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Flashcards in Enzymes Deck (57)
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1
Q

By what factorcan enzymes accelerate chemical reactions?

A

10^5- 10^19

2
Q

What enzyme accelerates reactions the most?

A

Arginine decarboxylase (10^19)

3
Q

What can enzymes be affected by?

A

Inhibitors and activators

4
Q

What is a holo enzyme?

A

Enzyme containing non-protein cofactor

5
Q

What is an apoenzyme?

A

Enzyme that doesn’t contain a non-protein cofactor

6
Q

What does the group EC1 Oxidoreductases do?

A

Catalyze redox reactions
NADPH oxidation to NADP+ ,molecule reduction

7
Q

What does the group EC2 Transferases do?

A

Transfer the functional group
tRNA AA is transferred to the created protein

8
Q

What does the group EC3 Hydrolases do?

A

Hydrolyze bonds
Digestive enzymes split bonds

9
Q

What does the group EC4 Lyases do?

A

Non-hydrolytic bond cleavage

10
Q

What does the group EC5 Isomerases do?

A

Molecular isomerization
Isomer is rearranged spatially (molecular weight stays the same)

11
Q

What does the group EC6 Ligases do?

A

Join 2 molecules covalently

12
Q

What does the group EC7 Translocases do?

A

Move the molecule around the cell

13
Q

Name the 4 enzyme regulation processes

A
  1. Bioavailability
  2. Covalent modification
  3. Allosteric regulation
  4. Compartmentation
14
Q

What does bioavailability do?

A

Cell controls how much of the synthesized enzyme will be used /available by the substrate
Degrades it if too much
Binds to regulatory molecule
Coucuent modification

15
Q

What is repression in bioavailability

A

Product of a biochemical pathway inhibits synthesis of a key enzyme in the pathway
Feedback inhibition

16
Q

What is induction in bioavailability?

A

Coulchanges the production of a specific enzyme to stimulate / inhibit activity

17
Q

What is the issue with bioavailability?

A

It is too slow to control all cell functions

18
Q

What is covalent modification?

A

Covalently attaching a moleculeto the enzyme to stimulate / inhibit activity
Much faster than genetic control
Uses (de)phosphorylation

19
Q

What catalyzes phosphorylation?

A

Catalyzed by enzymes kinases
ATP isthe source ofthe phosphate

20
Q

What catalyzes dephosphorylation?

A

Catalyzed by phosphatase enzymes

21
Q

What other molecules covalently modify enzymes?

A

Methyl/acetyl groups, sugars, lipids
Less commonly Than phosphate

22
Q

What are the sites for phosphorylation?

A

The OH side chain of serinine, threonine, tyrosine

23
Q

What is an example of covalent modification?

A

Proteolytic processing to activate and deactivate enzymes

24
Q

What is allosteric inhibition?

A

Feedback inhibition
Catalyzes the committed step in a metabolic pathway- controls the vote
Doesn’t always follow the Michaelis-Menten kinetics

25
Q

What is an exampleof allosteric regulation?

A

Phospho-fructokinase (step 3 of glycolysis)
ATP is a negative regulator

26
Q

What is compartmentation?

A

Storing enzymes in specific compartments
Keep them from doing damage or provide proper conditions for activity

27
Q

Describe the lock and key model

A

Enzyme and substrate possesses specific complementary shapes that fit exactly into eachother
Doesn’t explain the transition state that ES complex achieve - proven inaccurate model

28
Q

Describe the induced fit model

A

Enzyme slightly changes shape upon substrate binding
Active site forms a complementary shape after substrate binds

29
Q

Describe the substrate in a transition state

A

Short-lived, unstable, requires less activation energy

30
Q

Describe conformational selection

A

Newer model of the induced fit model
Enzyme adapts to substrate dependent on the environment and presence of regulatory molecules

31
Q

How enzymes affect the activation energy?

A

Lower the activation energy of a chemical reaction by the randomness of collisions between molecules
Help bring the substrates together in proper orientation so that the reaction can occur

32
Q

What information enzyme kinetics give?

A

About enzyme catalysis, mechanism, activity regulation, basis of enzyme assays

33
Q

What are enzyme kinetics affected by?

A

By enzyme, substrate, ph, temperature, co-enzymes, activators, inhibitors

34
Q

What is a steady state?

A

When ES builds up initially and then remain constant
Will persist until thesubstrate runs out
takes nearly all of the reaction time

35
Q

Describe 1st order reaction

A

The reaction rate is proportional to the substrate
There is move enzymethan substrate

36
Q

Describe 2nd order reaction

A

More substrate than enzyme
Substrate is not proportional to the reaction rate
Rate depends only on the enzyme

37
Q

Describe michaelis-menten kinetics.

A

Under physiological conditions enzymes are not saturated with substrates
Reaction rate is dependent on substrate concentration

38
Q

What does the Michaelis constant describe

A

The affinity of an enzyme for a substrate
Lower Km = higher affinity

39
Q

What is the turnover number?

A

K cat
Number of substrate molecules cleaved per enzyme molecules per time when enzyme is fully saturated

40
Q

What plots describe the Michaelis-menten kinetics

A

Lineweaver- Burk plot
Hanes-woolf plot
Eddie- hofsteeplot

41
Q

What are inhibitors?

A

Interact with enzymes to reduce their catalytic activity
Structurally similar to natural substrate of an enzyme

42
Q

Features of reversible inhibition

A

Reversibly bind and dissociate from enzyme
Activity of enzyme recovers when inhibitor is diluted out
Non covalent interactions

43
Q

Name reversible inhibition types:

A

Competitive inhibition
Non-competitive inhibition
Uncompetitive inhibition

44
Q

Features of irreversible inhibition

A

Inactivators that irreversibly associate with an enzyme
Activity of enzyme doesn’t recover with dilution
Covalent interactions

45
Q

Describe competitive inhibition:

A

Direct competition between I and S for binding
I binds to active site of S
I only bina to free enzymes
Most common type of inhibition

46
Q

What are examples of competitive inhibition

A

HIV protease inhibitor
Phosphodiester-5 inhibitor

47
Q

Describe the kinetics of competitive inhibition

A

Vmax is unchanged
Km increases as higher S concentration is needed to reach max
Low Ki = higher affinity
Less affinity for S occurs

48
Q

Feature of uncompetitive inhibition

A

Inhibitor binds to ES complex (not free E)
Binds to allosteric site
Common in multi-substrate reactions

49
Q

Example of uncompetitive inhibition

A

Lansoprazole for gastric reflux

50
Q

Kinetics of uncompetitive inhibition

A

Km is lower
Vmax is lower

51
Q

Features of non-competitive inhibition

A

Inhibitor binds to both free enzymes and ES complex
Binds to allosteric site
ESI complex doesn’t react

52
Q

Example of non-competitive inhibition

A

Nifedipine inhibits CYP29 (cytP450 enzyme involved in drug metabolism)

53
Q

Kinetics of non-competitive inhibition

A

Km is unchanged
Vmax is lowered
At high S, the inhibitor is still bound to the enzyme

54
Q

Detailed Features of irreversible inhibition

A

Enzyme inactivated or suicide inhibition
Inhibitors form covalent bonds with their target enzymes leading to permanent inactivation
Used to identify the functional AA within the active site

55
Q

Describe the irreversible inhibition on aspirin

A

Aspirin covalently modifies the enzyme prostaglandin H synthase
Prevents prostaglandin synthesis and lowers inflammation
Occurs vidacetylation of serine-530 at the active site of PGH synthesis

56
Q

Describe the irreversible inhibition on eflornithine

A

Is a suicide inhibitor treating sleeping sickness
Binds irreversibly to cysteine residue on ornithine decarboxylase
Reduces production of polyamides necessary for parasite growth

57
Q

Describe the irreversible inhibition on penicillin

A

Is a irreversible inhibitor of bacterial wall synthesis
Innibits peptidoglycan cell wall synthesis and makes bacteria susceptible to osmosis
Without thePG layer bacteria lyse
Penicillin covalently modifies glycopeptide transpeptidase