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USMLE Biochemistry > DNA Replication > Flashcards

DNA Replication Flashcards

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USMLE® Step 1 flashcards
1
Q

What 3 building blocks make up a nucleotide?

A
  • Nitrogenous base
  • Sugar (deoxyribose/ribose)
  • Phosphate group
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2
Q

What is removed from the deoxy-Base Triphosphate when it is added to the growing DNA strand?

A

2 phosphates

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3
Q

Where does DNA replication begin?

A

Origin of replication

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4
Q

What does DNA helicase require to carry out its role?

A

ATP

- Hydrolyses ATP

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5
Q

What dosingle strand binding proteins do

A
  • Assist helicase

- Stabilise and straighten single strands of DNA

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6
Q

What sequences of DNA do origins of replication usually have?

A

AT rich sequences (easier to open)

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7
Q

What DNA polymerases are found in prokaryotes?

A

DNA polymerase I-IV

  • Polymerase III: Major DNA polymerase
  • Polymerase I: Removes RNA primers
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8
Q

What are the DNA polymerases in eukaryotes?

A

alpha, Beta, gamma, delta, epsilon

- Polymerase y: located in mitochondria

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9
Q

What DNa polymerase in eukaryotes is not located in the nucleus and located in the mitochondria?

A

Polymerase y (gamma)

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10
Q

What makes primers?

A

DNA primase

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11
Q

What do primers contain?

A

RNA not DNA

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12
Q

Where does DNA polymerase add to on the DNA strand the new nucleotide?

A

3’ end

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13
Q

Where does the energy come from to add a nucleotide to the DNA strand?

A

From the 3 phosphates

- 2 phosphates are removed

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14
Q

In what direction are new nucleotides added?

A

5’ to 3’ direction

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15
Q

The eading and lagging strands are oriented in what direction?

A

Leading strand

  • 3’ to 5’ direction
  • Allows the replicating DNA to be added continously in a 5’ to 3’ direction

Lagging strand
- 5’ to 3’ direction

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16
Q

In prokaryotes what enzyme removes the RNA primer /okazaki fragment and replaces it with DNA?

A

DNA polymerase I

17
Q

In eukaryotes what enzyme removes the RNA primer / okazaki fragment and replaces it with DNA?

A

DNA polymerase delta

18
Q

What is the RNA primer known as on the lagging strand?

A

Okazaki fragment

19
Q

WHat is the function of DNA ligase?

A
  • Joins Okazaki fragments

- Creates phosphodiester bonds

20
Q

What is the function of topoisomerase?

A

Prevents DNA tangling

- Breaks DNA then reseals to relieve tension/twists

21
Q

What is the difference between topoisomerase I and II?

A

Topoisomerase I
- Breaks single strands of DNA then reseals

Topoisomerase II
- Breaks double strands then reseals

22
Q

What do quinolone antibiotics target?

A

Prokaryotic topoisomerases

23
Q

What strand replication is continuous and what strand replication is dicontinous?

A

LEading strand
- Continous

Lagging
- Discontinous

24
Q

Why is DNA replication known as being semi-conservative?

A

New DNA: one old strand and one new strand

25
Q

When may DNA polymerase move in a 3’ to 5’ direction?

A

To correct an error

26
Q

What enzyme will remove an incorrect nucleotide?

A

Exonuclease

27
Q

What are telomeres?

A

Nucleotides found at the end of chromosomes

28
Q

What sequences are found on telomeres?

A

TTAGGG

29
Q

What cannot attach on telomeres?

A

RNA primer on lagging strand

30
Q

What does telomerase do?

A
  • Recognises telomere sequences

- Adds these sequences to new DNA strands

31
Q

What genetic material do telomerases use?

A

RNA which it uses as a template to synthesize telomere DNA

32
Q

What can telomerase also be known as?

A

RNA-dependent DNA polymerase

33
Q

What enzyme is telomerase similar to that can be found in certain viruses?

A

Reverse transcriptase

34
Q

What side of the DNA does telomerase bind to?

Explain how telomerase allows the formation/duplication/extension of the telomere

A

3’ flanking end of the telomere

  • Complementary to telomerase RNA
  • Bases are then added using RNA as a template
  • DNA polymerase then adds the NTs to the lagging strand (5’ end) in a 5’ to 3’ (opposite) direction
35
Q

What kind of cells have many telomerase enzymes?

A

Cells that require controlled indefinite replication

  • Hamatopoetic stem cells
  • Epidermis, hair follicles, intestinal mucosa
36
Q

How can telomerase play a role in cancer?

A

Allows immortality of cells

- Increased telomerase may lead to cancer

USMLE Biochemistry (44 decks)

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