All Free Biology MCQs with Answers

4521. A peptide bond is formed between

• A. An aldehyde group and an amino group
• B. An aldehyde group and a carboxyl group
• C. An aldehyde group and an ester group
• D. A carboxyl group and an amino group

Explanation: A peptide bond is a covalent bond that forms between the carboxyl group of one amino acid and the amino group of another amino acid. This reaction occurs through a dehydration synthesis process, where a molecule of water is released. The incorrect options all include an aldehyde group, which is not involved in peptide bond formation. Peptide bonds specifically involve the carboxyl and amino groups of amino acids.

4522. Assertion: Vitamin D can be stored in our body.Reason: Vitamin D is a fat-soluble vitamin.

• A. Assertion and reason both are correct statements and reason explains the assertion
• B. Assertion and reason both are correct statements but reason does not explain assertion
• C. Assertion is a correct statement and reason is a wrong statement
• D. Assertion is the wrong statement and the reason is the correct statement

Explanation: Assertion and reason both are correct statements, and reason explains the assertion. This option suggests that both the assertion and the reason are correct, and the reason provided correctly explains why the assertion is true. In this case, the assertion is that "Vitamin D can be stored in our body," and the reason is that "Vitamin D is a fat-soluble vitamin." The reason supports the assertion because fat-soluble vitamins, including Vitamin D, can be stored in the body's fat tissues. Given the accuracy of both the assertion and the reason and the fact that the reason correctly explains why the assertion is true, the correct answer is option A: "Assertion and reason both are correct statements, and reason explains the assertion." This is a tough question and has been added to help you fully prepare for the AKU test.

4523. In fibrous proteins, polypeptide chains are held together by

• A. Van der Waals forces
• B. Electrostatic forces of attraction
• C. Hydrogen bonds
• D. Covalent bonds

Explanation: This is the correct answer. Fibrous proteins often have secondary structures stabilised by hydrogen bonds. These bonds form between the hydrogen atom of one amino acid and the oxygen or nitrogen atom of another amino acid. Therefore, the correct answer is option C: "Hydrogen bonds," as they play a significant role in holding polypeptide chains together in fibrous proteins.

4524. If one strand of DNA has the sequence ATGCTTGA, the sequence in the complementary strand would be

• A. TCCGAACT
• B. TACGTAGT
• C. TACGAATC
• D. TACGAACT

Explanation: To determine the complementary strand of DNA, you need to use the base-pairing rules:- Adenine (A) pairs with Thymine (T),- Thymine (T) pairs with Adenine (A),- Guanine (G) pairs with Cytosine (C),- Cytosine (C) pairs with Guanine (G).Given the DNA sequence "ATGCTTGA":

4525. Which type of interactions are responsible for making the a-helix structure stable?

• A. Peptide bonds between -NH2 and CO groups of adjacent carbon chains
• B. Hydrogen bonds between NH of amino acid in one turn with CO of amino acid in adjacent turns
• C. OH group of one amino acid with CO group of other amino acids on the turn
• D. Hydrogen bonds between adjacent amino acids

Explanation: In an alpha-helix, hydrogen bonds form between the carbonyl oxygen (CO) of one amino acid and the amide hydrogen (NH) of an amino acid located four residues ahead in the sequence. These hydrogen bonds contribute significantly to the stability of the alpha-helix structure. So, option B is correct as it accurately describes the hydrogen bonding pattern crucial for stabilising the alpha-helix structure.

4526. The secondary order of protein structure is

• A. The sequence of amino acids in the polypeptide chain
• B. The formation of hydrogen bonds leading to alpha-helices and beta-pleated sheets
• C. The formation of peptide bonds between amino acids
• D. The folding of the coiled polypeptide chain into a three-dimensional shape

Explanation: The secondary structure of a protein refers to the regular local structures that form within a polypeptide due to hydrogen bonding. These include alpha-helices and beta-pleated sheets. Option C correctly identifies this structural level as the coiling of the polypeptide chain into these specific shapes.Option A is incorrect because it describes the primary structure, which is the linear sequence of amino acids. Option B is incorrect because peptide bonds form the primary structure by linking amino acids together. Option D is incorrect as it describes the tertiary structure, which involves the further folding of the secondary structures into a three-dimensional conformation.

4527. Polysaccharides are synthesised in plants by the process of

• A. Condensation
• B. Glycolysis
• C. Hydrolysis
• D. Oxidation

Explanation: Polysaccharides in plants are synthesized through condensation reactions. This process involves the joining of monosaccharide units (such as glucose) with the release of water molecules. Therefore, Option A is correct. Glycolysis (Option B) is a catabolic process that breaks down glucose for energy, not for building polysaccharides. Hydrolysis (Option C) is the reverse process, breaking down polysaccharides into simpler sugars with water. Oxidation (Option D) is related to the loss of electrons and energy release, not polymer synthesis.

4528. Which one of the following reactions results in the conversion of amino acids to proteins?

• A. Condensation
• B. Deamination
• C. Hydrolysis
• D. Phosphorylation

Explanation: The correct answer is condensation. This reaction involves the joining of amino acids through the formation of peptide bonds, releasing a molecule of water in the process. This is how proteins are synthesized. The other options are incorrect because they describe different biochemical processes: deamination involves removing an amino group from an amino acid, hydrolysis involves breaking molecules down by adding water (contrary to building up proteins), and phosphorylation involves adding a phosphate group, which does not pertain to protein synthesis from amino acids.

4529. Which substance might include this molecule?

• A. Cellulose
• B. Cholesterol
• C. Glycerol
• D. Insulin

Explanation: Glycerol has three OH groups as it forms bonds with three fatty acid molecules.

4530. Which one out of A-D given below correctly represents the structural formula of the basic amino acid?

• A. Option A
• B. Option B
• C. Option C
• D. Option D

Explanation: Basic amino acids have an additional amino group without forming amides thus they are diamino monocarboxylic acids e.g., arginine, lysine, etc.