Biology: Protein Structure, Enzymes, and Metabolic Pathways

Amino Acid

Central carbon bonded to an amino group (-NH₂), carboxyl group (-COOH), hydrogen, and variable R group; monomers of proteins; sequence determines protein shape and function

Carboxylic Acid Group (-COOH)

Carbon double-bonded to oxygen and single-bonded to -OH; acts as an acid (donates H⁺); participates in peptide bond formation

Amino Group (-NH₂)

Nitrogen bonded to two hydrogens; acts as a base (accepts H⁺); forms peptide bonds

R Group (Side Chain)

Variable group attached to central carbon (can be polar, nonpolar, charged); determines chemical properties, interactions, and final protein shape

Peptide Bond

Covalent bond between carboxyl group of one amino acid and amino group of another; links amino acids to form polypeptides (proteins)

Dehydration Synthesis

Reaction that removes H₂O to form a bond; builds polymers like proteins (forms peptide bonds)

Primary Structure

Linear sequence of amino acids; determines all higher levels of protein structure

Secondary Structure

α-helices and β-pleated sheets formed by hydrogen bonds; provides local folding and stability

Tertiary Structure

3D shape from interactions between R groups (hydrogen bonds, ionic bonds, disulfide bridges); determines protein function (e.g., enzyme specificity)

Quaternary Structure

Multiple polypeptide chains assembled together; allows complex protein function (e.g., hemoglobin)

Enzyme

Protein with a specific 3D shape; biological catalyst that speeds up reactions by lowering activation energy

Substrate

Reactant molecule that binds to enzyme; gets converted into product during enzymatic reaction

Active Site

Specific region of enzyme shaped to fit substrate; where substrate binds and reaction occurs

Activation Energy

Energy barrier that must be overcome for reaction; determines reaction rate; enzymes lower this

Catalyst

Substance (often protein) that is not consumed; speeds up chemical reactions

Hydrolysis

Reaction that adds water to break bonds; breaks polymers into monomers (e.g., proteins → amino acids)

Denaturation

Loss of protein shape due to heat, pH, etc.; causes loss of function (especially enzymes)

Competitive Inhibitor

Molecule similar to substrate that binds active site; blocks substrate from binding, slowing reaction

Noncompetitive Inhibitor

Binds to a site other than active site; changes enzyme shape, reducing activity

Allosteric Site

Regulatory site separate from active site; binds molecules that alter enzyme activity

Cofactor

Non-protein helper (metal ion or organic molecule); assists enzyme function

Metabolic Pathway

Series of enzyme-controlled reactions; transforms molecules step-by-step in cells