Protein Function and Enzymes

Question 0

What type of curve does oxygen binding to myoglobin show?

Answer 0

Hyperbolic

Question 1

Which two complexes transport oxygen in the body?

Answer 1

Haemoglobin and myoglobin

Question 2

Describe the features of haemoglobin structure

Answer 2

2 polypeptide chains - 2 alpha and 2 beta

Each chain contains a haem prosthetic group

Question 3

What type of curve does haemoglobin show on binding to oxygen?

Answer 3

A sigmoidal curve

Question 4

What gives haemoglobin its shape of binding curve?

Answer 4

It can move between the T state and the R state

Question 5

What does the binding of oxygen in haemoglobin promote?

Answer 5

The R state

Question 6

What is meant by ‘cooperative binding’ of haemoglobin?

Answer 6

The binding of one oxygen molecule promotes the binding of subsequent oxygen molecules

Question 7

What effect does 2,3-BPG have on the affinity of haemoglobin for oxygen?

Answer 7

2,3-BPG decreases its affinity by stabilising the T state

Question 8

How do H+ and carbon dioxide affect haemoglobin’s affinity for oxygen?

Answer 8

Decrease its affinity - the Bohr effect

Question 9

How does foetal haemoglobin differ to the mother’s haemoglobin (affinity)

Answer 9

It has a higher affinity

Question 10

What is the mutation in sickle cell anaemia?

Answer 10

Glutamate (negative hydrophilic) to valine (neutral hydrophobic)

Question 11

What happens to BPG concentrations at high altitudes and what effect does this have?

Answer 11

Increases. This promotes oxygen release at tissues from haemoglobin

Question 12

What type of inheritance is sickle cell anaemia?

Answer 12

Autosomal recessive

Question 13

In sickle cell anaemia, what is the result of the mutation?

Answer 13

A sticky hydrophobic pocket forms allowin deoxygenated haemoglobin to polymerise.

Question 14

Why are sickle cells bad?

Answer 14

More prone to lysis and leading to anaemia

More rigid so block microvasculature

Question 15

What are thalassaemias?

Answer 15

A group of genetic disorders where there is an imbalance in the alpha and beta sub-units in haemoglobin.

Question 16

What is beta-thalassaemia?

Answer 16

Decreased/absent beta chain production so alpha chains are unstable to form tetramers

Question 17

When do symptoms occur in beta-thalassaemia?

Answer 17

After birth

Question 18

When do symptoms occur in alpha-thalassaemia?

Answer 18

Before birth

Question 19

What is alpha-thalassaemia?

Answer 19

Decreased/absent alpha-chain production.

Question 20

What is the activation enthalpy?

Answer 20

The minimum energy a substrate must have for the reaction to occur

Question 21

What is the transition state?

Answer 21

The high energy intermediate between substrate and product

Question 22

How does increasing the temperature increase the rate of an enzyme reaction?

Answer 22

Increases the number of molecules with the activation enthalpy.

Question 23

How does increasing the concentration increase the rate of an enzyme reaction?

Answer 23

Increases the chance of molecular collisions

Question 24

What is an enzyme?

Answer 24

A biological catalyst that increases the rate of a reaction by lowering the activation enthalpy

Question 25

What does Vmax mean?

Answer 25

Maximal rate when all active sites are saturated with substrate

Question 26

What is Km?

Answer 26

The substrate concentration that gives half of the maximal velocity

Question 27

Does a low Km mean an enzyme has a high or low affinity for its substrate?

Answer 27

High affinity

Question 28

In a Lineweaver-Burk plot, what does the intercept at the x-axis mean?

Answer 28

-1/Km

Question 29

In a Lineweaver-Burk plot, what does the gradient of a line mean?

Answer 29

Km/Vmax

Question 30

In a Lineweaver-Burk plot, what does the intercept at the y axis mean?

Answer 30

1/Vmax

Question 31

What is an enzyme inhibitor?

Answer 31

Molecules that slow down or prevent an enzyme reaction

Question 32

What type of bonds do irreversible inhibitors form?

Answer 32

Covalent bonds

Question 33

Do competitive inhibitors affect Vmax or Km?

Answer 33

Km

Question 34

Do non-competitive inhibitors affect Vmax or Km?

Answer 34

Vmax

Question 35

What is product inhibition?

Answer 35

The build of a product inhibits an enzyme reaction

Question 36

What is an allosteric enzyme?

Answer 36

A multi-subunit enzyme with more than one active site for the substrate

Question 37

What do allosteric activators do?

Answer 37

Increase the proportion of enzymes in the R state

Question 38

Which way do allosteric inhibitors shift the sigmoid curve for the rate of an enzyme reaction?

Answer 38

To the right

Question 39

Name two allosteric activators

Answer 39

AMP | Fructose-2,6-bis phosphate

Question 40

Name two allosteric inhibitors

Answer 40

ATP, citrate, H+

Question 41

What type of enzyme is phosphorylation catalysed by?

Answer 41

A kinase

Question 42

What is phosphorylation?

Answer 42

The addition of a phosphate group to an -OH group on an amino acid

Question 43

What is a zymogen?

Answer 43

The inactive precursor of a proteolytic enzyme

Question 44

Give examples of enzymes which have zymogens

Answer 44

Digestive enzymes eg pepsin, chymotrypsin, trypsin | Some protein hormones eg insulin

Question 45

What activates the intrinsic pathway for the clotting cascade?

Answer 45

Membrane damage

Question 46

What is a zymogen?

Answer 46

An inactive precursor of an enzyme

Question 47

What initiates the intrinsic pathway of the clotting cascade?

Answer 47

Damage to endothelial lining of blood cells. This releases factor 12.

Question 48

What initiates the extrinsic pathway

Answer 48

Trauma to tissue. This releases factor 3.

Question 49

Give an example of an enzyme which is controlled allosterically and name it's inhibitors and activators.

Answer 49

Phosphofructokinase Activators: AMP, fructose 2,6-bisphosphate Inhibitors: ATP, citrate, H+

Question 50

Give an example of an enzyme inhibited by substrate/product concentration

Answer 50

Hexokinase in glycolysis. | Inhibited when glucose 6-P concentration increases.

Question 51

Give two examples of zymogens and their active enzymes

Answer 51

Trypsinogen ➡️ trypsin Pepsinogen ➡️ pepsin Prothrombin ➡️ thrombin Fibrinogen ➡️ fibrin