Hemoglobin

Question 1

this makes up 95% of RBC cytoplasmic contents

Answer 1

Hb

• O2 and CO2 transporter molecule
• also functions in maintaining acid-base balance

Question 2

T or F. Free Hb has a short life span outside of the RBC

Answer 2

T

- carried in RBCs to protect from denaturation and loss

Question 3

biconcave disc shape of RBCs purpose

Answer 3

provides max SA for gas exchange

Question 4

Hb structure

Answer 4

• large, globular protein; tetramer
• 4 globin chains, each attached via iron to a heme molecule
• 2 different pairs of polypeptide chains: 2 alpha and 2 non-alpha; 8 helices per globin chain
• 4 heme groups; suspended between 2 helices

NOTE: synthesis occurs mainly in the nucleated stage of RBC maturation

Question 5

requirements for Hb production

Answer 5

1. adequate globin synthesis
2. adequate synthesis of protoporphyrins (heme precursor)
3. adequate iron supply

Question 6

Hb structure in order

Answer 6

• primary: AA sequence of polypeptide
• secondary: chain arrangements in helices and non-helices
• tertiary: helices in pretzel-like configuration
• quaternary: tetramer, spherical

NOTE: AAs that are hydrophobic and heme are tucked away inside; hydrophilic = stays outside = helps Hb be soluble inside RBC cytoplasm

Question 7

globin synthesis occurs between these stages

Answer 7

pronormoblast to reticulocyte

• forms heterodimer with another globin chain
• two heterodimers combine to form a tetramer

Question 8

genes code for # different globin proteins on these chromosomes

Answer 8

6;6; 16 or 11

Question 9

where does heme synthesis occur?

Answer 9

mitochondria and cytoplasm of RBC precursors

Question 10

Protoporphyrin IX + iron = ?

Answer 10

heme

- four pyrroline rings joined by methene bridges + divalent ferrous iron (Fe 2+)

Question 11

T or F. Each iron reversibly binds to one O2 molecule

Answer 11

T!

- if iron becomes oxidized to ferric state (Fe 3+), it can no longer bind O2

Question 12

(#) of the body’s iron is bound to heme

Answer 12

2/3

- converts from ferric to ferrous form several times

Question 13

Plasma transporter molecule

Answer 13

transferrin

- travels to bone marrow for incorporation into Hb ; iron carrier is transferrin

Question 14

impaired production of porphyrins and heme

Answer 14

porphyria
- may be hereditary or acquired
- increased production, accumulation, and excretion of heme precursors
=> leads to photosensitivity, hematologic effects, hepatic effects

Question 15

oxygen dissociation curve

Answer 15

• % O2 saturation vs pO2
• sigmoid shape
  > low affinity for O2 at low tension
  > high affinity for O2 at high tension
• once one molecule of O2 binds, remainder of Hb molecule becomes saturated quickly: cooperativity

Question 16

P50

Answer 16

• denotes Hb’s affinity for oxygen

- partial pressure of O2 when Hb is 50% saturated with O2 = normal (when 37C, pH 7.4) is 26-30 mmHg

Question 17

More O2 required in dissociation curve

Answer 17

shifts right
O2 affinity decrease,
P50 increases

Question 18

Less O2 required

Answer 18

curve shifts left
O2 affinity increases,
P50 decrease

Question 19

Left shift in dissociation curve

Answer 19

• increased affinity for O2
• lower pressure required to reach 50% O2 saturation
• causes: decreased temp, increased pH (Bohr effect), decreased 2,3-BPG

Question 20

red cell organic phosphate formed during RBC metabolism

Answer 20

2,3-BPG

Question 21

an allosteric modifier of Hb

Answer 21

2,3-BPG

• deoxy = tense state
• oxy = relaxed state

Question 22

this causes conformational change and modifies Hb’s affinity for O2

Answer 22

2,3-BPG

- enters between beta chains of hemoglobin

Question 23

a shift in the oxygen dissociation curve due to a change in pH

Answer 23

Bohr effect

• increased CO2 = decreased pH = more need for O2 = right shift
• Hb acts as a buffer

Question 24

Dyshemoglobins

Answer 24

methemoglobin, carboxyhemoglobin, sulfhemoglobin

Question 25

methemoglobin

Answer 25

• reversible binding of Fe 3+
• can’t bind O2
• < 1% is normal
• acquired or hereditary causes of increased amounts
• toxic at > 50%

Question 26

carboxyhemoglobin

Answer 26

• reversible binding of CO to heme iron
• CO affinity is 200 times greater than O2
• toxic at > 5%

Question 27

sulfhemoglobin

Answer 27

• irreversible binding of sulfur to heme
• caused by drugs or exposure to sulfur chemicals
• toxic at > 0.5%