Erythrocyte Biochemistry Flashcards
Structure of Hb
Hb is a tetramer, made up of [2 alpha globulin subunits] and [2 beta globulin subunits]
Heme
Heme is a HYDROPHOBIC prosthetic group that binds O2. There is 1 heme/subunit in Hb. So 4 hemes total.
Heme is made up of protophoryin IX and Fe2+.
For O2 to bind to heme, Fe must be in the ___ state
2+
Fe2+ is called
ferrous
What is erythropoiesis?
Erythropoiesis is the creation of RBC
What is the process of erythropoiesis
- Stem cell (hemocytoblast)
- Committed cell (proerythroblast)
- It then undergoes a developmental pathway where
A. ribosomes are made
B. Hb is made
C. nucleus and a majority of organelles are ejected
because RBC do not have organelles and have already
made their Hb - Erythrocyte
In the formation of a RBC, a majority of the ____ is made before the nucleus is ejected
Hb
Embroyonic Hb
- Hb Gower 1
- Hb Gower 2
- Hb Portland
By 8 weeks of gestation, they’re destroyed
Fetal Hb
- Hb F (alpha2gamma2)
Adult Hb
- Hb A (alpha2beta2) –> 97%
2. Hb A2 (alpha2delta2)–> 3%
What chromosome are responsible for the creation of Hb?
Chromosome 16
Chromosome 11
Sickle cell anemia is caused by a change in?
In HbS. the AA at position #6 of B-globulin chain changes from Glu–> Val
What are researchers trying to do to tx Sickle Cell Anemia?
Researchers are trying to induce the expression of HbF using hydroxyurea.
However, it is chemically.
Heme is stabilized by _____
Histadine
There are 2 histadines
- Histidine F8
2. Histidine E7
Histidine F8
Histidine F8 is the proximal histidine.
It connects the heme to the Hb.
Histidine E7
Histidine E7 is the distal histidine.
O2 binds to the Fe that is located between heme and Histidine E7.
Myoglobin has a _____ curve
hyperbolic
Hemoglobin has a ____ curve
sigmoidal because it participates in positive cooperativity
hb switches between ____ and _____ affinity
high and low
Is the binding of 02 reversible?
Yeth
positive cooperativity in hb
the binding of 1 O2 molecule will facilitate the binding of another O2 molecule.
A conformational change in 1 globin subunit will induce a conformational change in another subunit. How does this happen? When O2 binds to Fe2+, it causes a 0.4A change, pulling down the proximal F8 histidine, which changes the interaction with the associated globin chain.
What happens when O2 binds to Fe2?
When O2 binds to Fe2,
It causes a 0.4A change, pulling down the proximal His F8. this changes the interaction with the associated globins to that O2 can better bind. POSITIVE COOPERATIVTY O
pO2 in lungs
98%
pO2 in tissues
20%
When Hb comes to our tissue, O2 will be delivered. Why is that
This is due to changes in our pH.
Actively metabolizing tissue has a pH of 7.2. This is lower than normal.
Decrease pH= (high H+ ions and high CO2), the Hb’s affinity for O2 will decrease and O2 will be delivered to the tissue.
His 146 will then come and pick up H+ ions
Decrease in pH causes what?
low pH means that there are alot of (H+ ions and CO2).
His 146 will come and pick up H+ ions and deliver to the RBC
Hb affinity for O2 will drop and this will facilitate the release of O2 from our tissue/
What picks up H+ ions to deliver to the RBC, which facilitates the release of O2
Histidine 146
High CO2, ______ Hb’s affinity for O2
decreases
Why does high CO2 decrease Hb’s affunity for O2
CO2 will eventually form H+
So when you see CO2 think of H
high 2,3 BPG will do what to the affinity of O2.
High 2,3 BPG will cause Hb’s affinity for O2 to decrease
In high altitudes, we have a decrease in pO2. How will our bodies production of 2,3 BPG change?
Our body will increase production of 2,3 BPG because it decreases Hb’s affinity for O2, causing O2 to be delivered to our tissue.
High 2,3 BPG will cause a shift to the _____ in the ODC curve
RIGHT.
while excerising, our pO2 ______
drops. Thus, Hb can deliver tissue.
Fetal RBC have a lower/higher affinity for O2 than mothers Hb. Why?
Higher
Fetal RBC have a higher affinity for O2 than mothers because fetal RBC does not bind well to 2,3 BPG.
*Remember, 2,3 BPG will decrease the affinity.
The higher affinity for O2 of fetal Hb allows what?
O2 to transfer from mother–> child.
Fetal RBC do/do not bind well to 2,3 BPG, causing them to have a lower/ higher affinity to O2.
does not bind well
causing them to have a higher affinity to O2
Because 2,3 BPG decreases Hbs affinity for O2
Iron travels in the blood as ______
transferrin
Where does transferrin go?
RBCs are made in the bone marrow. Thus, transferrin will go to the bone marrow to provide the Fe, and create our
RBCs!!!!!
Every ____ days, RBCs are broken down and release ____ and _____
Ever 120 days, RBCs are broken down by macrophages and release Hb and iron (as transferrin).
Sites where iron travels
- intestines
- blood
- bone marrow
- eaten by macrophage and taken to liver
then released bak into blood stream
Where is the iron mostly located in our bodies?
67% of our iron is in hemoglobin
27% of our iron is stored
-ferritin (H20 soluble)
-hemosiderin (H20 insoluble)
What are our storage forms of iron?
Ferritin
and hemosederin
If ferritin water soluble or not?
Yes, ferritan is H20 soluble
Is hemosiderin H20 soluble or not?>
No, H20 insoluble
Fe2+
ferrous
Fe3+
ferric
Absorption of animal product heme iron
Animal product heme iron has (Fe2+: ferrous)
- Fe2+ goes inside of the enterocyte and is converted to ferric (Fe3+)
- Ferric is then converted to storage form ferritin (H20 soluble)
- Ferric can then be degraded to hemosiderin
What are the 2 storage forms of Fe
- Ferritin (H2O soluble)
2. Hemosiderin (H2O insoluble)
Plant products have what kind of iron?
Non-heme iron (Fe3+: Ferric)
Can Fe3+ (ferric) be easily transported into the enterocyte?
No. It needs to be converted to Fe2+ using ferric reductase (duodenal cytochrome C).
How does Fe2+ derived from Fe3+ enter the enterocyte?
Divalent transporter 1
What happens to plant derived Fe2+ now that it is in the enterocyte?
- It can be converted to Fe3+ via ferroxidase and then go into the storage form.
- it can go into the blood via ferroportin
Now that plant derive Fe2+ is in the blood, what happens?
- Converted to ferric (Fe3+) using ferroxidase/ceruloplasmin/haphaestrin
- Fe3+–> transferrin
What allows plant derived Fe2+ to enter the blood stream?
ferroportin
What converts Fe2+–> Fe3+
Ferrous–>ferric
Ferroxidase
Ceruloplasmin
Haphaestrin
Other names for Ferroxidase
ceruloplasmin
Haphaestrin
Plant Fe absorption pathway
Plants have non-heme iron: Fe3+ (called Ferric)
Fe3+ cannot be easily absorbed across the membrane. Thus, it must be converted to Fe2+
- Fe3+–> Fe2+ via [ferric reductase/duodenal cytochome C]. these are dependent on vitamin C
- Fe2+ is now taken inside of the enterocyte using divalent transporter I (DMT1)
- Once inside; two things can happen to Fe2+
A. It can be converted to Fe3+ (ferric) and converted to
storage forms (ferritin and hemosiderin) via
ferroxidase/haphaestrin/ceruloplasmin
B. It can be taken into the blood via [ferroportin]
4. Once in the blood
A. Fe2+ is converted to Fe3+ via
[ferroxidase/haphaestrin/ceruloplasmin]. this is
dependent on Cu.
B. Fe3+ is converted to transferrin
What is the role of ferric reductase?
Ferric reductase will convert plant derived ferric (Fe3+) into Fe2+, which can more easily be transported into the enterocyte.
Dependent on vitamin C
What is the role of divalent transporter 1 (DMT1)?
Transports plant derived Fe2+ into the enterocyte
What is the role of ferroxidase, haphaestrin and ceruloplasmin?
The convert Fe2+ to Fe3+
Dependent on copper (Cu)
What is the role of ferroportin?
Transports Fe2+ from the cell, into the blood
Free iron is
Fe2+
ferrous
Dietary iron is
Fe3+
ferric
Where is transferrin taken?
Transferrin is taken to the spleen, liver, bone marrow but also the MITOCHONDRIA
Transferrin transfer to the mitochondria
Transferrin wants to go here because thats where heme is made
Transferrin is uptaken by receptor-mediated endocytosis via tranferrin receptors (TfR)
It is enclosed in clatherin encoated vesicles and then delivered directly inside the mitochondria.
No transporter is necessary
Is a transporter necessary to deliver transferring to the mitochondria?
Noo. transferrin is transferred directly inside
Iron deficiency
- result of a deficiency in dietary fiber (Fe3+)
- Most common in menstruating women and aspirin overuse
Iron deficiency can cause
hypochromic microcytic anemia
Tx of iron deficiency
dietary fiber supplement
Hereditary hemochromatosis
Too much iron (15g) compared to normal (3-5g) due to a problem uptaking and exporting iron via enterocytes
Result: organ dysfx–> cirrhosis, arthritis, endocrinopathy
Hepcidin
Hepcidin regulates levels of iron by having an affect on ferroportin.
When hepcidin increases, it causes the internalization and destruction of ferriportin, decreasing the amount of iron that leaves.
Hepcidin structure
25 AA peptide that is made by the liver
How does hepcidin affect levels of iron
when hepcidin is high, its does not let iron leave the cell. so it decrases blood iron levels
When iron is high, what affect was hepcidin have
Hepcidin increase
Ferroportin decrease
Blood iron levels decrease
When iron is low, what affect does hepcidin have?
Hepcidin levels are low
Ferroportin is high
Absorption if iron increases
What is hepcidins receptor?
Ferroportin
How are hepcidin levels controlled?
Hepcidin levels are controlled by transferrin levels.
- Transferrin will bind to receptors (Tfr1).
- Hfe gets transported to Tfr2
- Tfr2 is internalized and goes to the nucleus to turn the levels of hepcidin up
this prevents iron from leaving
What happens if you have a mutation in [Hfe]?
mutation in [hfe]
prevents hepcidin from being activated
which means that ferroportin transporter will stay
which means that levels of blood iron will increase!
decrease hepsidin
increase ferriportin
increase blood Fe
The production of RBCs depend on
folate vitamin b12 (cobalamin)
a decrease in vitb12 and folate lead to
megaloblastic macrocytic anemia
Megaloblastic macrocytic anemia occurs when
we have a decrease in vitb12 or folate.
As RBCs are being produced in the bone marrow, dna synthesis is impaired
because folate is responsible for making DNA!!!!
What do the RBCs of megaloblastic macrocytic anemia look like
Large RBC, but normal Hb content.
Blood smear of someone with megaloblastic macrocytic anemia
large RBCs
oval macrocytes
Bone marrow of someone with megaloblastic macrocystic anemia
large erythroblasts hypersegmented neutrophils (like 5 lobes)
Folate is also called
pteroglutamic acid
Folate has ___ parts
- pteridine ring
- PABA
- glutamate
what is the dietary form of folate
Dihydrofolate (DHF)
What is the active form of folate
Tehtrahydrofolate (THF)
How do we go from the dietary DHF–> to the active THF?
dihydrofolate reductase
Importance of THF
Tetrahydrofolate is important in DNA synthesis!!!
it has more carbons so it serves asa ONE-CARBON donor
FH2 is
dihydrofolate
FH4 is
tetrahydrofolate
THF serves as a _____-carbon donor
ONE-carbon donor for the synthesis of nucleotides
Which part of folate metabolism is responsible for nucleotide synthesis
methenyl-THF
Which part of the folate metabolism gets stuck?
methyl-THF
How do we get methyl THF unstuck
it needs vitamin B12 (cobalamin) to make THF again!
THF can become
- methnyl THF (nucleotide synthesis)
- N 5,10 methylene THF ( donates carbon to dUMP–>dTMP then converted back to DHF)
- methyl-THF gets stuck and needs vit B12 to remove methyl and make THF again! :)
a decrease in folic acid can lead ________, which can cause _____________
a decrease in folic acid can lead to DECREASED DNA SYNTHESIS, which can lead to MEGALOBLASTIC MACROCYTIC ANEMIA
folate metabolsim
folate–> DHF–>THF
THF can become three things
1. N5,10 methylene THF–> methyl THF
2. methynl THF (nucleotide synthesis
Folate (DHF) is found
in most food like eggs, yeast and milk
the main carbon transfer of folate occurs when
the main carbon transfer occurs
when the carbon side chain of serine is transferred to THF to form
N-5,10-methylene TFH
Folic acid is absorbed in the ________
jejunum of the small intestine
Once folic acid is absorbed in the small intestine, what happens?
it becomes methyl-THF. Thus, to activate it, it needs vitamin b12/cobalamin
What is the primary circulating form of THF in the blood?
methyl-THF
thus, to free it we need to add vitamin b12 or cobalamin
Why do we need vitamin b12
vitamin b12 is needed so that it can demethylate our methyl-THF and it can be freed into the blood.
addition of vitaminb12 makes [methyl-vitab12] to free our THF
recommended daily allowance of vitamin b12 is
3ug
B12 absorption
We intake vitamin b12
- B12 will bind to R-binder proteins in the stomach
- Parietal cells will secrete intrinsic factors
- Pancreas will release proteases, which will degrade R-binder proteins and release b12 in the duodunum
- b12 will bind to intrinsic factors and be taken to the ileum, where they are taken to the blood via receptor mediated endocytosis.
where is folate absorbed at?
jejunum
Where is b12 absorbed at?
ileum
What method are folate and b12 absorbed with?
receptor mediated endocytosis
cobalamin is carried in the blood via ______
transcobalamin
Pernicious anemia
pernicious anemia is caused by a deficiency in vitamin b12.
this lack of b12 can be a result of lack of intrinsic factors
is pernicious anemia a megaloblastic macrocystic anemia?
YES!!!!!
to detect pernicious anemia?
SCHILLING TEST!
