Erythrocyte Biochemistry Flashcards
What makes up fetal hemoglobin?
- 2 alpha
- 2 gamma
What makes up adult hemoglobin type A?
- 2 alpha
- 2 beta
What makes up adult hemoglobin type A2?
- 2 alpha
- 2 delta
- only makes up 3%
Describe the structure of hemoglobin?
- tetramer
- one heme per subunit
- Has ferrous iron
- carries oxygen
- hydrophobic
What happens to hemoglobin once oxygen binds?
- Before o2 binds iron is outside the plane of porphyrin
- Once it binds it moves into the plane of heme
- The change pulls down the proximal histiidine of Hb and changes interaction assoc with globin chain
What will the ODC look like for myoglobin vs hemoglobin?
- Myoglobin is hyperbolic
- Hemoglobin is sigmoidal due to interactions between globin subunits (+ coorperativity, binding of one oxygen facilitates binding of next and so on)
Where is the steepest part of ODC and what is the significance?
- It is between 40 torr which is pO2 at rest and 20 torr which is during exercise
- It indicates that Hb is very efficient during exercise with providing oxygen to tissues
What does 2,3-BPG do to the ODC?
- reduces oxygen’s affinity so hemoglobin will give up oxygen easier to tissues
How does the Bohr effect modify the ODC?
- CO2 and H are by products of actively respiring tissues, this enhances the oxygen delivery/release from hemoglobin
- pH of active tissue drops from 7.4 to 7.2
- This drops the binding affinity of Hb for O2
Compare Fetal ODC and Mother ODC.
- Oxygen flows from mom to baby
- The gamma subunits have higher affinity than the beta for oxygen so the baby will not let it go as easy
What mutation causes SCA?
- Glutamic acid changes to valine at position 6 in the beta chain
- This causes polymerization of Hb and sickle shaped RBC’s which impede circulation and cause hemolytic anemia
How is iron regulated?
By modulating its absorption
What is ferritin?
- Protien that will bind ferric iron to help store it
What happens to ferrous iron when it enters an enterocyte?
- It gets oxidized to ferric iron by ferroxidase (Cerruloplasmin)
- It gets stored as ferritin and degraded to homosiderin
How is non heme iron (Fe3) absorbed stored and transported?
- Plant products are difficult to absorb
- They get converted to Fe2 by ferric reductase (Dcytb) in the presence of vitamin C
- Fe2 will enter the enterocyte via divalent transporter 1 (DMT1)
- Gets converted to Fe3 by ferroxidase for storage or exported out via ferroportin
What does ferroportin require to function?
- Needs hephaestin for function
- Ferroportin levels are regulated by hepcidin
What protein binds Fe3 for transport to target tissues?
Transferrin
How does uptake of transferrin occur?
- Via receptor mediated endocytosis with transferrin receptor
- It gets internalized with clathrin coated pits into endosomes and the low pH of endosomes releases transferrin from the receptor
- Iron gets taken up in mitochondria when the endosome docks and transfers it via DMT1 this is where heme is made
What happens when hepcidin binds ferroportin?
- It causes internalization of ferroportin and its degradation in lysosomes
- It will bind when iron content is too high
What regulates hepcidin?
- complex signaling path involving transferrin, receptor and a protein called human homeostatic iron reguolator protein
When iron is high, hepcidin expression goes ___, ferroportin levels go ____, and iron absorption is now ____.
When iron is high, hepcidin expression goes up, ferroportin levels go down, and iron absorption is now decreased.
When iron is low, hepcidin expression goes ___, ferroportin levels go ____, and iron absorption is now ____.
When iron is low, hepcidin expression goes up, ferroportin levels go up, and iron absorption is now high.
Iron deficiency slilde 195
what is hereditary hemochromatosis?
- Increased absorption of iron which accumulates in the heart, liver, and pancreas
- It causes liver cirrhosis, hepatocellulalr carinoma, diabetes, arthritis and heart failure
- Auto recessive mutation in HFE
What does a deficiency of folalte and B12 cause?
- megaloblastic macrocytic anemia due to decreased syntheiss of DNA in developing RBC bone marrow
- characterized by large erythrocytes
Describe folate metabolism.
- folate gets reduced to DHF by DHF reductase
- DHF gets reduced to THF via DHF reductase
- THF is the active form and important for synthesis of purines and pyrimidine thymine
- Serves a vital role in DNA synthesis
How long does the storage of folate last?
3-6 months in the liver
What is the primary active form of THF in the blood?
- Folic acid gets reduced to N5-methyl-THF once absorbed into the intestine
What is methotraxate?
- Binds to DHF reductase and inhibits it
- It is an antineoplastic agen that will inhibit DNA synthesis
What happens to THF if B12 isn’t available?
- Folate trap occurs, as the B12 is a methyl acceptor and creastes Methyl-B12 and releases THF
How is B12 absorbed?
- Dietary B12 will bind to R-binder proteins
- Intrinsic factor made by parietal cells degrade R binder proteins in duodenum releasing B12
- IF carries B12 to ileium where it gets released in blood
- IF-Cobalamin is carried by Transcobalamin II in the blood and getss taken up by cells throug hreceptor mediated endocytosis
What is pernicious anemia?
- B12 deficiency can occur due to lack of IF, leads to a megaloblastic macrocytic anemia
What is the Schilling test?
- Used to figure out cause of Pernicious anemia
- Give radioactive Coalbamin and collect urine for 24 hrs looking for the radioactive B12
- if present it means normal absorption of B12 and the deficiency is in the diet
- If absent B12 isnt absorbed so pernicious anemia
- From pernicious anemia you give another dose of radioactive B12 PLUS IF
- Collect urine for 24 hours and if radioactive B12 is present its pernicious anemia due to lack of IF
What are the two key features of porphyrin rings?
- Four 5 membered rings with nitrogen
- Iron in ferrous state
- Oxidation to ferric state inactivates hemoglobin
Where does biosynthesis of heme occur?
- liver and erythroid cells of bone marrow
Where do phases one two and three of heme synthesis occur?
- Mitochondria
- Cytosol
- Mitochondria
- Defects in any stage causes porphyrias
What happens in phase one of heme synthesis?
- Within the mitochondria delta aminolevulinic acid is synthesized from glycine and succinyl coenzyme A
- It gets released from the Mitochondria
- ALA Synthase
What happens in phase two of heme synthesis?
- In the cytosol condensation of two delta ALAs form porphobilinogen (PB)
- Condensation of four PBs assemble the tetrapyrrole ring of coproporphyrinogen III
What happens in phase three of heme synthesis?
- Two oxidation reactions of coproporphyrinogen III to install side chain vinyll groups in protoporphyrinogen IX and make fully ocnjugated ring of protophorphyrin IX
- insertion of Fe2 with ferrochelatase
Succinyl CoA + GLycine=___? This also requires what vitamin?
ALA is made and it requires B6 (PLP)
What does lead inhibit within the heme synthesis pathways?
- ALA dehydratase and ferrochelatase
- ALA is neurotoxic it contributes to the neuro sx of lead poisioning
- Heme production lowered
- Causes microcytic and hypochromic anemia
What are porphyrias?
- inherited metabolic disorders caused by defects in heme synthesis
- Purple pigment
- Can be acute hepatic or erythropoietic
- hepatic-neuro sx
- erythropoietic-photosensitivity
A defect in PBG deaminase in the liver will lead to ____.
- Acute intermittent porphyria
- It is auto dominant
- Deficiency leads to excessive production of ALA and PBG resulting in periodic attacks of ab pain and neuro dysfxn
- Hepatic
Uroporphyrinogen III synthase defect results in what condition?
- Congenital Erythropoietic porphyria
- Results in build up of Uroporphyrinogen I and its oxidation product of uroporphyrin I
- Produces red color in urine, teeth, and destroys RBC and causes skin photosensitivity
What is “Celebrity Porphyrias”?
- Variegate porphyria
- Includes intermittent episodes of abdomen pain, delirium, hallucinations, convulsions
what does heme oxygenase do?
- Clips heme and opens up the ring into a linear form to make biliverden
What does biliverdin reductase do?
- Adds two protons to biliverdin to make bilirubin
How do we get conjugated bilirubin from unconjugated and what does this do?
- add two glucuronate acid to bilirubin with Bilirubin UDP glucuronyltransferase
- Makes bilirubin more soluble
When bilirubin is released to blood what occurs after all the way to the end?
- It complexes with albumin and travels to liver where it gets conjugated with UDP glucuronyltransferase
- conjugated/direct bilirubin-diglucuronide goes to gall bladder
- galll bladder releases it to SI and it gets converted into bilirubin and then microbiota makes urobillinogen
- Urobillinogen either gets reabsorbed and converted in kidneys to urobilin OR not reabsorbed and converted into sterocobilin in LI and excreted as feces
What is jaundice?
- hyperbilirubinemia
- Elevated levels of BR in blood stream
- It is an imbalance btw production and excretion of bilirubin
What is a pre-hepatic jaundice?
- Increased production of unconjugated BR
- Excess hemolysis
- Internal hemorrhage can cause this as well as maternal fetal incompatibility
- Problem occurs before liver
What is intra hepatic jaundice?
- Impaired hepatic uptake conjugation or secretion of ocnjugated BR
- Can be causaed by general hepatic dysfxn
- Criggler-Najjar syndrome
- Gilbert syndrome
- Liver cirrhosis
- Viral hepatitis
What is post hepatic jaundice?
- AKA Cholestatic jaundice or cholestasis
- Problems with BR excretion caused by:
- cholangiocarcinoma
- gall stones
- Liver disease
- drugs
- obstruction to bile drainage
- Conjugated BR in the urine so dark urine
- Pale stool
Complete UDP-GT deficiency?
- Criggler Najjar syndrome
- Type one is complete absent of the gene resulting in severe hyperbilirubinemia causeing kernicturus
- Tx:
- blood transfusion
- phototherapy
- heme oxygenase inhibitors
- liver transplant
Mutation in UDP GT gene?
- Criggler Najar syndrome type II
- enzyme has about 10% activity
Gilbert syndrome?
- Common benign disorder resuts from reduced UDP GT
- 25% activity
- fasting stress or alcohol can increase BR
What is hepatitis?
- Inflammation of liver leading to dysfunction
- Caused by virus, alcoholic cirrhosis, or cancer
- Increased levels of unconjugated and conjugated BR in the blood
What is neonatal jaundice?
- Called Physiological jaundice
- Immature hepatic metabolic paths unable to conjugate and excrete bilirubin
- Deficiency of UDP GT enzyme bc not mature yet
- Breakdown of fetal hemoglobin as its replaced with adult
