6 - Erythrocyte & Heme Biochemistry

Question 1

Majority of Hb synthesized before extrusion of nucleus from the normoblast to become a…

Answer 1

Reticulocyte

***Small amount made in reticulocyte

Question 2

Describe the structure of adult Hb.

Answer 2

2 alpha-globin chains
2 beta-globin chains
1 Heme per subunit (chain)

Question 3

Heme has an ________ atom and it carries O2. It is hydrophobic.

Answer 3

Iron (Ferrous: Fe2+)

Question 4

There is a conformational change in Hb upon oxygen binding. The iron ion lies slightly outside the plane of porphyrin in heme. Upon oxygen binding, it moves into the plane of the heme. This 0.4 A change pulls down the proximal _________ of Hb and changes interaction with associated globin chain.

Answer 4

Histidine

Question 5

What are the two types of curves for myoglobin and hemoglobin?

Answer 5

Hyperbolic curve = Myoglobin

Sigmoidal curve = Hemoglobin

Question 6

Hb binds O2 in a __________ manner. The binding of one molecule of O2 to one heme facilitates the binding of an O2 to another heme.

Answer 6

Cooperative

Question 7

The pH of actively respiring tissues is lower, it drops from 7.4 to 7.2. As pH decreases, binding affinity of Hb for O2 decreases. _________ picks up H+ from tissue. This changes conformation of Hb in a way that favors release of O2.

Answer 7

Histidine

Question 8

This shifts the Oxygen Dissociation Curve to the right because it reduces the O2 affinity so Hb gives up more O2 to tissues. It provides a signal to Hb to let go of O2.

Answer 8

2,3-BPG

Question 9

The drop in pO2 from _______ to ______ torr in exercising tissues corresponds to the steepest part of the Oxygen-binding curve. Consequently, Hb is very effective in providing Oxygen to exercising tissues.

Answer 9

40

20

Question 10

The fetus needs Hb that has higher affinity for O2 than maternal Hb. O2 flows from mother to fetus. HbF does not bind well to _________, therefore it has a higher affinity for O2.

Answer 10

2,3-BPG

Question 11

What is fetal and maternal Hb?

Answer 11

Fetal = HbF (2 alpha, 2 gamma) 
Maternal = HbA (2 alpha, 2 beta) 

***The HbF has a left shift on the ODC because it has a higher affinity for oxygen!

Question 12

Sickle cell anemia is due to a mutation in the Hemoglobin (HbS). There is a mutation at amino acid position 6 in Beta-globin. ________ ________ (negatively charged) changes to _________ (hydrophobic). This causes polymerization of Hemoglobin.

Answer 12

Glutamic Acid

Valine

Question 13

Sickle shaped RBCs will impede circulation and cause hemolytic anemia. It can cause pain, organ damage, stroke, increased infections, etc. Research is ongoing to induce expression of HbF as a cure. Currently using __________ to induce HbF. It works but causes inflammation and is a toxic chemotherapeutic agent.

Answer 13

Hydroxyurea

Question 14

Iron readily exchanges electrons, which makes it an ideal catalyst for oxidation-reduction reactions. Exists in Fe2+ (ferrous) or Fe3+ (ferric) state. Plays a role in ________ transport (is a component of Hemoglobin and Myoglobin).

Answer 14

Oxygen

Question 15

Total body iron is about 3-5 g, most of it is in _______ (about 2.7 g). The average American male ingests 10-20 mg iron daily. We need _______ each day to support Hb production.

Answer 15

RBCs

25 mg

Question 16

Too much _______ can promote cellular damage if not regulated by protein binding.

Answer 16

Iron

Question 17

What is the distribution of iron in humans?

Answer 17

Hemoglobin = 67%
Myoglobin = 5%
Fe-Containing Proteins = 1%
Stored Iron = 27%

Question 18

What are the Fe-Containing proteins in humans?

Answer 18

Cytochromes
Iron-sulfur Clusters
Enzymes using non-heme iron

Question 19

Stored iron is in cells that line the intestines, liver, spleen, and bone marrow. The storage proteins are…

Answer 19

Ferritin – A protein that binds to ferric iron

Hemosiderin – Product of Ferritin breakdown

Question 20

Heme iron (Fe2+ - from animal products) is easily absorbable. It enters the enterocyte, oxidized to Fe3+ by ___________, aka ___________.

Answer 20

Ferroxidase

Cerruloplasmin

Question 21

The Fe3+ (from animal products) is stored in the form of ________ and its degradation product ________.

Answer 21

Ferritin

Hemosiderin

Question 22

Non-Heme iron (Fe3+ - from plant products) is difficult to absorb. It is converted to Fe2+ by Ferric Reductase aka ________ in the presence of Vitamin C.

Answer 22

Dcytb (Duodenal Cyctochrome-Like B protein)

Question 23

Fe2+ enters the enterocyte (from plant products) via _________ _________. After this, it is either converted to Fe3+ by __________ for storage or exported out of enterocyte by __________.

Answer 23

DMT1 (Divalent Transporter-1)
Ferroxidase (aka Cerruloplasmin)
Ferroportin

Question 24

Ferroportin (exports Fe2+ out of enterocyte) requires ________ for its function. Ferroportin levels are regulated by ________.

Answer 24

Hephaestin

Hepcidin

Question 25

Once in blood, Fe2+ is converted to Fe3+ by _________. Fe3+ gets bound to _________ for transport to target tissues.

Answer 25

Ferroxidase | Transferrin

Question 26

Uptake of Transferrin occurs by receptor-mediated endocytosis via ________ ________. Once bound, it is internalized via clathrin-coated pits into endosomes. The low ______ of endosome releases Transferrin from its receptor.

Answer 26

``` Transferrin Receptor (TfR) pH ```

Question 27

The uptake of iron in the __________ (where Heme is made) is very efficient. The endosome transiently docks on it and transfers iron directly via ________.

Answer 27

Mitochondria | DMT1

Question 28

Iron content in body is regulated by modulating its absorption by the peptide hormone _________.

Answer 28

Hepcidin

Question 29

Hepcidin is a 25 amino acid peptide made by the liver. It exerts its regulatory effect by binding to _________. The binding of Hepcidin to _________ causes its internalization and its subsequent degradation in lysosomes.

Answer 29

Ferroportin | Ferroportin

Question 30

Levels of Hepcidin are controlled by a complex signaling pathway involving the protein Transferrin, its receptor and a protein called _______.

Answer 30

HFE (Human Homeostatic Iron Regulator Protein)

Question 31

When iron is (HIGH/LOW) -- Hepcidin expression is up, Ferroportin levels are down, and Iron absorption is low.

Answer 31

High

Question 32

When iron is (HIGH/LOW) -- Hepcidin expression is down, Ferroportin levels are up, and Iron absorption is high.

Answer 32

Low

Question 33

If iron absorption is low, then there is Fe...

Answer 33

Deficiency

Question 34

If iron absorption is high, then there is Fe...

Answer 34

Overloading

Question 35

Iron deficiency can cause _________ _________ _________, and the treatment is dietary iron supplementation.

Answer 35

Hypochromic Microcytic Anemia

Question 36

This is the increased absorption of iron which then accumulates in the heart, liver, and pancreas. It causes liver cirrhosis, hepatocellular carcinoma, diabetes, arthritis, and heart failure.

Answer 36

Hereditary Hemochromatosis (HH or Iron Overload)

Question 37

Classical HH is autosomal recessive and is caused by mutations in the ________ protein. It causes a dysregulation of iron uptake and export by enterocytes (increased absorption). Treatment is blood letting and iron chelators.

Answer 37

HFE ***Remember HFE is important for Hepcidin, which is what causes the internalization of Ferroportin. Ferroportin is the transporter of iron out to the tissues.

Question 38

What are the iron levels for HH?

Answer 38

15 g ***Normal is 3 to 5 g!

Question 39

RBC production is dependent on ________ and ________. Deficiency of these can cause a severe anemia called Megaloblastic Anemia. This occurs due to diminished synthesis of _______ in developing RBC in bone marrow. Continual _______ synthesis is required for production of erythroblasts.

Answer 39

Folate (Folic Acid) Vitamin B12 (Cobalamin) DNA DNA

Question 40

This is caused by deficiency of Folate (Folic Acid) and Vitamin B12 (Cobalamin). It is characterized by large erythrocytes. There is normal Hb content in relation to size.

Answer 40

Megaloblastic Macrocytic Anemia

Question 41

For Megaloblastic Macrocytic Anemia, the bone marrow shows large erythroblasts (called _________). There are also hyper-segmented ________ (more than 5 lobes -- normally 3 to 4).

Answer 41

Megaloblasts | Neutrophils

Question 42

Folic acid exists in a number of derivatives collectively known as folates. Folic acid has 3 parts, which are...

Answer 42

1) Pteridine -- nitrogen containing ring 2) PABA (p-amino-benzoic acid ring) 3) Glutamate residue

Question 43

Folate can be reduced to DHF by dihydrofolate reductase. It is then further reduced to ________ by dihydrofolate reductase. This is the active form.

Answer 43

THF (Tetrahydrofolate)

Question 44

This is important for the synthesis of purines and the pyrimidine thymine. It serves a vital role in DNA synthesis.

Answer 44

THF

Question 45

Folic acid is absorbed in the small intestine (jejunum). The liver stores 5 to 10 mg folate which can last 3 to 6 months. Most dietary sources have folate present in the ______ form. Once absorbed in the intestine, it's reduced to ________. This is the primary circulating for in the bloodstream.

Answer 45

DHF | N5-Methyl-THF

Question 46

This is an antineoplastic agent and inhibitor of DNA synthesis. It is a strong inhibitor of Dihydrofolate Reductase.

Answer 46

Methotrexate

Question 47

If _______ is not available, then folate is stuck as N5-Methyl-THF. This is called the folate trap.

Answer 47

Vitamin B12

Question 48

Vitamin B12 removes the ________ group from N5-Methyl-THF to make Methyl-Cobalamin (B12-CH3) and release THF.

Answer 48

Methyl

Question 49

B12 is found in ________ products, and it can cause Megaloblastic Macrocytic Anemia because of its impact on DNA synthesis. 85% of B12 deficiency is from the lack of a protein called ________ ________.

Answer 49

Animal | Intrinsic Factor

Question 50

Dietary B12 binds to ________ proteins. Proteases from the pancreas degrade R-binder proteins in the duodenum releasing B12. ________ ________ then carries B12 to the ileum from where it is released into the blood stream.

Answer 50

R-binder | Intrinsic Factor

Question 51

Intrinsic Factor-Cobalamin complex is carried by ___________ in blood. The complex is taken up by cells via receptor-mediated endocytosis.

Answer 51

Transcobalamin II

Question 52

Vitamin B12 deficiency can occur due to lack of Intrinsic Factor (necessary for B12 absorption). This is called __________ __________, which is a type of Megaloblastic Macrocytic Anemia. Condition results from failure to absorb Vitamin B12 resulting from unavailability of Intrinsic Factor (IF).

Answer 52

Pernicious Anemia

Question 53

Pernicious Anemia can be tested via routine CBC. We test serum B12 and folate (folate deficiency vs. B12 deficiency). In a B12 deficiency, it is important to know how the deficiency occurred. We need to know if it's lack of B12 in diet or a difficulty in absorption. What is the "gold standard" for testing this?

Answer 53

Schilling Test

Question 54

Describe part one of the Schilling Test.

Answer 54

0.5-1.0 ug oral dose of 57Co-labeled B12. Also give injection of 1,000 ug unlabeled B12 cobalamin. This saturates all B12 cobalamin receptors in the liver to prevent radioactive B12 binding. If absorbed from the GI, it will pass into urine. Urine is collected for 24 hours, looking for presence of radioactive B12. If present = Normal absorption of B12 and radioactivity shows in urine. B12 deficient diet is answer. If absent = B12 not absorbed -- Pernicious Anemia -- Continue to Part 2

Question 55

Describe part two of the Schilling Test.

Answer 55

0.5-1.0 ug oral dose of 57Co-labeled B12 plus Intrinsic Factor. Also give injection of 1,000 ug unlabeled B12 cobalamin. This saturates all B12 cobalamin receptors. Urine collected after 24 hours, looking for presence of radioactive B12. If present = Pernicious Anemia due to lack of Intrinsic Factor

Question 56

Briefly describe the composition of Hb and Heme.

Answer 56

Hb composed of 4 globular protein sub-units, each bound to an iron containing heme. Heme has a heterocyclic porphyrin ring with iron present in the center. Porphyrin rings are four 5-membered rings.

Question 57

In Heme, iron is present in the _________ state and oxidation to ________ states will inactivate Hemoglobin.

Answer 57

Ferrous | Ferric

Question 58

Where does biosynthesis of Heme occur?

Answer 58

Primarily in liver and erythroid cells of bone marrow

Question 59

What are the phases of Heme and where do they occur?

Answer 59

Phase I -- in Mitochondria Phase II -- in Cytosol Phase III -- in Mitochondria

Question 60

This phase of Heme synthesis occurs in the Mitochondria and is the synthesis of ALA from Glycine and Succinyl CoA.

Answer 60

Phase I

Question 61

This phase of Heme synthesis occurs in the Cytosol and is the condensation of two delta-ALAs to form PB. Condensation of four PBs to assemble the tetrapyrrole ring system of coproporphyrinogen III.

Answer 61

Phase II

Question 62

This phase of Heme synthesis occurs in the Mitochondria and consists of two oxidation reactions of coproporphyrinogen III to install the side-chain vinyl groups in protoporphyrinogen IX and generate the fully conjugated ring system of protoporhyrin IX. Insertion of Fe2+ by ferrochelatase gives heme.

Answer 62

Phase III

Question 63

Defects in one or more stages of heme synthesis causes...

Answer 63

Porphyrias

Question 64

For Phase I of Heme synthesis, ALA Synthase needs ______. A deficiency in this can cause diminished Heme synthesis, making RBCs pale. Iron stores are usually elevated (anemia).

Answer 64

B6 (Pyridoxal Phosphate)

Question 65

In lead poisoning, lead inactivates 2 important enzymes in the heme synthesis pathway. These enzymes are...

Answer 65

``` ALA Dehydratase (contains Zn) Ferrochelatase (contains Fe) ```

Question 66

In lead poisoning, both _______ and _________ accumulate.

Answer 66

ALA | Protoporphyrin IX

Question 67

In lead poisoning, ALA is neurotoxic, which continues to neurological symptoms of lead poisoning. ALA resembles the neurotransmitter ________. Heme production is lowered. This causes anemia (microcytic and hypochromic). It also impacts _______ synthesis and energy metabolism because cytochromes (heme containing compounds) are not synthesized.

Answer 67

GABA | ATP

Question 68

Porphyrias are inherited metabolic disorders. They are caused by defects in Heme synthesis. There are different types depending on the enzyme defect, which are...

Answer 68

Acute Hepatic -- neurological symptoms | Erythropoietic -- affect skin, photosensitivity

Question 69

This type of porphyria is a defect in the enzyme PBG Deaminase (in liver). It is hepatic and has the following characteristics: - - Autosomal dominant - - Deficiency leads to excessive production of ALA and PBG - - Periodic attacks of abdominal pain and neurologic dysfunction

Answer 69

Acute Intermittent Porphyria

Question 70

This type of porphyria is a defect in the enzyme Uroporphyrinogen III Synthase (in erythrocytes). It is erythropoietic and has the following characteristics: - - Autosomal recessive - - Deficiency leads to accumulation of Uroporphyrinogen I and its red-colored, air oxidation product Uroporphyrin I - - Photosensitivity; red color in urine and teeth; hemolytic anemia

Answer 70

Congenital Erythropoietic Porphyria

Question 71

This type of porphyria is a defect in the enzyme Uroporphyrinogen Decarboxylase. It is hepatoerythropoietic and has the following characteristics: - - Autosomal dominant - - Deficiency leads to accumulation of Uroporphyrinogen III, which converts to Uropporphyrinogen I and its Uroporphyrin oxidation products. - - It is the most common porphyria in the United States; photosensitivity resulting in vesicles and bullae on skin of exposed area; wine red-colored urine

Answer 71

Porphyria Cutanea Tarda (PCT)

Question 72

This type of porphyria is a defect in the enzyme Protoporphyrinogen IX Oxidase. It is hepatic and has the following characteristics: - - Autosomal dominant - - Photosensitivity and neurologic symptoms and developmental delay in children

Answer 72

Variegate Porphyria

Question 73

This celebrity has Variegate Porphyria. He had intermittent episodes of abdominal pain, delirium, hallucinations, and convulsions. Medicines were given to him that contained arsenic which likely triggered these episodes. Became insane towards the last years of his life.

Answer 73

King George III

Question 74

What system handles the degradation of Hemoglobin into Globin and Heme?

Answer 74

Reticulo-Endothelial System

Question 75

Briefly describe the degradation of Heme into Bilirubin.

Answer 75

Heme Oxygenase removes bridge between pyrrole rings of Heme (requires oxygen) --- Carbon Monoxide released. Taken up by Hemoglobin --- Iron oxidized from ferrous to ferric --- Biliverdin (green pigment) synthesized and reduced to Bilirubin (red-orange) by Biliverdin Reductase (needs NADPH)

Question 76

Bilirubin is released into the bloodstream. Free/unconjugated/indirect Bilirubin is insoluble. Therefore it is bound to ________. This complex is transported to the liver.

Answer 76

Albumin

Question 77

Hepatic uptake of Bilirubin is mediated by a protein carrier. In hepatocyte microsomes, Bilirubin is conjugated with _______ _______, making it soluble. This is called conjugated/direct Bilirubin.

Answer 77

Glucuronic Acid

Question 78

Briefly describe the conjugation of Bilirubin.

Answer 78

Glucose is activated by the enzymatic conversion to UDP-glucose --- Then converted to UDP-glucuronic acid --- UDP glucuronyl transferase enzymes in liver conjugate free Bilirubin with UDP-glucuronic acid --- This makes Bilirubin-Monoglucuronide and then Diglucuronide

Question 79

What is the rate-limiting step of Bilirubin conjugation?

Answer 79

UDP glucuronyl transferase ***Remember, this takes free Bilirubin with UDP-glucuronic acid and makes Bilirubin-Monoglucuronide and then Diglucuronide

Question 80

Conjugated Bilirubin is secreted by hepatocyte to biliary canaliculi which connect to form bile duct, which empties into the...

Answer 80

Gall Bladder

Question 81

Bilirubin-Diglucuronide is released into the gall bladder as ________. This is then secreted into the small intestine in response to food. In the intestines it undergoes microbial reduction to __________.

Answer 81

Bile | Urobilinogen

Question 82

Some Urobilinogen is reabsorbed and processed by the kidneys to produce the yellow pigment _______, found in urine. Some Urobilinogen undergoes further microbial reduction to the red-brown pigment _________, found in the feces.

Answer 82

Urobilin | Stercobilin

Question 83

This is caused by elevated levels of Bilirubin in blood stream. There is an imbalance between production and excretion of Bilirubin.

Answer 83

Jaundice

Question 84

What are the types of jaundice?

Answer 84

Pre-hepatic Intra-hepatic Post-hepatic

Question 85

This type of jaundice is due to increased production of unconjugated Bilirubin. There are elevated blood levels of unconjugated or indirect Bilirubin (normal blood levels of conjugated Bilirubin).

Answer 85

Pre-hepatic

Question 86

This type of jaundice is due to impaired hepatic uptake, conjugation, or secretion of conjugated Bilirubin. There is generalized hepatic dysfunction.

Answer 86

Intra-hepatic

Question 87

Examples of this type of jaundice are due to liver cirrhosis (alcoholism), viral hepatitis, Criggler-Najjar Syndrome, and Gilbert Syndrome.

Answer 87

Intra-hepatic

Question 88

T/F. For Intra-hepatic jaundice there are variable increases in unconjugated and conjugated Bilirubin depending on the cause (pre- or post-conjugation). There is an increase in serum ALT and AST.

Answer 88

True

Question 89

This type of jaundice is due to problems with Bilirubin excretion. There is decreased bile flow. There can be dark urine or pale stool.

Answer 89

Post-hepatic

Question 90

In this type of jaundice there is elevated blood levels of conjugated Bilirubin. The conjugated Bilirubin is present in urine (dark).

Answer 90

Post-hepatic

Question 91

Many newborns develop jaundice due to elevation of unconjugated Bilirubin. This is called physiological jaundice. The immature hepatic metabolic pathways are unable to conjugate and excrete Bilirubin. There is a deficiency of the enzyme __________. There is a breakdown of fetal Hb as it is replaced with adult Hb. Accumulation of excess Bilirubin in blood leads to the symptoms of jaundice. Prematurity aggravates this.

Answer 91

UDP-GT

Question 92

In neonatal jaundice, Bilirubin may diffuse into basal ganglia and cause encephalopathy. This is called...

Answer 92

Kernicturus

Question 93

What are treatments for neonatal jaundice?

Answer 93

-- Phototherapy with blue fluorescent light -- Intramuscular injection of tin-mesoporphyrin (strong inhibitor of heme oxygenate) to prevent heme breakdown of Bilirubin

Question 94

This type of UDP-GT disorder results from a deficiency of the enzyme. This is Type I, meaning there is complete absence of the gene to produce it. Results in severe hyperbilirubinemia. Causes encephalopathy (kernicturus) and brain damage.

Answer 94

Criggler-Najjar Syndrome

Question 95

This is the benign form, which results from a mutation in the UDP-GT gene. The enzyme has less activity at about 10% (not completely absent).

Answer 95

Criggler-Najjar Syndrome Type II

Question 96

This UDP-GT disorder is relatively common. It is a benign disorder affecting 2-10% of population. Results from reduced activity of UDP-GT at about 25%. Serum Bilirubin is <6 mg/dL but may increase with fasting, stress, or alcohol consumption.

Answer 96

Gilbert Syndrome

Question 97

This is inflammation of the liver and leads to liver dysfunction. Its causes are from viral infections, alcoholic cirrhosis, and liver cancer. It causes increased levels of unconjugated and conjugated Bilirubin in the blood.

Answer 97

Hepatits

Question 98

Hepatitis causes accumulation of Bilirubin in the _______ and ________ of the eyes, causing yellow discoloration. There is dark, tea colored urine.

Answer 98

Skin | Sclera

Question 99

Describe the colors of bruises based on Hemoglobin breakdown.

Answer 99

Heme -- Red Biliverdin -- Green Bilirubin -- Orange/Yellow Hemosiderin -- Reddish-Brown