All Free Biology MCQs with Answers

• A. Ribose
• B. Maltose
• C. Cellulose
• D. Glucose

Explanation: The correct answer is glucose. Glucose is the most abundant monosaccharide found in nature. It is a crucial energy source for living organisms and is a fundamental building block for many carbohydrates. In contrast, ribose is a component of RNA and is not as abundant as glucose. Maltose is a disaccharide consisting of two glucose molecules, and cellulose is a polysaccharide made from glucose units, primarily found in plant cell walls. Neither maltose nor cellulose is a monosaccharide.

• A. Enzymes
• B. Coenzymes
• C. Vitamins
• D. All of these

Explanation: The correct answer is coenzymes. Ribose is a crucial component of coenzymes such as NAD+ (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide). These coenzymes are essential for various biochemical reactions in the body, including energy production. The other options are incorrect because enzymes are primarily protein-based, and vitamins do not typically contain ribose.

• A. 1
• B. 2
• C. 4
• D. 2/4

Explanation: A dipeptide is formed when two amino acids are joined by a single peptide bond. This bond is a covalent bond that specifically links the carboxyl group of one amino acid to the amino group of another, releasing a molecule of water in the process. While other interactions and bonds may exist within the overall structure of proteins, the question specifically asks about the bonds in a dipeptide, which is singular: 1 peptide bond. Options B, C, and D incorrectly count additional or irrelevant bonds that do not contribute to the peptide linkage.

• A. Hydrogen bonds
• B. Ionic bonds
• C. Disulphide bonds
• D. Both A and B

Explanation: The correct answer is Option A: Hydrogen bonds. Hydrogen bonds are crucial for maintaining the integrity of the secondary structure of proteins, such as the alpha-helix. They form between the carbonyl oxygen of one amino acid and the amide hydrogen of another, stabilizing the helical structure. Option B is incorrect, as ionic bonds are more relevant to the tertiary structure of proteins. Option C is incorrect because disulfide bonds stabilize tertiary, not secondary, structures. Option D is incorrect because it includes ionic bonds, which do not play a primary role in helical secondary structures.

• A. Monopeptide
• B. Dipeptide
• C. Tripeptide
• D. Tetrapeptide

Explanation: The correct answer is Option B: Dipeptide. When two amino acids are joined together by a peptide bond, the resulting molecule is called a dipeptide. Option A, Monopeptide, is incorrect because it refers to a single amino acid. Option C, Tripeptide, is also incorrect, as it involves three amino acids. Option D, Tetrapeptide, is incorrect because it involves four amino acids. Both of these options contain more than the two amino acids specified in the question.

• A. Protein
• B. Lipid
• C. Carbohydrate
• D. Glycoprotein

Explanation: The correct answer is glycoproteins. Glycoproteins are proteins with carbohydrate groups attached and play a crucial role in cellular secretions, such as mucus and cell signalling molecules. While proteins and lipids are important biological molecules, they do not primarily constitute cellular secretions. Carbohydrates alone do not form the main component of secretions either.

• A. Glycoproteins
• B. Glycolipids
• C. Phospholipids
• D. All of these

Explanation: The correct answer is phospholipids. These molecules form a bilayer that serves as the fundamental structure of cell membranes, providing a semipermeable barrier between the cell and its environment. Glycoproteins and glycolipids are important for cell recognition and signalling but do not form the basic structural framework of membranes. The option 'All of these' is incorrect because only phospholipids form the core structural framework, despite the presence of other molecules in the membrane.

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

Explanation: Frederick Sanger is renowned for his groundbreaking work in determining the amino acid sequence of proteins, most notably insulin. His research marked the first time a protein's sequence was fully understood, which was a major milestone in biochemistry and earned him a Nobel Prize. The other options, such as haemoglobin, fibrin, and keratin, were not the proteins whose structure Sanger determined. Haemoglobin's structure was elucidated by Max Perutz, while fibrin and keratin were not part of Sanger's key research accomplishments.

• A. - NH2 group
• B. -COOH group
• C. R-group
• D. All of the above

Explanation: The properties of amino acids are determined by their R-groups, also known as side chains. These groups vary among different amino acids and can impart different characteristics, such as hydrophobicity, charge, and size, which influence the amino acids' behaviour and role in proteins. The -NH₂ and -COOH groups are constant among all amino acids and do not contribute to these variations. Therefore, the correct answer is the R-group.

• A. 20
• B. 25
• C. 100
• D. 56

Explanation: The correct answer is 20. Cells use 20 standard amino acids to synthesize proteins, which are encoded by the genetic code. These are often referred to as the 'canonical' amino acids. While some organisms or proteins may incorporate additional amino acids, the core set used universally in protein synthesis is 20. Options B, C, and D suggest higher numbers that do not align with the standard amino acids used in cellular processes.