Enzymes Flashcards
What are enzymes?
Proteins that catalyze an increase in rate of a chem reaction
-Selectively convert starting molecules - substrates - into diff molecules - products.
What do enzymes do to the energy of activation?
Lower it
What important roles do enzymes play?
-All biochem reactions are enzyme catalyzed in living organism
-Digestion, metabolism, diagnosi, therapeutics
-Level of enzyme in blood are of diagnostic importance - good indicator in myocardial infarction
-Can be used therapeutically such as digestive enzymes
-Activity can be therapeutically targeted - inhibited or activated
What are the 6 functional classes of enzymes?
- Oxidoreductases - oxidation-reduction
- Transferases - transfer groups of atoms
- Hydrolases - hydrolysis
- Lysases - add/remove atoms to/from a double bond
- Isomerases - rearrange atoms
- Ligases - Use ATP to combine molecules
What do Oxidoreductases do? Examples?
-Catalyse oxidation/reduction rxns
-Act on many chemical groups to add or remove hydrogen atoms
-E.g Lactate dehydrogenase, catalase, peroxidase, phenylalanine hydroxylase
What do Transferases do? Examples?
-Transfer a functional group (e.g amino acid or phosphate) between donor and acceptor molecules
-E.g Transaminases- transfer amino group NH2, Phosphotransferases (kinases), Transmethylases, transpeptidases, transacylases
What do hydrolases do? Examples?
-Catalyse the cleavage of bonds by addition of water across a bond
E.g
-Protein hydrolysing enzymes - peptidases and proteases
-Carbohydrases - amylase, maltase, lactase
-Lipid hydrolyzing enzymes - lipase
-Deaminases, phosphatases
What do Lyases do? Examples?
-Cleave various bonds (C-C, C-S, and certain C-N bonds) by means other than hydrolysis and oxidation
-E.g aldose, fumerase, carbonic anhydrase
What do isomerases do? Examples?
-Catalyse inter-conversion of optical, geometric or positional isomers within a single molecule
-E.g isomerase, mutase
What do Ligases (synthases/synthetases) do? Examples?
-Join 2 molecules w covalent bonds
-Catalyse reactions in which 2 chemical groups are joined w the use of energy from ATP
-E.g Acetyl-CoA Carboxylase, pyruvate carboxylase, glutamine synthetase
Structure of enzymes?
-Proteins
-Globular shape
-Complex 3D structure
Cofactor vs Coenzyme
Cofactor - small inorganic molecule or atom (Zn2+ or Fe2+). - tightly bound to apoenzyme
Coenzyme - small organic molecules (NAD+ or FAD)
What is the apoenzyme part of the complex or holoenzymes?
Protein part
Enzyme without its non-protein moiety - inactive
What is the Holoenzyme ?
Enzyme with its non-protein component - active
Examples of inorganic ions that serve as cofactors for enzymes?
-Cu2+ - Cytochrome oxidase
-Fe2+ por Fe3+ - Cytochrome oxidase, catalase, peroxidase
-K+ - pyruvate kinase
-Mg2+ - hexokinase, glucose -6- phosphatase, pyruvate kinase
-Mn2+ - Arginase, ribonucleotide reductase
-Mo - Dinitrogenase
-Ni2+ - Urease
-Zn2+ - Carbonic anhydrase
What does magnesium regulate?
Glycolysis
Whta is the specificity of an enzyme determined by?
The active site
What does the active site of an enzyme have?
-Contains amino acid side chains that participate in substrate binding and catalysis
-The shape and chemical environment inside the active site permits a chemical reaction to proceed more easily
What are types of enzyme specificity and give examples?
- Absolute - catalyze one type of rxn for a single substrate e.g urease catalyzes only the hdrolysis of urea
- Group - catalyze one type of reaction for similar substrates e.g hexokinase adds a phosphate group to hexoses
- Linkage - catalyze one type of rxn for a specific type of bond e.g chymotrypsin catalyses the hydrolysis of peptide bonds
What is the free activation of energy?
The energy barrier separating reactant and products
-crossing the barrier requires activation energy
When are molecules in the reaction said to be in transition state?
-When they are crossing the free energy of activation barrier
Velocity
v = change in conc / time
-over time conc of substrate decreases and conc of product increases
What did Michaelis and Menton postulate?
- The enzyme first combines reversibly w its substrate to form ES complex in a relatively fast reversible step
- The ES complex then breaks down in a slower second step (rate-limiting step) to yield the free enzyme and the product
What is the Michaelis-Menten equation?
-The rate equation for an enzyme-catalyzed reaction
-Describes how reaction velocity varies w substrate conc
V (initial) = Vmax (substrate conc) / Km-constant + substrate conc
Km - the subtrate conc at which the reaction velocity is half of max velocity
-Use graph - vmax/2 - hit graph and go down to find substrate which is Km
