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MCAT Biochemistry > DNA & Replication > Flashcards

DNA & Replication Flashcards

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MCAT flashcards
1
Q

Nucleoside

A

5C sugar bonded to a nitrogenous base

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2
Q

Nucleotide

A

Nucleoside + 1 to 3 phosphates attached

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3
Q

Which histone protein stabilizes the nucleosome?

A

H1

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4
Q

DNA coiled around histone protein

A

Nucleosome

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5
Q

DNA and its associated histones

A

Chromatin

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6
Q

Dense, transcriptionally silent DNA

A

Heterochromatin

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7
Q

Less dense, transcriptionally active DNA

A

Euchromatin

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8
Q

Telomeres contain a high content of what two nucleotides? Why?

A

GC, to prevent DNA from unraveling

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9
Q

How many origins of replication in Eukaryotes vs. Prokaryotes?

A

Euk - multiple per chromosome

Pro - one per chromosome

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10
Q

Enzyme responsible for unwinding DNA during replication

A

Helicase

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11
Q

Stabilize unwound template strands to prevent reannealing or degradation

A

SSB’s (single stranded binding proteins)

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12
Q

Enzyme responsible for the synthesis of short RNA primer in 5’ –> 3’ direction to start replication on each strand

A

Primase

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13
Q

Enzyme responsible for actual synthesis of new DNA strands

A

DNA Polymerase

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14
Q

What DNA pol is used in eukaryotes vs. prokaryotes?

A

Euk - DNA pol alpha, sigma, and epsilon

Pro- DNA pol III

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15
Q

What is the enzyme responsible for removing primers in prokaryotes, and what type of activity does it exhibit?

A

DNA polymerase I (5’ to 3’ exonuclease)

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16
Q

What is the enzyme responsible for removing RNA primers in eukaryotes, and what type of activity does it exhibit?

A

RNase H (5’ to 3’ exonuclease)

17
Q

What polymerases fill in the gaps left behind when RNA primers are removed in eukaryotes and prokaryotes?

A

Euk - DNA pol sigma

Pro - DNA pol I

18
Q

What enzyme is responsible for joining of Okazaki fragments?

A

DNA ligase

19
Q

What enzyme is responsible for removal of positive supercoils ahead of advancing replication forks?

A

DNA topoisomerases (DNA gyrase)

20
Q

Enzyme responsible for synthesis of telomeres?

A

Telomerase

21
Q

Proto-oncogenes

A

name given to oncogenes before mutation

22
Q

What kind of proteins do oncogenes primarily encode?

A

Cell-cycle related proteins

23
Q

Name of genes that code for proteins that reduce cell cycling or promote DNA repair

A

Tumor suppressor genes

24
Q

T/F: tumor suppressor genes can also lead to cancer

A

True

25
Q

What enzyme is responsible for proofreading?

A

DNA polymerase

26
Q

During proofreading activity, how does DNA polymerase discriminate between the parent and daughter strands?

A

By level of methylation: parent strand has existed for longer time period and thus is more heavily methylated

27
Q

DNA composed of nucleotides from two different sources

A

Recombinant DNA

28
Q

What is the name of the enzyme machinery (and the genes that encode these enzymes) in the G2 phase of cell cycle which detects and removes errors introduced in replication that were missed during S phase of cell cycle?

A

Mismatch repair
genes = MSH2 and MLH1 in eukaryotes
and MutS and MutL in prokaryotes

29
Q

What kind of damage does UV light cause in DNA?

A

induces formation of dimers between Thymine residues which interferes with DNA replication and normal gene expression and disorts the DNA double helix

30
Q

How is DNA damage induced by UV light repaired?

A

Nucleotide excision repair (NER) mechanism which uses an excision endonuclease along with DNA polymerase and DNA ligase to cut-and-patch Thymine dimers

31
Q

Thermal energy absorption leads to what kind of DNA damage?

A

Cytosine deamination and conversion to Uracil

32
Q

What kind of damage does base-excision repair fix and how?

A

Fixes nondeforming DNA lesions (such as cytosine deamination) by removing affected base & leaving behind an AP site which is recognized by an AP endonuclease that functions to remove and replace affected base

MCAT Biochemistry (11 decks)

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