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Cells > DNA replication > Flashcards

DNA replication Flashcards

1
Q

By what process does DNA replicate?

A

Semi-conservative replication

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2
Q

What bases are purines?

A

Adenine (A)

Guanine (G)

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3
Q

What bases are pyrimidines?

A

Thymine (T)

Cytosine (C)

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4
Q

What are the 2 stages to DNA replication?

A

Initiation and Elongation

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5
Q

What is the first step of initiation?

A

Unwinding DNA supercoil by topiosomerases

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6
Q

What is the second step of initiation?

A
  • Separation of DNA strands, breaking the hydrogen bonds between bases using helicase
  • Single stranded DNA binding proteins (SBBs) bind to prevent re-annealing
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7
Q

What are SSBs?

A

Single stranded DNA binding proteins (SBBs) that bind to the DNA to prevent re-annealing once it has been seperated

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8
Q

Describe the initiation process of DNA replication?

A
  • Unwinding DNA supercoil by topiosomerases
  • Separation of DNA strands, breaking the hydrogen bonds between bases using helicase
  • Single stranded DNA binding proteins (SBBs) bind to prevent re-annealing
  • creating 2 replication forks
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9
Q

At each replication fork, what are the names given the the 2 types of strands being synthesised?

A

Leading strand

Lagging strand

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10
Q

How is the leading strand synthesised?

A

Synthesised continuously from 5’ to 3’ end

-RNA primer added, then DNA polymerase on a sliding clamp moves along the strand adding bases

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11
Q

How is the lagging strand synthesised?

A

Synthesised discontinuously

  • Multiple RNA primers placed along the lagging strand.
  • DNA polymerase joins at the RNA primer and then dissociates when it reaches the next- forming Okazaki fragments
  • RNase H removes the RNA primers and DNA ligase synthesises phosphodiester bonds between the fragments to join them
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12
Q

What is the potential problem when the RNA primers are removed in the synthesis if new strands?

A

The primers are removed so the ends are unreplicated, meaning chromosomes get shorter with each cell division

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13
Q

What is the solution to stop chromosomes getting shorter when the RNA primers are removed?

A

Adding telomeres, which are stretches of DNA with no informational role
-means if they are replicated it doesn’t matter

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14
Q

Do we run out of telomeres?

A

When we are born our telomeres are longer, each time a cell divides and replicates, the telomeres shorten. This continues until the telomeres run out, and the cell becomes inactive or dies, which leads to disease

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15
Q

What are telomeres?

A

Stretches of DNA that have no informational role

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16
Q

How do some immortal cells (e.g cancer cells) maintain telomere length?

A

By using telomerase, which is a reverse transcriptase that is responsible for the synthesis of telomeres

17
Q

Why is the error rate for DNA replication so low?

A
  • Structural differences of purines/pyrimidines
  • Proof reading activity of DNA polymerase
  • Mismatch repair
18
Q

How does DNA polymerase proof read?

A

DNA polymerase has 3’ to 5’ exonuclease activity (backwards)

-checks the last nucleotide added, and if it is correct adds another nucleotide or if it is wrong chops it off

19
Q

What is the mismatch repair of DNA?

A

Where newly synthesised DNA is compared and matched to the template DNA it was copied from
-if there is a change that segment is cut and replaced with the correct segment

20
Q

What are the 3 types of point mutations?

A

Silent
Missense
Nonsense

21
Q

What is a silent mutation?

A

Change in base, but codes for the same amino acid

22
Q

What is a missense mutation?

A

Change in base that codes for a different amino acid, but doesn’t change the function of the protein

23
Q

What is a nonsense mutation?

A

Change in base that produces a stop codon in the midst of the mRNA, stopping translation early, which can produce a non functional protein

24
Q

What are the types of chromosomal mutations?

A

Deletions
Duplications
Inversions
Translocations

25
Q

What is a deletion mutation?

A

A mutation in which one or more pairs of nucleotides are removed from a gene

26
Q

What is a duplication mutation?

A

A mutation that involves duplication of a region of DNA on the same strand

27
Q

What is an inversion mutation?

A

A mutation in which a chromosome piece reattaches to the original chromosome but in reverse orientation

28
Q

What is a translocation mutation?

A

A mutation in which one part of one chromosome breaks off and attaches to another
-can be reciprocal or Robertsonian translocation

29
Q

What are the 2 types of translocation?

A

Reciprocal

Robertsonian

30
Q

What is reciprocal translocation?

A

A form of translocation where portions of two chromosomes break off and are exchanged
-no net loss of genetic information

31
Q

What is Robertsonian translocation?

A

(also known as non-reciprocal)

A form of translocation where a portion of a chromosome breaks off and attaches to another

Cells (8 decks)

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