Topic 13 Genetics

Front 1

What sites are methylated in DNA?

Back 1

- Cs that precede Gs

Front 2

What is the purpose of DNA methylation?

Back 2

- regulate gene expression (inactivates a gene)
- cell differentiation
- genomic imprinting
- X-chromosome inactivation
- DNA replication
- viral latency
- carcinogenesis
- aging

Front 3

What is the purpose of maintenance methylation?

Back 3

- maintains the established methylation pattern (uses paternal strand as a template to methylate the daughter strand after replication)

Front 4

What does azacytidine do? this effects?

Back 4

- inhibits maintenance methylation
- removes methylation from either strand, which reactivates gene

Front 5

What is the purposes of de novo methyltransferases?

Back 5

- add methyl groups to previously unmethylated DNA

Front 6

What causes pryimidine dimers and what are they?

Back 6

- UV radiation
- adjacent thymines covalently bond together, distorting helix and preventing proper replication

Front 7

What are the 2 ways to correct a pyrimidine dimer? describe them

Back 7

Direct repair
- directly removes the covalent bond
Excision repair
- section of DNA with dimer is removed, DNA polymerase adds nucleotides, DNA ligase brings ends together

Front 8

What happens in mismatch repair?

Back 8

- DNA polymerase incorporates an incorrect nucleotide
- usually corrects by 3' exonucleolytic actions
- still isn't fixed= mismatch repair
- GATC sequence is used as a template to discover which strand is the paternal
- this area is brought together with the mismatch pair and all of the daughter DNA is excised out
- DNA polymerase adds correct sequence

Front 9

Describe the steps in recombination that cause crossing over

Back 9

- double strand break of DNA
- creates gap by exonuclease
- ends invade neighboring chromatid
- DNA polymerase/ligase repair gap
- cross over resolved by endonuclease that nicks the DNA
- only isomerizes at 1 end leads to crossing over

Front 10

What is different about recombination that does ntoo lead to crossing over?

Back 10

- isomerizes at both ends leading to same chromosome

Front 11

What are the general consequences of transposon recombination?

Back 11

- inversions or deletions

Front 12

How do transposon recombination induce an inversion?

Back 12

- oppositely oriented sites around a nucleotide sequence match up together and recombine (jump to other side)
- causes the nucleotide sequence between to flip and destroys function

Front 13

How do transposon recombination induce a deletion?

Back 13

- identically oriented sites ( same polarity)
- sites match up but have to loop in order to do so
- sites 'jump' to other end
- cause nucleotide loop to come off of the chromatid with one of the 'sites' (deletion)

Front 14

What happens when tumor cells that are resistant to methotrexate are in the presence of this drug? (general)

Back 14

- amplify the dihydrofolate reductase gene (DHFR)

Front 15

What are the 2 ways the DHFR gene may be amplified in a tumor cell?

Back 15

1) homogeneously staining region: enlarged chromosome with the longer area being repeats of the DHFR gene which soaks up poison
2) Double minute chromosomes: extrachromosomal copies of the DHFR region w/o centromeres but are present in such high numbers they are bound to get into at least one of the cells

Front 16

What are the 2 proposed mechanisms for anticipation?

Back 16

1) replication slippage: DNA polymerase transiently dissociates resulting in DNA unpairing and may reanneal to the wrong repeat, causing an increase
2) Aberrant recombination: chromosome with the repeat becomes misaligned with which repeat it is on creating an increase in repeats

Front 17

What mechanism causes DNA to be unstable in HNPCC (hereditary nonopolyposis colorectal cancer)?

Back 17

- microsatellite DNA: short 1/2/3 nucleotide repeats which have undergone gains/losses of these repeats which affects how accurate DNA replication is

Front 18

Is microsatellite sequence instability in familial or sporadic cancer?

Back 18

- has been found in both