sdl123

Sdl 1- haemoglobin disorders
Adult haemoglobin – 2α and 2B subunits
Fetal haemoglobin - α2γ2 (2 alpha, 2 gamma subunits)

structure-
A polypeptide chain, a globin and a prosthetic haem grp

types of genetic haem disorders
structural variants- sickle-cell anaemia
thalassemias- inbalance in A:B globin ratio
HPFH- hereditary persistence of fetal haem

HbS (sickle-shaped), mutation in the B-globin chain
single substitution of 6th a.a. of B-globin from glutamic acid to valine
polymerisation of HbS- blockage, vascular occlusion, ischemia, anaemia

rbc turns sickle under low oxygen tension
due to polymerisation of two wild-type a and two mutant B under low oxygen, losing elasticity and oxygen capacity
resistance in heterozygotes (carriers) due to rupturing of rbcs & unabling plasmodium to reproduce

α-thalassaemia
low α, might have deletions
xs B forming homotetramer B4
hypoxia, anaemia, hydrops fetalis(generalised fluid acc)

B-thalassemia
Xs α chains produced due to B mutations
Unlike B chains, α chains do not form tetramer
Instead bind to rbc membrane, damage it

Homozygous for B-mutations (2 alleles) leads to a severe microcytic, hypochromic anemia called β thalassemia major
Heterozygous for B-mut (1) leads to β thalassemia minor, a mild anemia with microcytosis

Sdl 2 – Gene therapy
Recessive disorders easy to treat than autosomal dominant by just having to introduce a functional (correct) copy of gene to compensate loss of function
Autosomal dominant requires dealing with gene replacement and inactivation of mutant gene, difficult

In-vivo approach: injecting gene into tissues or uptake of extracellular fluid of interest by target cells

In-vivo approach
Adv- allow specific binding of target cells to vectors, no need culture patients cells, no need re-intoduction of cultured cells into patients
disadv: adverse reactions, possibility of clinical hazard

Adv of non-viral over viral
No harmful mutations are introduced during integration step

Add. info
Some other approaches include that target cancer include delivery of suicide genes to target site. Enzyme-encoding genes that allow cancer to metabolise prodrug and administered separately into a potent cytotoxin that diffuse to neighbouring cells causing bystander effect

By-stander effect
A stimulus is presented to just a group of target cells (not all). The effect of the stimulus is dissipated to neighbouring cells, also mediating effects on these cells. Very good for treating cancer as all cancer cells occur in clumps

Sdl 3 – Melanoma
Types of skin cancer
Basal-cell/squamous-cell carcinoma & cutaneous melanoma

Basal-cell or squamous derives from epidermal keratinocytes
Cutaneous melanoma derives from epidermal melanocytes

Linkage analysis of families with high incidence of melanomas isolated two susceptibility genes i.e. CDKN2A and CDK4 (familial)

CDKN2A hot-spot marked to chromosome 9p21
(20% familial, 0.2-2% sporadic)

encodes for:
INK4A (p16) - inhibits CDK4-mediated inactivation of Rb
ARF (p14) - inhibits degradation and ubiquitylation of p53

2 upstream exons (1alpha and 1B) and exons 2 and 3
exons driven by separate promoters, 2 distinct reading frames
transcript initiated frm proximal promoter (1 alpha) encodes INK4A
second transcript frm upstream exon 1 beta encodes ARF
(see diagram)

CDK4 is normally inhibited by its kinase inhibitor INK4A
Mutations to cdk4 lead to change in binding site unable binding to ink4a and subsequent inactivation
Activity combined with ras co-activation in several mouse (animal) studies show melanoma genesis

experiment info:
Studies for CDKN2A make use of conventional gene-targeting approach to delete exons 2 and 3 of Cdkn2a locus in germline, generating mutant mouse null for both Ink4a and arf. With Hras mutation co-operated, mice are highly prone to cutaneous melanomas.

uva vs uvb (sporadic)
uva- 320-400m
involves in oxidative DNA damage, immunosuppression
prevents immunological protection from uv

uvb- 290-320mm
prinicipal DNA lesions, form pyrimidine dimers & photoproducts
leading to mutations

melanin as a protective figure
function to absorb UV photons & reactive oxygen species by uv radiation