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Flashcards in Enzymes Deck (52):
1

What are ribozymes?

Catalytic RNA molecules with no protein component

2

What is a cofactor?

A non-protein component needed for activity, usually metal ions

3

What is a co-enzyme?

A complex organic molecule, usually produced from a vitamin FAD NAD+

4

What is a prosthetic group?

A non-protein group forming part of or combined with a protein. 

i.e - A cofactor covalently bound to an enzyme or very tightly associated with an enzyme

5

What is an apoenzyme?

An inactive enzyme, activation of the enzyme occurs upon binding of an organic or inorganic cofactor.

6

What is a holoenzyme?

WHole enzyme, the apoenzyme plus the cofactor

7

Why isn't a spontaneous reaction instantaneous?

Because of the activation energy barrier

8

What is the activation energy used for?

Positioning chemical groups correctly

9

What is the transition state?

The moment that chemical bonds are formed and broken The reaction from this point could then go to products or reactants

10

What type of bonds occur between substrate and enzyme?

Non-covalent

11

What is the active site complementary to?

The transition state

12

How do enzymes reduce activation energy?

Entropy reduction Desolvation Induced fit

13

How does entropy reduction reduce activation energy?

Molecules react by bumping into each other, enzymes orientate the substrates improving the chance of a successful collision and a resulting reaction

14

How does desolvation decrease the activation energy?

H bonds with the substrate and the solution are replaced by the weak bonds between the substrate and the enzyme.

15

How does induced fit decrease activation energy?

Conformational changes occur in the protein structure when the substrate binds

16

Which part of an enzyme reaction occurs more slowly?

The second part of the equation, producing E and P from the enzyme substrate complex

17

Which stage of an enzyme reaction is reversible?

The formation of ES from E and S K1 denotes the forward reaction K-1 denotes the reverse reaction

18

What is Km?

It is the substrate concentration when the reaction velocity is exactly half of the max velocity

19

On a lineweaver burke plot what does the y intercept represent?

1/VMax

20

On a lineweaver burke plot what does the X intercept represent?

1/Km

21

What does Km measure?

The ration of rate constant for breakdown of ES to E+S compared to the rate constant for formation of ES from E+S It gives you a clue to the affinity of the enzyme with it's substrate

22

What does a large Km value indicate?

Less stable ES complex

23

Which enzyme activity fluctuates directly with blood glucose intake?

Glucokinase Catalyses Glucose + ATP to glucose - 6 - phosphate

24

What is used to determine normal enzyme activity?

Arbitrary values such as 1U/ml or 100%

25

How are enzymes separated?

Gel electrophoresis

26

Where can you find creatine kinase?

In the heart Elevation of plasma CK2 is diagnostic for myocardial infarction

27

What are the possible reaction mechanisms for enzymes with two or more substrates

Random or ordered with a ternary complex No ternary complex formation

28

Describe the reaction involving a ternary complex
Random order

Can bind to either substrate first

Eventually complexes with both substrates

Forms two products

29

Describe the reaction involving a ternary complex
Ordered

Attaches to one substrate first, it is the fed the other substrate

30

Describe the reaction with no ternary complex formed

Reaction occurs with enzyme and substrate producing altered enzyme and a product

 

Second reaction occurs with the altered enzyme and the second substrate, producing a second product

31

What type of reactions have no ternary complex formation?

Transamination reactions

32

How does temperature affect the function of an enzyme?

Increase temperature will increase molecule collisions and it will increases the internal energy of molecules

 

Eventually denautres the enzyme

33

How does pH alter the function of an enzyme?

pH changes the charge of an amino acid, can stop the active site functioning if the amino acids in the active sites change charge.

 

Extreme pH will denature the enzyme

 

pH will affect the substrates

34

What effect does a competetive inhibitor have on the Vmax and Km?

Same Vmax

Km increases (since affinity active site has for the enzyme substrate complex decreases)

35

What is an example of a transition state anologue?

Oseltamavir

36

What does a catalytic antibody resemble?

It resembles the active site of the original enzyme, since it is specific to a transition state molecule

37

What effect do non-competitive inhibitors have on the Vmax and the Km values?

V max will decrease - inhibition remains the same regrdless of the change in substrate concentration

Km remains the same as the substrate is still able to bind to the active site

38

Which type of inhibitors bind in an rreversible manner?

Those that bind in a covalent manner

39

Which enzyme in a pathway holds the regulatory step for that pathway?

Often the first one in the pathway

40

What are the regulatory types of enzymes called?

Allosteric enzymes and covalently modified enzymes

41

What is feedback inhibition?

When there is a build up of an end product in a pathway or a key junction in a pathway that ultimately slows down the entire pathway

42

How is the change in the structure of an enzyme brought about in allosteric control?

An allosteric effector (usually a metabolite) binds non-covalently to a site on the enzyme that is not the active site, changing the enzymes structure

43

What are the two different types of allosteric effectors?

Activators and inhibitors

44

How does the concerted model show how a small amount of substrate increases an enzymes sensitivity to a substrate?

Concerted model suggests that enzyme sub-units are always flipping between two conformational formations

Binding of S to one substrate locks the other subunits in the same conformation

45

How do allosteric inhibitors and activators function in the concerted model?

Activators - stabilise the  the open conformation, allowing S to bind more effectively

Inhibitors - stabilise the ‘closed’ conformation and make it difficult for S to bind effectively

46

How does the sequential model show how a small amount of substrate increases an enzymes sensitivity to a substrate?

Substrate binding causes a change in ONE sub unit, this causes a change in another sub-unit allowing it to bind to S more readily

47

What enzymes are responsible for covalent modification?

 

Protein kinases (add phosphoryl groups to proteins)

Protein phosphatases (remove phosphoryl groups)

48

What do multiple phosphorylation sites allow?

Very fine control of enzyme funciton

49

What is an inactive precursor of an enzyme called?

A proprotein or a proenzyme

50

What can be produced when a proprotein is cleaved?

Proteases

51

Give an example of a an enzyme that is regulated by proteolytic cleavage

Trypsin - activated in the small intestine

Its precursor trypsinogen is formed in the pancreas

 

52

Describe the bonding between a protein and :

  • A prosthetic group
  • A coenzyme

Prosthetic group - Tight bonding (sometimes even covalent bonds)

Coenzyme - Loose bonding