B/B Flashcards
(26 cards)
Hayflick Limit
The number of times a normal human cell type can divide until telomere length stops cell division
What is the function of reverse transcriptase enzymes?
These enzymes read RNA and make DNA
What is a telomerase?
It is a ribonuclease complex that contains an RNA primer and a reverse transcriptase enzyme, which allows for chromosome extension of the parental DNA strand to create telomeres that are disposable during the cell cycle.
When is the telomerase found?
In most organisms, telomerase is only expressed in the germ line, embryonic stem cells, and some white blood cells.
How can UV light damage DNA?
If two pyrimidines are next to each other in the DNA backbone, UV light can cause them to be covalently linked to EACH OTHER and cause a distortion in the backbone that will cause trouble for DNA replication when it is not fixed and can cause mutations.
Missense Mutations
This is caused by one amino acid being replaced with a different amino acid. If the amino acids are very similar in characteristics, then it might not be detrimental.
Nonsense Mutation
This is when a stop codon replaces a regular codon and prematurely shortens the protein.
Silent Mutation
A codon that is changed into a new codon for the same amino acid so there is no change in the protein’s amino acid sequence
What is an inversion of the chromosome?
This is when a segment of a chromosome is reversed end-to-end. The chromosome undergoes a breakage and rearrangement within itself
What is the difference between recombination and translocation?
Recombination is when genetic information is exchanged between homologous chromosomes whereas translocation happens between non-homologous chromosomes. Translocation is common in many types of cancer and can be either balanced (where no gene information is lost) or unbalanced (where genetic information is lost or gained).
Hemizygous
Condition in which there is only one gene copy in the diploid organism
Hemizygosity
This is a situation in which there is haploid expression in a diploid organism
Haploinsufficiency
A diploid organism has only a single functional copy of a gene and this single copy is not enough to support a normal state.
What are inborn errors of metabolism?
They are a huge group of genetic diseases that involve disorders of metabolism; can be due to a single mutation in a ingle gene that codes for some sort of metabolic enzyme. Symptoms are caused by either the build-up of toxic compounds that can’t be broken down or by the deficiency of an essential molecule that cannot be synthesized.
What is an oncogene?
An oncogene is a gene that can cause cancer when it is mutated or expressed at high levels.
What is the direct reversal DNA repair (and give an example)?
Some enzymes can repair UV light induced pyrimidine photodimers using visible light. This process is called photoreactivation, and directly repairs the UV damage to DNA. If pyrimidine diners are not directly reversed, nucleotide excision repair can be used instead however this mechanism can introduce a mutation when trying to complete the repair. If the covalent cross linking between pyrimidines are left unrepaired then the dimers may lead to melanoma in humans.
Homology-dependent repair
This is when the cell uses the un-damaged complementary strand to repair the damage on the other strand; this is because DNA is double stranded! Very nice!
Excision Repair
This involves the removal of defective bases or nucleotides and replacing them before replication
Post-replication repair/mismatch repair pathway
This targets bp that were not repaired by the DNA polymerase proofreading during replication. Methylation can be used here to identify which base pairs it needs to repair! Pg 92 of the book
How can you repair a double-strand break (DSB)?
You can use homologous recombination or no homologous end joining (if not done right you can have deletions or translocations)
Homologous recombination
This is a process in which one sister chromatid can help repair a DSB in the other. First, the DSB is identified and trimmed at 5’ ends to generate single-stranded DNA (done by nucleases) and helicase.Many proteins bind these ends and start a search of the genome to find a sister chromatid region that is complementary to the single strand DNA. Once found, the complementary sequences are used as a template to repair and connect the broken chromatid. This requires a “joint molecule”, where damaged and undamaged sister chromatids cross over. DNA polymerase and ligase build a corrected DNA strand.
Heterogenous nuclear RNA (hnRNA)
Immature/precursor of mRNA
What are the four types of ribosomal RNA units?
18S, 5.8S, 28S, 5S
In transcription, what do you call the DNA strand that is actually being transcribed by the RNA polymerase?
Template, non-coding, transcribed, or antisense strand and it is complementary to the transcript.