Erythrocyte Biochemistry Flashcards
65% of Hb is synthesized before the nucleus is extruded; the remaining 35% is made where?
In the reticulocyte
Hemoglobin is a multi-subunit protein (tetramer) made up of 2 ___________ chains and 2 ___________ chains
There is one heme per subunit which contains a _______ atom. It carries oxygen and is _______________ (hydrophobic or hydrophilic?)
Alpha globin; beta globin
Fe2+/ferrous; hydrophobic
Embryonic hemoglobin contains what various types of globin chains?
Zeta
Epsilon
Alpha
Gamma
[Hb Gower 1, Hb Gower 2, Hb Portland]
Fetal hemoglobin contains what type of globin chains?
HbF (alpha2gamma2)
The majority of adult hemoglobin is alpha2beta2, what is the remainder at approx 3%?
Alpha2delta2
Hbs is present in Sickle Cell Anemia, due to what genetic mutation?
Missense mutation at amino acid position 6 in beta-globin
Glutamic acid –> valine
This causes polymerization of hemoglobin –> sickle shaped RBCs impede circulation –> hemolytic anemia
In terms of oxygen dissociation curves, the Mb curve is _____________ and the Hb curve is ___________
The binding of oxygen is _____________ (reversible or irreversible?)
Hyperbolic; sigmoid
Reversible
The oxygen dissociation curve is primarily influenced by what 3 factors?
2,3-BPG, H+, and CO2
Hb binds O2 in a cooperative fashion, meaning what?
As one O2 binds to one heme, it facilitates the binding of an O2 to another heme
Conformational change in one globin subunit induces a conformational change in another subunit
What effect does increased 2,3-BPG have on the oxygen dissociation curve?
2,3-BPG reduces oxygen affinity, so Hb gives up more O2 to tissues
The pH of actively respiring cells is __________, what effect does this have on the oxygen dissociation curve?
Lower; affinity for Hb for oxygen decreases as the pH decreases, favoring the release of oxygen to tissues
A fetus needs Hb that has a higher affinity for O2 than the mother’s Hb (HbF = a2y2). What accounts for the fact that oxygen will flow from mother to fetus?
HbF does not bind well to 2,3-BPG, therefore it has a higher affinity for O2
_________ readily exchanges electrons; thus it is an ideal catalyst for biological redox reactions
Fe
________ is ferrous iron
_________ is ferric iron
Fe2+
Fe3+
Iron plays a role in _______ in the mitochondria
ETC
Most iron is in ___________, and total body iron is 3-5 g
RBCs
Iron is stored in ___________ (liver) and is regulated by modulating absorption
Ferritin
Dietary iron is typically in __________ form
Ferric (Fe3+)
Ferric iron is reduced to Fe2+ by ____________, then transported into the enterocyte by _________ on the apical surface.
Fe2+is transferred to the basolateral side of the enterocyte and is transported outside the cell to the blood and circulation by ___________, which requires a _______________ to perform this transport.
Fe2+ is then changed to Fe3+ so ___________ can carry it to the bone marrow.
Iron content in the body is regulated by modulating absorption - via __________
Dcytb (duodenal cytochrome b); DMT1
Ferroportin; ferroxidase (hephaestin)
Transferrin
Hepcidin
Transferrin binds iron with __________ affinity and carries it to tissues in a non-toxic form, where it is needed including the bone marrow undergoing _____________
High; erythropoeisis
Transferrin Receptor (TfR) - Mediated Endocytosis
Transfer of iron to ______________ (where heme is made) involves the endosome docking on the mitochondria tranferring iron directly - not through a cytoplasmic transport protein.
______ transports iron out of the endosome
Fe3+ is then reduced to Fe2+ by ______________
Mitochondria
DMT1
ferrireductase
What is the primary cause of hypochromic microcytic anemia?
Iron deficiency
What types of physiologic conditions might cause an iron deficiency?
Insufficient dietary iron
Menstruation
Aspirin abuse
GI tract ulcers
What autosomal recessive condition is defined by organ dysfunction due to iron overload: cirrhosis, arthritis, endocrinopathy, skin pigmentation, cardiomyopathy, and usually manifests in the 6th decade?
Hereditary hemochromatosis
Normal body iron is 3-5g. What is the total body iron in someone with hereditary hemochromatosis?
15g
What is the primary treatment for hereditary hemochromatosis?
Blood-letting
To understand hereditary hemochromatosis, you must understand ___________, which is the regulator of iron homeostasis. It is a peptide made by the liver
Hepcidin
Hepcidin binds to _______________ and causes its internalization so that it can be destroyed by proteolysis
Ferroportin
When iron is high, hepcidin expression is ________ and ferroportin levels are _________
Up; down
When iron is low, hepsidin expression is __________ and ferroportin levels are ______
Down; up
_______ regulates hepcidin expression
HFE
If HFE is mutated, it cannot bind to ______. Mutant HFE cannot turn on Hepcidin expression, therefore, there is no control over ________ activity
TfR2; ferroportin
Production of RBCs is dependent on what 2 vitamins?
Vitamin B12 (cobalamin) and folate (folic acid)
Anemia occurs as a result of diminished synthesis of _________ in bone marrow erythroblasts
DNA
____________ anemias are characterized by large RBCs, increased mean corpuscular volume, many oval RBCs on blood smear, and red cell volume elevated
Macrocytic
What type of anemia is characterized by large erythroblasts in bone marrow and hypersegmented neutrophils (more than 5 lobes)?
Megaloblastic macrocytic anemia
___________ is made up of 3 parts: pteridine, PABA, and a chain of glutamate residues
Folate
Folate can exist as dihydrofolate (FH2), this can be reduced to THF by ____________ ____________
THF is the active form, with the function of transferring carbon units from donors to acceptors.
It serves a vital role in ______ synthesis
Dihydrofolate reductase
DNA
In folate metabolism, the main carbon transfer occurs when the carbon side chain of serine is transferred to THF to form what?
N5,10-methylene-THF
The carbon of N5,10-methylene-THF is then transferred to _______ to form ______, during which dihydrofolate (DHF) is made; then reduced by dihydrofolate reductase to THF to start the cycle again
dUMP; dTMP
Folate is available as an N5-methyl-THF, but it will not give up a single methylene group to dUMP to make dTMP for DNA synthesis – so what needs to happen?
An N5-methyl-THF needs to be de-methylated to enter folic acid cycle as THF
N5-methyl-THF requires vitamin B12 to become demethylated
___________ is a vitamin with a nucleotide, protoporphyrin-like ring, cobalt, sugar, and nitrogen ring
Vit. B12
What is the folate trap?
If B12 is not available, folate is stuck as N5-methyl-THF and cannot participate in DNA synthesis
Vitamin B12 removes the methyl group from N5-methyl-THF to make methyl-cobalamin and release THF
Then B12 transfers methyl group to homocysteine to create _____________ using ____________ ____________
Methionine; methionine synthase
What type of anemia can be caused by a vitamin B12 deficiency because of its impact on DNA synthesis?
Megaloblastic macrocytic anemia
Dietary deficiency of vitamin B12 is rare; 85% of B12 deficiency is from the lack of what protein?
Intrinsic factor
B12 Absorption:
Dietary B12 binds to proteins called R-binding proteins made by ________ __________ cells.
Intrinsic factor is made by ____________ cells of the stomach. Proteases from the pancreas degrade R-binder proteins in the duodenum releasing B12.
Intrinsic factor carries B12 to the _______ where receptors bring it into body. IF-cobalamin is taken up by receptor mediated endocytosis. The receptor is ___________.
Cobalamin circulates through the blood carried by ___________.
Gastric mucosa
Parietal
Ileum; cubulin
Transcobalamin
What type of anemia results in the case of vitamin B12 deficiency due to lack of intrinsic factor?
Pernicious anemia (specific type of megaloblastic macrocytic anemia)
[this condition results from failure to absorb vitamin B12 resulting from unavailability of IF which results from destruction of IF and the cells producing it. Gastric mucosa is destroyed through an AUTOIMMUNE mechanism]
In B12 deficiency it is important to distinguish whether that is dietary or an issue with absorption (intrinsic factor). What test is used to distinguish between the two?
Schilling test - give oral dose of radioactive B12, as well as an injection of unlabeled B12 to saturate all B12 receptors in the liver to prevent radioactive B12 binding. If it is absorbed from the GI tract, it will pass in the urine
Schilling test - give oral dose of radioactive B12, as well as an injection of unlabeled B12 to saturate all B12 receptors in the liver to prevent radioactive B12 binding. If it is absorbed from the GI tract, it will pass in the urine.
If radioactive cobalamin is absent from the urine, what has the test indicated?
Pernicious anemia, because the cobalamin has not been absorbed
What is part 2 of the Schilling test, after you have gotten a positive test for pernicious anemia?
Positive test for pernicious anemia is absence of radioactive cobalamin in the urine.
Part 2 = give oral dose of radioactive B12 AND intrinsic factor, as well as injection of unlabeled B12 to saturate all liver receptors. Collect urine and look for radioactive B12. If radioactive B12 is present, the patient has pernicious anemia due to lack of intrinsic factor
