1-6 DNA Replication Flashcards Preview

MSI Unit I > 1-6 DNA Replication > Flashcards

Flashcards in 1-6 DNA Replication Deck (30)

Replication occurs in the _____ direction of the ____ strand. How does it move compared to the fork?

5'--->3' direction of the leading strand, same direction


the strand which is extended continuously

the leading strand


new nucleotides are added to the ____ end during replication

3' end


the strand which is replicated discontinuously, forming ___

lagging strand, okazaki fragments


Initiation takes place at the ____, which is marked by a protein complex called _______ which is responsible for?

origin of replication, origin replication complex (ORC), recruiting other initiation proteins to the origin


What does DNA helicase do?

aka MCM, unwinds the double stranded DNA


what prevents the exposed strands of the unwound dna from reannealing?

the binding of single-stranded dna (ssdna)binding protein (RPA)


what does primase do?

it is a specialized RNA polymerase that lays down an RNA primer because DNA polymerase can't work without it


how many primers are necessary for the leading strand? lagging strand?

leading strand - continuous, just one

lagging strand - discontinuous, multiple


what does POL alpha do?

makes a complex with primase, takes over the RNA primer and synethesizes a short stretch of DNA which then is taken over by DNA polymerase to synthesize longer stretches of DNA


which DNA polymerase is for what strand?

DNA polymerase ε for leading strand. (E for leading)

DNA polymerase δ for lagging strand


what is PCNA?

a sliding clamp, loaded by clamp loader RC-F that keeps dna polymerase firmly on the DNA template



loads the clamp(PCNA) that keeps dna polymerase tightly engaged to dna template


How is the lagging strand turned to a continuous piece of DNA?

the RNA primer and some DNA polymerase alpha synthesized DNA are removed:

1. DNA polymerase δ genetrates a flap by displacing the DNA pol-alpha synthesized DNA and primer.
2. Flap cut by flap endonuclease (FEN-1)
3. template gap is filled by DNA polymerase δ
4. gap between adjacent nascent strands sealed through phosphodiester bonds via DNA LIGASE


Define the mechanism limiting chromosome DNA replication to once per cell cycle

When S phase begins, Orc1 (origin recognition complex) is suppressed or degraded through phosphorylation by cyclin A/Cdk2. Cdt1 is also degraded, and any that remains is sequestered by geminin. Finally, Cdc6 is phosphorylated by cyclin A/Cdk2 and removed from the nucleus.


Describe the nucleic acid and protein components of chromosomal DNA replication and their coordinated composition at the replication fork.

Replication forks begin at origins of replication. Replication itself begins with a pre-replicative complex (pre-RC). Orc1 (origin recognition complex) recognizes the origin and recruits other replisome proteins to form the pre-RC, including the MCM2-7 complex (which includes helicase), Cdt1, and Cdc6. Helicase unwinds the double helix structure. The DNA primase/DNA polymerase alpha complex allows for the placement of an RNA primer and the synthesis of new DNA along the original copy. ssDNA binding protein stabilizes the unwound ssDNA. DNA polymerase epsilon is the polymerase for the leading strand, and DNA polymerase delta is the polymerase for the lagging strand. PCNA (the clamp protein) engages epsilon and delta onto the strands. RF-C (the clamp loader) allows for new clamp protein assembly. Ligase ligates the Okazaki fragments together.


explain different mechanisms of replication stress-induced genome instability

In cancer cells, expression of pre-RC proteins is increased


explain different mechanisms of replication stress-induced genome instability

1. In cancer cells, expression of pre-RC proteins is increased

2. if the cell runs out of dNTP's (deoxynucleotides) during replication, fork needs to be protected until dNTP supply is restored and replication can be reinitated

3. intereference between transcription and translation occurs more frequently on longer genes and leads to stress.

4. If a cell cycle checkpoint is reached, and DNA damage not repaired, the DNA damage response (DDR) pathway is initiated. ATM protein kinase is recruited to activate p53, which leads the cell to senescence or apoptosis.


unprotected replication forks give rise to..

formation of single stranded DNA gaps and ultimately doubel strand breaks.


what are CFS?

chromosomal fragile sites - genomic loci that are hot spots for genomic rearrangements and are implicated in diseases ranging from cancer to neurological disorders.


replication of DNA requires a primer for DNA synthesis because

DNA polymerase requires a base-paired nucleotide with a free 3' end before it can add a new nucleotide


molecule of bacterial DNA introduced into yeast cell is imported into nucleus but fails to replicate. Which yeast protein is likely unable to use the bacterial DNA as a substrate?

Initiator Proteins


Takes 40 minutes for e.coli chromosome to completely replicate. How are bacterial cells able to divide every 20 minutes? How can cells divide more rapidly, apparently, than their DNA can be copied?

e.coli origin of replicaion initiates a second round of replication before the first is complete


mutations in pre-RC components as well as over-expression of pre-RC components can both lead to ______. How?

genome instability

mutations in pre-RC components reduce/inhibit origin activation whereas over-expression of pre-RC components can lead to re-replication.


Describe the biological importance of replication timing control.

Genes that are transcribed more frequently will be replicated earlier on. This regulation is important for development of certain cells. For example, as pro-B cells develop into mature B cells, they need to rearrange certain loci, including the IgH locus, in order to generate particular immune receptors. Early replication of the IgH locus is necessary to achieve this rearrangement. Asynchronous gene replication is implicated in X-inactivation and genomic imprinting (expressing certain copies of genes and not their homologous copies): two cases in which one copy of a length of genetic material is replicated before its homologous copy.


replication fidelity is due mostly to?

the proofreading activity of DNA polymerase


describe the polymerase switch event

primase in complex with pol-a, which takes over RNA primer and lays down a short stretch of DNA.

Pol alpha is then replaced by a more processive (able to be engaged on DNA template for longer periods) dna polymerase (sigma for leading, & for lagging)


enzymes involved in telomere replication


TERC is an RNA template that TERT can use to add multiple copies of DNA at the 3' template of the lagging strand. lagging strand then gets completed by dna polmerase


In BER, lesion is removed by

dna glycosylase


aicardi goutieres syndrome

mutation in the RNASEH2A gene

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