Lipid metabolism Practice Questions

Q: Colipase is an enzyme found in secretions from which of the following? (Recent NEET Pattern 2018)

Pancreas. ***Pancreas*** - The pancreas is the primary source of **colipase** secretion in the digestive system. - Colipase is an essential co-factor for **pancreatic lipase**, helping it to anchor to the surface of **lipid droplets** and digest triglycerides in the presence of bile salts. - Colipase is secreted by pancreatic acinar cells along with other pancreatic enzymes into the duodenum. *Salivary glands* - The salivary glands (parotid, submandibular, sublingual) produce saliva containing enzymes like **amylase** and **lingual lipase**. - These glands do not secrete colipase, which is involved in fat digestion in the small intestine, not in the mouth. *Gallbladder* - The gallbladder stores and releases **bile**, which aids in fat emulsification. - Bile does not contain colipase; colipase is produced by the pancreas and works synergistically with bile salts during fat digestion. *Small intestine* - The small intestine is where most nutrient absorption occurs and produces some enzymes (e.g., brush border enzymes like maltase, lactase). - The small intestine does not synthesize colipase; it receives colipase from pancreatic secretions via the pancreatic duct. *Liver* - The liver produces bile, which is stored in the gallbladder and released into the duodenum to emulsify fats. - The liver does not produce colipase; this enzyme is specifically secreted by pancreatic acinar cells.

Q: Name the mechanism shown as $X$ below.

Nonenzymatic decarboxylation. ***Nonenzymatic decarboxylation*** - The image shows **acetoacetate converting into acetone**, with the release of **carbon dioxide (CO2)**. This process is a spontaneous, **nonenzymatic decarboxylation** that occurs in conditions like diabetic ketoacidosis. - The absence of an enzyme indicated at "X" further supports that this is a **nonenzymatic reaction**. *Thiolase* - **Thiolase** is an enzyme involved in the synthesis of acetoacetyl CoA, and also in the breakdown of fatty acids, but not in the conversion of acetoacetate to acetone. - This enzyme catalyzes the **condensation of two acetyl-CoA** molecules to form acetoacetyl-CoA or the cleavage of acetoacetyl-CoA. *HMG CoA Lyase* - **HMG CoA lyase** is an enzyme that catalyzes the cleavage of HMG-CoA to **acetoacetate and acetyl-CoA** during ketogenesis. - It works upstream in the ketone body synthesis pathway, not directly converting acetoacetate to acetone. *HMG CoA synthase* - **HMG CoA synthase** is an enzyme that catalyzes the condensation of **acetoacetyl-CoA and acetyl-CoA** to form HMG-CoA, the first committed step of ketogenesis. - It works upstream in the pathway, not in the conversion of acetoacetate to acetone. *L-beta hydroxyl butyrate dehydrogenase* - The image already labels **beta-hydroxybutyrate dehydrogenase**, which interconverts **acetoacetate and beta-hydroxybutyrate** using NADH and NAD+. - This enzyme is responsible for the reversible reduction of acetoacetate to beta-hydroxybutyrate, and not for the formation of acetone.

Q: Which is the location of HMG CoA synthase in cholesterol metabolism?

2. ***2*** - HMG CoA synthase is a key enzyme in the cholesterol synthesis pathway, specifically converting acetoacetyl-CoA to **hydroxymethylglutaryl-CoA (HMG-CoA)**. - This step occurs in the **cytosol**, which is indicated by '2' in the diagram. - The cytosolic form of HMG-CoA synthase is specifically involved in cholesterol biosynthesis. *1* - '1' points to the **nucleus**, which is primarily involved in DNA replication and transcription, not cholesterol synthesis. - While gene expression control for cholesterol synthesis occurs here (e.g., SREBP regulation), the enzymatic reaction itself does not take place in the nucleus. *3* - '3' indicates the **smooth endoplasmic reticulum (SER)**, which is involved in later steps of cholesterol synthesis, such as the conversion of squalene to cholesterol. - However, the initial steps catalyzed by HMG CoA synthase occur in the cytosol, not directly on the SER. *4* - '4' points to a **mitochondrion**, which is involved in energy production through the citric acid cycle and oxidative phosphorylation. - Note: There is a mitochondrial HMG-CoA synthase, but it is involved in **ketone body synthesis**, not cholesterol metabolism. *5* - '5' represents another cellular structure not involved in the HMG-CoA synthase step of cholesterol synthesis. - The cholesterol synthesis pathway begins in the cytosol with the formation of HMG-CoA before proceeding to other compartments.

Question 1

Colipase is an enzyme found in secretions from which of the following? (Recent NEET Pattern 2018)

Accepted Answer

Pancreas

Answer

Salivary glands

Answer

Gallbladder

Answer

Small intestine

Answer

Liver

Question 2

Name the mechanism shown as $X$ below.

Accepted Answer

Nonenzymatic decarboxylation

Answer

Thiolase

Answer

HMG CoA Lyase

Answer

L-beta hydroxyl butyrate dehydrogenase

Answer

HMG CoA synthase

Question 3

Which is the location of HMG CoA synthase in cholesterol metabolism?

Accepted Answer

2

Answer

1

Answer

3

Answer

4

Answer

5

Question 4

An adult male presented with a protruding abdomen, diarrhea, visual symptoms, and neurological manifestations. His LDL is low. Based on the peripheral smear finding shown in the image, what is the likely diagnosis?

Accepted Answer

Abetalipoproteinemia

Answer

EDTA changes

Answer

Uremia

Answer

Burns

Answer

Liver disease

Question 5

A patient came to the hospital with severe abdominal pain, and lipase levels were elevated. On imaging, a stone is found in the common bile duct (CBD). Which enzyme is most likely elevated in this condition?

Accepted Answer

ALP

Answer

ALT

Answer

GGT

Answer

LDH

Answer

AST

Lipid metabolism — MCQs

Lipid metabolism — MCQs

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