Maintenance of Genetic Information

Question 1

Eukaryotic cell cycle?

Answer 1

M = mitosis
G1 = Gap 1 (cells cease division)
S phase = DNA synthesis
G2 = Gap 2 (leads back to mitosis)
Signal commits cell to replicate DNA received in G1, if no signal is received then G0 phase is entered

Question 2

What is Semi-conservative replication?

Answer 2

Replication fork formed as DNA helicase unwinds the strand
immediate reformation of the helix is prevented by single strand binding proteins
pulling strands apart increases winding further down the molecules which is positive supercoiling
Topoisomerase breaks the phosphodiester bind in one of the parental strands ahead of the replication fork so the rest of the helix can unwind releasing DNA supercoils
DNA polymerase synthesises in 5’ to 3’ direction (one strand synthesised continuously and the other discontinuously
RNA polymerase initiates RNA synthesis so DNA synthesis begins with the synthesis of a short primer
DNA polymerase takes over extending the 3’ of the RNA primer
The lagging band consists of okazaki fragments, to join them, DNA polymerase extends DNA in 5’ to 3’ direction until it reaches the next primer.
Primer is then degraded by exonuclease leaving a gap and DNA ligase fills this, Okazaki fragments are now joined
DNA is now replicated

Question 3

What removes the wrong nucleotides?

Answer 3

3’-5’ exonuclease removes the wrong nucleotide and adds the correct one

Question 4

What is the end-replication paradox?

Answer 4

where a small amount of DNA is lost from each end of the linear chromosome after each round of DNA replication

Question 5

How to stop the loss of information when DNA is shortened?

Answer 5

Telomeres extend DNA which maintain base pairing and allow DNA synthesis to continue

Question 6

Uses of Telomerase?

Answer 6

Extends the chromosome ends as template RNA anneals to DNA
Telomerase adds nucleotides and then telomerase translocates further along DNA maintaining base pairing and allowing DNA synthesis to continue

Question 7

What happens when telomerase is switched off in somatic cells?

Answer 7

With every DNA division, telomerase gets shorter, so eventually telomeric sequences are lost and useful DNA will be lost which contributes to ageing

Question 8

What is a point mutation?

Answer 8

Where a single base is changed

Question 9

What is a frame shift?

Answer 9

Where the reading frame is lost (if a multiple of 3 bases aren’t implemented)

Question 10

What is Inversion?

Answer 10

Chromosome rearrangement where DNA segment breaks away and goes elsewhere

Question 11

What is Deletion?

Answer 11

Where a section of DNA is removed

Question 12

What is Duplication?

Answer 12

Where a section is duplicated

Question 13

What is Translocation?

Answer 13

Where a portion reattaches to another chromosome

Question 14

How are spontaneous mutations formed?

Answer 14

Errors in DNA replication, replication slippage and deamination where C to U now pairs with A

Question 15

How are induced mutations formed?

Answer 15

Ionising radiation, ultraviolet light, distorting DNA, Nitrous acid, alkylating agent and free radicals

Question 16

How is DNA damage repaired?

Answer 16

Direct repair, removal of damaged region, repair of double strand breaks

Question 17

What are the effects of tight association of DNA?

Answer 17

If DNA is condensed with nucleosomes the it inhibits the access of DNA to proteins that are involved in transcription, regions that bear actively transcribed genes must be decondensed.
if DNA is made accessible the RNA polymerase and transcription factors can reach it

Question 18

How can gene expression be disturbed?

Answer 18

By activation of genes that promote cell division, by decreasing transcription of genes or by promoting angiogenesis with increasing transcription

Question 19

What is metastasis?

Answer 19

The loss of cell to cell adhesion meaning they can invade vasculature and colonise other tissues