L2 Flashcards by Asma 1

Starts the initiation of DNA replication

DNAa

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Binds to the replication fork and unwinds duplex DNA by breaking hydrogen bond using ATP

Helicase

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Uses ATP

Helicase

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Keeps strands to separate

SSBP

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Protects single strand DNA from nucleases

SSBP

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Breaks one strand from super coil

Topoisomerase 1

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Breaks the two strands from super coil

Topoisomerase2

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Synthesizes RNA primer from polymerases (prokaryotes)

Primase

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A Holoeenzyme that includes 10 subunits that work together for DNA replication (prokaryotes)

DNA polymerase 3

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Removes incorrect nucleotides when proofreading

3’-5’ exonuclease

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A holoenzyme that fills the gap in the DNA due to the removal of primers (prokaryotes)

DNA polymerase 1

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Removes primer from 5’-3’ creating gaps

5’-3’ exonuclease of dna pol1

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Links DNA fragments with phosphodiester bonds

Ligase

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The origins of replication in prokaryotes is about ___ bplong

245

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Ori is mostly contains A/T-rich sequences. Why?

ThedoublehydrogenbondedA/T-rich regions are relatively weaker to break than the triple bonded G/C-rich sequences

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Stretches the double stranded DNA

DnaA

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Creates a bubble or Y-shaped structure

Stretching of DNA by the help of DNAa

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What is the significance of the Y-shaped replication fork

Bi directional replication

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SSB function (2)

protect the DNA from nucleases that might degrade single stranded DNA.

helps to keep the two strands of DNA separated so that the DNA polymerase can bind and start replication.

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Cytidinetriphosphate —> Cytidine monophosphate what had happened?

-2p by DNA polemerases 3 when catalyzing a strand

Explanation: Itcatalyzesaddingdeoxynucleotidetriphosphatess(dATP,dTTP, dGTP & dCTP) to the elongating chain & releasing two phosphate molecules (pyro phosphate) from them thereby incorporating a deoxy nucleotide monophosphates.

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The DNA strands synthesized from the origins of replication to the replication fork is called

Leading strand

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DNA strands synthesized from the replication fork to the origin of replication is known as

Lagging strand

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DNA polymerases reads the parental strand in ___ Direction
what synthesize is a complementary strand in _ direction

3’-5’
5’-3 Antiparallel

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Interpret: DNA synthesis is semicontinuous

The lagging strand is this continuous, while the leading strand is continuous

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The 3'→5' exonuclease activity of DNA polymerase III will remove the incorrect nucleotide”proof read” , why is it 3'→5' ?

Because DNA polymerases runs antiparallel from 5 to 3, so the last sequence is 3.

DNA polymerase 3 can naturally make an error in every ___nucleotide pairs

10^7

Leading strand __#gap__# primer Lagging strand __#gap__# primer

1,1 Many, many

After synthesizing the lagging strand DNARNA primers should be removed. The removal of RNA primers will create gaps in the newly synthesized complementary DNA how to fix this problem.

DNA polymerase one will fill the gap with DNA nucleotides

What are the three major activities of DNA polymerase one

5'→3' Exonuclease • removes the RNA primer from 5’ to 3’ direction. 3'→5' Exonuclease •proof reads and corrects the nucleotide mismatch error during synthesis. 5'→3'Polymerase • fills the gap with DNA • However, polymerase needs a primer. Where is the primer ?. • The 3’ end of Okazaki fragment will be used as primer.

What is the major difference between DNA polymerase 1 and 3 using the following terms: 5’-3’ Polymerase 3’-5’ Exonuclease 5’-3’ Exonuclease

Both have 5’-3’ Polymerase —> synthesis 3’-5’ Exonuclease —> proof reading 1 has 5’-3’ exonuclease to remove rna primer

What is the difference between endonuclease and exonuclease

Endo—> cunts between dna Exo —> cuts at the end

In eukaryotes, multiple(ori) sites are needed for replication. Why?

greater length of the eukaryotic DNA.

contrast between prokaryotes first and eukaryotes next: Ori

1 Many

contrast between prokaryotes first and eukaryotes next: RNA primer synthesis

Primase Polymerase alpha

contrast between prokaryotes first and eukaryotes next: Leading strand synthesis

DNA polymerase 3 Polymerase E

contrast between prokaryotes first and eukaryotes next: Lagging strand synthesis

DNA polymerase 3 Polymerase s

contrast between prokaryotes first and eukaryotes next: Proof reading

3’-5’ exonuclease for both

contrast between prokaryotes first and eukaryotes next: RNA primer removal

5’-3’ exonuclease of DNA POL1 RNase + REN1

contrast between prokaryotes first and eukaryotes next: RNA primer gap is filled with DNA by

DNA POL1 Polymerase E

During eukaryotic somatic cell division replication at thechromosome end (telomere) is always a problem in the___ strand.

lagging

the gap created at the 5’ end of the lagging strand upon the removal of the primer can’t be filled with DNA by polymerase because

There is no primer for DNA POL

Eukaryotic normal somatic cells, telomeres will therefore be shortened with each successive cell division why?

After FEN1 and RNase remove the primers, polymerase E cannot add nucleotides therefore it will permanently be shortened.

No end replication problem in cancer cells, germs cells or stem cells why?

Dna telomerases

Telomerase is an enzyme and composed of

Reverse transcriptase RNA nucleotides template

Reverse transcriptase is also known as

RNA-dependent DNA polymerase—> synthesize complementary DNA from RNA template.

In germ, stem and cancer cells, telomerase helps synthesizing ____DNA at the end of the____ strand using its RNA template

telomeric repeat lagging

In Normal somatic cells synthesizing telomeres at the telomeric end is it not possible why

Because telomerase activity in naturally inhibited

Telomerase synthesizes telomere DNA repeat at the 3’ end of the leading strand, instead of filling the gap in lagging strand, Why...?

Because,polymerase can add nts ONLY in the5’-3’direction using the 3’-OH of last nucleotide

T/F? polymerase can add nts ONLY in the 5’-3’direction using the 3’-OH of last nucleotide

Telomerase synthesizes telomere DNA repeat steps

1- Polymerase a (primase) synthesizes a RNA primer on the LAGGING strand complementary to the leading strand 2-DNA Polymerase s(pol s) fills the gap till it hits the 5’ end of the lagging strand. 3-Ligase seals the DNA fragments 4-RNA primer will be removed by RNase H & FEN1

T/F? its better that telomerase synthesizes telomeric repeats and looses few bases

T Because telomeres sacrifice themselves

Telomerase synthesizes telomere DNA repeat on the __ strand

Lagging

Explain how Didanosine or 2',3'-dideoxyinosine (DDI) works

* is an analog of ATP (Adenosine). the 3'-OH group on the deoxyribose sugar moiety has been replaced by hydrogen —> prevents formation of phosphodiester bonds between the 3’-OH and 5’-phosphate

Azidothymidine (AZT) also known as

Zidovudine

Azidothymidine is an analog of

Thymidine

In AZT, the 3'-OH group on the deoxyribose sugar moiety has been replaced by

azido group (N3)

What are the 2 nucleoside analogs

AZT=thymidine DDI=adenosine

Inhibition of DNA replication in cancer cells by Anti-cancerous drugs include

Camptothecin, T1 inhibitor Etoposide, T2 inhibitor

How does Anti-cancerous drugs work

binds to the DNA at the topoisomerase I cleavage site and prevents the uncoiling of DNA and thus inhibiting the replication of cancer cells

Results in replication fork

Helicase

Releases torsional strains

Topoisomerase

How are the okazaki fragments bound together

By ligase

Although somatic cells have telomerase, they cannot synthesize telomeres why

It is naturally inhibited

Stretches DNA

DnaA

Aids in genetic motility

Reverse transcriptase

Antiviral drugs DNA termination Depends on failing ___ While Anti-can serious drugs depends on failing ___

Phosphodiester bonds Topoisomerase 1 and 2

What is the last step of DNA replication

Ligation of okazaki fragments

MAIN function of DNA polymerase

Adding nucleotides

Synthesis complementary DNA using DNA template

DNA polymerase

Synthesize complementary RNA using DNA template

RNA polymerase, primase

Synthesize complementary DNA using RNA template

Reverse transcriptase, telomerases

What type of a polymerase is Telomerase

RNA dependent DNA polemerase, reverse transcriptase

Why primer is needed to synthesize RNA primer for the initiation of DNA replication why not use the DNA polymerase to synthesize the RNA primer

Because DNA polymerase is DNA dependent DNA not RNA dependent DNA.

T/F: primase is an DNA dependent RNA polymerase Or RNA dependents DNA polymerase

L2 Flashcards

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