Protein Function

Question 1

Describe the structure of myoglobin

Answer 1

Single subunit containing 1 haem group for binding and transporting of O2
153aas
Interior composed of mostly non polar AAs packed closely together forming a structure stabilised by hydrophobic interactions
Haem group contained in crevice in molecule

Question 2

Where can you find myoglobin?

Answer 2

Skeletal muscle and heart

Question 3

What type of binding does myoglobin show ?

Answer 3

Hyperbolic O2 binding- no cooperativity

Question 4

Describe the structure of haem

Answer 4

Consists of a portoporphyrin ring and an Fe atom, which is bound to 4 N atoms of the ring

Question 5

What happens when O2 binds to haem?

Answer 5

As O2 binds the Fe ion pulls on the rest of the polypeptide changing the conformation from Tstate to Rstate

Question 6

Describe the structure of haemoglobin

Answer 6

Tetraemric protein (2a and 2B)

Question 7

What type of binding does Hb show?

Answer 7

Sigmoidal binding - shows cooperativity

Question 8

What happens when 2,3-bisphosphoglycerate binds?

Answer 8

It acts to decrease the affinity of Hb to O2 therefore moves the sigmoid curve to the right

Question 9

Why is the binding of 2,3-BPG good?

Answer 9

It is produced during metabolism, so more O2 is released in tissues performing increased amounts of metabolism

Question 10

What does the binding of CO2 and H+ do and what is it called?

Answer 10

Decreases the affinity of Hb for O2

Bohrs shift

Question 11

Talk me through CO poisoning

Answer 11

CO binds 250x more readily to Hb than O2
Is a poison as binds to ferrohaemoglobin and ferromyoglobin and blocks O2 transport
Fatal when CO is >50%
CO bindings actually acts to increase the affinity of the unaffected subunits to O2

Question 12

What are the 3 types of Hb?

Answer 12

HbA
HbF
HbA2

Question 13

Why does HbF have a higher affinity than HbA to o2 ?

Answer 13

HbF is the major Hb in foetal blood
The foetus needs to get O2 from the maternal blood supply therefore it needs to have a higher affinity to the O2 than the maternal Hb (HbA ) so it can actually get O2

Question 14

Why does sickle cell anaemia occur?

Answer 14

Autosomal recessive genetic blood disorder caused by a mutation of glutamate —> valine in B globulin (HbS)

Question 15

What does this mutation cause?

Answer 15

Sticky hydrophobic pockets to form by valine as it allows deoxygenated HbS to polymerise

Leads to distortion of RBCs into sickle cell shape

Question 16

What does the change in shape cause?

Answer 16

Stress to cell membrane
Premature cell lysis
Blocks microvasculature

Question 17

What is thalassaemia?

Answer 17

Group of genetic disorders with imbalance between a and B chains

Question 18

Describe B thalassaemia

Answer 18

Decreased or absent B chains
a chains unable to form stable Tetramers
Symptoms appear after birth

Question 19

Describe a thalassaemia

Answer 19

Decreased or absent a chains
Several levels of severity due to multiple copies of the a-chain gene present
B chains cam form stable Tetramers with increased affinity for O2
Onset before birth

Question 20

How do enzymes work ?

Answer 20

By lowering the activation energy of the reaction by the binding if the substrate to the active site which increases its local conc and stabilises the formation of the high energy transition state

Question 21

What may be needed for an enzymatic reaction?

Answer 21

Additional co factors or co enzymes

Question 22

Do the enzyme affect the =bm?

Answer 22

NO

Question 23

What is the Vmax?

Answer 23

Maximal rate of the enzyme when it is saturated with substrate

Question 24

What is Km?

Answer 24

Substrate conc giving half of maximal velocity

Question 25

2 main types of inhibitors

Answer 25

Irreversible

Reversible

Question 26

Two types of reversible inhibitors

Answer 26

Competitive

Non competitive

Question 27

Differences between competitive and non competitive inhibitors

Answer 27

Competitive = binds at active site, reduces Km but Vmax stays the same

Non competitive = binds at other site to active site, reduces Vmax but keeps Km the same