11 - Hemoglobin Structure and Function Flashcards

1
Q

What is the most common biological function of globular proteins?

A

The precise binding of ligands

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2
Q

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

A

The heme group, for the reversible binding of oxygen

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3
Q

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

A

A central iron (Fe) loosely bonded to 4 nitrogens

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4
Q

Where is myoglobin mostly found?

A

Cardiac and skeletal muscle

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5
Q

What is the protein component of myoglobin called?

A

Globin

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6
Q

What is the structure of the single protein globin?

A

A single protein with eight α-helices

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7
Q

What are the two structural components of myoglobin?

A

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

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8
Q

Where is hemoglobin found?

A

Red blood cells

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9
Q

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

A

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.

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10
Q

What is the primary function of hemoglobin

A

To transport oxygen from the lungs to tissues

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11
Q

What are the four subunits of hemoglobin?

A

α1
α2
β1
β2

Each subunit contains a heme group that binds reversibly with oxygen

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12
Q

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

A

α1β1 α2β2

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13
Q

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

A

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

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14
Q

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

A

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

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15
Q

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

A

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

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16
Q

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

A

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).

17
Q

What state is deoxygenated hemoglobin in?

A

The T (taut) state

18
Q

What state is oxygenated hemoglobin in?

A

The R (relaxed) state

19
Q

How many stable states does hemoglobin have?

A

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

20
Q

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

A

Cooperative binding, this causes a sigmoidal oxygen dissociation curve.

21
Q

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

A

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

22
Q

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

A

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.

23
Q

How does hydrogen change the configuration of hemoglobin?

A

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

24
Q

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

A

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.

25
Q

Where does BPG come from?

A

It is an intermediate in breakdown of glucose (glycolysis)

26
Q

What are classical motors (of molecular machines)?

A

Myosins, dyneins and kinesin

27
Q

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

A

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.

28
Q

What are microprocessing switching devices (molecular machine type)

A

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

29
Q

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

A

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.

30
Q

What are the four classes of molecular machines?

A

Classical motors
Timing devices
Microprocessing switching devices
Assembly and disassembly factors