Dna Synthesis In Eukaryotes

Front 1

What are the activities of e.coli DNA polymerases?

Back 1

1. Polymerization
2. Proofreading
3. Primer removal

Front 2

What is step 5 in this replication?

Back 2

Template priming -
Primiosome initiates Okazaki fragments on the lagging strand

- Unwinds DNA and synthesizes RNA primer.

Front 3

What occurs in step 6?

Back 3

Polymerization -

Primers extended by pol III
Primers then removed and replaced with DNA by pol I
Gaps are filled by DNA ligase

Front 4

What does the replisome in this replication consist of?

Back 4

The primosome + 2 Pol III holoenzymes

Lagging strand forms loop to connect to pol III core that is bound to the pol III core replicating the leading strand

Front 5

What are the main differences between DNA replication in prokaryotes and eukaryotes?

Back 5

PRO
- 4.6x10^6 bp in 40 min
- DNA synthesis is continuous
- 1 circular chromosome
- 1 origin of replication
- replicase has 2 catalytic cores

EUK
- Human: 3.3 x 10^9 bp in 9 hours
- DNA synthesis during S-phase
- Several pairs of linear chromosomes
- Each have multiple origins of replication
- 2 or more polymerases engaged at replication fork
- DNA packaged in nucleosomes

Front 6

What three polymerases are required in DNA replication?

Back 6

Pol E: replicates the leading strand

Pol o: extends the 30 nucleotide RNA/DNA primer on the lagging strand

Pol a: together with DNA primase prime and synthesize the short (30 nucleotide) Okazaki fragments on the lagging strand.

Front 7

Prol O and E lack ____ --> RNA primers removed by ribonucleases

Back 7

5'-3' exonuclease activity

Front 8

Pol o and E require ___ and ____ to be processive

Back 8

PCNA and replication factor C

Front 9

What are the steps in DNA replication?

Back 9

1. Synthesis of RNA primer by DNA polymerase a
2. Extend primer with DNA: lagging strand (pol o), leading strand (pol e)
3. Remove RNA primers: ribonuclease H1 and FEN-1
4. Fill gaps with DNA: DNA pol e and o
5. Seal nicks: DNA ligase

Front 10

TRUE or FALSE: replication forks can pass through nucleosomes

Back 10

FALSE: they cannot pass through nucleosomes, however nucleosomes can be seen on both sides of the fork.

Front 11

Nucleosomes must be ____ to allow the replisome to replicate the DNA and then reassemble on both strands of DNA

Back 11

disassembled

Front 12

Histones must be ____ to keep up with chromatin duplication

Back 12

synthesized

Front 13

Nap-1

Back 13

Transports histones to the nucleus

Front 14

CAF-1

Back 14

Brings histones to sites of nucleosome assembly (binds PCNA)

Front 15

Newly assembled nucleosomes contain a mixture of ____ and ____ histones

Back 15

Pre-existing and newly synthesized

Front 16

Describe nucleosome assembly during chromosome replication

Back 16

- Apper to have same structure and spacing immediately being replication fork as they do in fornt
- DNA replication and nucleosome assembly are tightly coupled
- Histone synthesis occurs throughout cell cycle, but there is still a bust of histone synthesis during chromosome duplication
- Nucleosome duplication seems to occur by dispersive mechanisms.

Front 17

What are the three important functions of telomere?

Back 17

Telomeres have a unique sequence and structure.

1. Prevent DNases from degrading end of linear DNA
2. Prevent fusion of ends with other DNA molecules
3. Facilitate replication of the ends of the linear DNA molecules without loss of material...

Essentially they : prevent fusion with other ends, degradation by endonulceases and facilitates end replication

Front 18

TRUE or FALSE: telomeres have tandem repeat sequences

Back 18

True

Front 19

Eukaryotic chromosomes have ____ ends

Back 19

Free

Front 20

TRUE or FALSE: Telomeres form F-loop structure

Back 20

FALSE: Telomeres form T-loop structures

Front 21

How are T-loop structures formed?

Back 21

By invasion of the 3' single stranded overhang into a region of complementarity.

Front 22

T-loop is coated with _____ complexes that protect the telomere from ____

Back 22

Shelterin
Degradation

Front 23

What does TRF1/TRF2 do?

Back 23

Binds double-strand repeats

Front 24

What does POT1 do?

Back 24

Binds single strand repeats

Front 25

What is the main problem?

Back 25

DNA pol I cannot fill gap at the end of the chromosome and therefore ends grow shorter with each cell division.

Front 26

What is the solution?

Back 26

The unique enzyme telomerase

Front 27

What does telomerase do?

Back 27

- Recognizes the repeat sequence
- Extends sequence 5'-3' one at a time
- Contains its own RNA template
- Composed of protein and RNA
- Enzyme is a reverse transcriptase: synthesizes DNA using RNA template
- DNA polymerase synthesizes the complimentary strand.

Front 28

Describe replication of chromosome termini by telomerase

Back 28

Telomerase:
1. RNA template binds to parental strand
2. nucleotides complementary to RNA added (5'-3' polymerase activity)
3. shifts to new position REPEATS PROCESS SEVERAL TIMES

4. DNA primase and DNA polymerases: fill in the bottom strand

5. RNA primer is removed
6. Terminal transferase adds G repeats to 3' end

Front 29

TRUE or FALSE: Cancer cells have low telomerase activity

Back 29

FALSE: cancer cells have high telomerase activity

Front 30

What is the difference between normal somatic cells, germline/stem cells and cancer cells?

Back 30

Normal somatic cells:
- limited number of cell divisions
- contain very little telomerase
- length decreases ~100 bp with each cell division
- shortening could act as a cell division clock

Germline/stem cells/cancer cells
- high telomerase activity
- stable telomeres

Front 31

Cancer cells are _____

Back 31

Immortal

Front 32

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Back 32

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