Lipids and Amino Acids

What is the primary advantage of storing energy as triacylglycerols rather than carbohydrates?
A) They store less energy per gram
B) They are hydrophilic and stored with water
C) They yield more than twice the energy of carbohydrates/proteins
D) They are easier to digest

They yield more than twice the energy of carbohydrates/proteins

Which enzyme initiates the breakdown of stored triacylglycerols during lipolysis?
A) Pancreatic lipase
B) Hormone-sensitive lipase
C) Acetyl-CoA carboxylase
D) Fatty acid synthase

Hormone-sensitive lipase

What role do bile salts play in lipid digestion?
A) Hydrolyze triglycerides into fatty acids
B) Emulsify fats into micelles for absorption
C) Transport chylomicrons into lymphatics
D) Activate hormone-sensitive lipase

Emulsify fats into micelles for absorption

1. How are long-chain fatty acids transported into mitochondria for β-oxidation?
   A) Direct diffusion through mitochondrial membrane
   B) Via the carnitine shuttle
   C) Bound to serum albumin
   D) Packaged into chylomicrons

Via the carnitine shuttle

1. Which molecule activates fatty acids before β-oxidation?
   A) NADH
   B) Coenzyme A (CoA)
   C) Carnitine
   D) ATP only

Coenzyme A (CoA)

What is the main product of fatty acid β-oxidation that enters the citric acid cycle?
A) Malonyl-CoA
B) Acetyl-CoA
C) Pyruvate
D) Citrate

Acetyl-CoA

Where does fatty acid biosynthesis primarily occur?
A) Mitochondrial matrix
B) Cytosol
C) Endoplasmic reticulum
D) Golgi apparatus

Cytosol

What is the first committed step in fatty acid synthesis?
A) Formation of acetyl-CoA
B) Conversion of acetyl-CoA to malonyl-CoA by acetyl-CoA carboxylase
C) Activation of fatty acids by CoA
D) Desaturation of palmitate

Conversion of acetyl-CoA to malonyl-CoA by acetyl-CoA carboxylase

Which enzyme complex catalyzes the sequential addition of two-carbon units during fatty acid synthesis?
A) Fatty acid synthase
B) HMG-CoA reductase
C) Lipoprotein lipase
D) Elongase

Fatty acid synthase

What is the product of de novo fatty acid synthesis?
A) Stearate (C18)
B) Palmitate (C16)
C) Oleate (C18:1)
D) Linoleate (C18:2)

Palmitate (C16)

What is the function of elongases in fatty acid metabolism?
A) Introduce double bonds
B) Shorten fatty acid chains
C) Lengthen fatty acid chains beyond 16 carbons
D) Convert fatty acids to ketone bodies

Lengthen fatty acid chains beyond 16 carbons

1. Which fatty acids are considered essential because they cannot be synthesized by humans?
   A) Palmitate and stearate
   B) Omega-3 and omega-6 fatty acids
   C) Oleic acid and linoleic acid
   D) Saturated fatty acids

Omega-3 and omega-6 fatty acids

What is the physiological significance of ketone bodies?
A) Primary fuel for liver cells
B) Alternative energy source for brain, heart, and muscle during fasting
C) Storage form of fatty acids
D) Precursor for cholesterol synthesis

Alternative energy source for brain, heart, and muscle during fasting

Which organ synthesizes ketone bodies?
A) Muscle
B) Liver
C) Brain
D) Adipose tissue

Liver

What distinguishes ketosis from ketoacidosis?
A) Ketosis causes blood pH to drop significantly
B) Ketoacidosis involves excessive ketone production leading to metabolic acidosis
C) Ketosis occurs only in diabetes
D) Ketoacidosis is a normal physiological state

Ketoacidosis involves excessive ketone production leading to metabolic acidosis

What is the rate-limiting enzyme in cholesterol biosynthesis?
A) Fatty acid synthase
B) HMG-CoA reductase
C) Acetyl-CoA carboxylase

D) Lipoprotein lipase

HMG-CoA reductase

Statins lower cholesterol by competitively inhibiting which enzyme?
A) Fatty acid synthase
B) HMG-CoA reductase
C) Acetyl-CoA carboxylase
D) Cholesterol esterase

HMG-CoA reductase

1. Which lipoprotein is known as “bad cholesterol” due to its role in delivering cholesterol to peripheral tissues?
   A) HDL
   B) LDL
   C) VLDL
   D) Chylomicrons

LDL

What is the primary role of HDL in lipid transport?
A) Deliver dietary fat to tissues
B) Transport endogenous fat from liver to tissues
C) Reverse cholesterol transport from tissues to liver
D) Carry triglycerides to adipose tissue

Reverse cholesterol transport from tissues to liver

Which enzyme converts acetyl-CoA to malonyl-CoA in fatty acid synthesis?
A) Fatty acid synthase
B) Acetyl-CoA carboxylase
C) HMG-CoA reductase
D) Lipoprotein lipase

Acetyl-CoA carboxylase

During lipolysis, free fatty acids released from adipose tissue circulate bound to:
A) Chylomicrons
B) Serum albumin
C) HDL
D) LDL

Serum albumin

Which hormone activates acetyl-CoA carboxylase to promote fatty acid synthesis?
A) Glucagon
B) Epinephrine
C) Insulin
D) Cortisol

Insulin

What cofactor is required by fatty acid synthase for reducing power during fatty acid synthesis?
A) NAD+
B) FAD
C) NADPH
D) ATP

NADPH

Which enzyme introduces double bonds into fatty acids?
A) Elongase
B) Desaturase
C) Lipase
D) Acetyl-CoA carboxylase

Desaturase

What is the fate of short- and medium-chain fatty acids after absorption?
A) Packaged into chylomicrons
B) Diffuse freely into enterocytes without chylomicrons
C) Converted immediately to ketone bodies
D) Transported via LDL

Diffuse freely into enterocytes without chylomicrons

Which amino acids are classified as essential?
A) Alanine, glycine, glutamate
B) Phenylalanine, valine, tryptophan
C) Arginine, proline, tyrosine
D) Glutamine, cysteine, histidine

Alanine, glycine, glutamate

What is the major route for non-essential amino acid synthesis?
A) Transamination reactions
B) Deamination reactions
C) Urea cycle
D) Beta-oxidation

Transamination reactions

Which coenzyme is critical for transamination reactions?
A) NAD+
B) Pyridoxal phosphate (PLP)
C) FAD
D) Biotin

Pyridoxal phosphate (PLP)

Alanine aminotransferase (ALT) catalyzes the reversible transfer of an amino group between alanine and:
A) Oxaloacetate
B) α-Ketoglutarate
C) Pyruvate
D) Glutamine

α-Ketoglutarate

Aspartate aminotransferase (AST) transfers an amino group from aspartate to:
A) Pyruvate
B) α-Ketoglutarate
C) Oxaloacetate
D) Glutamate

α-Ketoglutarate

What is the purpose of the glucose-alanine cycle?
A) Transport ammonia safely from muscle to liver
B) Synthesize glucose in muscle
C) Convert alanine to urea in kidney
D) Store excess nitrogen in muscle

Transport ammonia safely from muscle to liver

In the urea cycle, what molecule activates the cycle linking protein intake to activity?
A) Arginine
B) N-acetylglutamate
C) Citrulline
D) Ornithine

N-acetylglutamate

The urea cycle takes place primarily in which organ?
A) Kidney
B) Liver
C) Muscle
D) Intestine

Liver

How many ATP molecules are consumed per urea molecule synthesized?
A) 1
B) 2
C) 3
D) 4

3

What is the consequence of defective urea cycle enzymes?
A) Hypoglycemia
B) Hyperammonemia
C) Ketoacidosis
D) Hypercholesterolemia

Hyperammonemia

During starvation, glucogenic amino acids contribute to:
A) Ketone body formation
B) Glucose production
C) Fatty acid synthesis
D) Cholesterol synthesis

Glucose production

Ketogenic amino acids are metabolized to produce:
A) Glucose
B) Ketone bodies
C) Urea
D) Fatty acids

Ketone bodies

Which amino acid is conditionally essential, especially during growth or illness?
A) Leucine
B) Arginine
C) Lysine
D) Methionine

Arginine

What toxic compound must be safely transported from extrahepatic tissues to the liver?
A) Ammonia (NH3)
B) Carbon dioxide (CO2)
C) Urea
D) Nitric oxide

Ammonia (NH3)

Glutamine plays a key role in ammonia detoxification by:
A) Releasing NH3 in muscle
B) Combining NH3 with glutamate to form glutamine for safe transport
C) Converting NH3 directly to urea
D) Acting as a neurotransmitter

Combining NH3 with glutamate to form glutamine for safe transport

Which enzyme catalyzes oxidative deamination releasing ammonia for the urea cycle?
A) Alanine aminotransferase
B) Glutamate dehydrogenase
C) Aspartate aminotransferase
D) Carbamoyl phosphate synthetase I

Glutamate dehydrogenase

Pyridoxal phosphate (PLP) is derived from which vitamin?
A) Vitamin B1
B) Vitamin B6
C) Vitamin B12
D) Vitamin C

Vitamin B6

What happens to pyruvate formed in muscle during the glucose-alanine cycle?
A) Converted to lactate
B) Used for gluconeogenesis in the liver
C) Converted to acetyl-CoA in muscle
D) Excreted in urine

Used for gluconeogenesis in the liver

Which amino acid serves as a nitrogen carrier in the glucose-alanine cycle?
A) Glutamate
B) Alanine
C) Aspartate
D) Glutamine

Alanine

What is the main reason for amino acid catabolism during prolonged starvation?
A) To provide substrates for fatty acid synthesis
B) To maintain blood glucose and supply energy when glycogen and fat stores are depleted
C) To increase ketone body synthesis exclusively
D) To generate cholesterol precursors

To maintain blood glucose and supply energy when glycogen and fat stores are depleted