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Flashcards in enzymes Deck (33)
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1
Q

how do enzymes decrease activation energy?

A

they provide catalytically competent groups for specific reaction mechanisms

by providing substrates such that their orientation is optimised for the reaction

by prefertially binding and stabilising the transition state(s) of the reaction

2
Q

what are 3 key features of the active site of enzymes

A

3D space comprising of crucial amino acid residues - provides specifity due to unique 3D arrangment

binds substrate via multiple weak interactions

may only represent a small part of the protein structure

3
Q

How is enzyme activity measured?

A

using the michaelis- menton model

4
Q

what is Vmax?

A

theoretical maximum rate of reaction - when all enzymes are saturated with substrate

5
Q

what is Km?

A

michaelis constant defined as the substrate concentration at half the maximum velocity

6
Q

what are 4 factors affecting the rate of enzyme catalysed reactions?

A

substrate/enzyme concentration

temperature

pH

inhibitors

7
Q

what is reversible inhibition?

A

inhibition usually non-covalent

ibuprofen - competiitve inhibitor but not covalently attached.

8
Q

what is irreverisble inhibition?

A

covalent modification of rthe enzyme usually at AA side chains in the active site
e.g. Aspirin which covalently modifies a serine residue in the active site, it is a competitive inhibitor

9
Q

what is competitive inhibiton?

A

either substrate or inhibitor can bind to enzyme but the inhbitor usually binds to the same site as the substrate - the active site , can be overcome by high substrate concentrations

e.g. iBuprofen

10
Q

what is non competitive inhibition?

A

inhibitor and substrate can bind simultaneously and binding occurs at a independent sites, it alters the conformation or accesibility of the active site

e.g. methotrexate inhibits dihydrofolate reductase

11
Q

what happens to Vmax and Km in compeitive inhibiton?

A

Vmax is unchanged

Km is increased

a higher substrate concentration is needed to reach Km

12
Q

what happens to Vmax and Km in non-competitive inhibition?

A

Vmax is decreased

Km is unchanged

increasing substrate concentration has no effect

13
Q

what are IC50 values?

A

inhibitor concentration that reduces enzyme activity by 50%

so higher IC50 = lower affinity the inhibitor has to the enzyme so less effective an inhibitor

14
Q

what are cofactors?

A

inorganic ions essential for enzyme function

15
Q

what are the roles of metal ions as cofactors?

A

metal ions may be part of the active site/ involved in electrostatic substrate binding

metal ions may act as redox agents

metal ions may regulate activity of enzymes

16
Q

what are coenzymes?

A

carriers of reaction components, including many water-soluble vitamins

17
Q

what do NADH and FADH2 do?

A

carry electrons

18
Q

what does coenzyme A do?

A

carry acetyl units

19
Q

what does bibtin and thiamine pyrophosphate carry?

A

CO2

20
Q

What does mutation in Glucose-6-phopshate dehydrogenase cause?

A

G6DPH deficieny causes metabollic defects
X linked recessive so most carriers are asymptomatic.

G6DPH produces lots of the bodys NADPH (which is needed to drive biosynthesis of nucleic acids and lipids atc)

a crisis can be triggered by certain drugs or food or infection

high incidence in malarial region, it results in ;primaquine induced haemolytic anaemia

21
Q

what is primaquine?

A

anti malarial drug

22
Q

what is favism?

A

development of haemolytic anaemia upon consumotion of fava beans

23
Q

what factors are involved in the control of enzyme activity?

A

inhibition

feedback regulation

covalent modification - protein phosphorylation, enzymes are phophorylated by kinase enzymes

proteolytic activation - when innactive precursor enzymes are made active by proteolysis

24
Q

describe the role of serine proteases in blood clotting

A

lysis of blood clots by plasmin.

TPA (tissue plasmin activator) adheres to clot and binds plasminogen - targets activity to the correct place.

this cleaves plasminogen to active plasmin

plasminogen digest clots to small polypeptides

25
Q

name 3 examples of enzymes with isoenzymes

A

lactate dehydrogenase (LDH)

cyclo-oxygenase (COX-1 and COX-2)

creatine kinase

26
Q

what subunits is LDH made from?

A

M and H, isoenzymes have different combinations of 4 of these subunits

27
Q

what subunits are creatine kinase made from?

A

M and B, made of 2 polypeptides as a combination of these

28
Q

diagnostic value of enzymes in liver damage?

A

measure of paracetamol levels in the plasma

measurement of glucose levels - immobilised enzymes on plastic strips gives quick and semiquantitative results

29
Q

diagnostic value of enzymes in AMI?

A

creatine kindase

myoglobin

cardiac troponin

lactate dehydrogenase

30
Q

how do you measure paracetamol levels?

A

in the plasma

using bacterial enzyme which breaks paracdetamol down into acetate and p-aminophenol

the p-aminophenol reacts to form a coloured dye product

31
Q

how do you measure blood glucose?

A

using immobilised enzymes and coloured reagents on plastic strips

32
Q

how can enzymes be used to treat thrombosis?

A

treat with TPA activates plasminogen to form plasmin which breaks down fibrin clot of thrombosis into peptides

33
Q

how can enzymes be used in cancer therapy

A

asparagine is not needed in normal cells as asparagine synthetase enzymes are present in these cells but tumour cells are deficient in Asn sythetase, therefore Asn is essential for them.

treating with asparaginase breaks down asparagine so the plasma level of asparagine are lowered and the growth of tumour cells is affected as they have no Asn sythetase to produce more.