Enzymes 2 Flashcards Preview

Science for Medicine > Enzymes 2 > Flashcards

Flashcards in Enzymes 2 Deck (71):
1

Give an example of two enzymes that catalyse the same reaction?

Glucokinase and hexokinase

2

What reaction to glucokinase and hexokinase catalyse?

Glucose + ATP → Glucose-6-phosphate + ADP

3

Where is glucokinase found?

In the liver

 

4

Where is hexokinase found?

Everywhere other than the liver

5

What kinetic properties do glucokinase and hexokinase have (KM and vmax)

6

What does a graph of the activity of glucokinase and hexokinase look like and explain it?

Hexokinase is constantly working flat out whereas glucokinase can respond proportionally to blood glucose

7

Why does hexokinase have a low KM?

So it can respond proportionally to blood glucose

When [glucose] is low you don't want the liver to break it down as you want it to be released into the blood

8

What is the difference between glucose-6-phosphate and glucose?

G-6-P cannot leave the cell

9

What do enzymes being found where they shouldn't be indicate?

Tissue damage, enzymes may escape from damaged cells

10

How is enzyme activity measured in clinical scenarioes?

With an arbitory value

1U/ml o 100% = normal

11

What is an isozyme?

Different enzymes that catalyse the same reaction

12

Where are isoenzymes often found relative to each other?

In different tissues

13

Are isoenzymes coded for by the same gene?

No, they are products of different genes

14

What is electrophoresis?

Process where you can seperate out biological molecules

15

How does electrophoresis work?

Larger molecules get stuck and so move less than smaller molecules, charge also has an impact

16

What is creatine kinase (CK)?

An example of an isoenzyme which is a dimer made up from two polypeptide chains B and M

17

What is a dimer?

Oligomer consisting of two monomers joined by bonds that can be strong or weak, covalent or intermolecular

18

What is an oligomer?

Molecule complex of chemicals that consists of a few monomer units

19

What are the 3 isomorms that creatine kinase (CK) can form?

CK1 (BB)

CK2 (BM)

CK3 (MM)

20

How are enzymes used in diagnosis?

Measure activity and compare with normal

Sepperate differnt forms of enzymes by electrophoresis

21

Are enzymes restricted to interacting with one substance?

No, most enzymes can interact with a variety of substances

22

How does the KM vary between enzymes and their different substrates?

Changes for each substrate

23

What does catalysing a reaction with two or more substances normally involve?

The transfer of groups from one to the other

24

What ways can the catalyse of two or more substances with the transfer of groups occur?

Random order or ordered with ternary complex

No ternary complex formation

25

What does a random order reaction involving a ternary complex look like?

26

What does an ordered reaction involving a ternary complex look like?

27

With does a reaction with no formation of a ternary complex look like?

28

What is an example of an enzyme that uses an ordered sequential mechanism?

Lactate dehydrogenase for the reaction of pyruvate to lactate

29

What is an example of an enzyme that uses a random sequential mechanism?

Creatine kinase (CK) for creatine to phosphocreatine

30

What do ordered and unordered squential mechanisms have in common?

The ternary complex is formed first

31

What is an example of an enzyme that uses a no formation of tertary complex mechanism?

Asparate aminotransferase, uses a double displacement reaction

32

What is a double displacement reaction?

Substrates bounce on and off the enzyme

33

What happens when you take an amino group of an amino acid?

It becomes a ketoacid

34

What notation is commonly used to show the mechanisms of enzyme reactions?

Clelend notation

35

What is an allosteric enzyme?

Enzymes made up of many subunits

36

What sites are on an allosteric enzyme?

Can contain many active sites, they have other sites that can be used for regulation

37

What do the kinetics of an allosteric enzyme look like and why is this?

Because of cooperative binding

38

What is cooperative binding?

One substance binds to an enzyme subunit causing a change in the acitve site of other sub units

39

What is an example of an enzyme that uses cooperative binding?

Haemoglobin

40

What factors affect the way that enzymes function?

Temperature

pH

Inhibition

41

How does temperature affect enzyme functionality?

As temperature increases, molecule collisions increase

As temperature increases, internal energy of molecule increases

If temperature increases further the enzyme will denature

42

How does pH affect enzyme functionality?

Changes charge of amino acids

If the active amino acids change charge will stop working

Extreme pH will denature the enzyme

Also affects substrates

43

What are the three types of inhibitors?

Competative inhibitor

Non-competative inhibitor

Uncompetative inhibitor

44

What is a competative inhibitor?

Binds to the active site non covalently, competing with the substrate

45

What do competative enzymes cause in terms of enzyme kinetics?

Decreased affinity (KM increase)

vmax remains the same as increasing [substrate] can overcome it

46

What does the best inhibitor look like and why?

The transition state because it binds better

47

Why are there not a lot of transition state drugs?

The transition state is hard to determine

48

What are non-competative inhibitors?

Bind to somewhere other than the active site non covalently

49

What do non-competative inhibitors cause in terms of enzyme kinetics?

KM unchanged as substrate can still bind

vmax decreases because cannot out compete the inhibitor

50

What do inhibitors on a Lineweaver-Burk plot look like?

51

What is an example of an irreversible inhibitor?

Cyanide (CN-)

52

What does biological reactions occuring in pathways allow?

Regulation of a key step byt regulating the enzyme, often the first step

53

What are the 2 main ways of regulating enzymes?

Allosteric enzymes

Covalently modified enzymes

54

What is feedback inhibition?

Build up of an end product inhibits an earlier enzyme

55

What kind of inhibition do pathways often use?

Feedback inhibition

56

What are allosteric effectors?

Cell metabolites that bind non covalently to a site on the enzyme that is not the active site

57

What do effectors do to an enzyme structure?

Cause it to change

58

What are the two types of effectors?

Inhibitor

Activator

59

What two models explain allosteric kinetics?

Concerted model

Sequential model

60

What does the concerted model state?

Sub units exist in two conformations (one binds well and the other doesn't)

With no substance the enzyme flips between the two conformations

All sub units must be in the same conformation (flip in concert)

61

What are allosteric activators?

Bind somewhere other than the active site, locking the open conformation

62

What are allosteric inhibitors?

Bind somewhere other than the active site, locking in the closed conformation

63

What are the properties of the sequential model?

Substrate binding causes a change in one subunit

Binding causes conformational change

64

What is an example of a reversible covalent modificaiton that can inhibit an enzyme?

Being phosphorylated

65

What are the two kinds of enzymes that catalyse the phosphorylation of an enzyme?

Protein kinases (adds phosphory group to a protein)

Protein phophotases (removes phosphoryl group)

66

What do multiple phosphorylation sites allow?

Fine control of an enzymes function, it is never completely off or on but is finely tuned

67

What is a proprotein?

Enzymes existing as an inactive precurser protein

68

What happens when the proprotein is cleaved of an enzyme?

Enzyme becomes active by proteases

69

What kinds of enzymes often use proprotein for regulation?

Digestive enzymes

70

What is proteolysis?

Process of breaking peptide bonds between amino acids

71

What is a protease?

Enzymes that perform proeolysis (protein catabolism by hydrolysis of peptide bonds)