Erythrocyte Structure and Function: Topic 1

Question 1

what are the three main types of cells in the blood?

Answer 1

1. erythrocytes (RBC)
2. leukocytes (WBC)
3. thrombocytes (platelets)

Question 2

why are RBCs red?

Answer 2

Hb in RBC contains iron that creates a red pigment when it binds to oxygen

Question 3

what is the function of RBCs?

Answer 3

they reversibly bind oxygen and carbon dioxide to deliver oxygen to the tissues and to remove carbon dioxide in the lungs

this reversible binding creates a difference in oxygen content between venous and arterial blood; therefore, blood can be classified as oxygenated or deoxygenated

Question 4

do RBCs have organelles or nuclei?

Answer 4

NO

the lack of these structures maximizes the available volume for hemoglobin

Question 5

what allows RBCs to bind with oxygen?

Answer 5

high concentrations of Hb within RBCs

Question 6

what’s the diameter of a RBC?

Answer 6

7.8 μm

RBCs are in all tissues and tumors so you can use them like a ruler to see how big stuff is

Question 7

why is the RBC a biconcave structure?

Answer 7

biconcave shape gives the RBC a relative excess of membrane, which affords the cell extraordinary flexibility and allows it to pass through openings much smaller in diameter than itself

Question 8

in what diseases is the biconcave structure of RBCs effected?

Answer 8

sickle cell disease

hereditary spherocytosis

Question 9

how does sickle cell decrease the flexibility of the structure of RBCs?

Answer 9

hemoglobin S forms a stiff rod inside the RBC and gives the cell a crescent or “sickle” shape

Sickle-shaped RBCs are not flexible and can accumulate in small blood vessels, blocking the flow of blood

Downstream tissues are deprived of oxygen, leading to a pain crisis

Question 10

how does hereditary spherocytosis decrease the flexibility of the structure of RBCs?

Answer 10

results from molecular defects in genes that code for RBC membrane proteins or anchoring proteins

mutations in these proteins cause RBCs to have a spherical shape, leading to cytoskeletal instabilities and frequent hemolysis

a shortage of RBCs due to hemolysis leads to hemolytic anemia

Question 11

what play an important role in maintaining the biconcave shape of RBCs?

Answer 11

plasma membrane proteins!

both integral membrane proteins and peripheral membrane proteins in the lipid bilayer of the plasma membrane of RBCs come together to form a lattice-like network that is anchored to the inner surface of the RBC plasma membrane

Question 12

which plasma membrane proteins play an important role in maintaining the biconcave shape of RBCs?

Answer 12

1. spectrin (most abundant)
2. actin
3. ankyrin
   4, band 3
4. band 4.1
5. band 4.2

Question 13

what does the cytoskeletal lattice of a RBC do?

Answer 13

the cytoskeletal lattice gives stability and flexibility to the RBCs

as RBCs make their way through vessels of different areas of the body, the chemical and physical environment changes

these changes prompt the membrane proteins to rearrange, and in turn the cell gains much flexibility

Question 14

which plasma membrane proteins anchor the cytoskeletal lattice of the RBC to the cell membrane?

Answer 14

ankryin, band 3, band 4.1, and band 4.2

Question 15

what is the structure of hemoglobin?

Answer 15

complex molecule containing four heme groups and four globin chains

Question 16

what is a heme group made of?

Answer 16

each Hb molecule has 4 heme groups

each heme group consists of a protoporphyrin ring with an iron molecule at its center, attached by four nitrogen bonds

the iron molecule reversibly binds oxygen and carbon dioxide, allowing hemoglobin to carry oxygen to tissues and return carbon dioxide to the lungs

each heme group is surrounded by a globular polypeptide molecule called a globin chain

Question 17

what are the types of globin chains in Hb?

Answer 17

Each heme group is surrounded by a globular polypeptide molecule called a globin chain

There are four types of globin chains – α, β, δ, and γ – and they always appear in pairs: two of one type of chain, and two of another

Question 18

which globin chain is always in Hb?

Answer 18

hemoglobin always has one pair of α chains, but the other pair varies with age

Question 19

what is adult hemoglobin?

Answer 19

hemoglobin A1

two alpha chains and two beta chains - each with their own heme molecule

Question 20

what is fetal hemoglobin?

Answer 20

hemoglobin F

two α chains and two γ chains

Question 21

is HbF or HbA better at binding oxygen?

Answer 21

hemoglobin F is much better at binding oxygen than hemoglobin A1, so that the fetus can extract oxygen from the mother’s bloodstream

Question 22

when does the switch from HbF to HbA happen?

Answer 22

around 6 months

at 4 months the infant begins to make β chains, and the production of γ chains begins to diminish

swap is basically complete around 8 months of age

Question 23

does γ chain production stop after 6 months old?

Answer 23

production of γ chains never entirely stops

a small amount (less than 1%) of total hemoglobin in the adult is composed of hemoglobin F

Question 24

what is hemoglobin A2?

Answer 24

two α chains and two δ chains

it always comprises a small (1-2%) amount of total hemoglobin but its function is unknown.