Ch 53 - Red Blood Cells

Question 1

The packaging of hemoglobin and carbonic anhydrase inside specialized cells called _____________ greatly amplified the capacity of circulating blood to carry oxygen to and carbon dioxide away from peripheral tissues.

Answer 1

erythrocytes

Question 2

Anemia, a deficiency in the level of circulating hemoglobin (______________), compromises health by reducing the ability of the blood to supply tissues with adequate levels of oxygen.

Answer 2

<120-130 g/L

Question 3

____________ help staunch the outflow of blood from damaged tissues.

Answer 3

Platelets

Question 4

Hence, replacements are constantly being produced from precursor _________.

Answer 4

stem cells

Question 5

Stem cells possess a unique capacity both to produce unaltered daughter cells (__________) and to generate a diverse range of specialized cell types (__________).

Answer 5

self-renewal

Potency

Question 6

Stem cells may be:

____________ - (capable of producing all the cells in an organism)
____________ - (able to differentiate into cells of any of the three germ layers)
____________ - (produce only cells of a closely related family)
____________ - (produce only one type of cell).

Answer 6

totipotent

pluripotent

multipotent

unipotent

Question 7

Differentiation of hematopoietic stem cells is regulated by a set of secreted glycoproteins called _____________.

Answer 7

Cytokines

Question 8

Stem cell factor and several colony stimulating factors collaborate with _______________ to stimulate the proliferation of hematopoietic stem cells in the bone marrow and their commitment to differentiate into one of several myeloid cell types.

Answer 8

interleukins 1, 3, and 6

Question 9

Binding of _______________ directs myeloid progenitor cells to eventually differentiate into erythrocytes or platelets, respectively.

Answer 9

erythropoietin or thrombopoietin

Question 10

_____________ Are Devoid of Internal Organelles

Answer 10

Mature Erythrocytes

Question 11

The structure and composition of red blood cells reflects their highly specialized function: to deliver the maximum quantity of ____________ possible to tissues and aid in the removal _____________, a waste product of cellular respiration, and ________.

Answer 11

oxygen

carbon dioxide

Urea

Question 12

The interior of a red blood cell contains a massive concentration of hemoglobin, roughly one-third by weight (_______________ for an adult).

Answer 12

30-34 g/dL

Question 13

As a consequence, _________ are unable to reproduce.

Answer 13

enucleated red blood cells

Question 14

Their _____________ possesses a much higher ratio of surface area to volume than more spherical geometries.

Answer 14

disc-like configuration

Question 15

By minimizing the distance to be traversed, these factors promote efficient gas exchange between capillary walls and the rapidly moving (up to ______) erythrocytes.

Answer 15

2 mm/s

Question 16

Erythrocytes generate ATP exclusively via ___________.

Answer 16

Glycolysis

Question 17

True or False:

Red blood cells lack mitochondria, and hence the enzymes of the TCA cycle, electron transport chain, β-oxidation pathway, or ATP synthase.

Answer 17

True

Question 18

Glucose enters red blood cells by ____________, a process mediated by the _______________, also known as glucose permease.

Answer 18

facilitated diffusion

glucose transporter (GLUT1)

Question 19

The glycolytic pathway in red blood cells also possesses a unique branch, or shunt, whose purpose is to isomerize 1,3-bisphosphoglycerate (1,3,-BPG) to ____________________.

Answer 19

2,3-bisphosphoglycerate (2,3-BPG)

Question 20

2,3-BPG binds to and stabilizes hemoglobin in the _________.

Answer 20

T-state

Question 21

Conversion of 1,3-BPG to 2,3-BPG is catalyzed by ______________, a bifunctional enzyme that also catalyzes the hydrolysis of 2,3-BPG to the glycolytic intermediate 3-phosphoglycerate.

Answer 21

2,3-bisphosphoglycerate mutase

Question 22

A second enzyme, _____________, catalyzes the hydrolysis of 2,3-BPG to the glycolytic intermediate 2-bisphosphoglycerate.

Answer 22

multiple inositol polyphosphate phosphatase

Question 23

The activities of these enzymes are sensitive to _______, which insures that 2,3-BPG levels rise and fall at the appropriate times during the oxygen transport cycle.

Answer 23

pH

Question 24

It accounts for ∼2% of the protein of the membrane of the RBC.

Answer 24

GLUT1

Question 25

GLUT1 exhibits specificity for glucose and related d-hexoses (____________ are not transported).

Answer 25

l-hexoses

Question 26

The transporter functions at ∼_____% of its Vmax at the physiologic concentration of blood glucose, is saturable, and can be inhibited by certain analogs of glucose.

Answer 26

75%

Question 27

It is a member of a family of homologous glucose transporters found in mammalian tissues.

Answer 27

GLUT1

Question 28

GLUT1 is not dependent upon _______, unlike the corresponding carrier in muscle and adipose tissue.

Answer 28

insulin

Question 29

Its 492 amino acid sequence has been determined.

Answer 29

GLUT1

Question 30

It transports glucose when inserted into artificial liposomes.

Answer 30

GLUT1

Question 31

GLUT1 is estimated to contain ____ transmembrane helical segments.

Answer 31

12

Question 32

It functions by generating a gated pore in the membrane to permit passage of glucose; the pore is conformationally dependent on the presence of glucose and can oscillate rapidly (∼900 times/s).

Answer 32

GLUT1

Question 33

____________ facilitate CO2 transport.

Answer 33

Carbonic anhydrase

Question 34

True or False:

Like oxygen, the solubility of carbon dioxide in aqueous solution is low, much too low to accommodate more than a few percent of the CO2 produced by metabolically active tissues.

Answer 34

True

Question 35

However, the solubility of the hydrated form of CO2, carbonic acid (H2CO3) and its protonic dissociation product, bicarbonate (HCO3−), are relatively ________.

Answer 35

high

Question 36

The presence in erythrocytes of high levels of the enzyme ______________ enables them both to concentrate waste CO2 by catalyzing its rapid conversion to carbonic acid, and to reverse this process in order to facilitate its expulsion in the lungs.

Answer 36

carbonic anhydrase

Question 37

While red blood cells carry some CO2 in the form of hemoglobin-bound carbamates, roughly ____% is carried internally as dissolved bicarbonate.

Answer 37

80%

Question 38

The RBC is highly dependent upon ___________ as its energy source, for which its membrane contains high-affinity glucose transporters.

Answer 38

glucose

Question 39

___________, producing lactate, is the mode of production of ATP.

Answer 39

Glycolysis

Question 40

True or False:

Because RBCs lack mitochondria there is no production of ATP by oxidative phosphorylation.

Answer 40

True

Question 41

The RBC has a variety of transporters that maintain _________ and __________ balance.

Answer 41

ionic and water

Question 42

Production of ____________ by reactions closely associ-ated with glycolysis is important in regulating the ability of Hb to transport oxygen.

Answer 42

2,3-bisphosphoglycerate

Question 43

The pentose phosphate pathway of the RBC metabolizes about 5%-10% of the total flux of glucose) and produces NADPH. Hemolytic anemia due to a deficiency of the activity of ______________________ is common.

Answer 43

glucose-6-phosphate dehydrogenas

Question 44

________________ is important in the metabolism of the RBC, in part to counteract the action of potentially toxic peroxides. The RBC can synthesize ______ and the ______ required to return oxidized glutathione (G-S-S-G) to the reduced state GSH.

Answer 44

Reduced glutathione (GSH)
GSH and NADPH

Question 45

The iron of Hb must be maintained in the ___________. Ferric iron is reduced to the ferrous state by the action of an NADH-dependent ____________________ involving __________ and ___________.

Answer 45

ferrous state
methemoglobin reductase system
cytochrome b5 reductase and cytochrome b5

Question 46

True or False:

While biosynthesis of glycogen, fatty acids, protein, and nucleic acids does not occur in the RBC, some lipids (eg, cholesterol) in the red cell membrane can’t exchange with corresponding plasma lipids.

Answer 46

False: Some lipids (eg, cholesterol) in the red cell membrane CAN exchange with corresponding plasma lipids.

Question 47

The RBC contains certain enzymes of nucleotide metabolism (eg, _____________, _____________ and ___________). Deficiencies of these enzymes are involved in some cases of hemolytic anemia.

Answer 47

adenosine deaminase
pyrimidine nucleotidase
adenylyl kinase

Question 48

When RBCs reach the end of their lifespan, the globin is degraded to _____________ (which are reutilized in the body), the iron is released from heme and reutilized, and the tetrapyrrole component of heme is converted to _____________, which is mainly excreted into the bowel via the bile.

Answer 48

Amino acids

Bilirubin

Question 49

Newly formed red blood cells retain portions of the __________, __________, _________, etc that were present in their nucleated precursors.

Answer 49

ribosomes, endoplasmic reticulum, mitochondria