All Free Biology MCQs with Answers

4681. Peptide bond is a:

• A. C-O bond
• B. C-N bond
• C. C-C bond
• D. C-O-P bond

Explanation: A peptide bond is a covalent linkage formed between the carbon atom of the carboxyl group of one amino acid and the nitrogen atom of the amino group of another amino acid, resulting in a C-N bond. This bond formation releases a molecule of water, a process known as a dehydration synthesis or condensation reaction. Options C-O, C-C, and C-O-P describe other types of chemical bonds that do not participate in forming peptide bonds.

4682. A dipeptide have an/a _ group at one end and a _ group at the other end of molecule.

• A. Amino, Carboxyl
• B. Amino, Functional
• C. Functional, Carboxyl
• D. Amino, Amino

Explanation: A dipeptide consists of two amino acids joined by a peptide bond. This bond forms between the amino group of one amino acid and the carboxyl group of the other. As a result, a dipeptide has an amino group at one end (N-terminus) and a carboxyl group at the other end (C-terminus). Options B, C, and D are incorrect because they either misidentify or omit the essential carboxyl group, or incorrectly suggest identical groups at both ends.

4683. Proteins have _ levels of organization.

• A. Two
• B. Three
• C. Four
• D. Five

Explanation: The four levels of protein structure are: Primary structure: The linear sequence of amino acids in a protein.Secondary structure: Local folding into structures such as alpha helices and beta sheets, stabilized by hydrogen bonds.Tertiary structure: The overall three-dimensional shape of a single polypeptide chain, stabilized by various interactions between side chains.Quaternary structure: The arrangement of multiple polypeptide chains into a functional protein complex. Not all proteins have quaternary structures, but those that do, like hemoglobin, require this level of organization.Options A and B are incorrect because they do not account for all the structural levels up to quaternary. Option D is incorrect because there is no recognized fifth level of protein structure.

4684. F. Sanger was the first scientist who determined the _ structure of a protein molecule.

• A. Primary
• B. Secondary
• C. Tertiary
• D. Quaternary

Explanation: F. Sanger was pivotal in determining the primary structure of proteins, specifically the insulin protein, by establishing the precise sequence of its 51 amino acids. This work laid the foundation for understanding how proteins are built at the most basic level. The primary structure is distinct from higher-level structures, such as secondary, tertiary, and quaternary, which involve various degrees of folding and assembly of the polypeptide chains. The incorrect options describe these higher-level structures, which were not the focus of Sanger's groundbreaking research.

4685. Hemoglobin is composed of:

• A. Two alpha chains
• B. Two beta chains
• C. Two alpha and two beta chains
• D. Four alpha chains

Explanation: Hemoglobin is a protein found in red blood cells that carries oxygen throughout the body. It is composed of two alpha and two beta polypeptide chains, forming a quaternary structure. Each alpha chain contains 141 amino acids, while each beta chain contains 146 amino acids. This combination allows hemoglobin to effectively bind and transport oxygen.Options A, B, and D are incorrect because they suggest that hemoglobin is composed solely of either alpha or beta chains, which does not accurately represent its quaternary structure.

4686. Number of amino acids incorporated in beta chains of a molecule of hemoglobin is:

• A. 280
• B. 282
• C. 292
• D. 290

Explanation: The correct answer is 292. Hemoglobin is composed of four protein subunits, including two alpha and two beta chains. Each beta chain contains 146 amino acids. Therefore, for two beta chains, the total number of amino acids is 146 x 2 = 292. The other options are incorrect as they do not match this calculation.

4687. Proteins in the human body are composed of unique and specific arrangement of:

• A. 25 types of amino acids
• B. 20 types of amino acids
• C. Over 20 types of amino acids
• D. Less than 20 types of amino acids

Explanation: Proteins in the human body are synthesized using 20 different amino acids, which combine in unique sequences to form the vast array of proteins essential for various functions. Options stating more or less than 20 amino acids are incorrect because, despite the existence of more than 20 amino acids in nature, only 20 are involved in human protein synthesis.

4688. For proper functioning, a protein should have its amino acids in:

• A. A random arrangement
• B. A specific medium
• C. A specific arrangement
• D. Ascending order

Explanation: The correct answer is that a protein should have its amino acids in a specific arrangement for proper functioning. This sequence is determined by the gene encoding the protein and dictates the protein's folding into its functional three-dimensional structure. This specific conformation is vital for the protein's interactions and biological activity. A random arrangement would disrupt the structure, leading to loss of function. While the medium can influence protein activity, it does not replace the need for a specific sequence. An ascending order is irrelevant to protein functionality and lacks biological significance in this context.

4689. The example of physiological effect of changing the amino acid sequence of a protein is:

• A. Uremia
• B. Hypoglycemia
• C. Goiter
• D. Sickle cell anemia

Explanation: Hemoglobin stops carrying oxygen if one amino acid (glutamic acids) in beta chain is replaced by the other (valine).

4690. The polypeptide chains in a protein molecule usually do not _.

• A. Remain linear
• B. Lie flat
• C. Acquire coiling
• D. Acquire folding

Explanation: The correct answer is that polypeptide chains do not lie flat. The properties of amino acids, particularly the polar and nonpolar groups, lead to interactions that cause the polypeptide chains to coil and fold instead of lying flat. This is essential for the formation of the protein's secondary, tertiary, and quaternary structures, which are necessary for their biological function. In contrast, polypeptide chains do acquire coiling and folding as they form their complex three-dimensional structures.