#protiens #biology #textbook #igcse

Pg:- 65,66

Ch:- 4

Proteins are large, complex molecules that play a critical role in nearly all biological processes. They are essential for the structure, function, and regulation of the body’s tissues and organs.

Basic Structure of Proteins:

• Amino Acids: Proteins are made up of smaller molecules called amino acids, which are linked together in chains. There are 20 different amino acids that can combine in various sequences to form a protein.

• Peptide Bonds: Amino acids are joined by peptide bonds, forming long chains known as polypeptides. When one or more polypeptides fold into a specific shape, they become a functional protein.

Levels of Protein Structure:

Proteins have four levels of structural organization:

• Primary Structure: The sequence of amino acids in a polypeptide chain. This sequence determines the protein's unique characteristics.

• Secondary Structure: Local folding of the polypeptide chain into structures like alpha-helices and beta-sheets, held together by hydrogen bonds.

• Tertiary Structure: The three-dimensional shape formed when the entire chain folds upon itself, stabilized by various bonds and interactions between amino acids.

• Quaternary Structure: Some proteins consist of multiple polypeptide chains (subunits) that work together. This is the level where those subunits assemble into a functional protein.

Types of Proteins:

Proteins can be broadly categorized based on their function:

• Structural Proteins: Provide support and shape to cells and tissues (e.g., collagen, keratin).

• Enzymes: Catalyze biochemical reactions, making them faster and more efficient (e.g., DNA polymerase, amylase).

• Transport Proteins: Carry molecules across cell membranes or through the bloodstream (e.g., hemoglobin, which transports oxygen).

• Hormones: Act as chemical messengers to regulate bodily functions (e.g., insulin, which regulates blood sugar levels).

• Antibodies: Part of the immune system, these proteins recognize and neutralize foreign invaders like bacteria and viruses.

• Contractile Proteins: Involved in muscle contraction and movement (e.g., actin and myosin).

• Storage Proteins: Store nutrients and ions (e.g., ferritin, which stores iron).

Functions of Proteins:

Proteins are essential to almost every cellular process.

• Provide structural support and maintain cell shape.

• Facilitate biochemical reactions by acting as enzymes.

• Transport substances across cell membranes.

• Communicate signals within and between cells.

• Defend the body against pathogens as part of the immune response.

• Enable movement through muscle contraction.

Protein Folding and Shape:

• A protein's function depends on its shape, which is determined by the sequence and folding of its amino acids. Misfolded proteins can lead to diseases like Alzheimer's and Parkinson's, where proteins lose their normal function or form harmful aggregates.

Sources of Proteins:

• Proteins are obtained from food sources like meat, dairy, legumes, and nuts. In the body, proteins are broken down into amino acids, which cells then use to build new proteins as needed.