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Biochem Ca1 Cram > Hb > Flashcards

Hb Flashcards

1
Q

Where is Hb found

A

Only in rbc

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2
Q

2 functions of Hb

A
  1. Transports O2 to tissues (main function)
  2. Transports CO2 and protons to lungs
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3
Q

Describe structure of Hb

A

Tetrameric protein – 4 subunits (a1,2 & B1,2)
2 identical dimers

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4
Q

Hb molecular weight

A

64500

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5
Q

2 Parts of Hb and makeup

A

• Two parts
haem (prosthetic group)
Globin

haem + globin = Hb

Prosthetic Apo. Holo
Group + Protein = Protein

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6
Q

Describe Mb and B globin chains of Hb

A
  • 8 α helical regions
  • Similar II ry and III ry structures -
  • But differ in I ry structure,
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7
Q

a globin chains

A
  • 7 α helical regions
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8
Q

• Where is haem found ?

A
  • in a hydrophobic pocket found between E & F helices of the globin.
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9
Q

Describe structure of Haem

A

. 4 pyrrole rings linked together thru methenyl bridges to make cyclic molecule porphyrin ( protoporphyrin IX)

. Protoporphyrin IX binds to Fe2+ to make Haem
. Fe2+ can form five or 6 covalent bonds depending on whether or not oxygen is bound to it

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10
Q

Describe bonds in Hb quartenary structure

A
  • Weak ionic and
    H bonds between the dimers

-Mainly strong hydrophobic interactions in between the members of the dimer ( B2-a2 and a1-B1)

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11
Q

Oxygenation of Hb leading to conformational changes

A

Iron moves towards the plane of haem when O2 is bound

Iron moves towards the plane of haem
Movement of the globin chains
Rupture of ionic and H bonds between 2 dimers

In R form ( Relaxed form = O2 bound ), rotation of αβ dimers
Changes in tertiary, quaternary structures
Increase affinity for O2 in other deoxygenated haem

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12
Q

4 things that affect ability of Hb to reversible bind to to O2

A
  1. pO2 (through haem-haem interactions)
  2. pH (of the environment)
  3. pCO2
  4. 2,3-bisphosphoglycerate (availability)
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13
Q

What is Cooperative oxygen binding ( haem-haem interaction)

A

Binding of 1 O2 to 1 haem group
Inc. O2 affinity other haem groups in Hb.
Affinity for the last O2 is 300 times more than for 1st.

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14
Q

What is 2,3 - bisphosphoglycerate ? How is it synthesised ? 3 functions ?

A

• Most abundant organic phosphate in RBC
• Synthesized from an intermediate of glycolytic
pathway

• Decreases oxygen affinity to Hb by binding to deoxyHb
• 2,3 BPG promotes efficient release of O2 by stabilizing T form of Hb
• Facilitates release of O2

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15
Q

How does 2,3- BPG (a.k.a 2,3 - DPG)modulate O2 release ?

A

1.when O2 is unloaded (deoxy Hb) b Chains pulled apart 2,3-BPG fits into the central pocket = Since pocket has positively charged amino acids and 2,3 BPG has negatively charged phosphate groups, ionic bond formed
2. Stabilize T form of Hb
3. Reduce O2 affinity

• When oxygenated
2,3-BPG is pushed out

• Presence of 2,3 BPG reduces the affinity of Hb for O2 and shifts the oxygen dissociation curve to the right

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16
Q

Describe co2 transport by Hb

A

Most of CO2 is transported as bicarbonate
15% transported as carbamino- hemoglobin
Hb-NH2 + CO2 reversibly change Hb-NH-COO- + H+
CO2 stabilizes deoxy form of Hb

17
Q

Describe binding of CO to Haem

A

CO binds tightly but reversibly to haem (forms carbon monoxyhaemoglobin)

Cause Hb to become R form

Increases oxygen affinity

Shifts the oxygen saturation curve to left

Hb is unable to release O2 to tissues Affinity of CO is greater (about 200x) than O2

Affected HB is unable to release O2 to tissues

18
Q

Described globulin chains found In Hb?

A

• Hb has 2 identical dimers – Eg : (αβ)1 and (αβ)2
α like =α ,ζ
β like = β , γ , δ , ε
(ζ= zeta, γ= gamma, δ= delta, ε = epsilon )

19
Q

What embryonic Hb formed in 1st 3 months of Intra uterine life synthesised in yolk sac

A

Hb Gower 1 = ζ 2ε 2 (zeta , epsilon)
Hb Portland = ζ 2 γ 2 (zeta, gamma)

20
Q

What is fetal Hb

A

FetalHb=HbF
- α2 γ2
Main type in fetus and new born (60%)
Levels falls by 6-12 months after delivery
< 2% in normal adults
Synthesis occurs in the fetal liver

21
Q

What is Adult Hb and when is it formed

A

• HbA is formed from 8th month onwards in the bone marrow
• Gradually replace HbF
• HbA1 = α2 β 2 >90%
• HbA2 = α 2 δ 2 2 %
- HbA2 is the minor adult Hb type

22
Q

Sites of erythropoiesis preconceptual and postnatal

A

Yolk sac pre week 6
Liver starts ariund week 6 until 36
Spleen starts week 12 till birth
Bone marrow around week 18 onward

23
Q

Functional difference between HbA and HbF

A

γ chains of HbF lacks (+) vely charged amino acids
HbF binds weakly with 2,3 – BPG
HbF has higher affinity for oxygen

24
Q

What is Glycosylated/ glycated Hb = HbA1C ?

A

Glucose covalently binds to the β chains
non-enzymatically
Reflects blood glucose concentration over a period
HbA1c test normal - 4.5-5.6% , prediabetes 5.6-6.5, diabetes >6.5

25
Q

Where does Haem synthesis in adults occur

A

• In adults mainly occur in ,
Bone marrow –(85%) - at a constant rate
Liver - (15%) – variable rate

26
Q

Synthesis of Hb

A

• Haem in mitochondria
• Globin in polyribosomes
• Mature RBC lacks mitochondria - unable to synthesize haem

27
Q

5 important points about Haem synthesis

A

• 8 enzymes
• Are irreversible reactions
• 1st step and last 3 steps in mitochondria
• Rest in cytoplasm
• Colourless intermediates are known as Porphyrinogens

28
Q

Steps of Haem synthesis

A

In mitochondria
1. Succinyl–CoA + Glycine
To. ALA Synthase catalyst
δ- Amino levulinic acid (ALA).

• Committed step and rate limiting step in hepatic porphyrin synthesis
• Coenzyme. Pyridoxal phosphate

In cytoplasm
2 ALA
TO Heavy metals (ex: Lead )
ALA dehydratase
Porphobilinogen

In cytoplasm
4 Porphobilinogen
TO
Hyroxymethylbilane
TO
Uroporphyrinogen III
TO
Coproprophyrinogen III

In mitochondria

Protoporphyrin IX
Heavy
To metals
Ferrochelatase
Fe2+ added

haem

29
Q

What Control haem synthesis - In liver

A

Excess haem ( Fe 2+). To. Hemin/Hematin (Fe3+)

30
Q

Consequence of Haem synthesis

A
  1. feedback inhibition
  2. Repression of ALA synthase
  3. Inhibition of transport of ALA synthase from cytosol to mitochondria
31
Q

3 Causes of extra Haem

A

Drugs (phenobarbital, insecticides, carcinogens)

32
Q

2 ways Control of haem synthesis - In bone marrow,

A
  1. Erythropoietin
  2. Availability of intracellular iron
33
Q

Iron-mediated regulation of ALAS mRNA translation

A

Adequate iron
To
Causes increased translation of ALA synthase mRNA
To
haem synthesis stimulated

34
Q

Importance of iron in Hb synthesis

A

• 2/3rd of body iron stores in Hb
• Inadequate iron
Iron deficiency anemia
Small red cells
with low amounts of Hb.
Called “ Microcytic hypochromic anemia”

35
Q

What is Porphyrias

A

• Rare , inherited (or occasionally acquired)
• Several types
• Classified as hepatic or erythropoeitic porphyrias
Deficiency of enzymes of haem synthesis
Causes Accumulation and inc. excretion of porphyrins or porphyrin precursors.

36
Q

What causes symptoms vary in phorphyrias

A

Symptoms vary depending on
Affected enzyme
 Severity of deficiency
 Type – hepatic / erythropoietic
“Porphyria “ means purple colour caused by
porphyrins in urine.

37
Q

3 clinical features of porphyrias

A

• Photosensitivity
• Neurological symptoms
• Urine darkens on exposure to light and air. (purple)

Biochem Ca1 Cram (13 decks)

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