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A heritable change in the genectic material. Essential to continuity of life and a source of variation for natural selection.
Mutation
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New mutations are more likely to be harmful that beneficial so hwat is in place to counter it?
DNA repair systems.
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Gene mutations may affecr amino aciud sequences. What are the ways?
Silent mutation, Missense mutation, nonsense mutaion, and frameshift mutation
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this mutation does not alter the maino acid sequence amd os due do degeneracu of genetic code.
Silent mutation
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This mutation Changes a single amino acid in a polypeptide. May not alter function is substituted amino acid is similar in chemistry to original. ex Sickle cell
Missense mutation
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This mustation is a change from a normal codon to a stop codon. Produces a truncated polypeptide.
Nonsense mutation
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This mutation is an addition or deletion of nucleotides and creates a completely different amino acid sequence downstream from mutation.
Framshift mutation
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A mutation may alter the sequence within a promoter and affect the rate of transcription. What will this cause?
It may enhance or inhibit transcription
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Mutations may occur in other regulatory elements or operator sites. what does this cause?
May alter DNA sequence of operator so that repressor protein does not bind
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What determines the severity and heritability of a mutation?
Time and location
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these cells give rise to gametes
germ-line cells
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These are all cells in the body
somatic cells
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in Germ-line cells where does the mutation occur?
In sperm, egg, or in gamete progenitor cells
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In somatic cells wher doe sthe mutation occur?
early or late development. gives a genetic mosaic with patches of mutamt tissue
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These mutations are From abnormalities in biological processes. Rates vary species to species and gene to gene. Background mutation rate ~1 mutation / million genes
Spontaneous mutations
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these mutations are caused by environmental agents
Induced mutations
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chemical or physical agents that alter DNA
Mutagens
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How do mutagens work?
They can disrupt base pairing by changing a c to u for ex. dsrupt replication by adding something between bases such has benzoyrene. also radiation causing deletions or gaps
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This radiation has high energy and penetrates deeply to create free radicals. X rays and gamma rays. Cause deletions or breaks in one or both DNA strands
Ionizing radiation
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This radiation has less energy and can only penetrate the surface. UV rays can cause formation of thymine dimers, causing gaps or incorporation of incorrect bases
Nonionizing raditation
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Uses Salmonella typhimurium that cannot synthesize histidine due to a point mutation. ? Test monitors rate at which second mutation occurs.
Ames test
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All organisms require the ability to repair DNA. What are the two components?
Detection of damage and repair of damage
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What are the types of repair?
Direct repair, nucleotide excision repair, and methy-directed mismatch repair
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in this repair A repair enzyme recognizes an incorrect structure in the DNA and directly converts it back.
direct repair
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in this repair portion of DNA strand containing an abnormal nucleotide is removed and replaced.
Nucleotide excision repair. (NER)
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in this repair a base pair mismatch is detected and a stran of surrounding DNA is removed and replaced
Methyl-directed mismatch repair
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What is the most common repair system?
NER nucleotide excision repair
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What where the diseases that led to the discovery of NER?
Xeroderma pigmentosum (XP), Cockaynes syndrome (CS), PIBIDS
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90% of cancers are due to exposure. About what percent is from carcinogens?
80%
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Can migrate to other parts of the body
metastatic
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An oncogene may promote cancer by keeping the cell division signaling pathway in a permanent
on position
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Oncogenic mutations may decrease ability of Ras to hydrolyze GTP or exchange GDP/GTP faster. What does this cause?
Both keep signaling pathways constantly open
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What is a proto-oncogene?
A normal gene that, if mutated, can become an oncogene.
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What are the four common genetic changes?
Missense mutations, gene amplifications, chromosomal translocations, and retroviral insertions.
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this mutation Increase in copy number results in too much protein
Gene amplifications
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In this mutation Two chromosomes break and switch ends. Very specific translocations associated with certain types of tumors. Can create chimeric genes
Chromosomal translocations
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What are the two ways that viruses cause cancer?
modifying host dna and carry oncogenes
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What are the typical functions of tumor-supressor genes
prevent cancerous growth, maintain genome integrity, and ihibitor of cell division
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Proteins called cyclins and cyclin-dependent protein kinases (cdks) are responsible for advancing a cell through the four phases of the cell cycle. what are these called?
checkpoint proteins
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about 50% of all human cancers are associated with defects in this gene
p53
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function as proteases that digest selected cellular proteins causing the cell to break down . It is beneficial for a multicellular organism to kill an occasional cell with cancer causing potential
Caspases
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