Enzymes Flashcards
What is an enzyme?
A biocatalyst, almost all protein and reduces the activation energy of a reaction
What are the different catalytic strategies of an enzyme?
Covalent, acid-base and metal ion
What are the 6 categories of enzymes?
- Oxidoreductases
- Transferases
- Hydrolases
- Lyases
- Isomerases
- Ligases
Enzyme cofactors
Acts as an electron carrier
What is the effect of pH on enzymes?
Enzyme works best at 6 pH but poorly at low and high pH
What is the effect of temperature on enzymes?
Increases chemical reactions but then denatures proteins (best at 55 degrees)
Competitive vs Non-competitive enzyme inhibition
Competitive: inhibitor mimics substrate and competes for binding site
Non-competitive: inhibitor changes binding site to prevent enzyme action
Phosphorylation
Catalysed by kinases, can either activate or inhibit enzyme
What are enzyme kinetics?
Rate of enzyme reaction in mathematical terms. Relationship between substrate concentration (S) and rate of enzyme reaction (Vo)
Michaelis-Menton equation
Vo=(Vmax .(S))/(Km+S)
Lineweaver-Burke equation
1/Vo=1/Vmax + Km/Vmax .(S)
What is the function of proteases?
Digestion, recycle amino acids and activate enzymes
What is chymotrypsin?
Covalent intermediate acid-base catalyst
Substrate specificity
Specially binds large hydrophobic R group
1st step of forming alkoxide ion
Histidine acts as a base and removes H from serine making alkoxide stronger
2nd step of forming alkoxide ion
Nucleophilic attacks carbon which breaks peptide bond and causes carbonyl group to form acyl bond with serine
3rd step of forming alkoxide ion
Amino acid group receives H from histidine and amine group departs
4th step of forming alkoxide ion
Water attacks acyl bond releasing carbonyl fragment and water attacks carbonyl group
5th step of forming alkoxide ion
Histidine removes H from water and the remaining OH group attaches to carbonyl group
6th step of forming alkoxide ion
Acyl bond breaks, carboxylic acid released and enzyme returns to original state