Week 2 Flashcards
Gene Expression
- TF and RNAP bind to cis-acting promoter sequences adjacent to mRNA TSS
- Distal enhancers and silencers bind TF
- Coactivators facilitate TF interactions
Splicing Errors
Mutation from missing splice signal (GU-AG)
- Leave out introns/cut out extra exons
- Generate new 3’ splice sites (truncated introns)
Gene Expression Locus (a and B-globin cluster)
- a: psi –> a2, a1, psi (pseudogenes; silenced)
> HS-40 (DNAse I hypersensitive site): open chromatin structure, regulatory element - B: E –> Gamma –> Delta –> Beta
> LCR (locus control region): HS4,3,2
> a2E2 (embryonic) –> HbF a2Gamma2 (Fetal) –> HbA2, A: a2Delta2 –> a2B2
> Yolk sac –> liver –> spleen –> bone marrow (increasing a, B and decreasing Gamma)
Sickle-Cell Anemia
- FIRST GENETIC DISEASE
- Low RBC (sickle shaped) or hemoglobin –> hypoxia
> RBC: 2 a chains, 2 b chains, iron, and heme group
> SCA: Both B-chains mutated in hemoglobin (S)
> RBC aggregate into rod-shaped fibers –>
erythrocyte distorted –> sickle –> heterogeneity –>
local ischemia (vessel obstructive infarction) - Vas. obstructive pain; death infancy; small bone lesion
> Loss of spleen function –> bacterial infections
> Acute chest syndrome, leg ulcer, bone aseptic necrosis - Single AA mutation in B-globin (one bp change)
> Glutamic Acid missense –> Valine at AA 6
> GAA –> GTA: HbSs only 1/5 as soluble
Restriction Fragment Length Polymorphism (RFLP)
BA (CCTGAGG) corresponds to MstII (CCTNAGG), but is altered in BS (CCTGTGG), which cuts once –> 1 band
SCA: Treatment
- Oxygen inhalation: aggregate HbSs dissociate to return to normal shape
- Transfusion: give good blood
- Antibiotics: infection with 250 mg of Amp 2x/day
Malaria
Hydroxyurea: Low frequency of painful crises
> Malaria: promodium parasites (Low SCA)
> Selective sickling and phagocytosis of infected RBC
> Merozoite: AA –> schizogonic cycles; AS –>
decrease macrophages and parasites out
> Use knob and Maurer’s cleft –> stick to vessels
> Treatment: low O2 concentration stall AS erythrocytes
> HbS polymerization at low O2 concentration
> Treatment: infected SC stick less than infected normal cells –> increase O2 in capillaries and parasite growth
Thalassemia
- MOST COMMON SINGLE-GENE DISORDER
- Imbalance of a- and B- globin chain synthesis –> hypochromic, microcytic and abnormal in shape
- Anemia, jaundice, bone marrow expansion
> Blood cells normally formed in BM try to form more
> Upper jaw protrusion and raised cheek bones - Heterozygote advantage: Independent mutate; NS
a- Thalassemia
- Missing a-globin
> deletion of 2 a-globin genes in meiosis
> Psi-a2-a1 becomes 1) Psi a or 2) Psi a2 a a1
> Reduced a-chain synthesis due to 1-4 gene deletion on Ch 16 due to unequal crossing over
> 1. Silent carrier, 2. a-thalassemia, 3. HgH disease, 4. Hydrops Fetalis
b- Thalassemia (100+ P-mutation)
- DNA mutation that decreases B-globin GE
> Unmatched a- accumulate –> RBC inclusion bodies
> Heinz body forms in RBC (no oxygen carried): upon removal of inclusion bodies, membrane is damaged
Thalassemia Treatment
- Blood Transfusion + chelation with Fe+ binding Resin
- BMT: only available cure (rejection risk)
- Clinical trials (increase fetal Hg expression)
- Gene therapy: stem cell –> transduction + chemo
HGP
- Sequence of 3 billion bp
- Genetic and physical mapping
> PM: retrieve DNA sequence with overlapping clones (contigs) in YAC, BAC, PAC, P1 and cosmid vectors
Common Disease Common Variant Hypothesis
- GWAS: 24 alleles associated with 1/7 diseases
Hereditary Persistence of Fetal Hemoglobin (HPFH)
- Active gamma-globin GE to compensate for B-globin –> increase in HbF in adult life –> mutations decrease in SCA and b-thalassemia
> GWAS: out of 361129 common SNP, rs11886868 in BCL 11A gene was strongly associated with fetal Hb and less b-thalassemia symptoms
> HU –> miR-26B –| MYB –> KLF1 –> BCL11A + B –| Gam
