia and gout.

Q: In type I diabetes, which of the following is the MOST characteristic metabolic change that distinguishes it from type II diabetes:-

Increased lipolysis. ***Increased lipolysis*** - In **type 1 diabetes** (T1D), there is an **absolute deficiency of insulin**, which is a potent **anti-lipolytic hormone**. [1] - This lack of insulin leads to unopposed **lipolysis**, resulting in increased free fatty acid (FFA) release, which can be metabolized into **ketone bodies** and contribute to **diabetic ketoacidosis (DKA)**. [2] *Increased protein catabolism* - While protein catabolism is increased in uncontrolled T1D due to the lack of insulin and increased counter-regulatory hormones, it is not the *most characteristic* metabolic change that clearly distinguishes it from type 2 diabetes (T2D), especially in early stages of T2D where some insulin may still be present. [1] - **Protein breakdown** produces amino acids for gluconeogenesis, contributing to hyperglycemia, but **lipolysis leading to ketosis** is more specific to severe insulin deficiency. [3] *Decreased glucose uptake* - **Decreased glucose uptake** by peripheral tissues (especially muscle and adipose tissue) is a characteristic feature of both T1D and T2D. [1] - In T1D, it's due to insulin deficiency, while in T2D, it's primarily caused by **insulin resistance**, making it less specific to distinguish T1D. *Increased hepatic glucose output* - **Increased hepatic glucose output** is a significant contributor to hyperglycemia in both T1D and T2D. [1] - In T1D, it's due to the lack of insulin's suppressive effect on the liver, whereas in T2D, it's due to **hepatic insulin resistance** and increased gluconeogenesis.

Q: Patient with Type I diabetes mellitus, with complaints of polyuria. Which of the following will occur normally in his body?

Increased conversion of fatty acid to acetyl CoA. ***Increased conversion of fatty acid to acetyl CoA*** - In response to **insulin deficiency** and **hyperglycemia** in Type 1 diabetes, the body shifts from carbohydrate to fat metabolism. - This leads to increased **lipolysis**, releasing fatty acids that are then converted to **acetyl CoA** in the liver for energy or ketone body production. *Incorrect: Increased protein synthesis* - **Insulin** is an **anabolic hormone** that promotes protein synthesis; its deficiency in Type 1 diabetes leads to decreased, not increased, protein synthesis. - Instead, there's often increased **protein catabolism** to provide substrates for gluconeogenesis. *Incorrect: Glycogenesis in muscle* - **Insulin** is required for the uptake of glucose into muscle cells and its subsequent conversion to **glycogen (glycogenesis)**. - In Type 1 diabetes, the lack of insulin significantly impairs muscle glucose uptake and glycogenesis. *Incorrect: Decreased cholesterol synthesis* - In uncontrolled Type 1 diabetes, there is actually **increased cholesterol synthesis**, not decreased. - The increased availability of **acetyl CoA** (from enhanced fatty acid oxidation) provides substrate for cholesterol synthesis via the **HMG-CoA reductase pathway**. - This contributes to the **dyslipidemia** commonly seen in poorly controlled diabetes, including elevated LDL cholesterol and total cholesterol levels.

Q: Which molecule serves as the primary source of energy during a prolonged fast?

Fatty acids. ***Fatty acids*** - During a **prolonged fast**, the body shifts from utilizing glucose to **fatty acids** derived from stored triglycerides as its primary energy source. - While most tissues can directly use fatty acids for energy, the liver converts them into **ketone bodies** to provide fuel for the brain. *Glycogen* - **Glycogen stores** (primarily in the liver and muscles) are rapidly depleted within the first **24-48 hours** of fasting. - It serves as a short-term energy reserve and is not sufficient for prolonged fasting. *Amino acids* - **Amino acids** are primarily used for protein synthesis and can be converted to glucose via **gluconeogenesis** to maintain blood glucose, especially for glucose-dependent tissues like red blood cells. - Excessive use of amino acids for energy is detrimental as it leads to the breakdown of **muscle protein**. *Glucose* - **Glucose** is the primary energy source in the fed state and the initial phase of fasting. - During a prolonged fast, **glucose levels drop significantly**, and the body conserves its limited glucose for critical cellular functions, shifting to other primary energy sources.

Q: Which of the following is the most characteristic metabolic change in type 1 diabetes mellitus?

Increased lipolysis due to fat breakdown. ***Increased lipolysis due to fat breakdown*** - In type 1 diabetes, **absolute insulin deficiency** leads to uncontrolled breakdown of **triglycerides** in adipose tissue, releasing massive amounts of **free fatty acids**. - This excessive **lipolysis** is the most characteristic metabolic change because it leads to **ketone body production** and the life-threatening complication of **diabetic ketoacidosis (DKA)**, which specifically distinguishes Type 1 from Type 2 diabetes. - The switch from **glucose metabolism to fat metabolism** with ketogenesis represents the hallmark metabolic derangement of Type 1 DM. *Decreased glucose uptake by cells* - While **decreased glucose uptake** by insulin-sensitive tissues (muscle, adipose) is the primary consequence of insulin deficiency, it occurs in both Type 1 and Type 2 diabetes. - This represents the **proximate cause** of hyperglycemia but is not the most characteristic metabolic change that defines the severe metabolic crisis of Type 1 DM. *Increased hepatic glucose output* - **Increased hepatic glucose output** via **gluconeogenesis** and **glycogenolysis** occurs due to unopposed **glucagon** action, contributing to hyperglycemia. - However, this is also seen in Type 2 diabetes and is not the most distinctive feature of Type 1 DM's metabolic profile. *Increased protein catabolism* - **Protein catabolism** increases as amino acids are mobilized for **gluconeogenesis**, leading to **muscle wasting** and negative nitrogen balance. - This is a **secondary response** to insulin deficiency and the metabolic shift, rather than the primary characteristic change.

Q: What happens to excess proteins in the body?

Converted to energy or stored as fat. ***Converted to energy or stored as fat*** - When protein intake exceeds the body's needs for structural and functional protein synthesis, excess **amino acids** are deaminated. - The carbon skeletons can then be converted into **glucose** (via gluconeogenesis) or **fatty acids** (which are stored as triglycerides). *Used to build structural proteins* - While proteins are essential for building structural components like **collagen** and **keratin**, the body has a specific need for this, and excess intake doesn't lead to endless structural growth. - Building structural proteins is a regulated process that depends on tissue repair and growth demands, not solely on protein availability. *Used to synthesize functional proteins* - Functional proteins, such as **enzymes** and **hormones**, are synthesized as needed to maintain specific metabolic processes and cellular functions. - The body doesn't synthesize an unlimited amount of these proteins just because there's an excess of amino acids; synthesis is regulated based on physiological demand. *Stored as amino acids in tissues* - The body has a very limited capacity to store free amino acids; there is no dedicated storage compartment akin to **glycogen** for carbohydrates or **triglycerides** for fats. - Instead, unused amino acids are rapidly catabolized rather than accumulated in significant quantities.

Question 1

All are actions of insulin except :

Accepted Answer

Gluconeogenesis

Answer

Glycolysis

Answer

Lipogenesis

Answer

Glycogenesis

Question 2

Starvation and diabetes mellitus can lead to ketoacidosis. Which of the following features is in favor of ketoacidosis due to diabetes mellitus?

Accepted Answer

Increase in glucagon/insulin ratio, increased cAMP and increased blood glucose

Answer

Decreased insulin, increased free fatty acid with normal blood glucose

Answer

Elevated insulin and free fatty acid with hyperglycemia

Answer

Decreased insulin, increased free fatty acid which is not equivalent to blood glucose

Question 3

Not done by insulin:

Accepted Answer

Ketogenesis

Answer

Glycolysis

Answer

Lipogenesis

Answer

Glycogen synthesis

Question 4

Primary link between citric acid cycle and urea cycle is:

Accepted Answer

Fumarate

Answer

Malate

Answer

Succinate

Answer

Citrate

Question 5

Gout results due to defective function of the following enzyme:

Accepted Answer

Glucose 6 phosphatase

Answer

Glucose 6 phosphate dehydrogenase

Answer

PRPP synthetase

Answer

Purine nucleotide phosphorylase

Question 6

In type I diabetes, which of the following is the MOST characteristic metabolic change that distinguishes it from type II diabetes:-

Accepted Answer

Increased lipolysis

Answer

Increased protein catabolism

Answer

Decreased glucose uptake

Answer

Increased hepatic glucose output

Question 7

Patient with Type I diabetes mellitus, with complaints of polyuria. Which of the following will occur normally in his body?

Accepted Answer

Increased conversion of fatty acid to acetyl CoA

Answer

Increased protein synthesis

Answer

Glycogenesis in muscle

Answer

Decreased cholesterol synthesis

Question 8

Which molecule serves as the primary source of energy during a prolonged fast?

Accepted Answer

Fatty acids

Answer

Glycogen

Answer

Amino acids

Answer

Glucose

Question 9

Which of the following is the most characteristic metabolic change in type 1 diabetes mellitus?

Accepted Answer

Increased lipolysis due to fat breakdown

Answer

Increased protein catabolism

Answer

Increased hepatic glucose output

Answer

Decreased glucose uptake by cells

Question 10

What happens to excess proteins in the body?

Accepted Answer

Converted to energy or stored as fat

Answer

Used to build structural proteins

Answer

Used to synthesize functional proteins

Answer

Stored as amino acids in tissues

Metabolic Integration — MCQs

Metabolic Integration — MCQs

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