All Free Biology MCQs with Answers

4591. A typical fat molecule is made up of :

• A. One glycerol and one fatty acid molecule
• B. Three glycerol and three fatty acid molecules
• C. Three glycerol molecules and one fatty acid molecule
• D. One glycerol and three fatty acid molecules.

Explanation: Neutral or true fats are triglycerides that are formed by esterification of three molecules of fatty acids with one molecule of trihydric alcohol, glycerol (glycerine or trihydroxy propane).

4592. Which one of the following organic compounds is correctly identified along with its related function?

• A. Lecithin - A component of cell membranes
• B. Adenine - A nucleotide that makes up nucleic acids
• C. Triglyceride - Major source of energy
• D. Uracil - A component of DNA

Explanation: The correct answer is A: Lecithin. Lecithin is a phospholipid that is essential for the structure and functionality of cell membranes, allowing cells to maintain their integrity and facilitate communication. Option B is incorrect because adenine, while a component of nucleotides in nucleic acids, is not a nucleotide by itself. Option C, while referring to triglycerides correctly as a source of energy, is vague and misleading since it does not specify the entire structure of triglycerides. Option D is incorrect because uracil is not a component of DNA; it is found in RNA instead, where it replaces thymine.

4593. Which pyrimidine base is found in RNA?

• A. Thymine
• B. Uracil
• C. Cytosine
• D. Guanine

Explanation: Uracil is the correct answer as it is the pyrimidine base that is unique to RNA. In RNA, uracil pairs with adenine, replacing thymine, which is used in DNA. While cytosine is also a pyrimidine, it is present in both RNA and DNA, thus not making it unique to RNA. Guanine is a purine base, not a pyrimidine, which rules it out as an option. Thymine is only found in DNA, not RNA.

4594. Amino acids are mostly synthesised from

• A. mineral salts
• B. fatty acids
• C. volatile acids
• D. a­ketoglutaric acid

Explanation: The correct answer is a­ketoglutaric acid. A-ketoglutaric acid plays a crucial role in the Krebs cycle, where it serves as an intermediate. It is a precursor for amino acids, such as glutamic acid, which is essential for protein synthesis. The other options do not act as direct precursors in the synthesis of amino acids. Mineral salts, fatty acids, and volatile acids have different roles in metabolism and do not directly contribute to amino acid synthesis.

4595. How many amino acids are present in the cell?

• A. 170
• B. 20
• C. 25
• D. 3000

Explanation: About 170 types of amino acids have been found to occur in cells and tissues. Of these, about 25 are constituents of proteins. Most of the proteins are, however, made of 20 types of amino acids.

4596. Which of the following amino acid is next to glycine with respect to the molecular structure?

• A. Alanine
• B. Serine
• C. Ethanolamine
• D. Aspartic acid

Explanation: Glycine is the simplest amino acid, having a hydrogen atom as its side chain. Alanine is the next amino acid in terms of molecular structure after glycine. Alanine has a methyl group (-CH3) as its side chain, which adds a single carbon and three hydrogen atoms to the structure compared to glycine.

4597. All of the following are examples of fibrous proteins except:

• A. Silk fiber
• B. Myoglobin
• C. Keratin
• D. Fibrin

Explanation: Myoglobin is the correct answer because it is a globular protein, characterized by a compact and spherical structure, in contrast to fibrous proteins which are elongated and strand-like. Silk fiber, keratin, and fibrin are fibrous proteins that play structural roles in biological tissues. Silk fiber is used for structural strength in silk, keratin is found in hair and nails, and fibrin is involved in forming blood clots.

4598. Haemoglobin exhibits a:

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

Explanation: Haemoglobin has a quaternary structure. It consists of two pairs of different proteins, designated the α and β chains. There are 141 and 146 amino acids in the α and β chains of haemoglobin, respectively. As in myoglobin, each subunit is linked covalently to a molecule of heme.

4599. Which of the following does not contain phosphodiester bond?

• A. DNA
• B. ATP
• C. RNA
• D. NAD

Explanation: ATP is a single nucleotide. Phosphodiester bond is present between nucleotides. Adenosine triphosphate (ATP) is a molecule that serves as the primary energy currency in cells. It is a nucleotide that plays a crucial role in the transfer and storage of energy for various cellular processes. ATP is composed of three phosphate groups, a ribose sugar molecule, and an adenine base. The three phosphate groups are linked together, and the energy stored in the high-energy phosphate bonds is what makes ATP an energy carrier. ATP is often referred to as the "energy currency" of the cell because it stores and releases energy to power various cellular activities. The energy is stored in the form of chemical potential energy within the phosphate bonds.

4600. Nucleic acid is:

• A. Monomer and Macromolecule
• B. Polymer and Macromolecule
• C. Monomer and Micromolecule
• D. Polymer and Micromolecule

Explanation: A polymer is a large molecule composed of repeating subunits called monomers. These monomers are covalently bonded together to form long chains or networks. Polymers are one of the most diverse and versatile groups of materials, and they can be found in a wide range of natural and synthetic substances. The properties and characteristics of polymers are determined by the type of monomers, the arrangement of these monomers, and the polymerization process. A macromolecule is a large, complex molecule made up of smaller subunits, called monomers, which are covalently bonded together. Macromolecules are often found in biological systems and are essential for life.