Heme-Iron metabolism Flashcards
What are the sites of heme synthesis? Where does it occur the most, and why?
erythroid cells (85%) and hepatocytes (15%) ERYTHROID CELLS cuz this is the major site of hemoglobin synthesis
Why will you find heme synthesis in hepatocytes?
because the cytochrome systems such as p450 and the mitochondrial electron transport chain are in the liver and need heme
Heme and iron metabolism are (blank)
tightly coupled
(blank) stimulates erythropoiesis
hypoxia
We eat iron and it is aborbed in the (blank) and transported through the circulatory system bound to (blank) and then most of the iron goes to the bone marrow because that is where most of the synthesis of (lank) is occuring.
duodenum
transferrin
hemoglobin
The rate of erythropoiesis is (blank) and is at the same rate as it is (blank)
high
broken down
What does erythropoiesis require?
iron
hemoglobin
heme
within the (blank) hematopoietic stem cells turn into erythroid progenitors to divide into erythroblast. The erythroblast then gets rid of its nucleus and becomes a (blank) and leaves the bone marrow
bone marrow
reticulocyte
What all do reticulocytes have to lose to be a erythrocyte?
mitochondria, ribosomes, nucleus
Mature erythocytes have three important processes associated with them, what are they
glycolysis, pentose phosphate shunt, reductive capacity
What is the most important protein for oxygen sensing?
HIF-1 (hypoxia inducable factor)
When cell becomes starved for oxygen what happens?
hif-1 binds to DNA to create oxygen-regulated gene expression
What happens under normal oxygen conditions
proyl hydroxylase binds to Hif-1 and adds an OH group to keep it from transcribing oxygen-regulated gene expression and thus gets degredated
What does HIF-1 do?
increases synthesis of erythropoietin (RBC production), transferrin, transferrin receptor and ceruloplasmin (iron oxidation; release of iron from stores)
Oxygen transport
upregulation of Anaerobic energy (glucose uptke and glycosis) -> if you are hypoxic you want to increase your ability to create ATP in the absence of oxygen
(blank) regulated genes that promote cell survival under ischemic conditions. SO it will effect what 4 things?
HIF-1
respiration, energy metabolism, vasculogenesis, regulates erythropoiesis
(blank) is a crucial regulator of erythropoiesis, which synchronizes cellular responses, hemoglobin and iron metabolism, and other metabolic pathways, assuring optimal red cell production to satisfy body needs
HIf-1
(blank) is a protein hormone produced by kidney
Erythropoietin
(blank) binds with receptors in bone marrow, where it stimulates production of RBC (erythrocytes)
erythropoietin (EPO)
(blank) is used to treat certain forms of anemia (e.g., due to chronic kidney failure)
EPO
Since (blank) accelerates erythrocyte production it also increases O2 carrying capacity
EPO
(blank) artifically increasing RBC to improve athletic performance. You can do this 2 ways, what are they? What are some side effects off blood doping?
Blood doping
via transfusion or EPO injection
stroke or heart attack
What is excessive proliferation of erythrocytes?
polycythemia
Recombinant EPO is identical to endogenous EPO so how do you detect is for abuse?
check hematocrit levels an reticulocyte count, soluble transferrin receptor count and concentration of beta globin mRNA
what does prolyl hydroxylase need and why is it important?
it needs oxygen and iron to become hydroxylated ,this is important because it tells us if we are under hypoxic conditions cuz if we dont have hydroxylated proline we dont have oxygen : )
What does the reaction or prolyl hydroxylase create other than itself?
CO2 and succinated
Describe heme synthesis
succinyl coa and glycine are coupled via ALA synthase> 2 molecules of ALA + dehydratase-> porphobilinogen-> 4 molecules of porphobilinogen condense and cyclize-> uroporphorinigen III-> coproporphyrinogen III-> protoporphyrinogen III-> protoporphyrin III + Fe 2+-> heme!
When you have 4 molecules of porphobilinogen condense and cyclize what happens?
you lose 4 ammonium ions and create uroporphyrinogen III
When you convert uroporphyrinogen III to coproporphyrinogen III what happens?
you convert all acetate side groups to methyl groups
When you convert corproporphyrinogen III to protoporphyrinogen IX what happens?
some proprionyl side groups are converted to vinyl groups
When you turn protoporphyrinogen IX into protoporphyrin IX what happens?
you add double bonds via protoporphyrinogen oxidase
When you convert protoporphyrin IX (III) to heme what do you add?
Fe2+ is coordinatd to the pyrrole nitrogens via ferrochetolase
Where are the enzymes 1, and 6-8 found in the synthesis of heme? Where are the others found?
in mitochondria
cytoplasm
Individuals with low activities of enzyme 1 develop (blank) , not porphyria
anemia
What does this:
Genetic or acquired abnormality in heme synthesis pathway
Depressions in activities of enzymes 3-8
porphyrias
(blank) is a genetic or acquired abnormality in heme synthesis pathway
porphyrias
Why does porphyrias occur?
1) deficiency of metabolic products downstream from enzymatic block (neuropsychiatric signs and symptoms)
2) accumulation of metabolites upstream from block (photosensitivity)
What is the rate-limiting step in the hepatic heme biosynthesis? Where does this reaction occur?
the ALA synthase catalyzed step
the mitochondria
What are the two major sites of heme synthesis?
in the liver and erythroic cells -> this results in two different versions of ALA
the synthesis of ALAS is under feedback inhibition by (blank)
heme
What are induces of ALAS?
- compounds that increase hepatic cytochrome p450 syntehsis (needs heme)
- accelerated destruction of heme
- if heme formation is inhibited somehow
Since you get two different places where heme synthesis occurs, you also get 2 different different kinds of ALAs, what are they?
ALAS-N (also called ALAS1) (liver) and ALAS2 (erythroic cells)
Which is under feedback inhibition by heme, ALAS-N or ALAS2?
ALAS-N
Most of the control of heme synthesis in the liver is due to what?
inducers of ALAS-N
(blank) increases during erythroid differentiation when heme synthesis is increased
ALAS 2
Thus, regulation of heme synthesis in erythroid cells is (blank) from regulation in liver
distinct
What is the first step of heme catabolism? What does this?
break the ring open via heme oxygenase
What is heme oxygenase?
the rate-limiting reaction in heme catabolism
When you use heme oxygenase on heme what does it create? why is this bad?
bilverdin (green colored) and side products of CO, Iron III, NADP
The reaction creates CO (gets excreted through the lung)
What does bilverdin get reduced into?
bilirubin which breaks some double bonds and now turns yellow
The conversion of heme to bilirubin occurs in (blank) cells. When do you see the conversion of heme to bilirubin grossly?
reticuloendothelial cells
upon bruising where it starts out purple (heme) and then turns yellow (bilirubin)
Where is biliribun produced?
the reticuloendotheial cells of the peripheral tissues
When you break down heme into bilirubin, this now allows bilirubin to do what?
enter the blood stream and connects to albumin which allows it to be taken up by the liver parenchymal cells
When bilirubin enters the liver what happens to it?
it gets conjugated (added sugar/glucuronate) and becomes soluble which allows it to be secreted into bile and then excreted
Bilirubin utilizes (blank) glucoses to become conjugated (put into polar soluble form)
two UDP
The readily excreted form of bilirubin is called (blank). Is that the last place bilirubin will react?
bilirubin diglucuronide
no it reacts further in the colon by bacteria
How do you get jaundice?
too much bilirubin!!!
What are the different ways to get jaundice?
over production of bilirubin
damaged liver
obstruction of excretory duct of liver
If bilirubin is not conjugated what is it called?
If bilirubin is conjugated what is it called?
indirect bilirubin ('free') (still bound to albumin)
direct bilirubinIf you have high concentration of unconjugated bilirubin in the plasma, what are the 3 causes of this?
overproduction
impaired uptake
impaired conjugation
If you have high concentration of conjugated bilirubin, what is the cause of this?
decreased excretion into bile ductules or backward leakage
What is the most common cause of unconjugated hyperbilirubinemia? Who is this common? Why?
physiologic jaundice
newborns
their hepatic system for the uptake, conjugation and secretion of bilirubin isnt completely developed
(blank) bilirubin can penetrate blood-brain barrier! AHH this is why we need to cure it quickly!
unconjugated bilirubin
Why do babies with jaundice get exposed to blue light?
it isomerizes the unconjugated bilirubin making it soluble and therefore excretable
