Hemoglobin 3 11.20.12 Flashcards
What is the ratio of CO:O2 affinity in Mb and Hb?
200:1
Hb combnes 200x more strongly with CO than with Oxygen to form cherry-red compound called CARBONOXYHEMOGLOBIN (Hb + 4CO –> Hb (CO)4)
What causes the Oxyghemoglobin Dissociation curve to shift left?
Methemoglobinemia
Carbon Monoxide Intoxication
How does Hb and Mb reduce affinity of CO for the heeme
by forcing a less preferred bend mode tof bidning
- Bendt mode of binding to CO to heme- distal HIS forces CO to be at an angle to heme plane
Neverless, affinity for CO is still stronger htan O2
What is Methemoblogin (HbM)
form of Hb in which iron is in the ferric state. It is different from oxygenated Hb, (oxyhemoblgobin) , in which oxygen is united loosely with ferrous iron. Mb cannot combine with and transport O2
What % of HbM in normal adult?
1.7%
Exposure to certain drugs and oxidizing agents can increase the concentration of methemoglobin
What is the cause of Familial Methemoglobinemia?
Deficiency in the enzyme methemoglobin reductase , which uses NADH –> NAD+ to go from methebmoblobin to hemoglobin
What happens to individual when methemoglobin exceeds 10% of total Hb,
affected individual will have clinically obvious cyanosis
What are the three types of inherited disorders of the hemoglbin?
structural variants,
thalassemias,
which are characterized by reduced rate of synthesis of one or more of the globin chains
hereditary persistance of fetal hemoglobin, where fetal hemoglobin synthesis continues beyond the neonatal period
What is genetically determined HbM?
it may have a TYR substituted for the PROXIMAL HIS - Fe gets oxidized to ferric form
Prox F8 HIS –> substituted by TYR F8
Also tru for TYR subststitution for DISTAL HIS
What happens wit trace Co in air. How much HbCO? Symptoms
Trace
5% HbCO
impaired vision
0.02% CO in air
20% HbCO
headach, nausea heavy smoker (smoke is not fully combustible, red color to circulation)
0.1% CO in air
40-60% HbCO
in garage) Death (RED COLOR
What is normal HbM (%)
1.7%
What is cyanosis HbM%
10%
What is genetic HbM %
15-30%
what leads to headache, weaknes, breathlessness with HbM %
> 35%
What %HbM is death
~70%
What are the three types of inherited disorders of the hemoglbin?
structural variants,
thalassemias, which are characterized by reduced rate of synthesis of one or more of the globin chains
hereditary persistance of fetal hemoglobin, where fetal hemoglobin synthesis continues beyond the neonatal period
How many structural variants of hemoglobin exist?
More than 400 structural Hb variants
What are the types of mutations that can result in teh production of essentially normal amounts of aberrant globin chains
- single base mutation
- Elongated globin chain variants
- Shortened Globin Chains
- Nonhomologous (or unequal) crossing over which produed hybrid globin chains
What causes Single Base Substitutions?
most common structural alteration producing hemoglobin variants is the substitution of one amino acid for anotehr.
Most of the amino acid substitutions can be explained by the Change of a SINGLE BASE in a triplet codon.
What causes Elongated Globin Chain Variatns
Caused either by single base substitutions in a chain termination codon, frameshift muations, or by mutations that cause failture of cleavage of the initiator methione residue.
What causes shortened Globin Chains
These variants involve deletion of one or more intact codons
What are nonhomologous (or unequal) crossing over
they are produced by hybrid globin chains
What type of structural mutations can result in molecular pathologies
- Altered exterior –> sickle cell anemia
- Altered active site
- Altered secondary and/or tertiary structure
- Altered quaternary structure
What is HbS and what causes sickle cell anemia
Hemoglobin S, a mutant form of Hb A in which a Glu is substituted by a Valine at position 6 of the beta chain ( replaces a polar maino acid with a non-polar one) produces sickle cell anemia
This substitution from polar to non-polar reduces the solubility tof the DEOXYGENATED HbS, but has little effect on the solubility of oxygenated HbS
Is solubility of deoxygenated HbS affected by Glu–>Val? Is solubitliy of oxygenated Hb S affected?
Deoxygenated is LESS soluble
Little effect on solubitlyt of oxygenated HbS
Explain the pathway of the “sickling crisis”
HbS aggregating/crystallizing in the capillaries where oxygen tension is lower –> this distorts RBC, increases blood viscosity causing increased stasis –> followed by further hypoxia
Vascular occlusion may occur iwth serious effects on organ funciton ,including the heart. Hypoxia, poor cicularion and hemolysis FEED BACK to lower oxygen concnetrations furtehr increasing extent of socklign and prolonging and intensifying teh criis
What happens if there is Vascular Hypoxia
Sudden ORGANOMEGALY - massive RBC sequestration in liver and spleen
What is the result of Perivascular Hypoxia
Vascular Occlusion
What is the intravascular Hypoxia
Hemolysis and severe anemia
What does Hypoxia in vascular, perivascular, and intravascluarl lead to?
HEART FAILURE
What is the genetic defect of Sickle cell disease (codon)
DNA base substitution: CTC –> CAC
mutant mRNA codon: GAG –> GUG
What is the molecular defect of sickle cell disease
Abnormal beta globain: Glu –> Val at position 6
What is the biochemical defect of sickle cell anemia
Anbormal HbS
altered isoelectric and solubility characterisitcs
What is the Pathophysiological defect of sickle cell
Sickling of Red Cell:
Increased Red Blood Cell Destruction
What are the clinical defects
Pleotropic manifestation
Anemia jaundice ischemia joint and abdominal pain, renal failure
How many afro-americans are heterozygous for hte HbAS, sickle cell trait
7-10%
How Many Afro-Americans are homozygous for HbSS, SCD
0.4%; 50,000-72,000 afflicted
How does HbAS protect from Malaria (Plasmodium falciparum) ?
inefected HbAS cells –> knobs, sticks to endothelial cells, sickle and CLEAR. !!!
Immunoregulatory mechanism
What is the treatment of Sickle Cell Anemia
Hydroxyurea (urea solubilizes protein)
5-azactidine (increases HbF, gamma chain)
Bone Marrow Transplant
Gene Therapy (experimental)
What is BC11A
inhibits HbF Silencing protein
What is an example of molecular pathology form Altered Active Site
Defective subunit cannot bind oxygen b/c of a structureal change near the heme that directly affects oxygen binding
When either proximal or distal His is replaced by TRYOSINE, the heme is stabilized in the FERRIC form and cannot bind oxygen
Sucha mutatng Hemoglobin is called Hemolgobin M
What is Hemoglobin M? What causes it?
Hemoglobin M is a mutatng hemoglboin caused by replacement of either proximal or distal HIS by Tyrosine. The heme is stabilized in the FERRIC form, which cannot bind oxygen.
The disease has only been seen in heterozygous form since homozygosity would be lethal.
Recognition of HbM is important in newborns wince accomapnying cyanosis may be mistakingly identified as a manifestation of congenital heart disease.
What kind of disease can be caused by alterend secondary and/or tertiary structure? How?
Congenital Heinz Body Hemolytic Anemia
amino acid substitutions can prevent the polypeptide chain from assumign its normal 3D conformation . The rusling hemoglobin is usually unstanble
Degree of severity depends on degree of instability of aparticular hemoglobin
loss a single salt bridge or H bond can tip equilibirum far enought toward unfolded form to denaure protien in vivo and cause idsease
What is an altered Quaternary Strucutre
Mutations at subunit interfaces can lead to loss of allosteric properties.
Such substituions raise the oxygen affinity of the moleul.e Less frequently the oxygen affinity is lowered.
What are the Thalassemia Syndromes?
group of inherited disorders in which teh production of a single type of globin chain is either diminished or absent
What is alpha thalassemia
means that the alpha chain is decreased or missing
What is beta thalassemia
means that the beta chain is decreased or absent
refers to heterogenous grup of conditions charcterized by QUANTITATIVE deficiency in BETA GLOBIN production relative to alpha glovein synthesis in erythroid cells
Wha ti sthe beta thalassemia diseroder of homozygous individuals called
it is generally severe and is called THALASSEMIA MAJOR or COOLEY’s ANEMIA
What is it called when no HbA is found?
condition is termed Beta O thalassemia (all beta is absent)
What some HbA is found it is called
Beta + (beta is depleted)
What is the presentiaton of patient with beta thalasemia at birth?
When does anemia ensue?
pat appears normal at birth b/c HbF comprises majority of hemoglobin at time.
Anemia ensues during 6 months as shift is made from HbF to HbA
Pts generally become dependent on transfusion to maintain a hemoglobin level compatible with life
What are the different forms that cause molecular basis of beta thalassemias
Nondeletion forms
Deletion forms
What are nondeletion forms that cause beta thalassemia
simple
involve SINGLE BASE SUBSTITUTION or SMALL DELETION or INSERTIONS within or immediately upstream of beta globin gene.
These changes ultimately affet genral aspects of gene functional transcription, RNA processing, and RNA translation
How do nondeletion forms affect gene???
affects gene fnctinoal transcription
RNA processing,
RNA translation
What are DELETIon forms that cause beta thalassemia
Deletions of differnt sizes involve beta glboin gene cluster tha produce different syndroms
Beta 0 thalassemia
Hereditary Persistance of Fetal Hemoglobin (HPFH)
detla-beta thalassemia
gamma-delta-beta-thalassemias
and hemoglobins due to HYBRID GENES (Lepore, Kenya)
What are hemoglobins due to hybrid genes of beta thalassemia?
Lepora, Kenya
Describe the anemia of severeity of delta beta thalassemia and HPFH
syntehsis of both delta and beta globin does not occur at all and only hemoglobin synthesized is HbF
anemia is delba beta is mild an
anemia in HPFH is absent
difference in clinical severity between beta thalassemisas is due to differences in levels of compensation by HbF
Homozygotes for beta thalassemia, level of HbF produciton is greater than normal, but insufficient to compensate for decreased or absent syntehsis of HbA
In delta beta thalassemia, HbF produciton is sufficiently increasee so that only a mild anemia results
in HPFH, compensation by HbF is complete
yep
What is the molecular basis of alpha thalassemia
alpha chain synthesis is diminished or absent
Since all tehnormal human hemoglobins otther than two of the embryonic hemoglobins contians alpha chians, the alpha thalassemisas lead to decreased productino of HbA, A2, and HbF.
Alpha-glboin haplotype may be written alpha-alpha representing the alpha1a and alpha2 respectively
A normal indiviual has genotype alpha-alpha/ alpha-alha
How many genes are responsible for alpha chain?
four!
What is alpha-thalassemia due to deletions? why is it more complex than beta thalassemia?
the most common molecular defects underlying alpha-thalassemia involve the delatino of one or more alpha-globin genes
since tehre are 4 alpha gene loci, the deltion pattern is more graded ad complex than with beta thalassemia
further comlicating the piccture is the prsence of the beta-like polypeptide, gamma chain, and teh ability of the beta or gamma chains by themselves to tetramize, although without allosteric or Hill properties (alpha chian does not tetramize tby themselves)
Do beta, gamma, or alpha chains tetramize by itself?
beta-yes
gamma-yes
alpha -no
What are non-deletion forms of alpha-thalasemia?
non-deletion forms are caused by the same type of mutations whih cause the no-deletion forms of beta-thalassemia.
However, unlike with Beta-thalassemia, these types ofmutatins are a relatively rare cause of alpha-thalasssemia
How many functional alpha genes does normal phenotype have?
4
how many Hb Bart’s at birth for normal phenotype?
0
what is %HbH/Inclusions for normal phenotyrpe
0/none
What is HbH
beta-4
still forms tetramer, but NOT regualted alone! no allosteric! not good
What is Hb Bart’s?
Consists of four gamma chains . It is moderately insoluble, and therefore accumulates in the red blood cells. It has an extremely high affinity for oxygen, resulting in almost no oxygen delivery to the tissues. It is produced in the disease alpha-thalassemia and in the most severe of cases, it is the only form of haemoglobin in circulation. In this situation, a fetus will develop hydrops fetalis and normally die before or shortly after birth, unless intrauterine blood transfusion is performed.Gamma-4
all 4 alleles gone (B4) ?
Descibe alpha-Thalassemia minor (mild)
3 functional alpha genes
0-2 Hb Bart’s at birth
0/rare % HbH/Inclusion
Describe alpha- thalassemia minor (sever)
2 functinoal genes
2-8 Hb Bart’s at birth
0/some % HbH/Inclusions
Describe HbH disease
1 fucntional alpha gene
10-40- Hb Bart’s at birth%
0/Some %HbH/Inclusions
Hb Bart’s Hydrops Fetalis
0 functional alpha genes
~80 Hb Bart’s at birth %
present/present % HbH/INclusions
What are some pathophysiological features of Beta Thalassemia
overall reduction in Hb synthesis
destruction of RBC precursor cells
Ineffective erythropoiesis
Destruction of mature RBCs
Hypoxia, anemia
What is the total iron in the body?
3.5 grams
How much iron does a male require to replace iron losses?
1 mg/day
How much Fe lost inurine
0.1 mg
How much Fe lost by skin desquamation and sweat
0.1 mg
how much iron lost by shedding of intestinal mucosa and biliary excretion
0.3 mg
How much Fe lost due to normal GI bleeding of 1 ml/day?
05 mg/day
Where is iron primarly abosrbed in our body?
from teh duodenum and proximal jejunum.
How much % iron ingested in our food is actually aosrbed
10%
What are the two types of absorbable iron in food
Heme iron found in meats, poultry, and finsh
non-heme iron prsent in foods sch as vegetables, fruit, legumes, nuts, breads, cereals
How is heme iron taken up
easily absorbe by mucosal cells and the iron is split form porphyring ring in the mucosal cytoplasm
How is non-heme iron taken up
as free iron and/or in protein-bound form
What subastanes in diet increase absorption of Fe
ascrobic acid or amino acids from meats
waht subtances decrease absorption of non-heme iron
phytates form bran
tannates in tea
polyphenosl in vegetable,s calcium salts,
phosphoprotein in egg yolk
factor in soy proetin
antacids
What is transferrin?
Serum Fe3+ transport protein
major protein in serum involve in the transport of iron
beta-1- glycoportien synthesized in teh liver, and consisting of a single polypeptirde chain with two iron-bidning sites
Iron must be in ferric steae tobe boudn by transferrin
What is the transferrin recetpor
a glycoprtein that mediates internatlizatino of transferrin
Both transferrin and transferrin R can be reuitlied for the transport and cellular uptake of iron.
What is ferritin?
Cellular Fe 3+ storage
primary and most readily avaialble irone storage protein in teh body
Ferritin is a protein that may contain as much as 23% iron by weight
Fe is prsent as micelles or colloidal particles, composed of a feric hydroxide-ferric phosphate complex, bound rather firmaly t the protein
It can be freed from iron without denaturing the protein, and this protein, apoferritien, is made up of 24 subunits with a MW of 44 kDa each
IN normal sujcets most of the Fe reserve is prsen in liver, Bm and sk muslces
what kind of complex is ferritinaand Fe
ferric hydorxide-ferric phosphate complex , boundrather fimraly to protein
How many subunits is apoferritin made up of?
24 subunits with a MW of 44kDa each
Wher eis most of the iron reserve presen in?
liver, BM, and sk muscles
what is correlatin of ferritn to Iron
1 ug of ferritin/L = 8 mg storage iron
What is Hemosdierrin
Denatured, insoluble, Ferritin
insoluble compoutn which is formed by denaturation of ferritin with ass. loss of apoferritin and micellalr aggregation; consequently hemosiderin contains a larger perecentatge of iron than its precursor
Hemosiderin aggregates into particles large enoguth to be seen microscopically
Whwer eis 95% of ferritin sotred?
in hepatovytes
where is hemosiderin stored?
in Kupffer cels.
iron sotred in either form may remain sequestered for prolonged peridos of time, or ay be returned almost immediately to a mroe active metabolic role.
How much iron does an average male store?
1000 mg storage iron
how much does menstruatoring female adult sore?
300 mg, since she requires about 1.7 mg/day
She has a dietary intake of 10-12 mg daily
what are the three facotrs that determien amt of iron absorbed
Quantitiy of iron in the diet
Composition of teh diet
Behavior of the mucosa of the duodenum and upper jejunum
when there is iron deficiency, the amount of …..increses
the amt of tranfer increases
when there is iron overload..teh amount …..is curtailed subtantially
amount transferred
what happens when little iron is reuqired by host
large amt of apoferritin is syntehsized trap iron within mucosal cell and prevent transfer to capillary bed
as cells turn over within one week, contnets are extruded into intestinal lumen without absorption ocurring.
what happens when there is iron deficiencty
no apoferritin is synthesized
so as not to compete vs the transfer of iron to tranferrin in teh plasma
what is Ferrochelatase
enzyme that catalyzes insertion of ferrous iron into porphyrin
What causes Elongated Chain Variants?
Caused by either single base substitutions in a chain termination codon
frameshift mutations,
or my mutations that cause failure of cleavage of the initiator methione residue
