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Biochemistry MBS > oxygen transporters > Flashcards

oxygen transporters Flashcards

1
Q

myoglobin

A

the oxygen transporter for muscle

-monomeric

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2
Q

prosthetic group of hemoglobin and its location

A
  • heme

- deep, nonpolar pocket which sequesters it from water and helps it to be in the +2 state

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3
Q

steric hinderance of carbon monoxide

-why this is important to myoglobin

A
  • oxygen binds to heme at a 120 degree angle whereas carbon monoxide binds at a 90
  • both oxygen and carbon monoxide must bind at 120 in myoglobin due to steric hinderance from a histidine residue
  • this allows for oxygen to bind more readily to myoglobin than carbonmonoxide (which is a biproduct of heme degradation)
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4
Q

when oxygen binds to myoglobin…

A

the structure changes a little bit but since it is a monomer, this has little significance

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5
Q

hemoglobin

A

composed of an alpha and a beta subunits (2 of each)

  • there is a heme in each subunit
  • globular
  • alpha and beta are nearly identical in sequence
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6
Q

Hill coefficient

A

-this defines the cooperativity of a molecule to its binding partner
->1 means positive cooperativity
-=1 no cooperativity
-

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7
Q

cooperativity of hemoglobin and myoglobin

A
  • myoglobin shows no cooperativity since there is onle one heme (n=1)
  • hemoglobin shows positive (n=2.8)
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8
Q

oxygen binding affinity of myoglobin and hemoglobin

A
  • myoglobin has a much higher affinity since it needs to carry oxygen in the muscle where oxygen concentration is very low
  • hemoglobin is more fit to deliver oxygen in other tissues throughout the body
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9
Q

T and R state of Hb

  • stability
  • contrast to myoglobin
A
  • T state is deoxygentated, Hb has the lowest affinity to oxygen in this state. this is a more stable form because it contains more electrostatic and hydrogen bonds (taut)
  • R state has an oxygen bound to heme, this triggers a conformational change in Hb. alpha subunit contacts the beta subunit, causing it take on the oxygen binding conf
  • thesse forms differ in the arrangement of the subunits
  • myoglobin is always set up to be a good oxygen acceptor
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10
Q

the bohr effect of Hb

A
  • H+ and CO2 reduce the O2 affinity of Hb
  • CO2 is in eq with carbonic acid and bicarb (pushes the dissociation curve to the right)
  • this allows H+ and CO2 to allow Hb to deliver O to metabolically active tissues
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11
Q

haldane effect: deoxygenation of the blood increases its ability to carry carbon dioxide;

A
  • deoxygenation of the blood increases its ability to carry carbon dioxide
  • conversely, oxygenated blood has a reduced capacity for carbon dioxide
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12
Q

binding sites of O2, CO, H+, and CO2 on Hb

A
  • O2 and CO bind to heme

- H+ and CO2 bind elsewhere on the protein and influence heme binding

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13
Q

BPG (DPG) binding to HbA

A
  • binds to a pocket formed by the beta subunits
  • lowers the affinity for O
  • rises under low oxygen conditions allowing O to be deliveres efficiently
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14
Q

developmental regulation of Hb

-HbF and HbA

A
  • composed of different subunits at different times in life
  • HbF = 2 alpha, 2 gama
  • HbA is 2 alpha, 2 beta
  • these two are very simlar in sequence, structure and function
  • except in their ability to bind another alosteric regulator (HbA for BPG)
  • HbF binds oxygen with a higher affinity
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15
Q

affinity of HbF to O

A
  • higher than HbA
  • has fewer positive charges in its corresponding pocket
  • HbF binds BPG less well and therefore binds oxygen with a higher affinity
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16
Q

histidines and Hb

A
  • the proximal histidine forms a ligand to the iron which moves upon binding of O
  • the distal histidine reduces CO binding
17
Q

negative allosteric effectors

A

-CO2, H+, BPG

18
Q

mutations in HbA

A
  • some are nonpathogenic

- others, such as HbM or HbS, disrupt structure and function

19
Q

Sickle cell anemia

A
  • sickle appearence of RBCdue to insoluble HbS
  • results in clogging of caps and organ dmage
  • anemia, jaundice, frequent infections
  • cna be homozygous (severe) or heterozygous (varies)
20
Q

precipitating symptoms of sickle cell anemia

A
  • reduced O levels during exercise can result in acute painful episodes due to the reduced O sickling the cells
  • this is called a pain crisis caused by microvascular occlusion of bones
  • treatment is hydration and pain control with NSAIDs
  • provide oxygen to reduce sickling
21
Q

mutation causing HbS

-subunit effected

A
  • point mutation converting glutamate to valine on the exterior of the beta subunit
  • can be diagnosed using electrophoresis as glutamate is very charged and val is neutral
22
Q

mechanical mechanism of sickling sure to low O

A
  • a hydrophobic hole it typically formed when there is no O in HbA
  • however in HbS, there are hydrophobic knobs sticking out of the cell in the deoxy state
  • alpah subunits are still normal in HbS
23
Q

treatment of sickle cell

A
  • antibiotic therapy: prevent secondary infection
  • hydroxyurea: stimulates the production of HbF
  • bone marrow transplant: replaces HbS with HbA
  • gene therapy: worked in mice, current clinical trials
24
Q

Methemoglobin (HbM)

  • cause
  • clinical manifestation
  • diagnosis technique
  • dietary cause
  • acquisition
A
  • this has an Fe3+ heme which can not carry oxygen
  • presents with shortness of breath, cyanosis, and mental status change, head ache, fatigue, exercise intolerance
  • methemoglobinemia is diagnosed by the absorbance spectrum of blood
  • ingestion of nitrates and nitrites can promote HbM
  • defects can also derive from a lack of reducing agents in the blood (vit C)
  • can be in-born or aquired
25
Q

thalassemias

  • definition
  • ethnical prev
  • terminology
  • treatment
A
  • imbalance of the synthesis of the alpha and beta subunits of Hb
  • prevelant in people of Mediterranean origin and some south asians have a carrier rate of 16%
  • termed alpha and beta thalassemia depending on which subunits is lacking
  • treatment usually involves transfusion

Biochemistry MBS (36 decks)

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