MCQs on Amino Acids & Proteins

Amino Acids – Nutritional & Structural Classification

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1. Which of the following is an essential amino acid?
A. Alanine
B. Serine
C. Valine
D. Glutamate

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2. Semi-essential amino acids are those that:
A. Are synthesized in excess amounts
B. Are always required in diet
C. Are required in diet during rapid growth
D. Are not required in diet at all

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3. Which of the following amino acids is classified as a non-essential amino acid?
A. Isoleucine
B. Leucine
C. Tyrosine
D. Lysine

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4. Which of the following amino acid is an essential amino acid?
A. Serine
B. Tyrosine
C. Phenylalanine
D. Glutamine

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5. Which of the following amino acids has a branched-chain structure?
A. Phenylalanine
B. Isoleucine
C. Tryptophan
D. Histidine

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6. Aromatic amino acids include all EXCEPT:
A. Tryptophan
B. Tyrosine
C. Phenylalanine
D. Valine

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7. Which of the following amino acids contains a sulfur atom?
A. Threonine
B. Methionine
C. Tyrosine
D. Glutamine

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8. Basic amino acids are characterized by:
A. Acidic side chains
B. Hydroxyl groups
C. Positively charged side chains at physiological pH
D. Aromatic rings

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9. Which of the following is a dicarboxylic (acidic) amino acid?
A. Arginine
B. Glutamic acid
C. Valine
D. Serine

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10. Which amino acid has a cyclic structure involving its amino group (an imino acid)?
A. Glycine
B. Alanine
C. Proline
D. Histidine

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✅ Answer Key

1. C. Valine

2. C. Are required in diet during rapid growth

3. C. Tyrosine

4. C. Phenylalanine

5. B. Isoleucine

6. D. Valine

7. B. Methionine

8. C. Positively charged side chains at physiological pH

9. B. Glutamic acid

10. C. Proline

 

Biologically Important Peptides

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1. Which of the following is a tripeptide involved in antioxidant defense?
A. Oxytocin
B. Bradykinin
C. Glutathione
D. Vasopressin

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2. The main function of oxytocin is:
A. Decreasing blood pressure
B. Increasing urine output
C. Stimulating milk ejection and uterine contraction
D. Promoting glycogenolysis

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3. Which peptide hormone is involved in water reabsorption by the kidneys?
A. Oxytocin
B. Vasopressin
C. Bradykinin
D. Glucagon

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4. Glutathione is composed of which three amino acids?
A. Glutamate, Cysteine, Glycine
B. Glutamine, Serine, Glycine
C. Aspartate, Cysteine, Alanine
D. Alanine, Cysteine, Glycine

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5. Which peptide acts as a vasodilator and increases vascular permeability?
A. Oxytocin
B. Bradykinin
C. Vasopressin
D. Glucagon

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6. Which of the following is a nonapeptide involved in childbirth and lactation?
A. Bradykinin
B. Vasopressin
C. Oxytocin
D. Angiotensin II

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7. Which peptide helps maintain redox balance in cells?
A. Vasopressin
B. Glutathione
C. Angiotensin
D. Oxytocin

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8. Angiotensin II is
A. Tripeptide
B. Pentapeptide
C. Octapeptide
D. Decapeptide

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9. Which of the following biologically important peptides is synthesized in the hypothalamus?
A. Glutathione
B. Bradykinin
C. Vasopressin
D. Angiotensin

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10. The function of vasopressin is to:
A. Promote water loss
B. Constrict blood vessels and promote water retention
C. Increase insulin secretion
D. Stimulate appetite

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✅ Answer Key

1. C. Glutathione

2. C. Stimulating milk ejection and uterine contraction

3. B. Vasopressin

4. A. Glutamate, Cysteine, Glycine

5. B. Bradykinin

6. C. Oxytocin

7. B. Glutathione

8. C. Octapeptide 

9. C. Vasopressin

10. B. Constrict blood vessels and promote water retention

 

Proteins – Functions & Functional Classification

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1. Which of the following proteins is classified as a structural protein?
A. Hemoglobin
B. Insulin
C. Collagen
D. Myosin

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2. Immunoglobulins are functionally classified as:
A. Regulatory proteins
B. Structural proteins
C. Defensive proteins
D. Transport proteins

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3. Hemoglobin functions primarily as a:
A. Hormonal protein
B. Structural protein
C. Transport protein
D. Storage protein

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4. Which of the following is a contractile protein?
A. Actin
B. Albumin
C. Keratin
D. Insulin

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5. Ferritin is classified as a:
A. Structural protein
B. Storage protein
C. Transport protein
D. Contractile protein

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6. Enzymes are functionally classified as:
A. Structural proteins
B. Catalytic proteins
C. Defensive proteins
D. Hormonal proteins

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7. Which of the following proteins regulates blood glucose levels?
A. Hemoglobin
B. Myosin
C. Insulin
D. Actin

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8. Which of the following is a fibrous protein?
A. Hemoglobin
B. Albumin
C. Myosin
D. Collagen

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9. The main function of albumin in blood is:
A. Enzymatic activity
B. Hormone transport
C. Maintaining oncotic pressure
D. Muscle contraction

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10. Which of the following proteins plays a role in blood clotting?
A. Thrombin
B. Ferritin
C. Immunoglobulin
D. Keratin

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✅ Answer Key

1. C. Collagen

2. C. Defensive proteins

3. C. Transport protein

4. A. Actin

5. B. Storage protein

6. B. Catalytic proteins

7. C. Insulin

8. D. Collagen

9. C. Maintaining oncotic pressure

10. A. Thrombin

 

Proteins – Definition & Chemical Classification

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1. Proteins are composed of which basic building blocks?
A. Fatty acids
B. Nucleotides
C. Monosaccharides
D. Amino acids

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2. Proteins are linked together by which type of bond?
A. Glycosidic bond
B. Peptide bond
C. Hydrogen bond
D. Disulfide bond

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3. Which of the following is a simple protein?
A. Hemoglobin
B. Casein
C. Albumin
D. Glycoprotein

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4. On hydrolysis, simple proteins yield:
A. Only amino acids
B. Amino acids and carbohydrates
C. Amino acids and lipids
D. Amino acids and metals

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5. Which of the following is a conjugated protein with a lipid as its prosthetic group?
A. Glycoprotein
B. Lipoprotein
C. Metalloprotein
D. Phosphoprotein

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6. Hemoglobin is an example of a:
A. Simple protein
B. Lipoprotein
C. Chromoprotein
D. Glutelin

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7. Which of the following proteins contains a phosphate group as a prosthetic group?
A. Casein
B. Albumin
C. Ferritin
D. Globulin

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8. Proteins derived by hydrolysis of simple or conjugated proteins are called:
A. Fibrous proteins
B. Conjugated proteins
C. Derived proteins
D. Structural proteins

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9. Which of the following is a metalloprotein?
A. Casein
B. Ceruloplasmin
C. Zein
D. Myosin

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10. Proteans belongs to which category of proteins?
A. Simple
B. Conjugated
C. Primary Derived
D. Secondary Derived

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✅ Answer Key

1. D. Amino acids

2. B. Peptide bond

3. C. Albumin

4. A. Only amino acids

5. B. Lipoprotein

6. C. Chromoprotein

7. A. Casein

8. C. Derived proteins

9. B. Ceruloplasmin

10. C. Primary Derived

Structural Organization of Proteins

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1. The primary structure of a protein refers to:
A. α-helix and β-pleated sheets
B. Sequence of amino acids in a polypeptide chain
C. 3D folding of protein
D. Association of multiple polypeptide chains

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2. Which type of bond is most important in maintaining the primary structure of proteins?
A. Hydrogen bond
B. Disulfide bond
C. Peptide bond
D. Ionic bond

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3. The α-helix is a feature of which level of protein structure?
A. Primary
B. Secondary
C. Tertiary
D. Quaternary

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4. Which bond is responsible for maintaining the secondary structure of proteins?
A. Peptide bond
B. Hydrogen bond
C. Disulfide bond
D. Ionic bond

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5. Which of the following contributes to the tertiary structure of proteins?
A. Peptide bonds only
B. Hydrogen and ionic bonds
C. Hydrophobic interactions, hydrogen bonds, ionic bonds, and disulfide bridges
D. Only disulfide bonds

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6. Quaternary structure is seen in proteins that:
A. Are made of a single polypeptide chain
B. Are only found in membranes
C. Have multiple polypeptide subunits
D. Are denatured

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7. Hemoglobin is an example of a protein with:
A. Primary structure only
B. Secondary structure only
C. Tertiary structure only
D. Quaternary structure

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8. The folding of a single polypeptide chain into a 3D structure represents the:
A. Primary structure
B. Secondary structure
C. Tertiary structure
D. Quaternary structure

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9. β-pleated sheet is stabilized mainly by:
A. Ionic bonds
B. Peptide bonds
C. Disulfide bonds
D. Hydrogen bonds

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10. Denaturation of a protein affects:
A. Only primary structure
B. Only quaternary structure
C. Secondary, tertiary, and quaternary structures
D. All levels of protein structure

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✅ Answer Key

1. B. Sequence of amino acids in a polypeptide chain

2. C. Peptide bond

3. B. Secondary

4. B. Hydrogen bond

5. C. Hydrophobic interactions, hydrogen bonds, ionic bonds, and disulfide bridges

6. C. Have multiple polypeptide subunits

7. D. Quaternary structure

8. C. Tertiary structure

9. D. Hydrogen bonds

10. C. Secondary, tertiary, and quaternary structures

 

Denaturation and Plasma Proteins

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1. Protein denaturation involves:
A. Breaking peptide bonds
B. Alteration of primary structure
C. Loss of secondary, tertiary, and quaternary structure
D. Complete hydrolysis of the protein

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2. Which of the following agents can cause protein denaturation?
A. Heat
B. Strong acids or bases
C. Alcohol
D. All of the above

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3. Denaturation of proteins is usually:
A. Reversible
B. Irreversible
C. Does not affect biological activity
D. Leads to peptide bond formation

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4. Which of the following structures is not affected during protein denaturation?
A. Primary
B. Secondary
C. Tertiary
D. Quaternary

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5. The major protein responsible for maintaining colloidal osmotic (oncotic) pressure in plasma is:
A. Globulin
B. Fibrinogen
C. Albumin
D. Hemoglobin

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6. Which of the following is a function of plasma proteins?
A. Enzyme catalysis
B. Transport of substances
C. Hormone synthesis
D. DNA replication

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7. Which plasma protein plays a role in blood clotting?
A. Albumin
B. Globulin
C. Fibrinogen
D. Ceruloplasmin

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8. Immunoglobulins belong to which class of plasma proteins?
A. Albumins
B. Globulins
C. Fibrinogen
D. Lipoproteins

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9. Plasma differs from serum in that plasma contains:
A. No proteins
B. More electrolytes
C. Fibrinogen
D. Hemoglobin

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10. The normal concentration of plasma proteins in human blood is approximately:
A. 2–3 g/dL
B. 4–6 g/dL
C. 6–8 g/dL
D. 10–12 g/dL

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✅ Answer Key

1. C. Loss of secondary, tertiary, and quaternary structure

2. D. All of the above

3. B. Irreversible

4. A. Primary

5. C. Albumin

6. B. Transport of substances

7. C. Fibrinogen

8. B. Globulins

9. C. Fibrinogen

10. C. 6–8 g/dL

 

Digestion and Absorption of Proteins

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1. Protein digestion begins in which part of the gastrointestinal tract?
A. Mouth
B. Stomach
C. Small intestine
D. Large intestine

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2. The enzyme pepsin is active in:
A. Acidic pH
B. Alkaline pH
C. Neutral pH
D. All pH

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3. The zymogen form of pepsin is:
A. Pepsinogen
B. Trypsinogen
C. Chymotrypsin
D. Enteropeptidase

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4. Which hormone stimulates the release of gastric juice rich in pepsinogen and HCl?
A. Secretin
B. CCK (Cholecystokinin)
C. Gastrin
D. Somatostatin

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5. In the small intestine, the enzyme that activates trypsinogen is:
A. Enterokinase
B. Pepsin
C. Amylase
D. Rennin

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6. Which of the following is NOT a brush border enzyme involved in protein digestion?
A. Aminopeptidase
B. Dipeptidase
C. Carboxypeptidase
D. Enteropeptidase

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7. End products of protein digestion absorbed in the small intestine are mainly:
A. Whole proteins
B. Polypeptides
C. Amino acids and dipeptides
D. Triglycerides

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8. Absorption of amino acids occurs mainly in the:
A. Stomach
B. Duodenum and jejunum
C. Colon
D. Esophagus

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9. Transport of amino acids across intestinal mucosa is primarily:
A. Passive diffusion
B. Simple diffusion
C. Secondary active transport with sodium
D. Primary active transport with potassium

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10. In infants, the enzyme that helps in curdling milk is:
A. Pepsin
B. Trypsin
C. Rennin (Chymosin)
D. Elastase

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✅ Answer Key

1. B. Stomach

2. A. Acidic pH

3. A. Pepsinogen

4. C. Gastrin

5. A. Enterokinase

6. C. Carboxypeptidase

7. C. Amino acids and dipeptides

8. B. Duodenum and jejunum

9. C. Secondary active transport with sodium

10. C. Rennin (Chymosin)

 

Urea Cycle, Disorders & Significance

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1. The urea cycle primarily takes place in the:
A. Kidney
B. Brain
C. Liver
D. Intestine

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2. The first step of the urea cycle occurs in which part of the cell?
A. Cytosol
B. Endoplasmic reticulum
C. Nucleus
D. Mitochondria

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3. Which of the following is the first enzyme of the urea cycle?
A. Argininosuccinate synthetase
B. Ornithine transcarbamoylase
C. Carbamoyl phosphate synthetase I
D. Arginase

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4. Which of the following molecules is directly converted into urea in the final step of the cycle?
A. Citrulline
B. Arginine
C. Ornithine
D. Aspartate

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5. Which of the following is an allosteric activator of Carbamoyl Phosphate Synthetase I?
A. Citrulline
B. N-Acetylglutamate (NAG)
C. Urea
D. Aspartate

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6. Inherited deficiency of ornithine transcarbamoylase leads to accumulation of:
A. Ammonia
B. Urea
C. Glucose
D. Creatinine

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7. Which of the following is a key function of the urea cycle?
A. Fat synthesis
B. Removal of carbon dioxide
C. Detoxification of ammonia
D. Hemoglobin production

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8. Urea is transported from the liver to the kidneys via:
A. Bile
B. Lymph
C. Portal vein
D. Bloodstream

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9. Hyperammonemia is dangerous primarily because it:
A. Causes dehydration
B. Leads to hyperglycemia
C. Is neurotoxic and can cause coma
D. Increases RBC production

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10. Which urea cycle disorder is X-linked recessive in inheritance?
A. Argininosuccinate lyase deficiency
B. Carbamoyl phosphate synthetase I deficiency
C. Ornithine transcarbamoylase deficiency
D. Argininemia

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✅ Answer Key

1. C. Liver

2. D. Mitochondria

3. C. Carbamoyl phosphate synthetase I

4. B. Arginine

5. B. N-Acetylglutamate (NAG)

6. A. Ammonia

7. C. Detoxification of ammonia

8. D. Bloodstream

9. C. Is neurotoxic and can cause coma

10. C. Ornithine transcarbamoylase deficiency

 

Transamination & Deamination

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1. Transamination is the process of:
A. Removal of amino group as ammonia
B. Transfer of amino group from one amino acid to a keto acid
C. Formation of urea
D. Protein synthesis

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2. Which enzyme catalyzes transamination reactions?
A. Deaminase
B. Transaminase (Aminotransferase)
C. Urease
D. Peptidase

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3. The coenzyme required for transaminase activity is:
A. NAD+
B. FAD
C. Pyridoxal phosphate (Vitamin B6)
D. Biotin

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4. Deamination primarily involves:
A. Transfer of amino group
B. Removal of amino group as ammonia
C. Formation of peptide bond
D. Transfer of phosphate group

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5. Oxidative deamination mainly occurs in:
A. Liver mitochondria
B. Cytosol of muscle cells
C. Blood plasma
D. Kidney cortex

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6. The most common amino acid undergoing transamination is:
A. Glycine
B. Glutamate
C. Alanine
D. Lysine

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7. Glutamate dehydrogenase catalyzes:
A. Transamination
B. Oxidative deamination of glutamate
C. Urea synthesis
D. Protein breakdown

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8. The amino group removed during deamination enters the urea cycle as:
A. Ammonia (NH3)
B. Nitrite (NO2-)
C. Nitrate (NO3-)
D. Urea directly

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9. Which of the following amino acids does NOT undergo transamination?
A. Alanine
B. Glutamate
C. Lysine
D. Aspartate

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10. Transamination is important for:
A. Synthesizing new amino acids
B. Breaking down carbohydrates
C. DNA replication
D. Fat metabolism

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✅ Answer Key

1. B. Transfer of amino group from one amino acid to a keto acid

2. B. Transaminase (Aminotransferase)

3. C. Pyridoxal phosphate (Vitamin B6)

4. B. Removal of amino group as ammonia

5. A. Liver mitochondria

6. B. Glutamate

7. B. Oxidative deamination of glutamate

8. A. Ammonia (NH3)

9. C. Lysine

10. A. Synthesizing new amino acids

 

Transmethylation & Decarboxylation

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1. Transmethylation is the process of:
A. Removal of a carboxyl group
B. Transfer of a methyl group from one molecule to another
C. Removal of an amino group
D. Formation of a peptide bond

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2. The common methyl donor in transmethylation reactions is:
A. S-adenosylmethionine (SAM)
B. Folic acid
C. Vitamin B12
D. Pyridoxal phosphate

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3. Which vitamin is essential for methylation reactions?
A. Vitamin C
B. Vitamin B6
C. Vitamin B12
D. Vitamin K

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4. Decarboxylation involves the removal of:
A. An amino group
B. A carboxyl group as CO2
C. A phosphate group
D. A methyl group

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5. Decarboxylation of amino acids produces:
A. Ammonia
B. Amines and CO2
C. Urea
D. Peptides

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6. Which enzyme catalyzes the decarboxylation of amino acids?
A. Decarboxylase
B. Transaminase
C. Deaminase
D. Kinase

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7. Which of the following is a product of decarboxylation of histidine?
A. Serotonin
B. Histamine
C. Dopamine
D. Acetylcholine

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8. The coenzyme required for amino acid decarboxylation is:
A. NAD+
B. Pyridoxal phosphate (Vitamin B6)
C. Biotin
D. FAD

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9. Which of the following neurotransmitters is formed by decarboxylation of L-DOPA?
A. Serotonin
B. Dopamine
C. Norepinephrine
D. GABA

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10. Transmethylation reactions are important for:
A. DNA methylation and gene regulation
B. Energy production
C. Protein degradation
D. Fatty acid synthesis

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✅ Answer Key

1. B. Transfer of a methyl group from one molecule to another

2. A. S-adenosylmethionine (SAM)

3. C. Vitamin B12

4. B. A carboxyl group as CO2

5. B. Amines and CO2

6. A. Decarboxylase

7. B. Histamine

8. B. Pyridoxal phosphate (Vitamin B6)

9. B. Dopamine

10. A. DNA methylation and gene regulation

Products of Glycine, Tyrosine & Tryptophan

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1. Glycine is a precursor for the synthesis of:
A. Creatine
B. Dopamine
C. Serotonin
D. Thyroxine

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2. Which molecule is formed from glycine and is a major component of heme?
A. Porphyrin
B. Melanin
C. Adrenaline
D. Histamine

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3. Tyrosine is a precursor for the synthesis of:
A. Melanin
B. Thyroxine
C. Dopamine
D. All of the above

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4. The neurotransmitter dopamine is synthesized from:
A. Glycine
B. Tryptophan
C. Tyrosine
D. Histidine

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5. Which hormone is synthesized from tyrosine in the thyroid gland?
A. Cortisol
B. Thyroxine (T4)
C. Insulin
D. Glucagon

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6. Tryptophan is the precursor of:
A. Serotonin
B. Melanin
C. Adrenaline
D. Thyroxine

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7. Which vitamin is required for the conversion of tryptophan to serotonin?
A. Vitamin B1
B. Vitamin B6
C. Vitamin C
D. Vitamin D

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8. Melanin is synthesized from which amino acid?
A. Glycine
B. Tyrosine
C. Tryptophan
D. Glutamate

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9. A deficiency in which amino acid could affect serotonin production?
A. Glycine
B. Tyrosine
C. Tryptophan
D. Alanine

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10. Creatine, important for muscle energy storage, is synthesized from:
A. Glycine
B. Tyrosine
C. Tryptophan
D. Phenylalanine

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✅ Answer Key

1. A. Creatine

2. A. Porphyrin

3. D. All of the above

4. C. Tyrosine

5. B. Thyroxine (T4)

6. A. Serotonin

7. B. Vitamin B6

8. B. Tyrosine

9. C. Tryptophan

10. A. Glycine

 

Phenylketonuria and Alkaptonuria

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1. Phenylketonuria is caused by a deficiency of which enzyme?
A. Tyrosinase
B. Phenylalanine hydroxylase
C. Homogentisate oxidase
D. Fumarase

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2. The primary amino acid that accumulates in phenylketonuria is:
A. Tyrosine
B. Phenylalanine
C. Homogentisic acid
D. Tryptophan

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3. One characteristic clinical feature of untreated PKU is:
A. Blue-black pigmentation of cartilage
B. Severe mental retardation
C. Hyperpigmentation
D. Hyperglycemia

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4. The diagnostic test for PKU in newborns is:
A. Guthrie test
B. Blood glucose test
C. Urine ketone test
D. Serum bilirubin test

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5. Alkaptonuria is due to deficiency of which enzyme?
A. Phenylalanine hydroxylase
B. Homogentisate oxidase
C. Tyrosinase
D. Dopachrome tautomerase

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6. The accumulation of which substance causes dark urine in alkaptonuria?
A. Phenylalanine
B. Homogentisic acid
C. Tyrosine
D. Melanin

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7. Which of the following is a clinical feature of alkaptonuria?
A. Intellectual disability
B. Blue-black pigmentation of connective tissue (ochronosis)
C. Hypoglycemia
D. Jaundice

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8. The pigment responsible for ochronosis in alkaptonuria is derived from:
A. Melanin
B. Homogentisic acid polymer
C. Bilirubin
D. Hemoglobin

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9. The inheritance pattern of both phenylketonuria and alkaptonuria is:
A. Autosomal dominant
B. X-linked recessive
C. Autosomal recessive
D. Mitochondrial

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10. Dietary management of PKU includes:
A. High protein diet
B. Restriction of phenylalanine
C. Vitamin B12 supplementation
D. High tyrosine intake

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✅ Answer Key

1. B. Phenylalanine hydroxylase

2. B. Phenylalanine

3. B. Severe mental retardation

4. A. Guthrie test

5. B. Homogentisate oxidase

6. B. Homogentisic acid

7. B. Blue-black pigmentation of connective tissue (ochronosis)

8. B. Homogentisic acid polymer

9. C. Autosomal recessive

10. B. Restriction of phenylalanine

 

Branched-Chain Ketoaciduria & Cystinuria

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1. Branched-Chain Ketoaciduria is also known as:
A. Phenylketonuria
B. Maple Syrup Urine Disease (MSUD)
C. Alkaptonuria
D. Cystinuria

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2. The defective enzyme complex in Maple Syrup Urine Disease is:
A. Branched-chain α-ketoacid dehydrogenase
B. Phenylalanine hydroxylase
C. Homogentisate oxidase
D. Cystathionine β-synthase

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3. Accumulation of which amino acids occurs in MSUD?
A. Phenylalanine, Tyrosine
B. Leucine, Isoleucine, Valine
C. Glycine, Serine
D. Cysteine, Methionine

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4. The characteristic odor of urine in MSUD is:
A. Musty
B. Sweaty feet / Maple syrup-like
C. Rotten fish
D. Mousy

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5. Cystinuria is caused by defective renal tubular reabsorption of:
A. Branched-chain amino acids
B. Sulfur-containing amino acids like cystine
C. Aromatic amino acids
D. Basic amino acids only

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6. Which amino acid forms crystals and stones in cystinuria?
A. Methionine
B. Cystine
C. Leucine
D. Phenylalanine

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7. The inheritance pattern of cystinuria is:
A. Autosomal dominant
B. Autosomal recessive
C. X-linked recessive
D. Mitochondrial

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8. The treatment for cystinuria involves:
A. Restriction of cystine in diet
B. Alkalinization of urine to increase cystine solubility
C. High protein diet
D. Low sodium diet only

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9. Which of the following is NOT a clinical feature of MSUD?
A. Mental retardation
B. Seizures
C. Blue-black pigmentation of cartilage
D. Vomiting and lethargy

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10. Diagnosis of cystinuria is confirmed by the presence of:
A. Sulfite crystals in urine
B. Cystine crystals in urine
C. Ketone bodies in urine
D. Hematuria only

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✅ Answer Key

1. B. Maple Syrup Urine Disease (MSUD)

2. A. Branched-chain α-ketoacid dehydrogenase

3. B. Leucine, Isoleucine, Valine

4. B. Sweaty feet / Maple syrup-like

5. B. Sulfur-containing amino acids like cystine

6. B. Cystine

7. B. Autosomal recessive

8. B. Alkalinization of urine to increase cystine solubility

9. C. Blue-black pigmentation of cartilage

10. B. Cystine crystals in urine

 

Revision Questions

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1. All amino acids are optically active except:

A. Glycine
B. Alanine
C. Leucine
D. Serine

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2. Which of the following amino acids contains a sulfur group?

A. Lysine
B. Methionine
C. Glutamine
D. Phenylalanine

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3. A patient presents with mousy odor of urine. The likely diagnosis is:

A. Alkaptonuria
B. Phenylketonuria
C. Maple syrup urine disease
D. Homocystinuria

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4. Transamination reactions require which coenzyme?

A. FAD
B. NAD+
C. Biotin
D. Pyridoxal phosphate (Vitamin B6)

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5. Which amino acid acts as a precursor for serotonin?

A. Tyrosine
B. Phenylalanine
C. Tryptophan
D. Histidine

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6. The amino acid that disrupts alpha-helix structure in proteins is:

A. Alanine
B. Glycine
C. Proline
D. Glutamate

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7. Which amino acid is both glucogenic and ketogenic?

A. Leucine
B. Lysine
C. Isoleucine
D. Valine

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8. In urea cycle, ammonia is derived from:

A. Glutamine and alanine
B. Glutamate and aspartate
C. Glutamate and free NH₃
D. Ornithine and NH₃

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9. Which enzyme is deficient in alkaptonuria?

A. Homogentisate oxidase
B. Tyrosinase
C. Phenylalanine hydroxylase
D. DOPA decarboxylase

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10. Maple syrup urine disease is due to defect in metabolism of:

A. Aromatic amino acids
B. Sulfur-containing amino acids
C. Branched-chain amino acids
D. Basic amino acids

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11. The positive nitrogen balance is seen in:

A. Starvation
B. Pregnancy
C. Cachexia
D. Liver failure

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12. Which protein has a triple helical structure?

A. Keratin
B. Collagen
C. Elastin
D. Myosin

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13. Which amino acid is a precursor of nitric oxide (NO)?

A. Citrulline
B. Glutamate
C. Arginine
D. Ornithine

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14. The enzyme deficient in homocystinuria is:

A. Homogentisate oxidase
B. Cystathionine β-synthase
C. Tyrosinase
D. Glutamate dehydrogenase

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15. Tyrosine is a precursor for all except:

A. Dopamine
B. Melanin
C. Thyroxine
D. Serotonin

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16. Which is a semi-essential amino acid?

A. Arginine
B. Leucine
C. Tryptophan
D. Threonine

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17. Which is a sulfur-containing amino acid?

A. Serine
B. Cysteine
C. Valine
D. Asparagine

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18. Protein digestion begins in:

A. Mouth
B. Stomach
C. Duodenum
D. Ileum

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19. Which plasma protein has the highest concentration?

A. Transferrin
B. Albumin
C. Globulin
D. Fibrinogen

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20. Which amino acid carries ammonia from muscle to liver?

A. Glutamate
B. Glutamine
C. Alanine
D. Aspartate

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21. The key enzyme in the urea cycle is:

A. Carbamoyl phosphate synthetase I
B. Ornithine transcarbamylase
C. Argininosuccinate synthetase
D. Arginase

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22. Which bond stabilizes secondary structure of proteins?

A. Hydrogen bonds
B. Disulfide bonds
C. Peptide bonds
D. Ionic bonds

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23. Which amino acid is ketogenic only?

A. Isoleucine
B. Tyrosine
C. Leucine
D. Phenylalanine

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24. In electrophoresis at pH 8.6, albumin migrates:

A. Toward cathode
B. Toward anode
C. Remains at origin
D. Moves slowly

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25. What is the end product of phenylalanine metabolism?

A. Tyrosine
B. Fumarate and acetoacetate
C. Pyruvate
D. Succinyl-CoA

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26. Basic amino acids include all except:

A. Arginine
B. Lysine
C. Histidine
D. Glutamine

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27. Most important buffering amino acid in plasma proteins:

A. Glutamate
B. Histidine
C. Glycine
D. Cysteine

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28. Which amino acid forms disulfide bonds?

A. Serine
B. Alanine
C. Cysteine
D. Methionine

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29. Amino acid with an imino group is:

A. Glycine
B. Proline
C. Alanine
D. Tryptophan

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30. Proteins are first digested by:

A. Trypsin
B. Pepsin
C. Aminopeptidase
D. Carboxypeptidase

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✅ Answer Key