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bio 113 Lecture 8
Mutation, DNA damage, DNA repair and Cancer
74
Biology
Undergraduate 1
02/01/2013

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Term
a mutation is a .......... change in the DNA of a cell
Definition
permanent
Term

true or false

a change in nucleotide sequence or change in gene position is a mutation?

Definition
true. mutations are rare and occur randomly. they are usually detrimental.
Term
which type of mutation is NOT passed onto offspring?
Definition
somatic mutations. these mutations are passed on to all the cells descending from the original mutant
Term
which mutations are passed onto offspring?
Definition
germ line mutations are passed on. 
Term
name a benefit of mutation
Definition
it is the raw material from which natural selection produces evolutionary change.
Term
there are 3 types of base pair substitution point mutations. what are they?
Definition
silent, missense and nonsense.
Term
what is a silent mutation?
Definition
for example GGC codes for glycine but the C is replaced with a U but it is okay because GGU also codes for glycine
Term
what is a missense point mutation?
Definition
substitution to make a different amino acid. for example GGC is for glycine but the first G is replaced with A making AGC which is serine. this is a missense mutation
Term
what can the insertion or deletion of one base pair cause?
Definition
a frameshift mutation
Term
why are frame shift mutations a pain in the ass?
Definition
they cause extensive missense (wrong amino acids being made) or nonsense (stop codon halting transalation)
Term
does the insertion or deletion of a 3 nucleotides cause a frameshift mutation?
Definition
no. it causes there to be one extra or one less amino acid but no frameshift mutation occurs.
Term
breakage of a chromsome can lead to 4 types of changes in chromosome structure. what are they?
Definition

deletion

duplication

inversion

(reciprocal) translocation

Term
what happens in a deletion of chromsome?
Definition
a part of the chromsomal segment is removed. eg. removal of a part in the short arm of chromsome 5 results in cri-du-chat syndrome
Term
a chromsome duplication...
Definition
repeats a segment.. if it adds it near the original alleles it is known as a tandem. if it doesnt it is known as non-tandem. eg. charcot-marie tooth disease. progressive loss of muscle tissue and touch sensation, arched feet, curled toes. result of duplication on long arm of chromsome 17
Term
when a chromosome fragment reattacthes to the original chromosome but in the reverse orientation is known as?
Definition
inversion. no specific conditions associated with inversions at present
Term
what happens in translocation?
Definition
a chromosomal fragment joins a nonhomolous chromsome. translocations can be reciprocal like Famillial downs syndrome (14:21) or Chronic myeloid Leukeamia (9:22)
Term
why can 5 bromouracil base pare with adenine and guanine?
Definition

it is a tautomer. the keto form is complementary to adenine.

the enol form is complementary to guanine.

Term
what point mutation can 5 bromouracil induce?
Definition
changing a AT bp to a GC base pair
Term
spontaneous mutations can occur due to the inheritent instability of DNA what does this mean?
Definition

nucleotides can change to other confirmations like isomers and tautomers thus during DNA replication an incorrect base is inserted to form mismatched pair.

 

eg, normal (amino) form of cytosine pairs with guanine but a tautomer of cytosine (an imino acid) pairs with adenine instead.

Term
spontaneous deamination of cytosine to uracil occurs in which condtions?
Definition
increased in acid conditions.
Term
what change would occur if replication proceeded with a deaminated C?
Definition
well normally cytosine pairs with guanine. when deaminated to uracil it results in A being inserted because Adenine pairs with uracil. thus daughter strand base pairing changed from CG to TA.
Term
what is the role of Uracil DNA glycosylase?
Definition
as uracil is not usually found in DNA, its role is to remove Uracil from DNA to prevent mutations
Term
what are chemicals that add hydrocarbon groups to nucleotide bases called?
Definition
alkylating agents
Term
what does O-6-ethylguanine pair with?
Definition
thymine. the normal guanine pairs with cytosine.
Term
what effect does o-6-ethylguanine have on base pairing?
Definition
it changes a CG bp to an AT bp.
Term
which bases specifically absorb UV radiation?
Definition
the pyramidine bases tymine and cytosine
Term
what happens if two T or two C residues are adjacent to each other on the same DNA strand?
Definition
covalent bonds can form between them forming a cross link
Term
what is the cross link between adjacent pyramidines called?
Definition
 a pyramidine dimer.
Term
what is the affect of pyramidine dimers?
Definition
it blocks DNA synthesis leaving a gap opposite the site of damage. the gap is filled by alternative polymrases.
Term
what is different about the special alternate polymerases that fill the gap that pyrimidine dimers create?
Definition
they are special because they are able to fill this gap. however the base pairing is relaxed.
Term
how can thymine dimers be removed?
Definition
by nucleotide excision repair (NER)
Term
what is nucleotide excision repair?
Definition
broad specificity repair system that recognises distortions in the dna helix.
Term
how does nucleotide excision repair work?
Definition
a nucelase enzyme cuts the damaged DNA strand at 2 points. DNA polymerase fills the gap with new synthesis of nucleotides. DNA ligase seals the remaining nick.
Term
which 3 components are important in nucleotide excision repair?
Definition

Nuclease enzyme - to cut the damaged DNA

DNA Polymerase - to synthesise complimentary strand

DNA Ligase - to seal the remaining nick.

Term
what is Xeroderma Pigmentosum?
Definition
a condition with deficiencey in nucleotide excision repair. thus development of skin cancer at early age but only to those parts of body exposed to the sun.
Term
name the disease in which cells escape from the control methods that normally regulate cell growth and division.
Definition
cancer
Term
when cells divide unchecked, they can give rise to tissue masses AKA?
Definition
tumors
Term
if a tumor cell stays together in a single mass it is said to be?
Definition
benign
Term
if the cells of a tumor can invade and disrupt surrounding tissues it is said to be?
Definition
malignant. it is when it is identified as cancer
Term
cells from malignant tumors can break off, move through blood and lymphatic system emerging and forming tumors at other locations in the body. this is known as?
Definition
metastasis
Term
what is the normal role of a proto-oncogene?
Definition
to stimulate cell division in a precisely controlled manner.
Term
how does a proto-oncogene transform into an oncogene?
Definition
a genetic chnage that leads to an increase in the proto-oncogene's protein or the activity of the protein.
Term
are oncogene mutations genetically dominant or recessive?
Definition
dominant
Term
how can viruses promote cancer development?
Definition
by intergrating their DNA into that of infected cells.
Term
name 3 ways a proto-oncogene can be transformed to an oncogene?
Definition

translocation - gene in a new locus under new controls

gene amplification - multiple copies of the gene

point mutation - mutation transforming into an oncogene resulting in a resistant protein.

Term
what is the normal role of a tumor suppressor gene?
Definition
to inhibit cell division
Term
how can mutations in tumour repressor genes contribute to cancer?
Definition
decrease in the normal activity results in loss of inhibition of cell division therefore more cell division takes place
Term
are mutations in tumor suppressor genes usually dominant or recessive?
Definition
recessive
Term
what is a RAS?
Definition
it is a G protein and a proto-oncogene. it is a component of a signal transduction pathway that stimulates cell cycle and division
Term
mutations in the ras proto-oncogene occurs in how many percent of human cancers? 
Definition
30%. this figure is higher in pancreatic and bowel cancers.
Term
what kind of mutation cause the ras proto-oncogene to send signals of its own?
Definition
a point mutation
Term
what is needed to activate the normal pathway of a ras proto-oncogene?
Definition
growth factor needs to bind and start a reaction cascade. when a mutation occurs, the ras oncogene doesnt rely on growth factors but issues signals of its own.
Term
what does RAS stand for?
Definition
rat sarcoma
Term
in the ras pathway where do the growth factors bind to?
Definition
tyrosine-kinase receptors 
Term
what reaction does the RAS proto-oncogene set off?
Definition
a phosphorylation cascade in protein kinases. they eventually reach transcription factors which activate gene expression.
Term
what kind of gene is p53?
Definition
a tumor suppressor
Term
how many % of cancers does mutations in p53 gene occur?
Definition
50%
Term
is promoting the synthesis of growth-inhibiting factors the NORMAL or MUTANT job of te p53 gene?
Definition
the normal job thus a mutation that knocks out the p53 gene can lead to excessive cell growth and cancer
Term
normally when is the p53 gene expressed?
Definition
when there is damage to cells DNA. it promotes growth-inhibiting proteins so the damage can be repaired before the DNA is replicated.
Term
what other gene can p53 activate and what does this other protein do?
Definition
it can activate the p21 gene. this halts the cell cycle.
Term
name 3 things the p53 gene can do
Definition

can activate p21 - halt cell cycle

turn on DNA repair genes - to fix damaged DNA

can initiate suicide genes when DNA is irreparable - leads to program cell death or apoptosis.

Term
in which ways do ras proto-oncogene and p53 differ?
Definition

ras proto-oncogene is part of a system that stimuates cell division. its mutation causes it to become hyperactive.

p53 stimulates synthesis of growth inhibiting factors. its mutation makes its function ineffective resulting in unregulated cell division.

Term
how many cell division check points must be inactivated for cancer to initiate?
Definition
all of them
Term
cancer involves mutations in multiples genes and what else?
Definition

at least 1 active oncogene and several tumor suppressor genes. most cancers occur over the age of 40

 

Term
in mutations that commonly lead to colorectal cancer the first stage is the loss of APC. what is this?
Definition
APC is a tumor repressor gene. (Adenomatous polyposis coli)
Term
loss of APC allows growth of a small benign growth. what is this growth known as?
Definition
a polyp.
Term
in colorectal cancer what will activation of the ras oncogene do?
Definition
stimulate uncontrolled cell division as the ras oncogene is hyperactively sending signals to stimulate transcription factors.
Term
what is dcc?
Definition
it is also a tumor suppressor gene called Deleted in Colorectal Carcinoma. the downfall of this results in a larger benign growth.
Term
what is the larger benign growth called in the stages to colorectal cancer?
Definition
adenoma. a benign tumor of glandular origin
Term
in colorectal cancer which is the last tumor supressor gene to be lost?
Definition
p53. this is when additional mutaions occur and the benign tumor becomes a malignant carcinoma.
Term
what is a carcinoma?
Definition
cancer that begins in the tissues that line the inner or outer surfaces of the body.
Term
altogether how many tumor suppressor genes are lost in the progression of colorectal canceR?
Definition
3. first APC then DCC then P53.
Term
consolidate the steps of colorectal cancer. 5 steps. 3 losses of tumor suppressor genes and one activation of ras oncogene
Definition

1. loss of APC (small benign growth polyp)

2. activation of ras oncogene (hyperstimulation of cell growth)

3. loss of DCC (larger benign growth, adenoma)

4. loss of P53 (additional mutations)

5. malignant tumor aka carcinoma

Term
what does smoking do?
Definition
causes cancer and reduces life expectancy
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