Collagen as a Fibrous Protein


Collagen as a Fibrous Protein

Introduction

Collagen is the most abundant protein in mammals, making up about 25-30% of the total protein content. It is a fibrous protein that provides structural support to tissues such as skin, bones, tendons, and ligaments.

Structure of Collagen:

1.     Fibrous Nature: Collagen is a fibrous protein with a unique triple-helix structure. Each helix consists of three polypeptide chains wound around one another.

2.   Primary Structure: Repeating units of the amino acid sequence Glycine-X-Y, where X is often proline and Y is often hydroxyproline.

3.   Tropocollagen: The basic unit of collagen, formed by three polypeptide chains (α-chains) twisted into a right-handed triple helix.


Function of Collagen:

1.     Structural Support: Collagen fibers provide mechanical strength and support to connective tissues. It is especially important in tissues that need to withstand tension, like tendons and skin.

2.   Tissue Repair: Collagen plays a critical role in wound healing by forming a scaffold for new tissue growth.

3.   Cell Signaling: Collagen interacts with cell surface receptors (like integrins) to influence cell behavior, including differentiation and migration.

NEET Focus: Collagen’s structure, its role as a fibrous protein, and its function in the body are often tested in NEET, especially in the context of protein structure and connective tissues.

Questions

Q 1. Collagen is;

(a) fibrous protein;

(b) globular protein;

(c) lipid;

(d) carbohydrate;

Structure and Function of Amino Acids


Structure and Function of Amino Acids

Introduction

Amino acids are the building blocks of proteins. There are 20 standard amino acids, each containing an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable R-group attached to a central carbon atom.

Structure of Amino Acids:

1.     General Formula: NH2-CHR-COOH (where R represents the side chain, which varies for each amino acid).

2.   Classification:

o    Non-polar (Hydrophobic): Glycine, Alanine, Valine, Leucine, Isoleucine, etc.

o    Polar (Hydrophilic): Serine, Threonine, Cysteine, Tyrosine, etc.

o    Acidic: Aspartic acid, Glutamic acid.

o    Basic: Lysine, Arginine, Histidine.


Function of Amino Acids:

1.     Protein Synthesis: Amino acids polymerize to form polypeptide chains, which fold into functional proteins.

2.   Metabolic Roles: Amino acids act as precursors for important molecules such as hormones (e.g., thyroxine) and neurotransmitters (e.g., dopamine).

3.   Buffering Capacity: Due to their amino and carboxyl groups, amino acids can act as buffers, helping maintain the pH of body fluids.

NEET Focus: Questions on amino acid classification (essential vs. non-essential, polar vs. non-polar) and their role in protein synthesis are common in NEET.

Questions

Q 1. Which is an essential amino acid?;

(a) Serine;

(b) Aspartic acid;

(c) Glycine;

(d) Phenylalanine;

Q 2. Amino acids are produced from;

(a) proteins;

(b) fatty acids;

(c) essential oils;

(d) \(\alpha\)-keto acids;

Q 3. Which one of the following amino acids is an essential part of human diet?;

(a) Glycine;

(b) Phenylalanine;

(c) Serine;

(d) Aspartic acid;

Q 4. Which of the following is the simplest amino acid?;

(a) Alanine;

(b) Asparagine;

(c) Glycine;

(d) Tyrosine;

Q 5. Which one out of \(A-D\) given below correctly represents the structural formula of the basic amino acid?;

(a) C;

(b) D;

(c) \(\mathrm{A}\);

(d) B;

Q 6. Which of the following is an amino acid derived hormone? [NEET 2018];

(a) Estradiol;

(b) Ecdysone;

(c) Epinephrine;

(d) Estriol;

Q 7. Identify the basic amino acid from the following.;

(a) Glutamic acid;

(b) Lysine;

(c) Valine;

(d) Tyrosine;

Q 8. Which of the following is not an aromatic amino acid ?;

(a) V aline;

(b) Tyrosine;

(c) Phenylalanine;

(d) Tryptophan;

Q 9. All the following amino acids are acidic, except;

(a) Aspartic acid;

(b) Tyrosine;

(c) Glutamic acid;

(d) Threonine;

Q 10. All the following are sulphur containing amino acids, except:;

(a) Cysteine;

(b) Methionine;

(c) Homocysteine;

(d) Threonine;

Structure and Function of Proteins


Structure and Function of Proteins

Introduction

Proteins are complex biomolecules made up of one or more polypeptide chains. They play a wide range of roles in biological processes, including structural support, catalysis, transport, and defense.

Structure of Proteins:

1.     Primary Structure: The sequence of amino acids in a polypeptide chain.

2.   Secondary Structure: Folding of the polypeptide chain into α-helices or β-sheets, stabilized by hydrogen bonds.

3.   Tertiary Structure: The three-dimensional folding of a polypeptide chain due to interactions between side chains (R-groups). This gives the protein its functional shape.

4.   Quaternary Structure: The association of two or more polypeptide chains to form a functional protein (e.g., hemoglobin).

Function of Proteins:

1.     Enzymatic Catalysis: Proteins function as enzymes to speed up biochemical reactions (e.g., DNA polymerase).

2.   Transport: Hemoglobin transports oxygen in the blood.

3.   Structural Support: Collagen provides strength to connective tissues.

4.   Defense: Antibodies (immunoglobulins) help in immune defense.

5.    Hormonal Regulation: Some proteins act as hormones (e.g., insulin).