MCQs on Amino Acids for Concept Clarity and Exam Practice

Amino acids make up the proteins. They are organic compounds of nitrogen, carbon, hydrogen, and oxygen with a variable side chain group. Human beings need 20 essential amino acids for the proper development and functioning of various organs in the body. Out of the 20, 9 are deemed as the most important amino acids. 

An amino acid is an organic compound that consists of a basic amino group (NH₂), an acidic carboxyl group (COOH), and a unique organic R group (or side chain). Each molecule has a core carbon (C) atom, referred to as the -carbon, to which amino and a carboxyl group are linked. A hydrogen (H) atom and the R group usually satisfy the remaining two bonds of the -carbon atom. Proteins are made up of amino acids, which are the building blocks of the molecule. They offer many of a cell's structural constituents and aid in the formation of tissues by binding cells together.

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List of 20 Amino Acids

• Alanine - Ala - A 

• Arginine - Arg - R 

• Asparagine - Asn - N 

• Aspartic acid - Asp - D

• Cysteine - Cys - C 

• Glutamine - Gln - Q 

• Glutamic acid - Glu - E 

• Glycine - Gly - G 

• Histidine - His - H 

• Isoleucine - Ile - I 

• Leucine - Leu - L 

• Lysine - Lys - K 

• Methionine - Met - M 

• Phenylalanine - Phe - F 

• Proline - Pro - P 

• Serine - ser - S 

• Threonine - Thr - T

• Tryptophan - Trp - W 

• Tyrosine - Tyr - Y 

• Valine - Val - V

Properties of Amino acid

• The melting and boiling points of these are extremely high.

• Amino acids are crystalline white solids with a high molecular weight.

• Few amino acids have a pleasant, flavorless, or bitter flavor.

• Inorganic solvents are insoluble in most amino acids, which are soluble in water.

Types of Amino Acids

There are 7 types of amino acids differentiated on the basis of side chains present. Thus, the seven types of amino acids are-

• Aliphatic

• Aromatic

• Basic

• Acidic

• Hydroxylic

• Sulfur-containing

• Amidic or the one with the amide group

How Important are Amino Acids

Amino acids are the compounds that form the building blocks of proteins. Proteins are essential components that makeup 75% of the human body. Proteins are responsible for proper overall development. 

Functions of Essential and Non Essential Amino Acids

• Essential amino acids like phenylalanine, valine threonine help maintain the nervous system, promotes muscle growth, and strengthen the immune system.

• Essential amino acid Tryptophan is involved in the production of vitamin B3 and serotonin hormones that play a vital role in regulating sleep, boosting mood, and maintaining appetite.

• Isoleucine plays a vital role in the formation of hemoglobin along with stimulating the pancreas to synthesize insulin and helps transportation of oxygen in the body.

• Nonessential amino acids like alanine, cysteine, glutamine help in the production of glucose and other amino acids, provide resistance, and help promote a healthy brain function.

There are many such actions of all the amino acids- essential and nonessential which help maintain regular processes in the body and promote growth. 

Let’s Practise Some Solved MCQs on Amino Acids and Check Our Knowledge of the Chapter

1. Which of the following is true regarding the solubility of amino acids?

1. Mostly soluble in water and insoluble in organic solvents

2. They are only water-soluble

3. They are only soluble in organic solvents

4. Mostly soluble in organic solvents and insoluble in water

Answer: (a)

Explanation: In general, amino acids are soluble in water but insoluble in non-polar organic solvents like hydrocarbons. This reflects the presence of zwitterions once more. The strong ionic attractions between polar water molecules and the zwitterions in water replace the ionic attractions between the ions in the solid amino acid.

2. Which of the following essential amino acids is not synthesized by the body?

1. Arginine

2. Glutamine

3. Histidine

4. Proline

Answer: (c)

Explanation: The body does not produce essential amino acids. As a result, they must be obtained through the consumption of food. Histidine, isoleucine, leucine, lysine, phenylalanine, threonine, tryptophan, and valine are the nine essential amino acids.

3. From which of the following components amino acids are generally synthesized?

1. Fatty acids

2. 𝜶-­ketoglutaric acid

3. Mineral Salts

4. Volatile acids

Answer: (b)

Explanation: Glutamate, glutamine, proline, and arginine are ketoglutarates. alpha -ketoacids are used to make most amino acids, which are then transaminated from another amino acid, usually glutamate. Aminotransferase is the enzyme involved in this process.

4. Amino acids with the non-polar aliphatic ‘R’ group are

1. Glycine, alanine, leucine

2. Serine, threonine, cysteine

3. Lysine, arginine, histidine

4. Phenylalanine, tyrosine, and tryptophan

Answer: (a)

Explanation: Amino acids contain aliphatic R groups that are non-polar or hydrophobic. Glycine, alanine, valine, leucine, isoleucine, and proline are among the amino acids in this category. The R groups in hydrocarbons are non-polar and hydrophobic.

5.  Amino acids with aromatic side chains are

1. tryptophan, asparagine, tyrosine

2. tryptophan, threonine, tyrosine

3. phenylalanine, tryptophan, serine

4. phenylalanine, tryptophan, tyrosine

Answer: (d)

Explanation: When a side chain has an aromatic ring system, it is aromatic. The number of electrons enclosed within the ring is the formal definition.

6. Which of the following amino acids yield Acetyl CoA during catabolism?

1. Ketogenic

2. Glucogenic

3. Essential

4. None of the above

Answer: (a) 

Explanation: Amino acid catabolism begins at metabolic entry sites. Ketogenic amino acids are those that create acetyl CoA. Leucine, lysine, phenylalanine, tyrosine, tryptophan, and isoleucine are among them.

7. Which of the following is a true statement?

1. Tryptophan and tyrosine are significantly more polar than phenylalanine

2. Leucine is commonly used as an ingredient in the buffers of the SDS page

3. Aspartate is an essential amino acid

4. Lysine is a non-essential amino acid

Answer: (a)

Explanation: Because of the tyrosine hydroxyl group and the nitrogen of the tryptophan indole ring, tryptophan and tyrosine are substantially more polar than phenylalanine.

8. Out of these, which one is the non-essential amino acid?

1. Lysine

2. Threonine

3. Serine

4. Histidine

Answer: (c)

Alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine are examples of non-essential amino acids.

9. Which of the following is an essential amino acid?

1. Cysteine

2. Asparagine

3. Glutamine

4. Phenylalanine

Answer: (d)

Explanation: The body does not produce essential amino acids. As a result, they must be obtained through the consumption of food. Histidine, isoleucine, leucine, lysine, phenylalanine, threonine, tryptophan, and valine are the nine essential amino acids.

10. The difference between amino acid and imino acid is

1. Bonding of carbonyl group with the amide group

2. Bonding of nitrogen in the amide group

3. Bonding of nitrogen in the carbonyl group

4. Presence of covalent bond between amide and carbonyl group

Answer: (b)

Explanation: The main distinction between an amino acid and an imino acid is that an amino acid has both an amino and a carboxylic group in the same molecule, whereas an imino acid contains both an imino and a carboxylic group.

11. Which of the following is an example of imino acid?

1. Alanine

2. Glycine

3. Proline

4. Serine

Answer: (c)

Explanation: Any molecule with both imine (>C=NH) and carboxyl (-C(=O)-OH) functional groups is called an imino acid.

12. Which of the following amino acids is both glucogenic and ketogenic in nature?

1. Leucine

2. Lysine

3. Isoleucine

4. histidine

Answer: (c) 

Explanation: As an energy source, isoleucine produces both glucose and ketone bodies. During catabolism, pyruvate metabolites are generated in the case of glycogenic amino acids, and acetoacetyl CoA is created in the case of ketogenic amino acids.

13. Which of the following is true in the case of an amino acid that yields acetoacetyl CoA during the catabolism of its carbon skeleton?

1. It’s glycogenic in nature

2. It’s ketogenic in nature

3. It’s an essential amino acid

4. It can be either glucogenic or ketogenic in nature

Answer: (b)

Explanation: Pyruvate metabolites are generated during the catabolism of glycogenic amino acids, while acetoacyl CoA is formed during the catabolism of ketogenic amino acids.

14. Among the 20 standard proteins which are coding amino acids, which of the following occurs the least number of times in proteins?

1. Glycine

2. Alanine

3. Tryptophan

4. Methionine

Answer: (c)

15. Which of these is the first amino acid in a polypeptide chain?

1. Serine

2. Valine

3. Alanine

4. Methionine

Answer: (d)

Explanation: The codon AUG, often known as the start codon, specifies the amino acid methionine. As a result, during protein synthesis, methionine is the first amino acid to dock in the ribosome.

16. Which of the following are sulfur-containing amino acids?

1. Cysteine and methionine

2. Methionine and threonine

3. Cysteine and threonine

4. Cysteine and serine

Answer: (a)

Explanation: In practically all eukaryotic proteins, methionine is the starting amino acid; in prokaryotes, N-formylmethionine performs the same function. Cysteine is important in protein structure and folding pathways because of its capacity to create disulfide bonds.

17. Which of the following are positively charged basic amino acids?

1. Lysine and arginine

2. Lysine and asparagine

3. Glutamine and arginine

4. Lysine and glutamine

Answer: (a)

Explanation: Five of the twenty most often used amino acids have a charged side chain. At pH=7, aspartic acid (Asp, D) and glutamic acid (Glu, E) (acidic side chains) are negatively charged, and lysine (Lys, K), arginine (Arg, R), and histidine (His, H) are positively charged (basic side chains).

18. Out of these, the acidic amino acids are-

1. Arginine and glutamate

2. Aspartate and asparagine

3. Aspartate and lysine

4. Aspartate and glutamate

Answer: (d)

Explanation: Aspartic acid, also known as aspartate (Asp), and glutamic acid, often known as glutamate, are the two acids in question (Glu). Their side chains include carboxylic acid groups with pKas low enough to lose protons, causing them to become negatively charged.

19. The 21st amino acid is

1. Hydroxy lysine

2. Hydroxyproline

3. Selenocysteine

4. citrulline

Answer: (c)

Explanation: The 21^st amino acid in the genetic code, selenocysteine (Sec), is an uncommon amino acid that is cotranslationally incorporated into proteins. UGA codons, which ordinarily serve as stop signals, are used to encode Sec.

20. Out of the following, amino acids with hydroxyl groups are-

1. Serine and alanine

2. Alanine and Valine

3. Serine and threonine

4. Valine and Isoleucine

Answer: (c)

Explanation: Serine and threonine are two amino acids that contain aliphatic hydroxyl groups (an oxygen atom connected to a hydrogen atom, denoted as OH). The total amino acid profile of a food protein in comparison to a standard is a useful predictor of its potential nutritional value, but it can be deceiving if one or more of the necessary amino acids are only partially available.