Module 6

Provide a specific environment i.e. active site for a given reaction to proceed rapidly

They are lined with functional groups that binds to substrate

Lower the activation energy required and perform this function with high degree of specificity

By forming a complex between enzyme and substrate (ES)

E + S <> ES <> EP <> E + P

–acid-base catalysis:give and take protons –covalent catalysis:change reaction paths –metal ion catalysis:use redox cofactors, pKa shifters

-convert carbon fuel source into cellular energy in a appropriate timescale -Forming ethanol from pyruvate. Pyruvate— pyruvate decarboxylase–> acetaldehyde — alcohol dehydrogenase–> ethanol

Excessive or deficiency in enzymatic activity. e.g. Phenylketonuria is caused by a deficiency in the enzyme Phenylalanine Hydroxylase

They target enzyme by inhibiting or activating the target

not all

cofactors (e.g. MG2+, K+) coenzymes (carries functional groups) e.g. Coenzyme A, FAD, NAD, biocytin

8 types – Kinases – Phosphorylases – Phosphatases – Dehydrogenases – Mutases – Isomerases – Hydratases – Synthases

Catalyses the phosphoryl transfer from one molecule (usually ATP) toanother;e.g.Hexokinase

Catalyses the covalent addition of inorganic phosphate(Pi)to a molecule; e.g.Glycogen Phosphorylase

Catalyses the cleavage of a phosphate to yield the dephosphorylated product and Pi;e.g.Glucose-6-phosphatase

Catalyses an oxidation/reduction reaction commonly using NADH/NAD+, NADPH/NADP+ or FADH2/FAD as cofactors; e.g.Glyceraldehyde-3-phosphate dehydrogenase

Catalyses the shift of a phosphoryl group from one atom to another within the same molecule;e.g.Phosphoglycerate mutase (tetrameric in yeast and dimeric in bacteria)

Catalyses the conversion of one isomer to another; e.g. Triose Phosphate Isomerase (step 5 of glycolysis)

Catalyzes the addition/removal of water e.g. enolase catalyses the conversion of 2-phosphoglycerate to phosphoenolpyruvate

Catalyses the synthesis of a product. e.g.citrate synthase. Addition of an acetyl group from Acetyl-CoA to oxaloacetate to form citrate in the first step of the Krebs (citric acid, TCA) cycle

energy barriers to prevent complex molecules from reverting spontaneously, reduce activation energy and thereby increase the rate of reaction

Do not affect : delta G transition states are transient species

the difference between the activation energies of the uncatalysed and catalysed reactions caused by the enzyme binding the transition state

– binding substrates in the correct orientation relative tot he active groups -providing catalytically active groups(side chains, acids, bases, metal ions) – Polarizing bonds, stabilising charged species (usually unstable) – stabilizing the transition state Weak binding interactions between the enzyme and the substrate provide a substantial driving force for enzymatic catalysis