2) RBC structure Flashcards by Samantha Boyer

3 main parts of RBC essential for survival and function

membrane
hemoglobin
metabolic pathways

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3 layers of RBC membrane and components

outer layer —glycolipids, glycoproteins, proteins
central layer —proteins, cholesterol, phospholipids
inner layer —proteins

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chemical composition of RBC membrane

40% lipids
52% proteins
8% carbs

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used to separate RBC membane proteins

SDS polyacrilamide gel electrophoresis (SDS-PAGE)

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examples of integral proteins

glycophorins A, B, C
Band 3

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most important integral protein

glycophorin A

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2 functions of band 3

anion exchange channel
anchors cytoskeleton to the lipid bilayer

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functions of glycophorins (3)

accounts for membrane sialic acid, giving RBCs a negative charge (repels others)
location of many antigens
anchors cytoskeleton to bilayer

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examples of peripheral proteins

spectrin
ankyrin
adducin
band 4.1
band 4.2
actin

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most abundant peripheral protein

spectrin

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structure of spectrin

helix of two polypeptide chains (α,β)
They form dimers which link with other αβ chains to form tetramers.
The chains bind with other peripheral proteins to form a skeletal network that creates the “cytoskeleton”.

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acts like a strong spring, giving membrane deformability

spectrin

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functions of the cytoskeleton

strengthens membrane
protects cell from shear forces
controls shape and deformability

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tie network of cytoskeleton together

the 2 spectrin complexes

require energy to stay together

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critical to RBC survival as it passes through vessels, and for O2 delivery

deformability

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2 causes of ↓ deformability

loss of ATP; ↓ phosphorylation of spectrin
deposits of Ca2+; ↑ membrane rigidity

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extravascular sequestration

spleen function
cells are squeezed through small sinusoidal orifices, and removed or fragmented

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passively transported across RBC membrane

H2O
anions (Cl and HCO3)

travel through band 3

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actively transported across RBC membrane

Na+ and K+

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intracellular:extracellular ratios for Na and K

Na—1:12
K—25:1

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Na-K pumps prevent ——- hemolysis

osmotic

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3 RBC membrane lipids

phospholipids
glycolipids
cholesterol

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Changes in body lipid transport and metabolism may cause abnormalities in —————– that may alter RBC membrane composition.

plasma phospholipid concentration

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interact with many glycoproteins to form antigens

glycolipids

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RBC cholesterol is in continual exchange with...

unesterified plasma cholesterol

# RBC morphology abnormality proportional ↑ phospholipid & ↑ cholesterol in membrane

target cells

# RBC morphology abnormality abetalipoproteinemia with cholesterol accumulation in membrane (↑chol:PL ratio)

acanthocytes

↓ LCAT (lecithin cholesterol acyltransferase)

schistocytes & target cells

# RBC morphology abnormality ↓ phosphorylated or altered spectrin

bite cells & spherocytes

RBCs are -----% Hgb

34%

Hgb is produced in...

65% in nRBCs 35% in reticulocytes (last stage in which hgb is made)

structure of hgb

- 4 heme groups (4 Fe + 4 protoporphyrin IX rings) - 4 globin chains

carries Fe to young RBC

transferrin

after Fe is added, it goes to the ----------- for insertion in to the protoporphyrin ring

mitochondria

major sites of heme synthesis

- young RBCs of marrow - hepatocytes

ALA term

aminolevulinic acid

byproducts of heme synthesis that do not produce heme

uroporphyrinogen I coproporphyrinogen I

lab tests measure --------- rather than unstable ---------

porphyrins porphyrinogens

only type ----- isomers of porphyrins form heme

III

vitamin required for heme synthesis

Vit B6

In conditions with ineffective utilization of protoporphyrin, there are ↑ amounts of...

free erythrocyte protoporphyrins (FEPs)

lead inhibits...

ALA dehydrase ferrochelatase

porphyria

defect in porphyrin synthesis, especially inherited

most common secondary porphyria

lead poisoning

ways to classify primary porphyrias

- organ — hepatic vs erythropoietic - symptoms — neurological or cutaneous

neurological porphyrias

- acute intermittent porphyria

mixed porphyrias

- variegate porphyria - hereditary coproporphyria

cutaneous porphyrias

- porphyria cutanea tarda - congenital erythropoietic porphyria - erythropoietic protoporphyria

neurological porphyria sx

- **acute attacks** - **↑ ALA and PBG in urine** - abd pain - weakness - nausea - constipation - perspiration - HTN - tachycardia - motor dysfunction - **sensory loss** - **mental disturbances**

cutaneous porphyria sx

- photosensitivity - characteristic skin lesions - no ALA/PBG (no neuro sx)

congenital erythropoietic porphyria sx

- ↑ uro I and copro I (feces, RBCs) - splenomegaly - brown pigment to teeth; fluoresces - blistering - pink urine

enzyme defect of PBG deaminase

acute intermittent porphyria

enzyme defect of protoporphyrin oxidase

variegate porphyria

enzyme defect of coproporphyrinogen oxidase

hereditary coproporphyria

enzyme defect of uroporphyrinogen decarboxylase

porphyria cutanea tarda

enzyme defect of ferrochelatase

erythropoietic protoporphyria

enzyme defect of uroporphyrinogen III cosynthase

congenital erythropoietic porphyria

↑ ALA in urine ↑ PBG in urine

acute intermittent porphyria

↑ ALA, PBG in urine ↑ proto in feces ↑ copro in feces

variegate porphyria

↑ ALA, PBG during attacks ↑ copro in feces

hereditary coproporphyria

↑ uro ↑ copro isomer I

porphyria cutanea tarda

↑ proto in RBC and feces ↑ FEP

erythropoietic protoporphyria

↑ uro I ↑ copro I

congenital erythropoietic porphyria

king george

variegate porphyria

most common porphyria

porphyria cutanea tarda

- ------ and ------ are water soluble so appear in urine. - ------ may be found in urine or feces. - ------ is found only in feces.

PBG and uro copro proto

globin chain production takes place in...

ribosomes in cytoplasm of nRBCs and retics

globin chains on chromosome 16 and 11

16: zeta, alpha 11: beta, gamma, delta, epsilon

3 types of normal adult hgb, structure, prevalence

- Hgb A—2𝛼, 2β—97% - Hgb A2—2𝛼, 2δ—3.5% - Hgb F—2𝛼, 2𝛾—<1%

we differentiate types of hgb by...

hgb electrophoresis

Fe in each heme is -----------; binding sites:

hexacovalent 4 — binding N of protoporphyrin 1 — binding histadine in globin 1 — reversibly binding O2

Fe in hemoglobin Fe in methemoglobin

ferrous (Fe2+) ferric (Fe3+) — no value in respiration

globins and protoporphyrins won't accumulate without one another, but ----- will, causing...

iron organ damage **pappenheimers** (ferritin aggregates) **siderocytes/sideroblasts** ringed sideroblasts

how does hemoglobin production change through gestation and infancy?

<3 months: Gower and Portland hgb (𝛇 and 𝛆) Hgb F replaces these 20th week—β production begins Birth—mostly Hgb F, some Hgb A 6 months—<8% Hgb F 1 year—<2% Hgb F

target cells

rate limiting step for heme synthesis influenced by EPO

1) glycine and succinyl CoA to δALA

acanthocytes

schistocytes