Erythrocyte Biochemistry Flashcards
What is erythropoiesis?
The development of an erythrocyte from stem cell.
What is the name of the stem cell that develops into an erythrocyte and what is the committed cell called?
A hemocytoblast that develops into a proerythroblast
What is the developmental pathway for erythrocyst?
The cell develops a large amount of ribosomes then begins mass synthesis of hemoglobin. The cell then begins to lose its nucleus and organelles before leaving the bone marrow.
What is the structure of hemoglobin?
a multi-subunit protein that consist of two alpha globin chains and two beta globin chains. There is also one heme group per globin that contains a ferrous atom.
What are the embryonic forms of hemoglobin? (3)
Hb Gower 1- Two theta and 2 sigma
Hb Gower 2- two alpha and two sigma
Hb Portland- two theta and two gamma
What is the fetal structure of hemoglobin?
Hb F- two alpha and two gamma
What are the two adult forms of hemoglobin?
Hb A- 2 alpha and two beta
Hb A2- two alpha and two delta
What chromosomes are the hemoglobin chains found on?
16 and 11
What is the AA change in sickle cell anemia?
Hbs- AA change to the 6th position on beta globin- a glutamic acid for valine
What are some therapies being researched to help with sickle cell anemia?
Trying to induce expression of HbF in sickle cell patients by using hydroxyurea. This is a toxic agent
What is the proximal histidine?
F8 histidine- binds to the heme
What is the distal histidine?
E7 histidine that binds to the O2 on the heme group, stabilizing it
What does the binding of histidine to O2 do to hemoglobin?
It induces a confirmational change that pulls down the proximal histidine. This will alter confirmation to the other globin units as well
What kind of oxygen dissociation curve does myoglobin have?
it has a hyperbolic curve
What kind of oxygen dissociation curve does hemoglobin have?
It has a sigmoidal curve due to the interactions of the globin subunits
What is positive cooperativity in hemoglobin?
When O2 binds to one globin, it induces a confirmation change and makes it more likely that the other subunits will bind to O2. This is true in the reverse. Release of one O2 molecule induces release of other O2.
What are the three factors that modifies the oxygen dissociation curve?
pH- lower pH, lower affinity for O2 in hemoglobin
2,3-BPG- higher levels will lower the affinity of O2 in hemoglobin
Exercise- an increase in exercising tissues will lower the affinity of O2 to hemoglobin
Does fetal hemoglobin have a higher or lower affinity for O2? Why/how?
Higher- needs to be higher in order to receive O2 from mothers blood. HbF does not bind well to 2,3 BPG so has a higher affinity
what is the distribution of iron in the blood?
67 percent hemoglobin
27 percent as storage
5 myglobin
1 other proteins
What is the role of ferric reductase in the absorption of iron?
Converts Fe3+ in non-heme iron to Fe2+
What is the role of Divalent transporter-1 in the absorption of iron?
takes up Fe2+
What is the role of Ferroportin in the absorption of iron?
Extrudes iron out of the cell
What is the role of hephaestin in the absorption of iron?
converts free iron to Fe3+
What is the role of transferrin in the absorption of iron?
Transports iron in the blood
What are the effects of iron deficiency?
Causes hypochromic microcytic anemia- can result from insufficient diet, menstruating, aspirin overuse or bleeding
What is hereditary hemochromatosis? Treatment?
Organ dysfunction due to excess levels of iron generally from a mutation in Hfe (hepcidin)- treated by blood letting
What is the function of hepcidin?
regulates iron- Hepcidin will bind to ferroportin and internalize it for destruction- When iron levels are high there is more hepcidin expression but when levels are low there is less expression
How is hepcidin regulated?
Tf-Fe will bind to TFr1 and displace Hfe causing it to bind Tfr2. This is a hepcidin signaling complex and will enduce transcription of hepcidin
What happens if there diminished synthesis of DNA in the bone marrow?
Developing erythrocysts will become enlarged and it will lead to megaloblastic anemia
What are some reasons that megaloblastic anemia occurs?
There is a deficiency in either folate or vitamin B12
What is the structure of folate?
Three parts- Pteridine ring, PABA and glutamate
What is the enzyme that “activates” folate and how does it achieve this?
The enzyme is dihydrofolate reductase that adds four hydrogens to the molecule converting it to the active form, THF
How does THF assist in DNA synthesis?
It acts as a carbon donor for nucleotide synthesis.
Why is B12 needed for DNA synthesis?
N5-methyl-THF will not give up carbons for DNA synthesis so needs to be demethylated by a complex that requires B12 in order to be used for synthesis.
What is pernicious anemia?
occurs when there is a b12 deficiency that is the result of loss of intrinsic factors- Results in megaloblastic anemia
What is the schilling test?
Used to test if there was a b12 deficiency from poor diet or lack of intrinsic factor
How is the Shilling test performed?
Pt is given .5-1 oral dose of 57Co-labeled b12. After 24 hours an UA is collected and if there is B12 in the urine then there is a diet issue. If not, then another labeled B12 with intrinsic factor is given and an UA is collected 24 hours later. If radioactive is present then there is intrinsic factor problem
What is the process of non-heme absorption?
Non-heme is in the ferric form (Fe3+) so must be converted to ferrous form (Fe2+) by ferric reductase then can be transported into the cell by DMT-1. When needed the iron will then leave the cell via ferroportin. It needs to be converted back to Fe3+ by hephastin then will be transported in the blood by transferin.
How is transferin picked up by the cell?
Through mediated endocytosis- The Tr-Fe complex will bind to the TFr1 receptor and where it will internalized via clathrin pits (endosomes). The pH of the endosomes is 5.5 so the iron will dissociate from transferin. The endosome will then either dock directly to mitochondria or DMT1 will release it to the cytoplasm
How is b12 absorbed by the body?
Dietary B12 binds to R binders in stomach till proteases degrade the r binder in the duodenum. They will then bind to intrinsic factors from parietal cells that will carry b12 to the ileum.
How is b12 taken to the appropriate tissues?
It is carried by intrinsic factors in the stomach till it is taken in the cells by receptor mediated endocytosis. The b12 will then be carried through the blood by transcobalamin
What are the enzymes involved in folate cycle?
dihydrofolate reductase- converts folate to THF
What are the enzymes that are involved in transport of iron?
Ferric reductase- converts non-heme Fe3+ to Fe2+
DMT-1- will transport the Fe2+ into the cell
Ferroportin- will transport Fe2+ out of the cell
Hephastin- will convert Fe2+ in the blood to Fe3+
Transferin- Transports Fe3+ through the blood to appropriate tissues
