Lipid Metabolism Practice Questions

Q: What is the role of insulin in lipid metabolism?

Activates lipoprotein lipase. ***Activates lipoprotein lipase*** - Insulin stimulates **lipoprotein lipase (LPL)** activity, leading to the uptake of **triglycerides** from chylomicrons and VLDL into adipocytes for storage. - This action promotes **lipid storage** in adipose tissue after a meal. *Increase lipolysis* - Insulin actually **inhibits lipolysis**, preventing the breakdown of stored triglycerides into free fatty acids. - The primary effect of insulin on lipid metabolism is to promote **lipid storage**, not breakdown. *Activate hormone sensitive lipase* - Insulin **inhibits hormone-sensitive lipase (HSL)**, which is responsible for breaking down stored triglycerides. - Inhibition of HSL is a key mechanism by which insulin prevents the release of **free fatty acids** from adipose tissue. *All of the options* - This option is incorrect because insulin **inhibits lipolysis** and **inactivates hormone-sensitive lipase**, directly contradicting two of the other statements. - Insulin's primary role in lipid metabolism is to **promote storage** and inhibit the breakdown and release of fats.

Q: All are required for conversion of progesterone to estrogen except

11-hydroxylase. ***11-hydroxylase*** - **11-hydroxylase** is involved in the synthesis of **cortisol** and **aldosterone** in the adrenal glands, converting 11-deoxycortisol to cortisol and 11-deoxycorticosterone to corticosterone. - It is **not involved** in the metabolic pathway for converting progesterone to estrogen. - This enzyme functions in the **glucocorticoid and mineralocorticoid pathways**, which are distinct from the sex steroid pathway. *Isomerase* - **3β-hydroxysteroid dehydrogenase/Δ5-Δ4-isomerase** is required for converting **pregnenolone to progesterone**, which occurs upstream before progesterone is formed. - Once progesterone is already synthesized, this isomerase is **not required** for the subsequent conversion of progesterone to estrogen. - The pathway from progesterone to estrogen proceeds via hydroxylation, lyase cleavage, and aromatization—not isomerization. *Reductase* - **17β-hydroxysteroid dehydrogenase** (which has reductase activity) is involved in the conversion of **androstenedione to testosterone** in the androgen synthesis pathway. - Since androgens serve as immediate precursors for estrogen synthesis, this reductase activity is **involved** in the overall pathway from progesterone to estrogen. - However, **5α-reductase** (testosterone → DHT) is not part of the progesterone-to-estrogen pathway. *Lyase* - **17,20-lyase** (part of the CYP17A1 enzyme complex) is **critical** for converting **17-hydroxyprogesterone to androstenedione** by cleaving the C17-C20 bond. - These **androgens** (androstenedione and testosterone) then serve as direct precursors for **estrogen synthesis** via the **aromatase enzyme** (CYP19A1). - Lyase is absolutely required in the progesterone-to-estrogen pathway.

Q: Most common progesterone metabolite in urine is:

Pregnanediol. ***Pregnanediol*** - **Pregnanediol** is the primary urinary metabolite of **progesterone** and is formed by the reduction of progesterone in the liver. - Its measurement in urine can be used as an indicator of **progesterone production** in the body, reflecting ovarian or placental function. *Pregnenolone* - **Pregnenolone** is a precursor to progesterone and other steroid hormones, not a direct metabolite excreted in the urine. - It is mainly metabolized within steroid-producing tissues rather than being excreted unchanged. *17 hydroxy pregnenolone* - **17-hydroxypregnenolone** is an intermediate in the synthesis of androgens and estrogens, originating from pregnenolone. - It is not a direct or "most common" urinary metabolite of progesterone itself. *Pregnanetriol* - **Pregnanetriol** is a urinary metabolite of **17-hydroxyprogesterone**, a downstream steroid from progesterone in the metabolic pathway. - Its presence is commonly used as a marker for **congenital adrenal hyperplasia (CAH)** due to 21-hydroxylase deficiency, not as the primary metabolite of progesterone.

Q: Alcohol is found in all except :

DHA (Docosahexaenoic Acid). ***DHA (Docosahexaenoic Acid)*** - **DHA** is an **omega-3 fatty acid**, not an alcohol. It contains a carboxyl group, characterizing it as a fatty acid. - Its structure consists of a long hydrocarbon chain with 22 carbons and 6 double bonds, making it highly unsaturated but lacking a hydroxyl group to be classified as an alcohol. *Sphingomyelin* - **Sphingomyelin** is a **sphingolipid** that contains the alcohol **sphingosine** as its backbone. - It also contains a phosphate group and choline, but the backbone alcohol is essential to its structure. *Glucocerebroside* - **Glucocerebroside** is a **glycosphingolipid** that contains the alcohol **sphingosine** linked to a fatty acid and a single glucose molecule. - The **sphingosine** component is the alcohol in its structure. *Lecithin* - **Lecithin** (phosphatidylcholine) is a **glycerophospholipid** that contains **glycerol** as its alcohol backbone. - It consists of a glycerol molecule esterified with two fatty acids and a phosphate group linked to choline.

Q: Hypothyroid state is characterized by

Increased cholesterol. ***Increased cholesterol*** - In a hypothyroid state, there is decreased activity of **lipoprotein lipase** and reduced expression of **LDL receptors** in the liver. - This leads to impaired clearance of **LDL cholesterol** and triglycerides from the bloodstream, causing elevated cholesterol levels. - Hypercholesterolemia is a **hallmark clinical feature** of hypothyroidism. *Increased lipolysis* - **Lipolysis** (the breakdown of fats) is typically *reduced* in hypothyroidism because thyroid hormones normally stimulate this process. - Decreased thyroid hormone levels result in less breakdown of fat stores and decreased lipolysis. *Increased protein synthesis* - Thyroid hormones generally have an **anabolic effect** on protein synthesis at physiological levels and are critical for normal growth and development. - In hypothyroidism, there is a *reduction* in overall metabolic activity, including protein synthesis. *Increased glycolysis* - **Glycolysis** (the breakdown of glucose) is generally *reduced* in hypothyroidism due to lower metabolic rates and reduced enzyme activity. - Thyroid hormones promote various metabolic processes, including glucose utilization, so increased glycolysis would not characterize hypothyroidism.

Q: Rothera's test is used for detection of:

Ketones. ***Ketones*** - **Rothera's test** is a qualitative test used to detect the presence of **ketone bodies**, primarily **acetoacetate and acetone**, in urine. - A positive test typically indicates **ketosis**, which can occur in conditions like **diabetic ketoacidosis** or prolonged fasting. *Proteins* - **Proteins** in urine are typically detected using tests such as the **sulfosalicylic acid (SSA) test** or **urine dipstick protein tests**. - **Rothera's test** does not react with proteins. *Fatty acid* - **Fatty acids** in urine are not routinely tested for specific detection with a single spot test like **Rothera's test**. - **Rothera's test** is specific for ketone bodies, not fatty acids. *Glucose* - **Glucose** in urine is commonly detected using **urine dipstick tests** which rely on the **glucose oxidase enzymatic reaction**. - **Rothera's test** does not detect glucose.

Q: A female child presents with hypertension, hyperpigmentation and virilization, she is most likely to be suffering from deficiency of?

11 beta hydroxylase deficiency. ***11 beta hydroxylase deficiency*** - This deficiency leads to an accumulation of **11-deoxycorticosterone (DOC)**, a potent mineralocorticoid that causes **hypertension**. [1] - The excess adrenal androgens (due to shunting of precursors down the androgen pathway) cause **virilization** and **hyperpigmentation** from increased ACTH stimulating melanocortin receptors. [1] *3 beta hydroxylase* - This deficiency causes a severe form of **congenital adrenal hyperplasia (CAH)** with impaired synthesis of all adrenal steroids. [1] - It presents with **salt wasting** and **ambiguous genitalia** in females due to lack of cortisol, aldosterone, and sex steroids. *21 alpha hydroxylase* - The most common form of CAH, resulting in decreased **cortisol** and **aldosterone**, and increased adrenal androgens. - It presents with **salt wasting** or **virilization** (depending on severity), but typically **hypotension** rather than hypertension. *17 alpha hydroxylase* - This deficiency impairs the synthesis of **cortisol** and **androgens**, leading to an accumulation of **mineralocorticoid precursors** like DOC. - Patients present with **hypertension**, **hypokalemia**, and **sexual infantilism** (lack of pubertal development) rather than virilization.

Q: Which of the following is a 17β-OH steroid?

Androgen. ***Androgen*** - **Testosterone** is the classic example of a **17β-hydroxysteroid**, containing a hydroxyl group (-OH) at the **17β-position** of its steroid nucleus. - Other androgens like **androstenediol** and **dehydroepiandrosterone (DHEA)** derivatives also possess the **17β-OH configuration**. - This structural feature is essential for **androgen receptor binding** and biological activity in target tissues. - The 17β-hydroxyl group distinguishes active androgens from their inactive 17-ketosteroid metabolites. *Estrogen* - **Estradiol**, the primary estrogen, also contains a **17β-hydroxyl group**, making it technically a 17β-OH steroid. - However, in the context of steroid chemistry and clinical biochemistry, **testosterone** (androgen) is more commonly referenced as the prototypical **17β-hydroxysteroid**. - Both androgens and estrogens can be 17β-OH steroids, but androgens are the primary class associated with this terminology in medical literature. *Progesterone* - **Progesterone** is a C21 steroid with a **ketone group at C3 and C20**, not a hydroxyl group. - At position 17, progesterone has an **acetyl side chain** (CH3CO-), not a hydroxyl group. - It lacks the 17β-OH configuration that characterizes androgenic and estrogenic steroids. *None of the options* - This is incorrect because **androgen** (specifically testosterone) is a well-established **17β-hydroxysteroid**. - The measurement of **17-ketosteroids** (oxidized metabolites of 17β-OH steroids) in urine was historically used to assess androgen production.

Q: Which cytochrome P450 enzyme is also known as 11-beta hydroxylase?

CYP11B1. ***CYP11B1*** - This enzyme is specifically known as **11β-hydroxylase**, responsible for converting 11-deoxycortisol to **cortisol** and 11-deoxycorticosterone to **corticosterone** in the adrenal cortex. - Deficiency leads to an accumulation of 11-deoxycortisol and 11-deoxycorticosterone, causing **congenital adrenal hyperplasia (CAH)** with hypertension due to mineralocorticoid activity. *CYP17A1* - This enzyme is **17α-hydroxylase/17,20-lyase**, involved in the synthesis of **androgens** and **estrogens** by converting pregnenolone and progesterone to their 17α-hydroxylated forms. - Its deficiency leads to impaired sex steroid synthesis and elevated mineralocorticoids, causing **hypertension** and **sexual infantilism**. *CYP21A2* - This enzyme is **21-hydroxylase**, critical for converting progesterone to 11-deoxycorticosterone and 17α-hydroxyprogesterone to 11-deoxycortisol. - It is the most common cause of **congenital adrenal hyperplasia (CAH)**, leading to a deficiency in cortisol and aldosterone, and an excess of androgens. *CYP11B2* - This enzyme is **aldosterone synthase**, responsible for the final steps in **aldosterone biosynthesis**, converting deoxycorticosterone to corticosterone, and then to 18-hydroxycorticosterone and aldosterone. - Its overexpression or mutations can lead to **primary aldosteronism**, while deficiency can cause **hypoaldosteronism**.

Q: Which of the following is caused by congenital 17 hydroxylase deficiency:

Hypertension. ***Hypertension*** - **Congenital 17-hydroxylase deficiency** leads to impaired synthesis of **cortisol** and **sex steroids**, resulting in an accumulation of **mineralocorticoid precursors (corticosterone and deoxycorticosterone)** [1]. - Increased levels of these mineralocorticoids cause **sodium and water retention**, leading to **hypertension** and **hypokalemia**. *Virilism* - **17-hydroxylase deficiency** impairs **androgen synthesis**, preventing the development of male secondary sexual characteristics [2]. - Individuals with this deficiency often present with **female external genitalia** regardless of their genetic sex, or **under-virilization** in genetic males, not virilism [2]. *Hyperkalemia* - The excess mineralocorticoids (deoxycorticosterone) in **17-hydroxylase deficiency** promote **sodium reabsorption** and **potassium excretion** in the kidneys [1]. - This leads to **hypokalemia**, which is the opposite of hyperkalemia. *Hermaphroditism* - **17-hydroxylase deficiency** affects the development of gonads and internal reproductive organs depending on genetic sex. - Genetic males (**XY**) with this deficiency typically develop **female external genitalia** (pseudohermaphroditism or 46, XY DSD), while genetic females (**XX**) typically present as normal females but with **primary amenorrhea** [2]. This genetic condition does not result in true hermaphroditism (presence of both ovarian and testicular tissue) [2].

Question 1

What is the role of insulin in lipid metabolism?

Accepted Answer

Activates lipoprotein lipase

Answer

Increases lipolysis

Answer

Activates hormone sensitive lipase

Answer

All of the options

Question 2

All are required for conversion of progesterone to estrogen except

Accepted Answer

11-hydroxylase

Answer

Isomerase

Answer

Reductase

Answer

Lyase

Question 3

Most common progesterone metabolite in urine is:

Accepted Answer

Pregnanediol

Answer

Pregnenolone

Answer

17 hydroxy pregnenolone

Answer

Pregnanetriol

Question 4

Alcohol is found in all except :

Accepted Answer

DHA (Docosahexaenoic Acid)

Answer

Sphingomyelin

Answer

Glucocerebroside

Answer

Lecithin

Question 5

Hypothyroid state is characterized by

Accepted Answer

Increased cholesterol

Answer

Increased lipolysis

Answer

Increased protein synthesis

Answer

Increased glycolysis

Question 6

Rothera's test is used for detection of:

Accepted Answer

Ketones

Answer

Proteins

Answer

Fatty acid

Answer

Glucose

Question 7

A female child presents with hypertension, hyperpigmentation and virilization, she is most likely to be suffering from deficiency of?

Accepted Answer

11 beta hydroxylase deficiency

Answer

3 beta hydroxylase

Answer

21 alpha hydroxylase

Answer

17 alpha hydroxylase

Question 8

Which of the following is a 17β-OH steroid?

Accepted Answer

Androgen

Answer

Estrogen

Answer

Progesterone

Answer

None of the options

Question 9

Which cytochrome P450 enzyme is also known as 11-beta hydroxylase?

Accepted Answer

CYP11B1

Answer

CYP17A1

Answer

CYP21A2

Answer

CYP11B2

Question 10

Which of the following is caused by congenital 17 hydroxylase deficiency:

Accepted Answer

Hypertension

Answer

Virilism

Answer

Hyperkalemia

Answer

Hermaphroditism

Lipid Metabolism — MCQs

Lipid Metabolism — MCQs

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