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Biochemistry

Metabolic pathways, enzymes, proteins

278 Q 3 Topics Take Test
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Difficulty: All Easy Medium Hard 71–80 of 278
Topics in Biochemistry
All Proteins & Enzymes 100 Carbohydrates 100 Lipids 78
Q.71 Medium Lipids
A patient with familial hypercholesterolemia shows extremely high cholesterol levels. What is the most likely defect?
A Deficiency in HMG-CoA reductase
B Absence or malfunction of LDL receptors
C Excessive HDL production
D Decreased acetyl-CoA levels
Correct Answer:  B. Absence or malfunction of LDL receptors
EXPLANATION

Familial hypercholesterolemia is caused by mutations in the LDL receptor gene, preventing cells from taking up LDL particles, resulting in elevated blood cholesterol levels.

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Q.72 Medium Lipids
Which of the following is a consequence of excessive cholesterol accumulation in arteries?
A Increased blood viscosity leading to faster flow
B Formation of atherosclerotic plaques causing narrowing of arteries
C Enhanced oxygen delivery to tissues
D Improved arterial elasticity
Correct Answer:  B. Formation of atherosclerotic plaques causing narrowing of arteries
EXPLANATION

High cholesterol, particularly LDL cholesterol, can accumulate in artery walls forming atherosclerotic plaques, leading to arterial narrowing (atherosclerosis) and increased risk of heart disease.

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Q.73 Medium Lipids
In the context of lipid metabolism, what does beta-oxidation primarily accomplish?
A Synthesis of new fatty acids
B Breaking down fatty acids into acetyl-CoA for energy production
C Formation of cholesterol from acetyl-CoA
D Conversion of glucose into triglycerides
Correct Answer:  B. Breaking down fatty acids into acetyl-CoA for energy production
EXPLANATION

Beta-oxidation is the catabolic pathway that breaks down fatty acids in the mitochondria, producing acetyl-CoA which enters the Krebs cycle for ATP production.

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Q.74 Easy Lipids
What is the difference between saturated and unsaturated fatty acids in terms of their chemical structure?
A Saturated acids have more carbon atoms
B Unsaturated acids contain one or more double bonds between carbon atoms
C Saturated acids are longer chain molecules
D Unsaturated acids contain oxygen atoms
Correct Answer:  B. Unsaturated acids contain one or more double bonds between carbon atoms
EXPLANATION

Saturated fatty acids have all single bonds between carbon atoms (straight chain), while unsaturated fatty acids have one or more C=C double bonds (kinked structure).

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Q.75 Easy Lipids
Which lipid type is essential for maintaining the structural integrity of cell membranes?
A Cholesterol and phospholipids
B Triglycerides and waxes
C Steroids and eicosanoids
D Only triglycerides
Correct Answer:  A. Cholesterol and phospholipids
EXPLANATION

Cell membranes are composed of a phospholipid bilayer with embedded cholesterol molecules that regulate membrane fluidity and maintain structural integrity.

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Q.76 Easy Lipids
Omega-3 fatty acids are beneficial for human health because they:
A Increase LDL cholesterol levels
B Are saturated and stable at high temperatures
C Reduce inflammation and support cardiovascular health
D Promote the synthesis of triglycerides
Correct Answer:  C. Reduce inflammation and support cardiovascular health
EXPLANATION

Omega-3 polyunsaturated fatty acids (found in fish, flaxseed) have anti-inflammatory properties and support heart health by reducing triglycerides and blood pressure.

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Q.77 Easy Lipids
What is the primary function of HDL cholesterol in the body?
A Provide energy to cells
B Transport cholesterol from tissues to the liver for elimination
C Form cell membranes
D Insulate nerve fibers
Correct Answer:  B. Transport cholesterol from tissues to the liver for elimination
EXPLANATION

HDL (High-Density Lipoprotein) is known as 'good cholesterol' because it transports cholesterol from peripheral tissues back to the liver for degradation and excretion.

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Q.78 Easy Lipids
Which of the following is NOT a component of a triglyceride molecule?
A Glycerol
B Fatty acids
C Phosphate group
D Ester bonds
Correct Answer:  C. Phosphate group
EXPLANATION

Triglycerides consist of glycerol and three fatty acids connected by ester bonds. Phosphate groups are found in phospholipids, not triglycerides.

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Q.79 Hard Carbohydrates
In the non-oxidative phase of the pentose phosphate pathway, ribulose-5-phosphate is converted to ribose-5-phosphate by the enzyme ribulose-5-phosphate isomerase. Which tissue shows MAXIMUM activity of this pathway and why?
A Red blood cells - for maintaining reducing power via NADPH
B Adipose tissue - for fatty acid synthesis requiring NADPH
C Bone marrow - for rapid nucleotide synthesis and cell division
D Liver - for glycogen storage and gluconeogenesis
Correct Answer:  C. Bone marrow - for rapid nucleotide synthesis and cell division
EXPLANATION

Bone marrow shows the highest pentose phosphate pathway activity because rapidly dividing cells require maximum ribose-5-phosphate for nucleotide (DNA/RNA) synthesis during cell division. While adipose tissue needs NADPH for lipogenesis and RBCs need it for antioxidant defense, bone marrow's continuous hematopoiesis demands the most nucleotide precursors. This is clinically relevant in leukemia and chemotherapy patients.

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Q.80 Medium Carbohydrates
A 45-year-old patient with Type 2 diabetes mellitus shows elevated fasting blood glucose (180 mg/dL) but normal HbA1c levels initially. Which carbohydrate metabolism pathway is primarily impaired in this patient's liver?
A Glycogenesis and increased gluconeogenesis
B Glycogenolysis and normal glycolysis
C Pentose phosphate pathway upregulation
D Lactate to pyruvate conversion
Correct Answer:  A. Glycogenesis and increased gluconeogenesis
EXPLANATION

Type 2 diabetes shows hepatic insulin resistance leading to impaired glycogenesis (reduced glycogen synthesis) and uncontrolled gluconeogenesis (excessive glucose production). This causes elevated fasting glucose despite normal HbA1c if glycemic control improves later. The liver fails to suppress glucose production in response to insulin.

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