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Cell Biology > DNA and Replication > Flashcards

DNA and Replication Flashcards

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1
Q

In terms of DNA and RNA structure, what is a nucleotide?

A

A nucleotide is a sugar molecule bonded to phosphate group/s and a heterocyclic base

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2
Q

The leading strand of a DNA molecule has the following sequence:
5’-CGCATGTAGCGA-3’

What is the complementary sequence?

A

3’-GCGTACATCGCT-5’

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3
Q

In what direction does DNA polymerase synthesise DNA?

A

DNA polymerase can synthesize DNA in the 5’ to 3’ direction

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4
Q

What is the role of topoisomerases in eukaryotic DNA replication?

A

Topoisomerase enzymes cut, uncoil and reseal the double stranded DNA

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5
Q

Which of the following statements is true of DNA damage?

a) All DNA damage results in diseases such as cancer

b) Most DNA damage is repaired by the cell

c) All DNA damage is caused by physical, chemical or biological agents

d) Most DNA damage is advantageous to the cell

A

B

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6
Q

Give the name of the enzyme that creates a short RNA oligonucleotide at initiation sites where replication is to be carried out

A

Primase

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7
Q

Give the name of the enzyme that stitches Okazaki fragments together along the lagging strand

A

DNA Ligase

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8
Q

Give the name of the repeating DNA sequence at the end of chromosomes that prevents them from losing base pair sequences at their ends and from fusing together

A

A telomere

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9
Q

Give the name of the enzyme (made of proteins and RNA) that elongates chromosomes by adding TTAGGG sequences to the end of existing chromosomes

A

Telomerase

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10
Q

Which of the following correctly pairs the DNA replication enzyme with its function?

a) Topoisomerases work ahead of the replication fork to prevent supercoiling.

b) DNA polymerase I opens up the DNA at the replication fork.

c) Helicase seals gaps between DNA fragments.

d) DNA primase extends primers by adding nucleotides to the 3’ prime end.

A

A

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11
Q

Which of the following statements best explains the mechanism for DNA replication?

a) DNA replication is reductive, because half the total DNA present is copied.

b) DNA replication is semi-conservative, because each DNA strand serves as a template during replication.

c) DNA replication is dispersive, because the two resulting DNA molecules are mixtures of parent and daughter DNA.

d) DNA replication is conservative, because one resulting molecule is identical to the original and the other consists of two new strands.

A

B

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12
Q

Which of the following statements about these strands is true?

a) Okazaki fragments are used to synthesize the leading strand of DNA.

b) The leading strand of DNA is synthesized continuously.

c) DNA polymerase can only synthesize DNA on the leading strand.

d) The lagging strand can only be synthesized once the leading strand has been completed.

A

B

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13
Q

The molecular structure of DNA was first discovered by which two of the following?

a) Isaac Newton

b) James Watson

c) Francis Crick

d) Rachel Carson

A

B and C

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14
Q

Name the 4 Bases in DNA and which ones bond together and with how many hydrogen bonds

A

Adenine to Thymine - 2 Hydrogen Bonds

Cytosine to Guanine - 3 Hydrogen Bonds

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15
Q

What is different about the bases in RNA?

A

Thymine is replaces with uracil

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16
Q

In what direction is DNA synthesised?

A

5’ to 3’

17
Q

Why does DNA Polymerase require a RNA primer to synthesize new DNA strands?

A
  • DNA polymerase cannot initiate DNA chain synthesis on its own from the beginning
18
Q

How is the leading and lagging strand synthesised using RNA Primer

A

The leading strand is synthesized continuously from a short single RNA primer which is about 10 nucleotides long in eukaryotes

The lagging strand is synthesised from multiple RNA primers that are formed periodically as each new region of the parental DNA duplex is unwound

19
Q

Explain what Okazaki fragments are

A

Short DNA fragments that are synthesised sequentially and then joined up, named after discoverer Reiji Okazaki

20
Q

Role of DNA Ligase and outline the steps

A

Seals gaps between the Okazaki fragments that are left in the lagging strand during DNA replication

Step 1 - DNA ligase uses ATP to activate the 5’ end at the DNA gap

Step 2 = A new phosphodiester bond is formed

21
Q

Explain what Telomerase is

A

Telomerase is an enzyme that uses an RNA template to complete ends of chromosomes

22
Q

Explain the role of topoisomerases

A

Prevent DNA tangling during replication. They are reversible nucleases that transiently break the phosphodiester bonds

23
Q

What are the 2 types of topoisomerases?

A

Type 1 topoisomerases:

  • Make nicks in one DNA strand and can relive supercoiling
  • Make nicks in both DNA strands (double strand break). Can relieve supercoiling and untangle linked DNA helices
24
Q

For DNA synthesis to take place the DNA double helix must be opened but it is very stable, how can the double helix be opened?

A

Very high temperatures

Proteins: DNA helicase and Single-stranded DNA-binding (SSB) proteins

25
Q

What is the role of Single strand binding proteins?

A

Single strand binding proteins bind single stranded DNA (ssDNA) generated by helicases. They straighten and stabilise ssDNA, cooperating with the DNA polymerase

26
Q

Name the 6 proteins involved in DNA replication

A

DNA polymerase

DNA Helicase

Topoisomerase

DNA primase

DNA ligase

Single strand DNA binding proteins

27
Q

What happens if DNA replication goes wrong?

A

There are enzymatic mechanisms in place for correcting error:

  • If the wrong nucleotide has been added by the polymerase, translocation of the enzyme to the next position along the template is inhibited. This pause provides the opportunity for a correction
  • DNA polymerase exhibits proofreading activity in which an incorrectly paired nucleotide is removed through exonuclease activity.
  • The cell has other DNA repair mechanisms

Cell Biology (11 decks)

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