All Free Biology MCQs with Answers

• A. One
• B. Two
• C. Three
• D. None

Explanation: The term 'dipeptide' indicates that the molecule is composed of two amino acids linked by a single peptide bond. In glycylalanine, glycine and alanine are joined through the formation of a peptide linkage, which involves the removal of a water molecule (a process called condensation). This results in only one peptide linkage. Options suggesting more than one peptide linkage are incorrect because they imply additional amino acids or bonds that do not exist in a simple dipeptide. Option D is incorrect because a dipeptide must have at least one peptide bond.

• A. Haemoglobin
• B. Myosin
• C. Silk
• D. Fibrin

Explanation: The correct answer is Haemoglobin. Haemoglobin is a globular protein, characterized by its compact and spherical structure, which is crucial for its function in oxygen transport. In contrast, proteins like Myosin, Silk, and Fibrin are fibrous. Myosin forms long fibrils necessary for muscle contraction, Silk's beta-pleated sheets grant it strength and flexibility, and Fibrin's fibrous networks are critical for blood clotting, all typical features of fibrous proteins.

• A. Keratin
• B. Albumin
• C. Dehydrogenases
• D. Rubisco

Explanation: Rubisco is the most abundant protein on Earth because it is essential for photosynthesis in plants, algae, and some bacteria. It catalyzes the fixation of carbon dioxide into organic compounds, a critical step in the Calvin cycle. In contrast, Keratin is abundant in external body structures but limited to animals; Albumin is limited to blood plasma; and Dehydrogenases, while important in cellular respiration, are restricted to mitochondrial processes and not as ubiquitously present as Rubisco.

• A. Fibril proteins
• B. Globular proteins
• C. Fibrous proteins
• D. Tough proteins

Explanation: Globular proteins are characterized by their spherical shape due to their tertiary and quaternary structures. This shape is crucial for their roles in biological processes. Enzymes, antibodies, hormones, and hemoglobin all fall under this category because their functions rely on complex folding patterns that allow for interaction with other molecules. In contrast, fibril and fibrous proteins are more structural, lacking the complexity needed for the dynamic roles of globular proteins. Tough proteins like keratin serve protective roles rather than biochemical functions.

• A. Glycoproteins
• B. Phospholipids
• C. Glycolipids
• D. Sphingolipids

Explanation: The correct answer is glycoproteins. Blood group antigens are mainly composed of glycoproteins, which include protein structures linked with carbohydrate chains crucial for identifying blood groups on the surface of red blood cells. Phospholipids, while essential for forming cell membranes, do not define blood group antigens. Glycolipids, though they have carbohydrate components, are not the primary molecules for blood group identity. Sphingolipids play a role in membrane integrity but do not directly participate in blood group antigen determination.

• A. Lipids
• B. Proteins
• C. Carbohydrates
• D. Nucleic acids

Explanation: Proteins make up over 50% of the dry weight of cells because they are involved in nearly every cell function, including serving as enzymes, structural components, and in cell signaling and transport. While lipids, carbohydrates, and nucleic acids are also vital to cellular function, they do not constitute the majority of the cell's dry weight. Lipids are primarily involved in membrane structure and energy storage, carbohydrates provide energy and structural support, and nucleic acids are crucial for genetic information storage and transmission, but they do not have the same abundance in terms of dry weight as proteins.

• A. 51
• B. 50
• C. 49
• D. 48

Explanation: The number of peptide bonds in a protein is determined by subtracting the number of polypeptide chains from the total number of amino acids. Insulin consists of 51 amino acids arranged in two polypeptide chains (A and B). Therefore, the calculation for the number of peptide bonds is 51 (total amino acids) - 2 (polypeptide chains) = 49. Option C is correct. Options A, B, and D incorrectly calculate the number of peptide bonds based on the given information.

• A. Globular protein
• B. Functional protein
• C. Fibrous protein
• D. Soluble protein

Explanation: The correct answer is 'Fibrous protein'. Spider silk is a fibrous protein, characterized by its strong and elongated structure, which is ideal for forming webs. Fibrous proteins are typically insoluble and serve structural roles, unlike globular proteins, which are soluble and perform a variety of functions. 'Functional protein' is a broad term that does not specifically address the structural nature of the spider's web. Similarly, 'Soluble protein' refers to proteins that dissolve in water, which does not apply to the structural nature of spider silk.

• A. Palmitic acid
• B. Linoleic acid
• C. Oleic acid
• D. Erucic acid

Explanation: Palmitic acid is a saturated fatty acid as it contains no double bonds between carbon atoms. Saturated fatty acids are characterized by having only single bonds between carbon atoms, which makes them 'saturated' with hydrogen atoms. In contrast, the other options are unsaturated fatty acids: Linoleic acid has two double bonds, Oleic acid has one double bond, and Erucic acid has one double bond as well, making them all unsaturated.

• A. mRNA
• B. rRNA
• C. snRNA
• D. tRNA

Explanation: Ribosomal RNA (rRNA) is the correct answer because it is a fundamental structural component of ribosomes, where it forms a significant part of the ribosome's mass, approximately 40 to 50%, alongside ribosomal proteins. Unlike mRNA, tRNA, and snRNA, rRNA's primary role is not in carrying genetic information or splicing but in forming the ribosome and facilitating protein synthesis.mRNA is incorrect as it serves to convey genetic information rather than forming part of the ribosome. snRNA is involved in RNA processing within the nucleus, not in the ribosome's structure. tRNA functions in translation by delivering amino acids to the ribosome and is not a structural component like rRNA.