All Free Biology MCQs with Answers

• A. Fibrous protein
• B. Coiled protein
• C. Globular protein
• D. Double coiled protein

Explanation: Haemoglobin is a globular protein, meaning it has a roughly spherical shape and is soluble in water, which allows it to transport oxygen in the blood efficiently. It is composed of four polypeptide chains, each containing a heme group that binds oxygen. This functionality and structure distinguish it from fibrous proteins, which are typically insoluble and structural, and from any simplistic descriptions like 'coiled' or 'double coiled,' which do not accurately describe its complex quaternary structure.

• A. 20
• B. 170
• C. 25
• D. 15

Explanation: The correct answer is 20. Proteins are synthesized from 20 different standard amino acids, which are encoded by the genetic code in organisms. These amino acids combine in various sequences to form the vast array of proteins necessary for life. The options 170 and 25 are incorrect because, although there are many amino acids in nature and some proteins include non-standard amino acids, only 20 are used by the ribosomes to build proteins in living organisms. Option 15 is incorrect, as it underrepresents the number of standard amino acids involved in protein synthesis.

• A. Intermediate
• B. Simple
• C. Globular
• D. Fibrous

Explanation: Myosin is a type of fibrous protein. It plays a crucial role in muscle contraction by interacting with actin filaments. Fibrous proteins are characterized by long strands or sheets, which make them well-suited for structural roles in the body. The other options are incorrect because:Intermediate: This is not a standard category for proteins based on structure.Simple: Simple proteins consist only of amino acids, whereas myosin is complex. Globular: These proteins are spherical and soluble, which does not describe myosin's function and structure.

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

Explanation: The primary structure of a protein is crucial because it refers to the linear sequence of amino acids, which dictates the protein's final three-dimensional shape and function. This sequence is held together by peptide bonds and is unique to each protein. The secondary, tertiary, and quaternary structures are higher levels of organization that result from the primary sequence but involve additional interactions and folding patterns. Secondary structures include alpha helices and beta sheets formed by hydrogen bonding in the backbone. Tertiary structures involve the overall 3D shape of the polypeptide, stabilized by side chain interactions. Quaternary structures occur when multiple polypeptide chains come together to form a functional protein complex. Therefore, the sequence of amino acids is directly related to the primary structure, making Option A the correct choice.

• A. Rubisco
• B. Collagen
• C. Elastin
• D. Albumin

Explanation: The correct answer is collagen. Collagen is the most abundant protein in the animal world and plays a critical role in providing structural support to connective tissues such as skin, tendons, and ligaments. It accounts for about 25% to 35% of the whole-body protein content.Rubisco is incorrect because it is primarily found in plants and is involved in the process of photosynthesis. Elastin is also incorrect, as it is a protein that provides elasticity to tissues, but it is much less abundant than collagen. Finally, albumin is abundant in blood plasma and helps in maintaining osmotic pressure and transporting substances, but it is not the most prevalent protein in animals.

• A. Haemoglobin
• B. Insulin
• C. Keratin
• D. Fibrin

Explanation: The quaternary structure of a protein involves multiple polypeptide chains coming together to form a functional unit. Haemoglobin is an example of a protein with quaternary structure, as it consists of four polypeptide subunits working together to transport oxygen in the blood. In contrast, insulin, keratin, and fibrin do not exhibit the classical quaternary structure characterized by multi-subunit complex formation. Insulin has two chains but does not form a typical quaternary complex, keratin is primarily known for its secondary structure, and fibrin's function in clotting is a result of polymerization rather than quaternary structure.

• A. 21
• B. 45
• C. 51
• D. 66

Explanation: Insulin is a protein hormone composed of 51 amino acids in two chains: the A chain with 21 amino acids and the B chain with 30 amino acids. Option A (21) only includes the A chain, while Option B (45) is close but does not account for the entirety of both chains. Option D (66) overestimates the number of amino acids. Therefore, the correct answer is Option C (51).

• A. α-helix
• B. β-pleated sheets
• C. Both A and B
• D. Salt bridges

Explanation: The correct answer is both α-helix and β-pleated sheets since they are the two major types of secondary structure in proteins. These structures are stabilized by hydrogen bonds between the backbone atoms in the polypeptide chain. The α-helix is a right-handed coil, while β-pleated sheets consist of β-strands connected laterally by hydrogen bonds. Salt bridges are not part of the secondary structural elements; they contribute to the tertiary structure by stabilizing the overall three-dimensional shape of the protein.

• A. Rubisco
• B. Collagen
• C. Cellulose
• D. Albumin

Explanation: Collagen is the most abundant protein in the human body, making up about 30% of the total protein content. It plays a crucial role in providing structural support to various tissues, including skin, bones, and connective tissues. This makes it integral to maintaining the body's architecture.Other options, such as Rubisco, are not relevant to human biochemistry, as they are plant-specific. Cellulose, while abundant in nature, is a carbohydrate not found in human tissues. Albumin, although plentiful in blood plasma, does not surpass collagen in overall abundance in the body.

• A. Collagen
• B. Haemoglobin
• C. Keratin
• D. Fibrinogen

Explanation: The most abundant protein in blood is hemoglobin, which is crucial for oxygen transport in red blood cells. Collagen is primarily found in connective tissues, not blood. Keratin is found in skin, hair, and nails, not in the circulatory system. Fibrinogen plays a role in blood clotting but is not as abundant as hemoglobin.