Enzyme Structure and Function

Study Notes

Enzymes are proteins that catalyze biochemical reactions, and their kinetics involve studying the rates at which they catalyze reactions.
Irreversible inhibitors permanently deactivate enzymes, reducing effective enzyme concentration and Vmax.
At low substrate concentrations, the reaction rate increases linearly with substrate concentration due to available enzyme active sites.
At high substrate concentrations, the reaction rate approaches Vmax as all enzyme active sites become saturated with substrate.
Km value reflects the enzyme's affinity for its substrate, with lower Km indicating higher substrate affinity.
Competitive inhibitors increase Km, while noncompetitive inhibitors do not affect Km.
Cooperativity occurs when substrate binding facilitates the binding of more substrates.

Serine (S), threonine (T), and tyrosine (Y) residues are often phosphorylated by kinases.
Glycine is achiral and optically inactive, and can disrupt alpha helices due to its small size and flexibility.
Proline disrupts alpha helices due to its inflexible secondary alpha-amino group.
Cysteine forms disulfide bridges and has an R absolute configuration.
Amino acids have different charges at different pH levels due to approximate pKa values for carboxylic acid (2) and amino groups (9).
Neutral polar amino acids contain OH, S, or amide groups, while neutral non-polar amino acids have uncharged alkyl or aromatic side chains.

Primary structure describes the linear sequence of amino acids stabilized by peptide bonds.
Secondary structure involves folding of a polypeptide into alpha helices and beta-pleated sheets due to backbone interactions.
Tertiary structure is the further folding of a polypeptide due to R-group interactions, which can be disrupted by changing the pH surrounding the protein.
Quaternary structure consists of the interactions between multiple polypeptides, and is also disrupted by pH changes.
Disulfide bonds are found in the extracellular space and are affected by denaturation.

Cofactors can be inorganic ions or organic molecules, while coenzymes specifically refer to organic molecules carrying specific chemical groups.
Cooperativity occurs when substrate binding facilitates further substrate binding, and is not explained by Michaelis-Menten kinetics.

Monosaccharides are simple sugars that serve as building blocks for more complex carbohydrates and are key energy sources in cellular respiration.
Disaccharides include maltose, sucrose, lactose, and cellobiose.
Polysaccharides include glycogen (energy storage in animals), starch (energy storage in plants), and cellulose (structural component in plant cell walls).