Enzymes Flashcards
What is an important enzyme for exercise?
Nitric oxide synthase: NO drives relaxation of arterial smooth muscle
How does the induced fit model work?
Enzyme puts pressure on bonds in substrate, and a slight conformational change of activation site is needed
What are cofactors?
Enable the enzyme to catalyse reaction; can be bound tightly or loosely
What are types of cofactors?
Coenzymes, metals, and vitamin derivatives (e.g. B vitamins)
What is the difference between loose and tight cofactors?
Loose bind to enzyme before reaction and are released after the reaction; tight remain bound all the time (e.g. Haem in Hb)
How do enzymes allow catalysis?
Enzyme reduces Eact of reaction; enzyme stabilises transition state
What type of enzyme reaction is more common: reversible or irreversible?
Reversible
Which type of enzyme reaction is a non-equilibrium reaction?
Irreversible
Why are irreversible enzymatic reactions important?
Essential to regulation of cell
What are five groups of enzymes?
Transferases; hydrolases; oxidoreductases; kinases; phosphotases
How can enzymes be classified?
By the group they fall under, and/or the specific reaction they catalyse
What do transferases do?
Catalyse group transfer
What do hydrolases do?
Catalyse hydrolysis
What do oxidoreductases do?
Catalyse redox
What do kinases do?
Catalyse phosphate addition
What do phosphotases do?
Catalyse phosphate removal
What is initial velocity?
V0; the highest rate of an enzyme catalysed reaction; occurs when substrate is at its greatest and product at lowest; occurs at initiation of reaction
What is maximal velocity?
Vmax; maximum possible initial rate of reaction
What is Michaelis Constant?
Km; concentration of substrate which allows enzye to work at half Vmax; is a measure of substrate-enzyme affinity
What is the significance of a higher Km?
Has lower affinity, so larger substrate is need to get Km
Why do cells normally have substrate concentration lower than Km?
Enzymes are working below saturation/ Vmax; enables enzymes to respond to changes easily, increasing or decreasing velocity as needed
What happens to Vmax and Km when enzyme concentration is increased?
Increases Vmax as Vmax is dependent on amount of enzyme; does not affect K as concentration of substrate is not affected as enzyme is in extreme excess
What happens to Vmax and Km when substrate concentration is increased?
No change
How does temperature affect the rate of an enzymatic reaction?
Rate increases as temperature increases until denaturing; Q10 values quantify change in relation to temperature (typically is 2)
What is competitive inhibition?
Competitive chemcial occupies active site and prevents ESC formation
How can competitive inhibition be overcome?
Adding more substrate
How does competitive inhibition affect Vmax and Km?
No change in Vmax, but increases Km
What is non-competitive inhibition?
Binds to allosteric site of enzyme; interferes with ans stops enzyme function
How does non-competitive inhbition affect Vmax and Km?
Vmax decreases, but no change in Km
How can enzymes be regulated?
Covalent modification turns them on or off: addition and removal of molecules will change enzyme’s conformation, causing increase or decrease in activity
What are common covalent modifications of enzymes?
Phosphorylation to a specific amino acid (~30%); acetylation; palmitoylation
