11 - Hemoglobin Structure and Function

Question 1

What is the most common biological function of globular proteins?

Answer 1

The precise binding of ligands

Question 2

What is the prosthetic group on myoglobin and hemoglobin called and what does it do?

Answer 2

The heme group, for the reversible binding of oxygen

Question 3

What is the general structure of the heme group in hemoglobin and myoglobin

Answer 3

A central iron (Fe) loosely bonded to 4 nitrogens

Question 4

Where is myoglobin mostly found?

Answer 4

Cardiac and skeletal muscle

Question 5

What is the protein component of myoglobin called?

Answer 5

Globin

Question 6

What is the structure of the single protein globin?

Answer 6

A single protein with eight α-helices

Question 7

What are the two structural components of myoglobin?

Answer 7

A heme group enclosed by the eight α-helices of a globin protein

Question 8

Where is hemoglobin found?

Answer 8

Red blood cells

Question 9

Which two amino acids are attached to the heme group of hemoglobin? What are their proximities? What does this accomplish?

Answer 9

A distal and proximal histidine are bound to the heme group in hemoglobin. By making a folded globin chain, an oxygen-binding site (composed of heme and two histidines) is made.

Question 10

What is the primary function of hemoglobin

Answer 10

To transport oxygen from the lungs to tissues

Question 11

What are the four subunits of hemoglobin?

Answer 11

α1
α2
β1
β2

Each subunit contains a heme group that binds reversibly with oxygen

Question 12

It can be said that there are 2 identical dimers in hemoglobin composed of four chains. What are the subunits involved in each dimer?

Answer 12

α1β1 α2β2

Question 13

What is a HbA molecule and what is it composed of?

Answer 13

Two α-chains and two β-chains, each chain being 1 subunit of 4 in hemoglobin.

Question 14

What is the HbA2 molecule and what is it composed of? How much of it is found in adult humans?

Answer 14

The HbA2 molecule is another type of hemoglobin that contains δ-chains instead of β-chains. About 2% of adult hemoglobin is HbA2 hemoglobin

Question 15

How is embryonic and fetal hemoglobin different from adult hemoglobin? What is the result of this?

Answer 15

It has ε-chains and γ-chains rather than alpha and beta chains. ε and γ chains have a higher affinity for oxygen gas.

Question 16

What happens to hemoglobin when it is oxygenated? What is the consequence of this?

Answer 16

Oxygenation of hemoglobin causes the 4 dimers to slide by each other and rotate 15 degrees. This brings it into the relaxed state and facilitates the binding of oxygen to the other binding sites on the four heme groups (there are max four oxygens in total).

Question 17

What state is deoxygenated hemoglobin in?

Answer 17

The T (taut) state

Question 18

What state is oxygenated hemoglobin in?

Answer 18

The R (relaxed) state

Question 19

How many stable states does hemoglobin have?

Answer 19

Hemoglobin alternates between its two stable states, T and R.

Question 20

What is the continued facilitation of oxygen binding on hemoglobin as it converts to R state called?

Answer 20

Cooperative binding, this causes a sigmoidal oxygen dissociation curve.

Question 21

What is myoglobin’s dissociation curve shaped like? Why is it not like hemoglobin’s?

Answer 21

Myoglobin has a hyperbolic oxygen dissociation curve because it lacks cooperative binding.

Question 22

What effect does pH have on hemoglobin? What is this called?

Answer 22

A decrease in pH (rise in acidity) enhances oxygen release from hemoglobin. This is called the Bohr effect. Increased CO2 (eg. due to cellular respiration) therefore causes increased oxygen deposition into muscles due to increased proton concentration.

Question 23

How does hydrogen change the configuration of hemoglobin?

Answer 23

H binds to several ionizable groups on hemoglobin and shifts it to the T state, where it is more likely to release oxygen.

Question 24

What does BPG do? What is its full name? Where is it found in high concentrations?

Answer 24

BPG, 2,3-Bisphosphoglycerate regulates hemoglobin function, by lowering its affinity for O2 by binding two positive amino acids in the central cavity of heme. It is found mostly in red blood cells. Its actions are reversed in the lungs.

Question 25

Where does BPG come from?

Answer 25

It is an intermediate in breakdown of glucose (glycolysis)

Question 26

What are classical motors (of molecular machines)?

Answer 26

Myosins, dyneins and kinesin

Question 27

What are timing devices in molecular machines? What is an example?

Answer 27

NTP-binding proteins that provide a delay period during a complex process that endures accuracy. Often uses relatively slow rate of GTP hydrolysis. EF-Tu is an example in translation.

Question 28

What are microprocessing switching devices (molecular machine type)

Answer 28

A variety of GTP binding proteins that act as one and off molecular switches in signal transduction pathways. For example, G proteins.

Question 29

What are assembly and disassembly factors in terms of molecular machines?

Answer 29

Cause the rapid and reversibly assembly of protein subunits into larger molecular complexes. Eg. Tubulin and actin into microtubules and microfilaments, via hydrolysis of GTP and ATP, promote subtle conformation changes that later allow disassembly.

Question 30

What are the four classes of molecular machines?

Answer 30

Classical motors
Timing devices
Microprocessing switching devices
Assembly and disassembly factors