Proteins - Lecture Seven

Question 1

Myoglobin (muscle globin)

Answer 1

Stores oxygen in the tissue

Question 2

Myoglobin primary structure

Answer 2

~150 amino acids

Question 3

Myoglobin secondary structure

Answer 3

Eight alpha-helices (A-H)
Connecting loops (AB, BC, etc)

Question 4

Myoglobin tertiary structure

Answer 4

Globing folds with a hydrophobic pocket

Question 5

Myoglobin quaternary structure

Answer 5

Monomeric (single polypeptide chain)

Question 6

Globin fold

Answer 6

Provides a hydrophobic pocket to bind a haem group

Question 7

Haem

Answer 7

Four pyrrole rings linked together (a protoporphyrin) in a plane that binds to His F8 in globulin protein

Question 8

Iron

Answer 8

Six coordinate bonds- 4 to N atoms of the haem, 1 to a N atom of histidine F8 the globin, 1 to O2 which bonds off at an angle. The double bonds are very hydrophobic

Question 9

Binding oxygen to the Fe2+

Answer 9

Is reversible interaction

Question 10

Electronic molecular orbits of protoporphyrin

Answer 10

Gives red colour

Question 11

Beer-Lambert Law

Answer 11

Converts from absorbance to concentration

Question 12

Shape of spectrum

Answer 12

Differs with colour and with chemical nature of solute

Question 13

Haem spectrum

Answer 13

Has visible absorbance (and therefore colour) that differs between bright red oxyhemoglobin (HbO2) and dull red deoxyhaemoglobin (Hb)

Question 14

His E7

Answer 14

Located on opposite side of haem and distorts binding of gas molecules to 6th coordination positive of harm Fe2+, this reduces the binding affinity of oxygen to myoglobin, making it easier to release oxygen to the muscle cell

Question 15

Binding affinity

Answer 15

Strength of the binding interaction between a single biomolecule

Question 16

Deoxyhaemoglobin

Answer 16

Dished haem

Question 17

Oxyhaemoglobin

Answer 17

Flat haem

Pulls histidine F8 and helix F towards the binding site, anything that keeps helix F away will weaken oxygen binding

Question 18

Allosteric control

Answer 18

Type of enzyme regulation involving the binding of a non-substrate molecule at locations on the enzyme other than the active site.

Question 19

Lactate

Answer 19

Decreases myoglobin’s affinity for oxygen but does not bind where oxygen binds but somewhere else on the myoglobin
Lactate build up in muscles promotes oxygen release from myoglobin, increasing O2 availability for respiration

Question 20

Myoglobin at low pO2

Answer 20

Is O2 saturated and only releases O2 ay low pO2

Question 21

pO2 in lungs

Answer 21

~100 Torr

Question 22

pO2 in resting muscle

Answer 22

~20 Torr

Question 23

The availability of O2 to cellular proteins depends on

Answer 23

The pO2 in the local environment

The binding affinity of O2 to myoglobin or haemoglobin

Question 24

Haemoglobin in red blood cells in the blood needs to be able to:

Answer 24

Bind O2 in the vicinity of the lungs where the pO2 is ~100 Torr
Release the O2 in the vicinity of peripheral tissues where the pO2 is ~20 Torr

Question 25

Haemoglobin

Answer 25

Four globin proteins associate together non-covalently
Each globin protein contains one haem and each can bind one O2 (1, 2, 3 or 4 O2 can bind per one Hb tetramer)
Haemoglobin is a tetramer instead of

Question 26

Similarities between haemoglobin and myoglobin

Answer 26

Oxygen binds to iron of haem
Shift from dull to bright red allows monitoring O2 binding
Affinity for oxygen is altered by molecules (e.g. lactate to myoglobin) binding elsewhere (allosteric control)

Question 27

Differences between haemoglobin and myoglobin

Answer 27

Monomer VS tetramer
Tighter, hyperbolic VS weaker, sigmoidal binding curve
Store in tissue VS transport molecule