All Free Biology MCQs with Answers

4611. Muscle haemoglobin possesses:

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

Explanation: Muscle haemoglobin, known as myoglobin, possesses a tertiary structure. This level of protein structure refers to the three-dimensional folding of a single polypeptide chain, enabling myoglobin to efficiently store and release oxygen. Primary and secondary structures are foundational but do not define the functional shape required for its physiological role. Quaternary structure is irrelevant to myoglobin as it is a monomer. Thus, the correct answer is the tertiary structure, essential for myoglobin's oxygen-binding function.

4612. Which level of protein structure maintains the helix shape of enzymes?

• A. Primary
• B. Secondary
• C. Tertiary
• D. Quaternary
• E. Both A and B

Explanation: The most common types of secondary structures are the α helix and the β pleated sheet. Both structures are held in shape by hydrogen bonds, which form between the carbonyl O of one amino acid and the amino H of another.

4613. Which type of bonds is required to maintain the alpha helix configuration of a protein?

• A. Hydrophobic interactions
• B. Disulfide bonds
• C. Hydrogen bonds
• D. Ionic bonds

Explanation: Hydrogen bonds are the primary type of bonds required to maintain the alpha helix configuration of a protein. In an alpha helix, the backbone of the polypeptide chain forms a helical structure stabilized by hydrogen bonds between the carbonyl oxygen atom of one amino acid and the amide hydrogen atom of another amino acid, typically four residues away in the sequence. These hydrogen bonds create a stable and regular helical conformation.

4614. Lipids store double amount of energy as compared to carbohydrates because of:

• A. High proportion of oxygen
• B. Low proportion of carbon
• C. Lower proportion of C-H bonds
• D. High proportion of C-H bonds

Explanation: Option D is correct. Lipids store more energy than carbohydrates primarily because they have a higher proportion of carbon-hydrogen (C-H) bonds. These bonds are strong and release a large amount of energy when broken, which accounts for the higher energy content of lipids. In contrast, carbohydrates have more oxygen-hydrogen bonds, which release less energy. Option A is incorrect because lipids have a lower proportion of oxygen, not higher. Option B is incorrect because lipids have a high proportion of carbon. Option C is incorrect as lipids have more C-H bonds, not fewer.

4615. Phosphodiester bond is:

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

Explanation: The correct answer is Option B: C-O-P-O-C. A phosphodiester bond forms the backbone of DNA and RNA molecules by linking the 5' carbon of one sugar molecule to the 3' carbon of the next sugar, with a phosphate group in between. This bond is crucial for the structural integrity of nucleic acids. Option A is incorrect as it suggests a direct linkage between phosphorus atoms and carbons that does not exist in phosphodiester bonds. Option C is partially correct but incomplete, as it fails to demonstrate the full linkage across two sugar molecules. Option D incorrectly suggests a carbon-carbon linkage, which is not a feature of phosphodiester bonds.

4616. Which of the following is the constituent of RNA molecule?

• A. Fatty acids
• B. Ribonucleic acid
• C. Ascorbic acid
• D. Deoxyribonucleic acid

Explanation: Option B is correct. Yes, ribonucleic acid (RNA) is the constituent of RNA molecules. RNA molecules are made up of nucleotides, which are composed of a sugar, a phosphate group, and a nitrogenous base. The sugar in RNA is ribose, while the sugar in DNA is deoxyribose. The phosphate group is the same in both DNA and RNA. The nitrogenous bases in RNA are adenine (A), guanine (G), cytosine (C), and uracil (U). Ribonucleic acid is a single-stranded molecule, while DNA is a double-stranded molecule. RNA is also found in the cytoplasm of cells, while DNA is found in the nucleus of cells.

4617. Which one of the following is an example of reducing sugar?

• A. Sucrose
• B. Starch
• C. Maltose
• D. Cellulose

Explanation: Option C is correct. Maltose is a reducing sugar because it has a free aldehyde group that can undergo oxidation, allowing it to act as a reducing agent in chemical reactions like the Benedict's test. In contrast, sucrose, starch, and cellulose do not possess free aldehyde or ketone groups due to their bonded structures, making them non-reducing sugars.

4618. Adenine and guanine are:

• A. Main nitrogenous bases of nucleic acids
• B. Main nitrogenous wastes of humans
• C. Main nitrogenous bases of phospholipids
• D. Main types of amino acids in proteins

Explanation: Option A is correct. Adenine and guanine are main nitrogenous bases of nucleic acids.Adenine (A) and guanine (G) are purines, which are a type of nitrogenous base. They are found in DNA and RNA, where they pair with thymine (T) and cytosine (C), respectively.Purines are made up of two rings of carbon and nitrogen atoms. The first ring is called the pyrimidine ring, and the second ring is called the purine ring. The purine ring contains two nitrogen atoms, while the pyrimidine ring contains one nitrogen atom.Adenine and guanine are the only two purines that are found in DNA and RNA. They are important for the structure and function of these molecules.

4619. Form of polysaccharides stored in bacteria and animals:

• A. Starch
• B. Cellulose
• C. Glycogen
• D. Chitin

Explanation: Glycogen is stored in both bacteria and animals. It serves as a primary energy storage molecule, a glucose polymer, in both organisms, with animals storing it mainly in the liver and muscles. In animals Location: Glycogen is primarily stored in the liver and muscle tissue.Function: It serves as a short-term energy reserve.Liver: Provides glucose to the bloodstream to maintain blood sugar levels between meals.Muscles: Provides glucose for the muscle cells' own energy needs during physical activity. In bacteria Location: Bacteria store glycogen within their cells.Function: It serves as a readily available source of carbon and energy that can be used when nutrients are scarce.

4620. A structural protein is:

• A. Pepsin
• B. Collagen
• C. Haemoglobin
• D. Immunoglobulin

Explanation: The correct answer is Collagen. Collagen is a structural protein, which means it provides support and strength to various body tissues, such as skin, bones, and connective tissues. In contrast, Pepsin, Haemoglobin, and Immunoglobulin are functional proteins. Pepsin is an enzyme involved in digestion, Haemoglobin transports oxygen in the blood, and Immunoglobulin plays a crucial role in the immune response.