RBC Flashcards
(50 cards)
Composition of blood
RBC
Buffy coat (WBC, Platelets)
Plasma
Normal pH of blood?
7.35-7.45
Plasma vs. Serum
Plasma
- no clotting factors
- centrifuged then add anticoagulant
- used in physiologic
Serum
- no clotting factors
- no fibrinogen!!
- used in lab reference
Can it synthesize new membrane proteins?
No but it can freely exchange in circulating lipoprotein lipids.
How does an RBC generate energy?
Anaerobic glycolysis
Shape of an RBC? Importance?
Biconcave disc for better gas exchange and most importantly, allows it to be deformable (it’ll undergo a lot of pressure inside vessels). If not deformable, will easily lyse.
RBC Proteins?
Peripheral (5)
integral (2)
How do you form a red blood cell? Major site of production?
Pluripotent stem cell — IL3 —> Mixed myeloid progenitor (CFU-GEMM) — Erythropoietin from kidney —> erythroid progenitor —> Erythroblast —-loss of nucleus —> Reticulocyte —-leaves BM into blood —> Erythrocyte
Major site of production: BM
Characteristics of a mature erythrocyte?
- components missing?
- ATP generation?
- replication
- life span
>No intracellular organelles >Can generate ATP by glycolysis ONLY >Like a dead bag containing hemoglobin >Cannot replicate >Has a finite life span
How does a red blood cell metabolize glucose?
- Embden-Meyerhoff Pathway (Glycolysis)
- Accts for 90% of glucose metabolism in RBC
- Anaerobic so: Glucose —-oxidized—> Pyruvate
- END PRODUCT: Lactate
- ATP: 2 per glucose molecule - Hexose Monophosphate Shunt (Pentose Phosphate Pathway)
- Accts for 10% of glucose metabolism
- Aerobic
- Alternative pathway for producing a 5C sugar
- Product: NADPH; keeps glutathione reduced
- No enzyme -> Low glutamine levels -> Oxidation of RBC -> Hemolysis -> Hemolytic anemia - Rapaport-Luebering Shunt
- Converts 1,3-bisphosphoglycerate to 2,3-bisphosphoglycerate (2,3 BG) via BPG mutase
- 2,3 BG = negative allosteric effector of O2 affinity, decreases oxygen affinity of hemoglobin, promoting its release in peripheral tissues; impt in high altitudes & cases of anemia - Glutathione System (Anti-oxidative system of RBC)
- Major defense against free radicals
- Oxidized glutathione reduces protective effects
- GSH is reduced glutathione
- GSSG is oxidized glutathione
What is the Warburg Effect?
Cancer cells predominantly produce energy by a high rate of glycolysis followed by lactic acid fermentation in the cytosol.
Myoglobin and hemoglobin structural similarities?
- Both contain heme
Structure of myoglobin?
What happens when to structure when O2 is bound vs unbound?
- CO binds 25k times better than O2 so why doesn’t it completely displace O2 from heme iron in both myoglobin and hemoglobin?
- Structure of hemoglobin?
- Similarities and differences of myoglobin and hemoglobin?
- Cooperative vs hindered binding?
- Dissociation curves
- Discuss
1. Myoglobin is rich in alpha helix. Its surface is rich in polar and charged amino acid side chains. Globular.
- Apoproteins of the globins create a hindered environment for their gaseous ligands. When C-O binds to free heme, all 3 atoms lie perpendicular to the plane of the heme maximizing overlap between the lone pair of electrons on the sp hybridized carbon of the CO molecule and Fe2+ iron. BUT DISTAL HISTIDINE sterically precludes this high affinity (= reduces binding strength) and permits O2 to attain most favorable orientation. Since O2 madami amt, it dominates.
- Hemoglobin is tetrameric composed of pairs of two diff polypeptide subunits (a2b2, a2y2, a2bs2, a2o2). Primary structures of greek letter chains of human Hemoglobin are highly conserved.
- Myoglobin and beta polypeptide of Hemo A share almost identical 2’ and 3’ structures - location of heme and helical regions, presence of amino acids specifically properties at comparable regions.
Diff: Hb has 8 rather than 7 helical regions - Hindered binding: #4;
COOPERATIVE BINDING: Hb can bind up to 4 molecules of O2/tetramer; 1 per heme. Hemoglobin will bind O2 if other O2 are already bound permitting Hb to maximize both qty of O2 loaded at PO2 of lungs and qty of O2 released at PO2 of peripheral tissues; exclusive property of certain multimeric proteins - Myoglobin good for O2 storage but not transport because the oxygen-binding curve for myoglobin is HYPERBOLIC (It loads O2 readily but inefficient release at PO2).
Hemoglobin behaves as if it were 2 proteins. High PO2, high affinity for O2 (this form is referred to as R for relaxed state Hb). At lower PO2, Hb has lower affinity for O2 (aka T or taut state) enabling release in large proportions. Dynamic change between states = sigmoidal O2-binding curve.
Role of CO and O2 in relation to heme structure?
> CO2
15% CO2 are carried by Hb as carbamates. Carbate formation changes CHARGE on amino terminals (+ —> -). Change in charge favors salt bridge formation between alpha and beta chains. Remaining CO2 carries as bicarbonate.
In venous blood CO2 —hydration —> H2CO3 —dissoc —> HCO3- + H+
T-state Hb binds 2H+/tetramer. Protein binding helps buffer against blood acidification. It enhances qty of CO2 absorbed by RBC by favoring conversion of CO2 to carbonic acid to bicarb.
CO2, in turn, enhances O2 delivery to respiring tissues by stabilizing T state by inducing carbamation and lowering pH.
In lungs, process reverses.
*Bohr effect
What is hemoglobinopathy?
Discuss:
1. Methemoglobin
- HbM
- HbS
Abnormalities resulting from mutations in genes encoding the alpha or beta Hb subunits affecting its biological function.
Examples:
- Methemoglobin
- heme iron: Fe2+ -> Fe3+
- result: methemoglobin unable to bind or transport O2
- normally, Fe3+ is returned to Fe2+ by methemoglobin reductase
- causes: agents, low methemoglobin reductase activity, inheritance of mutated gene for Hb called HbM - HbM
- His F8 replaced by Tyr
- Fe of HbM forms a tight ionic complex with phenolate anion of Tyr stabilizing Fe3+ form
- In alpha chain HbM, R-T equilib favors T state (low O2 affinity and bohr effect absent)
- In beta chain HbM, switching - HbS
- Nonpolar aa valine —> polar surface residue Glu6 os the beta subunit
- effect: generating hydrophobic “sticky patch” on surface of beta subunit of both oxyHbS and deoxyHbS
- char: deoxyHbS polyermizes to form long, insoluble fibers; binding of deoxyHbA terminates fiber polymerization; since HbA lacks 2’ sticky patch; twisted helical fibers DISTORT ERYTHROCYTE INTO SICKLE SHAPE rendering it vulnerable to lysis
Biomedical implications
- Myoglobinuria
- Anemia
- Thalassemias
- Glycated Hemoglobin (HbA1c)
- Myoglobin may appear in urine
Scenario: Ff massive crush injury in skeletal muscle then renal damage. Mb can be detected in plasma ff a MI; enzyme assays more sensitive index of myocardial injury - Reduction in no. of RBC or Hb in blood
Causes: Impaired synthesis of Hb (lack of Fe) or erythrocytes (lack of folic acid/Vit B12) - Genetic defect resulting from partial or total absence of 1 or more alpha or beta chains of Hb
Common: alpha thal, beta thal mutations
Nomenclature: (alpha^0) = absent alpha chain; (alpha^-) = alpha chain synthesis reduced
Remedies: marrow transplantation + treatment - Glycation: Blood glucose enters erythrocytes and forms a covalent adduct with e-amino groups of lysyl residues and the N-terminal val of Hb beta chains
- not enzyme-catalyzed unlike glycosylation
- fraction of Hb glycated is proportionate to blood glucose concentration
- Measurement provides info for diabetes mellitus management
- represents mean blood glucose conc over preceding 6-8 weeks
Heme biosynthesis. Which of the enzymes are mitochondrial? Cytosolic?
8 steps!
Mitochondrial: Enzyme 1, 6-8
Cytosolic: 2-5
Where does heme biosynthesis occur?
Almost all mammalian cells except mature erythrocytes (no mitochondria). 85% heme made in erythroid progenitor in bone marrow and the majority of the remaining in hepatocytes.
Porphyrinogen vs Porphyrin
Porphyrinogen
-colorless
Porphyrin
- colored due to conjugate double bonds in the pyrrole rings linking methylene groups
- has a Soret band (sharp absorption band near 400 nm)
ALAS1 vs ALAS2?
ALAS1
- throughout body tissues
- reaction catalyzed by ALAS1 is rate-limiting for biosynthesis of heme in liver
- has a short half-life
- heme acts as a negative regulator of ALAS1 synthesis & also affects translation and translocation from cytosolic site of synthesis to mitochondrion.
ALAS2
-expressed exclusively in erythrocyte precursor cells
What happens in lead poisoning?
Lead poisoning
Pb inactivates Ferrochelatase and ALA dehydratase by combining with essential thiol groups.
Signs: Elevated levels of protoporphyrin in erythrocytes and elevated urinary levels of ALA and coproporphyrin.
Heme catabolism
- Globin -> degraded to constituent amino acids
- Release Fe -> Enters the iron pool
- Iron-Free portion of heme -> degraded mainly in reticuloendothelial cells of liver, spleen, bone marrow
-Heme catabolism from all heme proteins:
Location: Microsomal fraction of cell
Enzyme: Heme oxygenase
Rxn: Hemin + 3 O2 + 7e- —-> Biliverdin + CO + Fe3+
Biliverdin +NADPH ——biliverdin reductase—-> Bilirubin + NADP+
Observed as the purple color of heme conversion to yellow bilirubin by reticuloendothelial cells
- Neonatal “Physiologic Jaundice”
Defects of Bilirubin UDP-Glucuronosyltransferase:
- Gilbert Syndrome
- Type I Crigler-Najjar Syndrome
- Type II Crigler-Najjar Syndrome
- Toxic Hyperbilirubinemia
- Most common cause of conjugated hyperbilirubinemia
* Dubin-Johnson Syndrome - Urobilinogen and Bilirubin as Clinical Indicators
- Unconjugated hyperbilirubinemia
- results from accelerated hemolysis and an immature hepatic system for the uptake, conjugation, and secretion of bilirubin
- Effect: Bilirubin-glucuronosyltransferase activity reduced
- UDP-glucuronate synthesis reduced
- If left untreated, bilirubin enter blood-brain barrier = hyperbilirubinemic toxic encelopathy or kernicterus - mental retardation
- Treatment: Phototherapy (Blue Light) and Phenobarbital administration - Harmless syndrome if 30% of bilirubin UDP-glucuronosyltransferase activity is retained
- Severe congential jaundice ( X> 20mg bilirubin/dL serum).
Symptoms: w/ Brenda = complete absence of hepatic UDP-glucuronosyltransferase; Fatal w/in 1st 15 months of life
Treatment: Phototherapy reduces plasma bilirubin but phenobarbital no effect - Some bilirubin UDP-glucuronosyltransferase activity is retained. More benign than type 1.
- Unconjugated hyperbilirubinemia can result from toxin-induced liver dysfunction caused by Cf, CCl4, etc.
Cause: Hepatic parenchymal cell damage impairing bilirubin conjugation
Treatment: Large doses of phenobarbital. - Most common cause: Blockage of hepatic or common bile ducts due to gallstone or cancer of the head of pancreas
Cause: Bilirubin diglucuronide cannot be excreted into hepatic veins and lymphatics
Manifestations: Pale blood, urine, and stool (Choluric jaundice)
Dubin-Johnson syndrome
- autosomal recessive consists of conjugated hyperbilirubinemia in childhood or adult life
- caused by mutations in gene encoding protein involved in secretion of conjugated bilirubin into bile
7.
Complete obstruction of bile duct
= bilirubin no access to intestine to be converted to urobilinogen
= no urobilinogen present in urine
= thus, w/ conjugated bilirubin but w/o urobilinogen = intrahepatic or posthepatic obstructive jaundice
Jaundice secondary to hemolysis
*Table
Function of Platelets? Low platelet count causes? What is thrombocytopenia?
Platelets - help staunch the outflow of blood from damaged tissues
Low platelet = increase patient’s vulnerability to hemorrhage
Thrombocytopenia - low platelet count in the case of anemia
