OIA1003 PROTEIN STRUCTURES & FUNCTIONS

Protein

A macromolecule composed of amino acids linked by peptide bonds.

Amino Acid

The basic unit of proteins, containing an amino group (-NH2), carboxyl group (-COOH), and side chain (R group).

Peptide Bond

A covalent bond between the carboxyl group of one amino acid and the amino group of another.

Polypeptide

A chain of amino acids before it folds into a functional protein.

Essential Amino Acids

Cannot be synthesized by the body; must be obtained from the diet (e.g., lysine, valine, leucine).

Non-Essential Amino Acids

Can be synthesized by the body (e.g., alanine, glutamine).

Hydrophilic Amino Acids

Polar amino acids that interact with water (e.g., serine, threonine, glutamate).

Hydrophobic Amino Acids

Nonpolar amino acids, usually found in the interior of proteins (e.g., valine, leucine, phenylalanine).

Zwitterion

At physiological pH (~7.4), amino acids exist with both positive (NH3⁺) and negative (COO⁻) charges.

Primary Structure

The linear sequence of amino acids in a polypeptide chain.

Secondary Structure

Local folding patterns stabilized by hydrogen bonds:

α-Helix: Right-handed coil stabilized by hydrogen bonds.

β-Sheet: Extended strands stabilized by inter- or intrachain hydrogen bonds.

Tertiary Structure

The 3D folding of a polypeptide, stabilized by hydrogen bonds, ionic interactions, hydrophobic interactions, and disulfide bonds.

Quaternary Structure

The association of multiple polypeptide chains into a functional protein (e.g., hemoglobin).

Hydrogen Bonds

Stabilize secondary, tertiary, and quaternary structures.

Disulfide Bonds

Covalent bonds between cysteine residues, stabilizing protein conformation.

Ionic (Electrostatic) Interactions

Occur between charged side chains (e.g., lysine and glutamate).

Hydrophobic Interactions

Help bury nonpolar residues in the protein core.

Van der Waals Forces

Weak attractive forces between closely packed nonpolar groups.

Molecular Chaperones

Assist in proper protein folding (e.g., Hsp70, Hsp60).

Misfolded Proteins

May aggregate and cause diseases like Alzheimer's and prion diseases.

Chaperonins

Large protein complexes that enclose misfolded proteins to refold them properly.

Structural Proteins

Provide mechanical support (e.g., collagen, keratin, elastin).

Enzymes

Biological catalysts that speed up reactions (e.g., DNA polymerase, trypsin).

Transport Proteins

Carry molecules across membranes (e.g., hemoglobin, albumin).

Contractile Proteins

Involved in muscle contraction (e.g., actin, myosin).

Signaling Proteins

Hormones and receptors (e.g., insulin, growth factors).

Immune Proteins

Defend the body against pathogens (e.g., antibodies).

Protein Denaturation

Loss of secondary, tertiary, or quaternary structure without breaking peptide bonds.

Causes of Denaturation

Heat, pH changes, organic solvents, detergents, or heavy metals.

Isoelectric Point (pI)

The pH at which a protein carries no net charge.

Sickle Cell Anemia

Mutation in hemoglobin (HbS) causes red blood cells to form a sickle shape.

Cystic Fibrosis

Caused by misfolded CFTR protein, leading to thick mucus buildup.

Prion Diseases

Infectious protein misfolding diseases (e.g., Creutzfeldt-Jakob disease, Mad Cow disease).

Alzheimer’s Disease

Accumulation of misfolded amyloid-beta proteins in the brain.

Osteogenesis Imperfecta

Mutation in collagen genes leading to brittle bones.

Hemoglobin vs. Myoglobin

Hemoglobin: Tetramer, transports oxygen in blood.

Myoglobin: Monomer, stores oxygen in muscles.

Enzyme-Linked Proteins

Combine catalytic and structural functions (e.g., kinases, receptors).

Glycoproteins

Proteins with carbohydrate modifications, involved in cell signaling and immune function.

Fibrous vs. Globular Proteins

Fibrous Proteins: Long, structural (e.g., collagen, keratin).

Globular Proteins: Compact, functional (e.g., enzymes, hemoglobin).

Heat Shock Proteins (Hsp)

Help refold misfolded proteins during stress (e.g., fever, oxidative damage).