Lecture 7 - Proteins in Action - Haemoglobin & Myoglobin (Similarities & Differences)

Question 1

Myoglobin (muscle globin)

Protein Primary structure

Answer 1

~ 150 amino acids

Question 2

Myoglobin (muscle globin)

Protein secondary structure

Answer 2

Eight a-helices

A-H and connecting loops (AB, BC, etc.)

Question 3

Myoglobin (muscle globin)

Tertiary structure

Answer 3

globin fold with a Hydrophobic pocket (Val E11 and Phe CD1) to bind a haem group.

Question 4

Myoglobin (muscle globin)

Quaternary structure

Answer 4

monomeric (a single polypeptide chain)

Question 5

Haem binds to

Answer 5

His F8 (the eighth amino acid in helix F, histidine) in globin protein.

bound in deep pocket

Question 6

Haem (heme) is a

Answer 6

prosthetic group, or cofactor.

Question 7

Haem has 4

Answer 7

pyrrole rings linked together (a protoporphyrin) in a plane

Question 8

How many co-ordinate bonds does Iron have in heme?

Answer 8

6 coordinate bonds –

4 to N of haem,
1 to N of histidine F8 the globin,
1 to O2

Question 9

what colour does Electronic molecular orbitals of protoporphyrin give?

Answer 9

red

Question 10

Is Binding of oxygen to the Fe2+ is a reversible interaction?

Answer 10

yes

Question 11

Spectroscopy

Answer 11

quantifies dissolved molecules.

Question 12

Spectroscopy

Higher concentration =

Answer 12

less transmitted light

higher absorbance

Question 13

Beer-Lambert Law converts

Answer 13

from absorbance to concentration

Question 14

Spectroscopy of globins measures

Answer 14

oxygen binding

Question 15

Spectroscopy of globins

Shape of spectrum differs with

Answer 15

colour and with chemical nature of solute.

Question 16

Protein is colourless but has

Answer 16

UV absorbance

Question 17

Haem has

Answer 17

visible absorbance and therefore colour

Hb bright red
HbO2 dull red

Question 18

oxyhaemoglobin (Hb) colour

Answer 18

bright red

Question 19

deoxyhaemoglobin (HbO2) colour

Answer 19

dull red

Question 20

What does Myoglobin do?

Answer 20

Stores Oxygen

in the tissue and increases the amount that can be there above its natural solubility

Question 21

Globin Fold provides a

Answer 21

hydrophobic pocket (Val E11 and Phe CD1) to bind a haem group.

Question 22

Different wavelengths are

Answer 22

absorbed more

less efficiency

Question 23

Myoglobin - Haem interaction with oxygen
(incl where heme sits, O binds to, heme held by what bond and between what, hydrophobic interactions, Iron, His E7, O affinity)

Answer 23

Haem sits between His F8 and His E7.

Oxygen binds on His E7

Haem held by a covalent bond between His F8 and Fe2+.

Hydrophobic interactions with Phe CD1 and Val E11.

Leaves the 6th position of iron to bind to oxygen

Large shift of His E7 when oxygen binds there

Reduces O binding affinity to myoglobin, makes easier to release O to muscle cell.

Question 24

Oxygen binding changes

Answer 24

haemoglobin’s shape.

Question 25

Deoxyhaemoglobin heme shape

Answer 25

dished haem.

Question 26

oxyhaemoglobin heme shape | what happens

Answer 26

O flattens haem pulls histidine F8 and helix F toward the binding site. Anything that keeps helix F away will weaken oxygen binding.

Question 27

Myoglobin shows

Answer 27

‘allosteric control’ of oxygen affinity

Question 28

how does Lactate effect myoglobin?

Answer 28

decreases myoglobin’s affinity for oxygen. Does not bind where oxygen binds.

Question 29

Lactate build up in muscles promotes

Answer 29

O release from myoglobin, increase O2 availability for respiration.

Question 30

‘Allosteric’

Answer 30

“without overlapping”. Not binding in the same place as oxygen. For enzymes away from the active site. For carrier proteins (haemoglobin and Myoglobin) away from the binding site for its ligand (oxygen).

Question 31

‘allosteric’ builds on

Answer 31

‘steric hindrance’, the impossibility of two atoms occupying the same space.

Question 32

Myoglobin binds

Answer 32

quite tightly to oxygen

Question 33

lactate binding to myoglobin

Answer 33

releases more oxygen

Question 34

When muscle is short of oxygen

Answer 34

it generates lactate.

Question 35

what curve shows myoglobin bind to O?

Answer 35

Hyperbolic curve

Question 36

To get myoglobin to release O need to go into

Answer 36

highly active tissue with oxygen pressure very low

Question 37

Binding curve / saturation curve. | Myoglobin

Answer 37

O2 saturated at low pO2 only releasing O2 to muscle cells when pO2 is very low. function “back-up” store of O2 in muscle cells.

Question 38

partial pressure of oxygen in | lungs, or pO2,

Answer 38

~100 Torr

Question 39

partial pressure of oxygen in resting muscle or pO2,

Answer 39

~ 20 Torr.

Question 40

haemoglobin functioning as an O2 transporter in blood evolved a much weaker binding affinity for oxygen. Why?

Answer 40

curve is ‘sigmoidal’.

Question 41

The availability of O2 to cellular proteins depends on:

Answer 41

- The pO2 in the local environment | - The binding affinity of O2 to myoglobin or haemoglobin

Question 42

Haemoglobin in RBC in the blood needs to

Answer 42

- Bind O2 in lungs where pO2 is ~100 Torr | - Release O2 in peripheral tissues where pO2 is ~20 Torr

Question 43

Haemoglobin evolved to bind O2

Answer 43

less tightly.

Question 44

Haemoglobin

Answer 44

tetramer – 4 globin proteins together non-covalently Each globin protein contains 1 haem and each can bind 1 O2

Question 45

Myoglobin

Answer 45

monomer acts as O2 store in muscle

Question 46

Two interchangeable crystal morphologies reveal two...

Answer 46

hemoglobin conformations

Question 47

Aerobic exposed to Oxygen crystal morphologies...

Answer 47

Interface of air and protein solution | Needle-shaped crystals

Question 48

Anaerobic zone no oxygen crystal morphologies...

Answer 48

Hexagonal, plate-shaped crystals

Question 49

In both Haemoglobin and Myoglobin

Answer 49

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). a-helices forms a hydrophobic cleft that holds the haem where oxygen binds

Question 50

Myoglobin versus haemoglobin

Answer 50

Monomer versus tetramer Tighter, hyperbolic (in myoglobin) versus weaker, sigmoidal binding curve (haemoglobin) Store in tissue versus transport molecule