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FMS > [FMS] MCG - DNA replication and Mutagenesis > Flashcards

[FMS] MCG - DNA replication and Mutagenesis Flashcards

1
Q

a nucleotide is made up of a nitrogen base, phosphate group, and deoxyribose sugar. Which position is the nitrogen base and phosphate group attached to?

A

nitrogen base attached to the 1’ position

phosphate group attached to the 5’ position

REMEMBER ‘ph’ in phosphate sounds like ‘f’ in ‘five’

fosphate is on carbon five

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2
Q

in DNA the sugar is deoxyribose, what does that mean?

A

that lacks an OH at the 2’ position.

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3
Q

what is a nucleoside

A

combination of the nitrogen base and the sugar.

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4
Q

what bond stabilises the 2 DNA strands

A

hydrogen bonds

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5
Q

what are the 2 classes of RNA

A

coding RNA and non-coding RNA

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6
Q

what is an example of coding RNA

A

mRNA RNA copies of genes (messenger RNA) that are produced via the process of Transcription

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7
Q

what are 5 examples of non-coding RNA?

A

rRNA RNA components of the ribosome

tRNA transfer RNA involved in the Translation of mRNA and guiding the incorporation of the correct amino acid in the synthesis of proteins

snRNA small nuclear RNA involved in the splicing of eukaryotic mRNA

miRNA microRNA involved in the regulation of gene expression

Xist involved in the inactivation of X-chromosome

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8
Q

where is replication initiated?

A

origin of replication

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9
Q

outline the process of DNA replication

A
  1. DNA helicase unwinds the DNA
  2. as a result 2 replication forks form
  3. SSB (single strand binding) prevents bonds from reforming
  4. TOPOISOMERASE prevents supercoiling
  5. DNA polymerase then synthesises new strands using old templates from 5’ to 3’ direction
  6. as a result theres a LEADING and LAGGING strand = OKOZAKI FRAGMENTS
  7. HOWEVER, DNA polymerase cannot initiate DNA synthesis so DNA synthesis begins with synthesis of a short RNA primer via PRIMASE
  8. The RNA primer is degraded by an exonuclease, leaving a gap
  9. DNA LIGASE joins the gap between the okozaki fragments
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10
Q

in DNA replication the immediate re-formation of the double helix is prevented by what?

A

single strand binding proteins (SSB)

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11
Q

whats an okozaki fragment?

A

leading strand and lagging strand formed in DNA replication

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12
Q

what does DNA polymerase require from the RNA primer to initate synthesis?

A

Free 3’OH

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13
Q

in DNA replication, when okozaki fragments are formed, how is this combatted? why is DNA polymerase not involved?

A

DNA polymerase cannot initiate DNA synthesis, it can only add nucleotides to pre-existing chains
RNA polymerase can initiate RNA synthesis, so DNA synthesis begins with synthesis of a short RNA primer

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14
Q

how many nucelotides long is the RNA primer and how is it synthesised in DNA replication?

A

8-10 nucleotides long, is synthesized by primase (an RNA polymerase)

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15
Q

role of helicase

A

Unwinds DNA strands

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16
Q

role of topoisomerase

A

Releases supercoils in DNA and PREVENTS SNAPPING

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17
Q

role of SSB

A

Stabilises single stranded DNA and prevent bonds forming on the strand when DNA helicase unwinds it during replication

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18
Q

role of primase

A

Makes RNA primer so that DNA synthesis can begin

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19
Q

role of DNA polymerase

A

Synthesises DNA

20
Q

role of exonuclease

A

Removes RNA primer

21
Q

role of DNA ligase

A

Joins adjacent Okazaki fragments

22
Q

how many origins of replication in eukaryote vs prokaryote chromosomes?

A

eukaryotic chromosomes = multiple origins

Bacterial chromosomes = single origin

23
Q

what prevents the loss of functional parts of the genome following DNA replication

A

during end replication paradox, end of linear chromosomes is lost, so Telomeres are added at the end

24
Q

what are telomeres made up of

A

5’ TTAGGG 3’

25
Q

what complex is formed when proteins bind to telomeres?

A

Shelterin complex

26
Q

what does Shelterin complex do?

A

complex prevents end to end chromosome fusions

27
Q

what happens in stem cells and gametes when the cells too short?

A

enzyme telomerase adds telomere repeats to the end of chromosomes

28
Q

What is telomerase made of?

A

a reverse transcriptase enzyme and an RNA telomere repeat template

29
Q

what are the 3 types of mutations?

A

point
indel
chromosomal

30
Q

what is point mutation? what are the 3 point mutations

A

point mutation – single base is changed

Silent mutation (synonymous) – change does not affect the encoded amino acid

Missense mutation – the encoded amino acid is changed

Nonsense mutation – change from encoding an amino acid to a stop codon

31
Q

what is an indel mutation? what are the 2 indel mutations

A

insertion

deletion

remember the word ‘indel’ is combination of insertion and deletion

Indel mutations can occur due to errors during DNA replication, repair, or recombination processes, or they can be induced by external factors such as mutagenic agents.

IF ANYTHING OTHER THAN 3 NUCLEOTIDES ADDED/REMOVED THEN FRAMESHIFT OCCURS

32
Q

What are the 4 types of chromosomal mutations?

A

Inversions (inverts, flips)

Deletions

Duplications

Translocations (changes location)

33
Q

what disease is caused by translocation?

A

CML

chronic mylegenous leukemia

chromsomes 9 and 22 affected

34
Q

what disease is caused by deletion?

A

cri du chat syndrome

limited mental and physical development

35
Q

what are the 7 causes of DNA mutagensis?

A
  1. Spontaneous errors in DNA replication – not detected via proof reading
  2. Replication slippage – associated with repetitive regions
    ^ 2 types of this, reverse slippage (gain of repeats)

forward slippage (loss of repeats)

  1. Spontaneous deamination of nitrogen bases
  2. UV induced formation of dimers between adjacent Thymines
  3. Ionising radiation causing single of double-strand breaks (DSB)
  4. Free radicals causing single strand breaks
  5. Alkylating agents causing addition of alkyl groups to Guanine
36
Q

how is aklylation repaired in damaged DNA?

A
  1. Direct repair of alkylation caused by methyl-nitrosourea by specific enzyme that removes the methyl group
  2. Removal of damage region following by re-synthesis (nucleotide excision repair NER)
37
Q

how is damaged DNA repaired in homologous recombination of eukaryotes?

A

Repair of DOUBLE STRAND BREAK

Exonuclease removes a few bases leaving protruding 3’ single-strand ends

Free strand invades homologous intact duplex, promoted by protein Rad51

Donor strand used as template for the re-synthesis

Complex junctions resolved to leave two duplexes

38
Q

3 drugs that affect cell division

A

Methotrexate – inhibits enzyme involved in the synthesis of thymine

Doxorubicin – binds to DNA and prevents action of topoisomerase

5-fluorouracil – inhibits enzyme involved in synthesis of thymine

39
Q

How does end replication paradox occur?

A
  • DNA polymerase only extends 3’ OH ends.
  • This results in the end replication paradox - i.e. a small amount of DNA is lost from each end of a linear chromosome after each round of DNA replication.

End replication paradox = Ends of linear chromosomes are lost after each round of replication.

40
Q

when are telomeres switched off?

A
  • In somatic cells telomerase is switched off.
  • So with every division telomeres get shorter.
  • Eventually the telomeric sequences are lost, and useful DNA will be lost due to the end replication defect.
  • This is thought to make a significant contribution to ageing.
41
Q

what is an example of a monosomy

A

TURNER SYNDROME

42
Q

which type of CFTR is dominant and which is recessive

A

Wild-type CFTR is Dominant - one wild-type copy is able to maintain the Cl- gradient

CFTRD508 is Recessive – no CFTR at the cell membrane, so no Cl- gradient

43
Q

in a pedigree for x linked disease, would the children be affected and would there be any carriers

A

Will occur most frequently in males.
Cannot be passed from father to son.
All daughters of affected fathers are carriers.

44
Q

What is g0 phase

A

A phase where a cell is quiescent

45
Q

what is g1 phase

A

Signal committing the cell to replicate DNA received in G1

46
Q

What is s phase

A

DNA synthesis

47
Q

What is g2 phase

A

Preparation for mitosis

FMS (33 decks)

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