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MCP Unit 3: Hemoglobin/Sickle Cell/Enzymes > Hemoglobin > Flashcards

Hemoglobin Flashcards

1
Q

Cells less than 1mm can diffuse oxygen across their membrane. Multicellular organisms are too big for diffusion. How have they adapted?

A

Oxygen carriers (Hb) and circulatory systems

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2
Q

Approximately how much hemoglobin is present in blood?

A

145 g/L = 10 mM Hb monomers

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3
Q

Why do we need oxygen?

A

Oxidative phosphorylation; oxygen is the final electron acceptor

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4
Q

Where is myoglobin found? What does it look like?

A

Muscle cells; a single chain of alpha helices with a heme group

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5
Q

What is the function of myoglobin?

A

Intracellular transport and storage of oxygen

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6
Q

What does hemoglobin look like? How many hemes are present? How much oxygen binds when the hemoglobin is saturated?

A 
4 subunits (tetrameric); each of these subunits has a heme and each heme binds a molecule of oxygen
1 hemoglobin molecule= 4 heme= 4 oxygen
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7
Q

What does apo mean in terms of hemoglobin?

A

Has the two alphas and two betas, but no heme

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8
Q

What does hol mean in terms of hemoglobin?

A

Has the two alphas and two betas, as well as 4 hemes

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9
Q

Hemoglobin forms when one alpha-beta dimer (a protomer) binds to another dimer (protomer). Why is this significant for the conformation?

A

Allows hemoglobin to switch between two conformations (T and R), each of which have different affinity for oxygen

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10
Q

Where does oxygen actually bind in hemoglobin?

A

To heme- at the sixth position on iron

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11
Q

What molecules have a higher affinity for iron than oxygen?

A

CO, NO, H2S

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12
Q

What is the difference between Fe3+ and Fe2+ in terms of oxygen binding?

A

Only Fe2+(ferro) can bind oxygen

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13
Q

What is the difference between oxidation state and oxygenation state?

A

Oxidation state refers to the charge on Fe (if it’s Fe2+ or Fe3+)
Oxygenation state refers to whether or not oxygen is bound to iron
-oxygenation is closely related to oxidation state

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14
Q

What is metHb?

A

Ferric (Fe3+) Hb that doesn’t function as an oxygen carrier

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15
Q

What is the pressure in the atmosphere? Arterial blood? Venous blood?

A

Atmosphere: 150 atm
Arterial blood: 120 atm
Venous blood: 20 atm

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16
Q

How do the oxygen dissociation graphs for myoglobin and hemoglobin differ? Why are they different?

A

Myoglobin is hyperbolic (because non-cooperative), Hemoglobin is sigmoidal (because cooperative binding)

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17
Q

What is the definition of the P50?

A

The pressure at which the binding is half maximal or 1/2 of the oxygen has been released

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18
Q

What are the approximate P50s for hemoglobin and myoglobin?

A

Hemoglobin: 3 atm (26 torr)
Myoglobin: 2.6 atm

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19
Q

What are some molecules that favor the T state?

A

BPG, CO2, H+, Cl-

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20
Q

A type of allostery where what’s happening at one site promotes the same thing to happen at an identical site, is known as what?

A

Cooperativity

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21
Q

In what organs/tissues is the T state favored? The R state?

A

T state favored in muscles/tissues

R state favored in lungs

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22
Q

What is the P50 with BPG? What does this mean given the venous blood has a pressure of 20 atm?

A

26 atm- in venous blood most of the Hb will be unloaded

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23
Q

Negative effectors that favor the T state cause the oxygen dissociation curve to shift in which direction- left of right?

A

Right shift

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24
Q

How does BPG favor the T state?

A

BPG is acidic and charged and binds to lysine/histidine/ N-termini in beta subunits

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25
Q

Does the Bohr Effect play a role in both hemoglobin and myoglobin?

A

No- only in hemoglobin

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26
Q

According to the Bohr effect, when hemoglobin binds oxygen it releases hydrogen ions. How does this effect further binding?

A

The release of hydrogen is a product, this increasing product leads to more oxygen binding

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27
Q

What is the pH, H+ concentration, and oxygen binding in the lungs?

A

High pH, low H+, high oxygen binding

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28
Q

What is the pH, [H+], and oxygen binding in muscles?

A

Low pH, high H+, low oxygen binding

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29
Q

CO2 is made in active tissues as a product. Why is this significant in terms of pH and oxygen saturation?

A

CO2 combines with H20 to form H2CO3 which then dissociated in H+ and HCO3-; thus H+ is released which decreases the pH and stabilizes the T state

30
Q

How is the H+ from oxygen binding cleared?

A

H+ binds with HCO3- and then exhaled as H2O and CO2

31
Q

What does HbF look like? Does it have an affinity higher or lower than HbA?

A

Two alphas and two gammas; has a greater affinity for oxygen than HbA

32
Q

Why does HbF have a greater affinity for oxygen?

A

Gamma is resistant to BPG, so BPG isn’t able to bind and stabilize the T state

33
Q

What is the mutation in HbS? What chain does it occur on?

A

Glutamate to valine at position 6 of the beta chain

34
Q

What happens when there’s a mutation that stabilizes methemoglobin?

A

Get methemoglobinemia- and cyanosis

35
Q

How does methemoglobinemia lead to cyanosis?

A

Ferric (3+) Hb can’t bind oxygen and any oxygen that is loaded can’t be released because the ferric ion moves into the plane with heme

36
Q

What is the structure of: HbA, HbA2, HbF, HbS, HbC, HbH, and HbBarts

A

HbA: 2 alpha, 2 beta
HbA2: 2 alpha, 2 delta
HbF: 2 alpha, 2 gamma
HbS: 2 alpha, 2 beta (with a glutamate to valine)
HbC: 2 alpha, 2 beta (with a glutamate to lysine)
HbH: 4 beta
HbBart: 4 gamma

37
Q

What is the affinity for HbBarts?

A

Tight and non-cooperative

38
Q

How are different types of Hb detected?

A

Natural state gel electrophoresis

39
Q

What does HbH look like in Asians? Africans?

A

Asians: both chromosomes can’t produce alpha
Africans: one chromosome has two alpha knockouts, but the other chromosome has normal Hb

40
Q

What is the structure of heme? What isomer is found in humans?

A

porphyrin ring (4 pyrrole rings with a central iron); protoporphyrin IX

41
Q

How heme A, B, and C different?

A

A: M, attachment, M, V, M, P, M, P
B: M, V, M, V, M, P, M ,P
C: M, modified vinyl and attach to cystine, M, P, M, P

42
Q

What do heme A and B bind to proximally and distally?

A

Histidine

43
Q

What step is regulated in heme synthesis? Show the substrates and products

A

First step

Succinyl CoA + Glycine—> ALA (enzyme ALAS)

44
Q

What two steps of heme synthesis can be affected by the presence of lead? What enzymes are involved?

A

Second step:
ALA + ALA –> PBG by ALAD because ALAD uses zinc as a cofactor
Last step:
Proto IX —> Heme by ferrochelatase

45
Q

What does lead poisoning cause? How can it be seen in the blood?

A

Children have developmental problems; seen as a buildup of ALA

46
Q

What is the last soluble precurser in heme synthesis? What does this mean when there’s a problem further down the pathway?

A

Copro III

A defect further down will show an increase in Copro III

47
Q

How much energy/ATP goes into making heme?

A

None

48
Q

How is heme used in liver cells? When is it needed?

A

Prosthetic group for cytochrome P450- need when need to detoxify

49
Q

What are 4 ways in which ALAS can be regulated?

A

Repress the mRNA, inhibit translation, inhibit the import of ALAS to the mitochondria, directly inhibit ALAS

50
Q

When is heme synthesis stimulated in liver cells?

A

When there are toxins/substances that induce cytochrome P450

51
Q

What are porphyrias? Are they normally heterozygous or homozygous?

A

Genetic deficiencies in heme synthesis- heterozygous

52
Q

Those that have congenital erythropoeitic prophyria are deficient in what enzyme? What builds up?

A

Deficient in uroporphyrinogen III cosynthase

Leads to a buildup of uroporphyrinogen I and copro I

53
Q

What are the symptoms of erythropoeitic porphyria?

A

Anemia, skin is photosensitive, red urine, teeth reddish-brown, more hair growth

54
Q

What enzyme is deficient in those with erythropoeitic porphyria? What do you see a build up of?

A

Ferrochelatase- see a build up of copro III

55
Q

What enzyme is deficient in Acute Intermittent Porphyria (AIP)? What accumulates?

A

PBG deaminase

Accumulation of ALA and PBG

56
Q

What are the symptoms of Acute Intermittent Porphyria?

A

Abdominal pain, vomit, diarrhea, neuro dysfunction, red urine

57
Q

What enzyme is deficient in porphyria cutana tarda? What builds up?

A

Uroporphrinogen decarboxylase

Build up of uroporphyrinogen III

58
Q

What parts of hemoglobin are recycled? What parts are just broken down?

A

Globin component is recycled; heme is just broken down except for the iron which is recycled

59
Q

What are the three general steps in heme breakdown?

A
  1. breakdown of the porphyrin ring
  2. reduction of the broken ring
  3. conjugate to sugars to make water soluble
60
Q

What is the function of heme oxidase? What is the product?

A

Converts heme into biliverdin; releases CO into the blood

61
Q

Is bilirubin lipid soluble or water soluble? How does it travel through the blood?

A

Lipid soluble- has to be attached to albumin to travel through the blood

62
Q

What does ALA look similar to? Why is this significant with lead poisoning?

A

GABA; have a build up of ALA with lead poisoning

63
Q

What color is bilverdin? Bilrubin?

A

Biliverdin is green; bilirubin is yellow

64
Q

Before bilirubin can be secreted in the bile it has to be made soluble. How is this achieved?

A

Conjugation of bilirubin; attach sugars to the bilirubin

65
Q

Is jaundice really a disease?

A

No- it’s a secondary disease; something else is going on that is causing an abnormal distribution of bilirubin

66
Q

What causes pre-hepatic jaundice? What would the blood work look like?

A

Massive breakdown of hemoglobin that the liver can’t keep up and conjugate the bilirubin fast enough; get a buildup of unconjugated bilirubin, normal liver function enzymes, no urine bilirubin, but do have urine urobilinogen

67
Q

What causes intrahepatic jaundice? What would blood work look like?

A

Diseased condition of the liver; have both conjugated and unconjugated bilirubin, increased liver enzymes, both bilirubin and urobilinogen in the urine

68
Q

What causes posthepatic jaundice? What would blood work look like?

A

Blockage of bile out of the liver (gallstone/tumor); buildup of conjugated bilirubin, normal liver enzymes, urine bilirubin present

69
Q

How is either stored?

A

As ferritin or hemosiderin

70
Q

What is the name of the iron transporter?

A

Transferrin

71
Q

What is it called when the transferrin releases the iron but remains bound to the receptor in the vesicle?

A

Apotransferrin

MCP Unit 3: Hemoglobin/Sickle Cell/Enzymes (2 decks)

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