CGIER 35 - Haemoproteins I: Structures of haemoglobin and myoglobin

Question 1

haemoglobin

Answer 1

in red blood cells - responsible for O2 transport in higher animals.
Contains ~ 65% of the iron in the human body

Question 2

myoglobin

Answer 2

in muscle cells - stores O2 and transports it across muscle cells.
- Contains ~ 6% of the iron in the human body.

Question 3

relative molecular mass of haemoglobin and myoglobin

Answer 3

Haemoglobin RMM ~ 66000 (~66 kDa)

Myoglobin RMM ~ 17800 (~17.8 kDa)

Question 4

2 groups that make myoglobin

Answer 4

haem group

globin chain

Question 5

constituents of haem

Answer 5

iron (II) and protoporphyrin

Question 6

constituents of globin

Answer 6

153 – 160 amino acid residues

Question 7

primary structure of protein is held by what bonds

Answer 7

by covalent bonds such as peptide bonds

Question 8

secondary structure

Answer 8

refers to highly regular local sub-structures. Two main types of secondary structure, the alpha helix and the beta strand or beta sheets

Question 9

what defines secondary structure

Answer 9

These secondary structures are defined by patterns of hydrogen bonds between the main-chain peptide groups

Question 10

tertiary structure

Answer 10

refers to the three-dimensional structure of the protein. The alpha-helixes and beta pleated-sheets are folded into a compact globular structure.

Question 11

examples of tertiary interactions

Answer 11

salt bridges, hydrogen bonds, and the tight packing of side chains and disulfide bonds

Question 12

quarternary structure

Answer 12

the three-dimensional structure of a multi-subunit protein and how the subunits fit together.

Question 13

structural difference of haem and myoglobin

Answer 13

haem - 4 subunits quarterniary structure

myoglobin - tertiary structre

Question 14

protoporphyrin

Answer 14

Porphyrins – family of tetradentate, planar ligands.
4N donor atoms.
Heteroaromatic.
4 pyrrole-like rings joined by CH groups.
Peripheral substituents.

Question 15

in haemoglobin molecule how does the haem group link with the globin group

Answer 15

has compact shape with protein chain
histidine residue links haem group with globin chain called proximal histidine - one with closest proximmity to haem unit

Question 16

describe amphipathic qualty of myoglobin

Answer 16

interior - hydrophobic

exterior - hydrophilicOnly two hydrophilic residues inside, both histidines essential for biological activity.

Question 17

why is Fe II unsaturated

Answer 17

co-ordination no = 5

has less than max co-ordination number

Question 18

quality of haem group that allows complex with oxygen to form

Answer 18

It has a vacant coordination site which can be used to complex with O2.

Question 19

The haem group is a 1.___ crevice 2.(___). This is essential otherwise 3.___

Answer 19

1. non polar
2. hydrophobic
3. the oxidation of Fe(II) would occur in the presence O2 and H2O

Question 20

The haem group is placed in a 1.\_\_\_\_ to prevent 2.\_\_\_\_\_
Unlike iron (II) iron (III) can not 3.\_\_\_

Answer 20

1. non-polar crevice
2. oxidation of the metal ion.
3. bind O2.

Question 21

forms, ion and colour of myoglobin

Answer 21

Myoglobin 			Fe(II) 			 His 			purple red.
Oxymyoglobin		Fe(II)	     		His & O2		bright red
Metmyoglobin		Fe(III)	    		His & H2O   	brownish-															red
Metmyoglobin does not bind O2.

Question 22

example of high spin IN HAEMOATOPROTEINS

Answer 22

Fe(II) In myoglobin,

haemoglobin

Question 23

example of low spin haematoproteins

Answer 23

Fe(II) in oxymyoglobin

& oxyhaemoglobin

Question 24

high spin - paramagnetic

Answer 24

fill all d orbitals first singly before in pairs - low splittings

Question 25

low spin - diamagnetic

Answer 25

fill low energy d orbitals in pairs before filling high energy d orbitals singly because it requires more energy - high splitting

Question 26

myoglobin in high spin

Answer 26

Iron(II), d6, is high spin, lies out of the porphyrin plane and has one empty coordination site.

Question 27

oxymyoglobin

Answer 27

Iron(II) is low spin and smaller in size (electrons are concentrated into three orbitals), can now fit into the porphyrin plane and is coordinatively saturated (CN = 6).

Question 28

where are haems in haemoglobin

Answer 28

Haems in non-polar crevices

Question 29

3D structure of each globin in haemoglobin

Answer 29

3D structure of each globin chain in Hb very similar to that in Mb although amino acids are identical at only 24 positions.

Question 30

how many subunits in haemoglobin - describe subunit

Answer 30

4 subunits – each Mb-like
2α and 2β globin chains
Salt linkages between chains

Question 31

describe shape of haemoglobin with regards to subunit

Answer 31

A tetrameric protein (α2β2).
α chain – 141 a.a.
β chain – 146 a.a.

Question 32

desecribe alpha and beta chains

Answer 32

Each α is in contact with both β chains.

Very few interactions between the two α chains or between the two β chains.

Question 33

most important interaction with subunit in haemoglobin

Answer 33

salt bridge linkages. These can take various forms in

proteins.

Question 34

how does co-ordination number and spin change in haemoglobin when it binds to oxygen

Answer 34

CN = 6 (coordinatively saturated)

low spin, diamagneticiron in porphyrin plane

Question 35

iron (II) co-ordination number in myoglobin is 5 what does the iron bond to in order to get this co-ordination number

Answer 35

4 Nitrogens in porphyrin functional group = 4 bonds

Fe attaches to N from proximal histidine

Question 36

through what process does oxymyoglobin go through to become metmyoglobin

Answer 36

Oxidation

Question 37

how come the iron is able to fit in the porphyrin when it binds to oxygen

Answer 37

iron (II) changes from high spin to low spin from paramagnetic to diamagnetic and the electron density is now in the bottom rather than being distributed to all d orbitals due to high splitting, thus making it smaller. Moves from out of porphyrin plane to inside plane of ring
Now has a CN of 6 and is fully saturated

Question 38

what is salt bridge interaction

Answer 38

A salt bridge in proteins is an interaction

between oppositely charged amino acid side chains