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Molecular Bio Midterm 1 > DNA Replication > Flashcards

DNA Replication Flashcards

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1
Q

DNA of different molecular weights are separated using the following method?

A

Cesium chloride density gradient centrifugation

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2
Q

What model of DNA is the correct model?

A

Semi-conservative model. Each daughter contains one parental and one daughter strand

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3
Q

Which enzyme catalyzes the formation of a phosphodiester bond between the 3’ hydroxyl group or one nucleotide and the 5’ phosphate of an adjacent one?

A

DNA-dependent DNA-polymerase

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4
Q

In the nucleotide addition reaction by DNA polymerase, the 2’-hydroxyl attacks the alpha phosphate from the adjacent nucleotide. T/F?

A

False

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5
Q

What direction are chains synthesized?

A

5’ –> 3’

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6
Q

Where does DNA copying start?

A

At origin of replication

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7
Q

Does DNA replication start in more than one place?

A

In bacterial cells no, in eukaryotic cells YES (10,000+ in humans). Starts at replication origins. Ends at terminus of replication.

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8
Q

Does DNA replication go in one direction or in two directions?

A

Bidirectional so 2

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9
Q

Does bidirectional DNA replication proceed continuously?

A

One strand is continuous (leading), the other is discontinuous (lagging). The lagging strands are OKAZAKI fragments.

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10
Q

What are autonomously replicating sequences (ARS)?

A

Multiple origins of replications. Multiple origins means less characterized (eukaryotes).

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11
Q

What enzymes are involved in bacteria replication?

A

DnaA- binds 9-mer sequences, bends DNA, breaks hydrogen bonds

DnaB- helicase that uses ATP to break hydrogen bonds of complementary bases to separate strands and unwind helix

DnaC- carries DnaB to helix

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12
Q

What enzymes are required only for initiation of bacterial replication?

A

DnaA and DnaC

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13
Q

What enzyme is required throughout process of replication?

A

DnaB, SSB, and topoisomerases

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14
Q

What else is needed for DNA replication?

A

A primer created by PRIMASE an RNA polymerase

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15
Q

DNA dependent DNA polymerase I function

A

Repairs enzymes and excise and replace mismatch nucleotides (fill gaps).

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16
Q

DNA dependent DNA polymerase II function

A

Repairs enzymes

17
Q

DNA dependent DNA polymerase III function

A

Major DNA replicase involved in replicating bacterial genome

18
Q

DNA dependent DNA polymerase IV and V

A

Primarily repair functions in SOS response (major DNA damage)

19
Q

What is a holoenzyme?

A

Multiprotein complex in which a core enzyme is associated with the additional components needed for full function

20
Q

How many copies of DNA Pol III are in the replisome?

A

2 (sometimes 3) at each replication fork. 1 copy elongates in same progression as fork progression (leading strand) and one elongates discontinuously in opposing direction (lagging strand).

21
Q

Activities of DNA polymerase I?

A
  1. 5’-3’ exonuclease activity that removes RNA primers.
  2. 5’-3’ polymerase activity that adds DNA nucleotides to 3’ end of DNA segment
22
Q

What enzyme seals the gap between DNA segments?

A

DNA ligase

23
Q

How many protein subunits are included in DNA polymerase III holoenzyme?

A

11 including 2 Pol III core polymerases

24
Q

What is DNA proofreading?

A

Correct occasional errors that occur because tautomers pair with the wrong patterns.

25
Q

What are tautomers?

A

DNA nucleotide bases that convert to alternative structures. Different base pairing preferences. MOST COMMON FORM OF REPLICATION ERROR

26
Q

What happens to a mismatched base pair on a daughter strand?

A

Displaced into the 3’-to-5’ exonuclease site of the enzyme. 3’ end returns to polymerase active site and incorporation of new nucleotides resumes.

27
Q

Steps:

A
  1. separate strands
  2. add RNA primers
  3. polymerize DNA from RNA
  4. remove RNA primers
  5. Fill in the gaps by extending DNA from 5’ ends
28
Q

What are telomeres?

A

Repetitive sequences at the end of chromosomes that ensure incomplete chromosome replication does not affect vital genes. Synthesized by telomerase.

29
Q

Telomerase parts

A
  1. RNA= template for copying to synthesize the DNA telomere sequences
  2. Protein part
30
Q

What kind of polymerase is telomerase?

A

RNA-directed DNA-polymerase

31
Q

Steps of telomerase:

A
  1. uses it’s RNA component to synthesize complementary DNA in short bursts
  2. DNA polymerase completes the lagging strand
32
Q

What is the relationship between telomeres, aging and cancer?

A

Chromosome stability, cell longevity, and reproductive success. active in germ-line cells and some stem cells

33
Q

What happens to reactivation of telomerase?

A

Lead to aging cells that continue to proliferate

34
Q

During DNA replication, the following strands are synthesized/extended in the 5’ to 3’ direction?

A

Both leading and lagging

35
Q

Which activity of the DNA pol I is used for RNA primer removal in prokaryotes?

A

5’-3’ exonuclease

Molecular Bio Midterm 1 (7 decks)

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