FCELL- Enzymes

Question 1

what are enzymes

Answer 1

proteins that speed up (catalyse) specific chemical reaction

Question 2

what are the functions of enzymes

Answer 2

digestion - carbohydrates, fats, proteins
blood clotting - fibrin clot
defence - immune system activation of complement
movement - muscle actomyosin is an ATPase
nerve conduction - membrane pumps - Na, K, Ca

Question 3

why are enzymes needed

Answer 3

proteases - break down proteins

Question 4

why are enzymes needed

Answer 4

proteases - break down proteins
nucleases - break down nucleic acids
polymerases - make polymers
kinases - transfer phosphate groups

increase rate 
show specificity 
unchanged at the end of the reaction 
do not alter reaction equilibrium 
facilitate reaction by decreasing free energy activation of the reaction

Question 5

outline some enzyme defects

Answer 5

phenylketonuria - cannot convert Phe to Tyr
glycogen storage disease- cannot mobilise glucose
Tay-sachs disease - defect in processing a membrane ganglioside - neuronal damage and death

Question 6

what are the features of a enzyme active site

Answer 6

3D cavity / cleft that binds the substrate
specificity through electrostatic, hydrophobic, hydrogen bonding and van der Waals interactions

formation of enzyme substrate (ES) complex at the active site is the first step in enzyme catalysis

Question 7

outline the lock and key vs the induced fit hypothesis

Answer 7

lock and key = active site is directly complementary to the shape of the substrate
induced fit - active site is not directly complementary - substrate binds - enzyme changes shape to fit the substrate

Question 8

how does substrate-enzyme binding contribute to rate enhancement

Answer 8

bring molecules together at the active site
strain particular bones in the substrate to make breakage easier
stabilise positive and negative charges in the transition state
exclude water from the active site - making the reaction go faster
provide a reaction pathway of lower energy
use cofactors - bring new chemistry to the active site

Question 9

what is Vmax

Answer 9

maximum velocity - all active sites are saturated - rate will no longer increase

Question 10

what is Vmax

Answer 10

maximum velocity - all active sites are saturated - rate will no longer increase

Question 11

what is the equation for velocity

Answer 11

Vmax ([S] / [s] + Km)

Question 12

what is Km

Answer 12

substrate concentration of Vmax / 2 - half of maximum rate - half of all active sites are filled - measure of substrate binding affinity

Question 13

what is Kcat

Answer 13

defines as the maximum number of substrate molecules handled per active site per second

Question 14

outline what is meant by competitive inhibitor

Answer 14

competes with the substrate for the active site – expect Km to be increased (takes more substrate to achieve Vmax / 2)

Vmax is unaltered as effects of inhibitor can be outcompeted at high substrate concentrations

Question 15

outline what is meant by non-competitive inhibitor

Answer 15

binds to a different site to the substrate
Km is unaltered - inhibitor affects the rate of reaction

Vmax is reduced

Question 16

what are the key properties of allosteric enzymes and how do they control metabolic pathways

Answer 16

control enzyme activity thorough control of gene expression - enzyme amount
compartmentation - sequences in enzyme polypeptide chain target enzyme to the ER / Mitochondria / nucleus

allosteric regulation - changes the enzyme conformation to influence the active site to decrease / increase enzyme activity

Question 17

which antibacterial agents act by inhibiting specific enzymes

Answer 17

gyrase inhibitor - novobiocin - competitively binds to ATP binding sites on gyrase

fluoroquinolones - inhibit DNA resealing by gyrase - bind to site of DNA breakage and interpolar DNA to prevent release - resulting in cytotoxic lesion in bacteria = cell death