Proteins: The Building Blocks of Life

These flashcards cover the fundamental concepts of protein structure, amino acid properties, levels of protein organization, types of chemical bonds, and specific examples like haemoglobin, collagen, and lipoproteins.

Proteins

Macromolecules made from amino acids ($20$ types) via condensation reactions, making up about $18\%$ of the human body and containing $C, H, O, N$, and often $S$.

Essential Amino Acids

The $8$ amino acids that the human body cannot synthesize and must be obtained from the diet.

Non-essential Amino Acids

The $12$ amino acids that the human body can synthesize on its own.

Amino Group

A functional group with the formula $-NH_2$ that is part of the basic structure of all amino acids.

Carboxyl Group

A functional group with the formula $-COOH$ that is part of the basic structure of all amino acids.

R Group (Side Chain)

The residual group of an amino acid that varies between types, does not participate in peptide bonds, and influences protein properties and tertiary structure.

Zwitterions

Bipolar ions formed when a hydrogen atom from the carboxyl group ($negative$) associates with the amino group ($positive$) in water.

Amphoteric

A property of amino acids where they have both acidic and basic characteristics, allowing them to act as buffer solutions.

Peptide Bond

The strong covalent bond formed by a condensation reaction between the amino group of one amino acid and the carboxyl group of another, releasing $H_2O$.

Dipeptide

A molecule formed by the joining of two amino acids.

Polypeptide

A chain consisting of three or more amino acids linked together.

Primary Structure

The specific sequence of amino acids in a polypeptide chain linked by peptide bonds.

Secondary Structure

The regular $3D$ arrangement of a polypeptide chain, such as an $\alpha$-helix or $\beta$-pleated sheet, stabilized by hydrogen bonds.

$\alpha$-Helix (Alpha Helix)

A spiral-shaped secondary structure where the peptide-bond backbone forms a helix and R groups project outward, common in keratin.

$\beta$-Pleated Sheet (Beta Pleated Sheet)

A secondary structure formed by regular pleats in the polypeptide chain, stabilized by hydrogen bonds between $N-H$ and $C=O$ groups.

Tertiary Structure

The complex final $3D$ folding of a single polypeptide chain, maintained by hydrogen bonds, disulfide bonds, and ionic bonds between R groups.

Disulfide Bonds

Strong covalent bonds formed by an oxidation reaction between the sulfur-containing R groups of two cysteine amino acids.

Ionic Bonds

Electrostatic attractions between oppositely charged atoms within a protein's side chains, often located deep within the hydrophobic core.

Quaternary Structure

The three-dimensional arrangement and fitting together of two or more separate polypeptide chains, such as in haemoglobin or collagen.

Denaturation

The loss of a protein's specific $3D$ shape and biological function due to the disruption of stabilizing bonds, often caused by changes in temperature or pH.

Fibrous Proteins

Proteins consisting of long, parallel polypeptide chains with little or no tertiary structure; they are insoluble, very strong, and suited for structural functions.

Collagen

A structural fibrous protein with a triple helix structure (three $\alpha$-chains) providing high tensile strength to tendons, ligaments, bones, and skin.

Osteogenesis Imperfecta

A genetic disorder where the collagen triple helix fails to develop properly, leading to brittle bones with reduced tensile strength.

Globular Proteins

Proteins folded into compact, spherical shapes with complex tertiary or quaternary structures; they typically have hydrophilic R groups on the outside and are soluble in water (forming colloids).

Haemoglobin

A globular protein consisting of four polypeptide chains connected by disulfide bonds, each surrounding an iron-containing haem group for oxygen transport.

Conjugated Proteins

Biological molecules where a protein is attached to a non-protein part, known as a prosthetic group, which is essential to its function.

Prosthetic Group

The non-protein molecule attached to a protein in a conjugated protein, such as the haem group in haemoglobin.

Glycoproteins

Conjugated proteins with a carbohydrate prosthetic group; they hold water, are resistant to proteases, and provide lubrication (e.g., mucus).

Lipoproteins

Molecular complexes formed when proteins are conjugated with lipids, essential for transporting cholesterol and fats through the bloodstream.

Low-Density Lipoproteins (LDLs)

Lipoproteins with a diameter of ~$22\,nm$ that have higher lipid content and lower density; they transport cholesterol from the liver to tissues.

High-Density Lipoproteins (HDLs)

Lipoproteins with a diameter of ~$8-11\,nm$ that have higher protein content and higher density; they transport cholesterol from tissues to the liver.