Myoglobin

Question 1

What is myoglobin and what is it abbreviated to

Answer 1

It’s found in muscle
It binds to oxygen in muscles
Mb is its abbreviation

Question 2

Write the equation for the forward and backward reaction between myoglobin and oxygen . What is this kind of reaction called

Answer 2

Question 3

What is the dissociation constant

Answer 3

Question 4

What is the equation for the fraction of myoglobin that has oxygen bound to it (initial and derived equation)

Answer 4

Underlined in purple

Question 5

What is a saturation binding curve

Answer 5

Shows the fraction of myoglobin saturated with oxygen at a particular partial pressure of oxygen

Question 6

Why does the curve on a saturation binding curve never reach the asymptote

Answer 6

Because in order for myoglobin to be completely saturated it would have to bind to an infinite amount of oxygen

Question 7

What is a Torr

Answer 7

Unit for partial pressure
1 Torr= 133 Pa

Question 8

What is the ratio of unprotonated to protonated histidine molecules

Answer 8

80% of histidine is unprotonated
20% of histidine is protonated

Question 9

What are the two resonance forms for protonated histidines side chain? Show the displayed formula and the distribution of electrons in molecular orbitals

Answer 9

All of the atoms in histidine side chain are sp2 hybridised
It can have resonance forms because one of the nitrogen’s only have one elctron in its p orbital whereas the other nitrogen has two electrons in its p orbital
(When nitrogen that is bonded to hydrogen it has 2 electron sin its p orbital)

Question 10

Show the displayed formula and the distribution of electrons in molecular orbitals of the two tautomers of histidine

Answer 10

Question 11

Show the protonation reaction of histidines side chain

Answer 11

Question 12

Show the deprotonation (of the protonated form) of histidines side chain

Answer 12

Question 13

What are prosthetic groups

Answer 13

Non polypeptide parts that are added to a protein

Question 14

What coordination does iron have and how are the ligands arranged around iron

Answer 14

Question 15

What is a ligand according to chemistry’s definition

Answer 15

They are donors of a pair of electrons

Question 16

How is porphyrin converted to heme

Answer 16

Question 17

Label the alpha helices in this myoglobin. Where would heme be in myoglobin

Answer 17

Question 18

How does oxygen bind to heme in myoglobin

Answer 18

Oxygen will be bound tilted, in the axial position to iron in heme

Question 19

Why does oxygen bind to heme in myoglobin tilted

Answer 19

The distal histidine imposes a steric constraint on the binding site, preventing oxygen from binding perpendicularly to the plane of the heme. Instead, oxygen binds at an angle to avoid a steric clash with this histidine residue

The tilted binding allows for optimal orbital overlap between the iron atom and the oxygen molecule, which stabilizes the oxygen-heme complex

The distal histidine can form a hydrogen bond with the bound oxygen molecule. This hydrogen bond helps stabilize the oxygen in its tilted position.

makes it easier for myoglobin to release oxygen under low-oxygen conditions as this binding is less stable

Question 20

What is heme

Answer 20

It is a the part of myoglobin that oxygen binds to
Heme is neutral

Question 21

What is the partial pressure of the atmosphere and what percentage of the atmosphere is oxygen

Answer 21

20% of the atmosphere is oxygen
Partial pressure is 750 Torr

Question 22

What is the partial pressure of oxygen in the atmosphere

Answer 22

150 Torr

Question 23

What is the partial pressure of oxygen that muscles get from the blood stream

Answer 23

Question 24

What is the solubility of oxygen in water and in muscle with myoglobin

Answer 24

Question 25

What is a ligand according to biochemistry

Answer 25

A molecule that binds reversible, forming a complex with a protein
E.g oxygen is a ligand for Mb

Question 26

What does it mean if Kd (dissociation constant) is high and if its low

Answer 26