Enzymes Flashcards
What is the active site of an enzyme?
The active site is a small section of the three-dimensional protein molecule which is specific to the substrate the enzyme acts on.
What is the name given to the model of enzymes and substrates fitting together?
The lock and key model.
How do enzymes catalyse reactions?
Enzymes catalyse reactions by lowering the activation energy required for a reaction to take place.
There are three catalytic strategies - name them.
Covalent catalysis, acid-base catalysis and metal ion catalysis.
How does covalent catalysis work?
By breaking and reforming active bonds.
What does acid-base catalysis require the presence of?
Proton donors or acceptors.
What does metal ion catalysis need?
A metal ion cofactor.
There are hundreds of enzymes, which can be classified according to…?
The reaction they catalyse.
Name some of the types of enzymes, as classified by the reactions they catalyse.
Oxxidoreductases, transferases, hydrolases, lyases, isomerases, ligases/synthases.
Many enzymes require …………., of which NAD(P) is an example.
Cofactors.
NAD(P) is a cofactor used by several oxidoreductases. What does it do?
It acts as an electron carrier.
Many cofactors are derived from…?
Vitamins.
Name two factors which can affect enzyme activity.
pH and temperature.
Why does a change in pH affect enzyme activity?
A change in pH changes the charge on amino acids, which is important for enzyme function.
How does temperature affect enzyme activity?
Temperature increases chemical reactions, but eventually the enzyme will be denatured and stop working.
Name the two types of enzyme inhibition.
Competitive and non-competitive.
Outline how competitive enzyme inhibition works.
The inhibitor mimics the structure of the substrate and competes for binding at the active site. The enzyme is therefore non-functional as the substrate cannot bind.
Can competitive enzyme inhibition be turned on and off?
No.
Outline non-competitive enzyme inhibition.
The inhibitor binds to the substrate and changes the binding site, preventing the enzyme from binding easily, although it might still be able to bind.
Can non-competitive enzyme inhibition be turned on and off?
Yes it can, to regulate enzymatic pathways.
Penicillin is a short peptide which is used as an antibiotic to kill bacteria - how does it work?
Penicillin inhibits glycopeptide transpeptidase, which cross-links bacterial cell walls. The cell walls are therefore not built properly, so the bacteria cells die.
Why does penicillin only kill bacteria cells?
Penicillin works on cell walls. Only bacteria have cell walls so it doesn’t affect other cells.
Give a common example of covalent modification.
Phosphorylation.
Which enzyme catalyses phosphorylation?
Kinase.
True or false? When ATP phosphorylates an enzyme, the enzyme can be activated OR deactivated?
True.
