All Free Biology MCQs with Answers

• A. Disulphide bonds
• B. Glycoside bond
• C. Hydrogen bond
• D. Peptide bond

Explanation: The correct answer is the 'Peptide bond.' Peptide bonds are the primary linkages formed between amino acids in a protein chain, specifically between the carboxyl group of one amino acid and the amino group of another amino acid. This covalent bond is crucial in forming the primary structure of proteins.Disulfide bonds, on the other hand, are involved in stabilizing the tertiary and quaternary structures of proteins by linking different parts of a single polypeptide or different polypeptides, but they do not form the main chain of amino acids.Glycoside bonds are involved in carbohydrate structures, not proteins. Hydrogen bonds play a role in the secondary and tertiary structures by linking different parts of the same or different polypeptide chains but are not responsible for the primary sequence of amino acids.

• A. Made up of 2-α and 2-β chains.
• B. Present in RBC.
• C. Used to carry O₂ & CO₂.
• D. All of these

Explanation: The correct answer is Option D: 'All of these.' Human haemoglobin is a protein made up of two alpha and two beta polypeptide chains. It is located in red blood cells (RBCs) and serves the critical functions of transporting oxygen from the lungs to the body's tissues and carrying carbon dioxide back to the lungs for exhalation. Each statement in options A, B, and C is individually correct, which is why 'All of these' is the most comprehensive answer. Option A is correct in describing haemoglobin's structure, Option B correctly identifies its cellular location, and Option C accurately describes its function.

• A. Amino acids are compounds containing both an amino group (-NH₂) and a carboxyl group (-COOH)
• B. Amino acids are derivatives of methane
• C. The properties and types of amino acids are determined by the nature of their 'R' group, or side chain
• D. Both A and C are correct

Explanation: The correct answer is only A & C. Option A is correct because amino acids contain both an amino group (-NH₂) and a carboxylic acid group (-COOH). Option C is also correct because the properties and classification of amino acids depend on the nature of their side chains, referred to as 'R' groups. Option B is incorrect because amino acids are not substitutes for methane; they have a distinct structure that includes both amino and carboxylic groups, which methane does not have.

• A. Glycine
• B. Alanine
• C. Leucine
• D. Valine

Explanation: The correct answer is glycine. Glycine is unique among amino acids because its side chain, or R-group, is just a single hydrogen atom. This simplicity gives glycine unique properties compared to other amino acids. In contrast, alanine has a methyl group (CH₃), leucine has an isobutyl group, and valine has an isopropyl group as its R-groups, all of which are more complex than a single hydrogen atom.

• A. Keratin
• B. Myosin
• C. Fibrin
• D. Hormones

Explanation: The correct answer is hormones. Hormones are biochemical messengers that are typically not proteins, and when they are, they are not fibrous. They serve regulatory functions rather than structural roles. Keratin is a classic example of a fibrous protein, providing structural support in hair and nails. Myosin, although having a fibrous appearance, is primarily a motor protein involved in muscle contraction. Fibrin is a fibrous protein that helps in blood clotting by forming a mesh structure. Therefore, hormones do not fit in the category of fibrous proteins.

• A. R-group
• B. Amino group
• C. Carboxyl group
• D. Peptide bond

Explanation: The correct answer is the R-group. Each amino acid has a central carbon atom to which four different groups are attached: an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom, and an R-group, which is a variable group or side chain that differs among amino acids. The characteristics and functions of amino acids are determined by their R-groups, which can be as simple as a hydrogen atom or as complex as a ring structure. The other options are incorrect because both the amino group and the carboxyl group are consistent across all amino acids and do not vary. The peptide bond is a type of covalent bond that links amino acids together in proteins and is not a distinguishing feature of individual amino acids.

• A. Water
• B. Proteins
• C. Carbohydrates
• D. Lipids

Explanation: Proteins are the most abundant organic compounds in mammalian cells. They are essential for numerous cellular processes, including catalyzing metabolic reactions, DNA replication, responding to stimuli, and transporting molecules. Water, while the most abundant molecule overall in cells, is inorganic. Carbohydrates and lipids, though critical, are present in lesser amounts compared to proteins.

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

Explanation: The correct answer is the quaternary structure because it specifically refers to the level of protein structure where multiple polypeptide chains, or subunits, associate to form a single functional protein complex. The other options refer to structural levels involving only a single polypeptide chain: the primary structure is the linear sequence of amino acids, the secondary structure involves local folding such as helices and sheets, and the tertiary structure is the overall 3D shape of a single chain.

• A. Blood
• B. Muscles
• C. Bones
• D. Nails and hair

Explanation: Keratin is a type of fibrous protein that is key to the structure of hair, nails, and the outer layer of skin. It provides strength and resilience to these tissues. In contrast, blood contains proteins like hemoglobin and albumin, muscles primarily contain actin and myosin, and bones are made up of collagen and minerals. Therefore, the correct answer is that keratin is found in nails and hair.

• A. Having amino acids
• B. Being soluble in aqueous medium
• C. Their repeating units are joined by a peptide bond
• D. Being non-crystalline

Explanation: Globular proteins are characterized by their spherical shape and are typically soluble in aqueous solutions due to their hydrophilic exterior. This solubility is crucial for their roles in metabolic processes, such as enzymes and antibodies. In contrast, fibrous proteins are generally insoluble and have structural roles, such as providing support and strength to tissues. Options A and C are incorrect because both types of proteins consist of amino acids joined by peptide bonds. Option D is incorrect because being non-crystalline is not a defining feature of globular proteins.