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EOM 1 - Test 1 > Lecture 9: Myoglobin/Hemoglobin > Flashcards

Lecture 9: Myoglobin/Hemoglobin Flashcards

Myoglobin and Hemoglobin

1
Q

Define Cooperativity

Example?

A

In multisubunit proteins, conformational changes in one subunit can affect the others (up or down)

Hemoglobin’s sigmoidal curve following binding/release of O2

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2
Q

Why must transition metals be contained within groups, e.g. why can’t they free float through the body bound to O2?

A

Their bonding would generate harmful free radicals

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3
Q

Where is myoglobin found?

A

Muscle

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4
Q

What causes hemoglobin to have greater oxygen deliver and release?

A

Tetrameric Structure

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5
Q

At low Oxygen levels, which will have bind faster–myoglobin or hemoglobin?

A

Myoglobin

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6
Q

How are the structures of hemoglobin and myoglobin similar and different?

A

Myoglobin is single polypeptide, Hemoglobin is a tetramer

Each polypeptide of hemoglobin is similar to myoglobin, and each contains a heme.

They have completely different amino acid primary sequences.

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7
Q

What is the overall structure of hemoglobin?

A

α2β2 tetramer

a = 141 AA

b = 146 AA

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8
Q

What is the prosthetic group in hemoglobin and myoglobin?

Oxygen will only bind to what state of Fe?

A

Porphyrin, which binds to an Iron (Fe) atom–resulting in Heme

(+2) Oxidation State

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9
Q

What is the result of O2 binding to Fe2+ in Heme in Myoglobin?

What ligand does the Iron move toward?

A

The Fe atom is pulled closer into the porphyrin ring, causing conformational changes

Proximal Histidine

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10
Q

What are the characteristics of the T-state of Hemoglobin?

A

T = TENSE state

More interactions

More stable

Lower Affinity for O2

Think Muscles here

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11
Q

What are the characteristics for the R-state of Hemoglobin?

A

R=RELAXED

Fewer Interactions, more flexible

Higher Affinity for O2

Think Lungs Here

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12
Q

What is the difference between Positive and Negative cooperativity?

A

Positive: First event INCREASES affinity for remaining sites

Negative: First event DECREASES affinity for remaining sites

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13
Q

An increase in [H+] causes what change to hemoglobin?

A

Release O2

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14
Q

What state is stabilized by 2,3-BPG?

A

T-State (deoxy Hb)

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15
Q

What conformational change does pH have on Hemoglobin?

A

As pH decreases, H+ becomes available to protonate His146 which forms a salt-bridge with Asp94

Stabilizes the T-state

O2 is released at the tissues

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16
Q

What does the pH difference between the lungs and tissues result in?

A

Efficiency of O2 transport; favors release in tissues and uptake in lungs

17
Q

What role does Hemoglobin have in CO2 management?

What does this result in?

How is the majority of CO2 exported?

A
  1. 15-20% exported via carbamate on the amino terminal residues
  2. Increased H+ concentration (release of O2)
  3. Further salt bridges (stabilize T-state)
  4. Disolved bicarbonate
18
Q

What is the source is much CO2 in the tissues?

What role does this have?

A

By-product of the Krebs Cycle

Increases release of O2 by hemoglobin

19
Q

Why is it important for 2,3-BPG to be released in the placenta?

A

HbF has a much lower affinity for 2,3-BPG; however the placenta gives extra O2 which can bind with HbF

20
Q

Why does CO bind 20,000x greater than O2 to Hb?

What can lower this ratio to 250x greater?

What are the physiological results of bound CO?

A

Forms triple bond

Distal-Histidine in the protein pocket

Hint: DIKEMBE Histidine

Blocks function of myoglobin, hemoglobin, and mitochondrial cytochromes

21
Q

What are the structures for:

Normal Adult HbA:

HbA2:

Sickle Cell HbS:

Infant HbF:

HbA1C:

A

HbA: α2β2

HbA2: α2δ2

HbS: α2βs2

HbF: α2γ2

HbA1C:α2β2-glucose

22
Q

Why does HbF have a higher affinity for O2?

Why is this non-optimal postpartum?

A

It must extract oxygen from the mother’s blood, so it must have a greater affinity than HbA

This greater affinity would result in low quantities of oxygen delivered to the tissues post-partum

23
Q

What is the cause of Sickle Cell Anemia (HbS)?

What is the half life for an HbS RBC?

A

Hb Glu -> Cal 6

(polar to non-polar)

20 days

24
Q

What is source of Hemoglobin C?

What is source for Hemoglobin SC?

A

Conversion of Glu6 → Lys6 in β-globin gene

One β-globin gene codes for HbS, other HbC

25
Q

What is Methemoglobinemia?

In severe cases, what is treatment?

A
  1. Hb with Fe3+ (not 2+), which results in reduced ability to carry oxygen

NADH-methemoglobin reductase deficiency will result in cyanosis (Papa Smurf Syndrome)

  1. Methylene Blue

EOM 1 - Test 1 (16 decks)

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