BIOL 121 Lecture Notes - Severe Combined Immunodeficiency, Growth Hormone Deficiency, Reverse Transcriptase
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Biol 121 225
Freeman 390-395, 407-411, 417-424
Ch. 19, Gene Technology
Pituitary dwarfism and growth
-people with pituitary dwarfism have defective copies of the gene GH1 which
codes for the GH1 growth hormone protein
-affected people are typically no more than 4 feet tall by adulthood
-growth hormone was injected into people just like insulin injections for diabetes
-only growth hormone from humans worked, and therefore it had to be extracted
from cadavers (dead bodies) and therefore was scarce/expensive
-even worse, infectious proteins called prions that cause degenerative brain
disorders emerged in patients – people can get prions by inheritance or by eating
-their growth hormone supply was contaminated with a prion protein from the
brains of the cadavers supplying the hormone
-retroviruses are currently the vector of choice in gene therapy
-they are viruses that have an RNA genome and can code for proteins that produce
DNA from their RNA and insert it into the DNA of the cell
-however, viruses usually cause disease and even when inactivated, altered
particles may be able to recombine with viral DNA that already exists in the
individual being treated and lead to the formation of a new infectious strain
Method of introducing alleles into
human cells using engineered viruses
1. Engineered retrovirus has recombinant RNA containing viral and human
2. Recombinant genes enter host cell.
3. Viral enzymes make double-stranded DNA version of introduced genes (reverse
4. Recombinant genes are inserted into host chromosome and transcribed.
-severe combined immunodeficiency
-lack normal immune system, cannot fight off infections
-“the boy in the bubble”
-defective gene for receptor protein necessary for development of T cells
Gene therapy with SCID (3 steps)
1. Stem cells are isolated from the patient’s bone marrow and grown in vitro.
2. Recombinant retroviruses carry the normal allele into host cells.
3. Cells that are expressing normal alleles are isolated and implanted into patient.
Problems with this
-two of the ten boys they initially treated developed cancer characterized by
unchecked growth of T cells
-a viral-borne receptor gene had been inserted near the gene for a regulatory
transcription factor that triggers growth of T cells – cancer
-although they managed to treat it, the researchers proposed to halt their trial of
the therapy to carefully assess the risks and benefits
Agrobacterium induces gall
-the gall/tumourlike growth at bottom of plant’s stem, is due to bacterial infection
1) Agrobacterium cells contain a Ti (tumour-inducing) plasmid
2) A section of DNA from the Ti plasmid called T-DNA incorporates into the
chromosomes of plant cells infected by the bacterium.
3) When transcribed, Ti genes induce the affected cell to begin growing and
dividing. The resulting gall encloses an increasing number of Agrobacterium cells.
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