Flashcards in Biotechnology and Human Disease Deck (18):
What is SCID?
Severe combined immunodeficiency disease (SCID): immune deficiency as a result of mutations in the gene for adenosine deaminase (ADA) or a gene coding for an interleukin receptor subunit. Patients with both kinds of SCID have been successfully treated by incorporating functional copies of the appropriate gene into their cells (called gene
What does the ADA enzyme do?
it converts adenosine to inosine
What does the pathology of ADA deficiency result in?
High adenosine levels lead to high dATP. dATP inhibits ribonucleotide reductase, a
key enzyme in the synthesis of dCTP, dGTP, and dTTP. No building blocks for DNA
synthesis causes the rapidly dividing cells of the immune system to be most affected.
How do we treat people with ADA deficiency using gene therapy?
We take some stem cells/T-cells from the patient and infect them with a retrovirus
modified to carry the normal gene for adenosine deaminase. The gene becomes
integrated into the cell’s chromosomes and is expressed. We then reintroduce the cells to
the patient and they regain immune function. NOTE: must be careful on where we
insert—if it goes to the wrong place it could cause cancer, specifically leukemia
What is the significant of gp120?
It’s a protein on HIV that binds to the CD4 receptor on the surface of T cells. It thus
allows HIV to enter our cells
How does HIV infect cells?
Viral particle (gp120) bids to CD4 on T cell. Viral envelope fuses with cell membrane allowing viral genome to enter the cell. HIV is a retrovirus. Reverse
transcriptase copies viral RNA genome into double-stranded DNA which is integrated
into the host DNA. The integration sites are random, although some areas are more
prone to accept foreign DNA and thus termed “hot spots”.
What enzyme integrates viral DNA into the genome
What are LTR (long terminal repeats)?
LTR are ends of viral DNA used by the virus to integrate into host chromosome
What is the DNA construct for gene therapy? Hint: give order of elements
LTR – Enhancer – promoter – ADA cDNA – poly(A) – LTR; Including
an intron is beneficial
If given a choice in gene therapy, what kind of promoter/enhancer do you use?
Choose a promoter that is highly active in blood cells and is a strong promoter +
Enhancer (makes lots of ADA mRNA molecules)
What is a Philadelphia chromosome? What disease does it cause?
A: It forms as a result of abnormal chromosome translocation. This translocation occurs between a piece of chromosome 9 and a piece of chromosome 22. This exchange results
in a longer than normal chromosome 9, and a shorter chromosome 22. The DNA in
chromosome 9 contains a gene called ABL, while chromosome 22 contains a gene called
BCR. The shorter combination of the two chromosomes, with a gene labeled BCR-ABL,
forms what is known as the Philadelphia Chromosome. It causes chronic myelogenous
What does the BCR-ABL mutated gene on the Philadelphia chromosome code for?
Protein tyrosine kinase. This tyrosine kinase is an enzyme which activates other
proteins by adding phosphate to them. This unregulated phosphorylation activates
enzymes important in cell division and growth.
What types of viruses are easier to make vaccines for?
Where is the BCR-ABL fusion kinase present?
ONLY in cancer cells—it’s completely absent in normal cells. If one can develop a
drug that specifically inactivates cancer-specific fusion kinase, you kill the cancer cells
with no effect on normal cells
What does Gleevec do?
It blocks BCR-ABL. It’s given as a one-a-day pill. Since blood cells turnover, when all mutant cells with chromosomal translocation are killed, the patient is cancer-free.
What types of cells lose contact inhibition and pile up?
Cancer cells. A single base change in an oncogene produces protein that is autosomal dominant and causes cells to proliferate abnormally. Normal cells are very respectful of their neighbors (in other words, they exhibit contact inhibition).
What is Ras? What does mutant Ras cause?
Ras is a GTPase that is involved in signal transduction. Activation of Ras causes cell growth. Since Ras communicates signals from outside the cell to the nucleus, mutations in ras genes can permanently activate it and cause inappropriate transmission inside the cell, even in the absence of extracellular signals. Because these signals result in cell growth and division, dysregulated Ras signaling can ultimately lead to oncogenesis and cancer. G-Proteins have intrinsic GTPase activity that allow it to be turned off. Mutant
Ras will cause the protein to stay active and promote cell division (this is b/c the intrinsic
GTPase activity is lost)