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Cells and Genes SF1 > DNA Replication > Flashcards

DNA Replication Flashcards

1
Q

What is the function of DNA helicase?

A

Uses ATP to move along the DNA and unwind the double helix

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2
Q

What stops DNA from binding to itself

A

Single strand DNA binding protein

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3
Q

Function of DNA Topoisomerase

A

Keeps DNA unwound to enzymes can bind easier

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4
Q

What is the 1st stage of DNA replication

A

DNA polymerase 3 binds to an RNA primer

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5
Q

What is the function of the RNA primer?

A

It is bound to the template strand by DNA primase, and help synthesise individual Okazaki fragments

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6
Q

What is the function of DNA polymerase 3

A

Join nucleotides to the RNA primer through a condensation reaction

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7
Q

Why is replication different for the different DNA strands

A

The leading strand is in 3’ 5’ direction so rep,Icarian is continuous. The lagging strand is in the 5’ 3’ direction, so replication is discontinuous

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8
Q

What is the purpose of Okazaki fragments

A

DNA on the lagging strand is synthesised in these fragments going backwards. It jumps 100/1000 fragments and then synthesised DNA in 5’ 3’ direction. The fragments are small so synthesis doesn’t fall behind so DNA doesn’t bind to itself

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9
Q

How does DNA polymerase stay attached to DNA

A

With the sliding clamps

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10
Q

What digests the RNA primer

A

RNase

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11
Q

What is the function of DNA Polymerase 1

A

Fills in the gaps where the RNA primer was

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12
Q

What is the function of DNA ligase

A

Joins fragments together

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13
Q

What is the base sequence of the telomeres

A

TTAGGG

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14
Q

What is the function of telomerase

A

Replicates the end of the chromosome to form an overhang so the Final Okazaki fragment can be synthesised.

Telomerase get shortened over every replication

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15
Q

What is fidelity

A

The ability to avoid mistakes

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16
Q

How is replication proofread

A

DNA polymerase proofreads in the 3’ 5’ direction and changes incorrect bases

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17
Q

What is Depuration

A

Purine removal

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18
Q

What is deamination

A

Cytosine converted to uracil

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19
Q

What are the different point mutations?

A

Silent, missence (conservative and radical), nonsense

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20
Q

Describe the difference missence mutations

A

Missence is when the incorrect base leads to a different a,ink acid.
Conservative is when the amino acid R groups are similar in size / charge. So protein function is conserved.
Radical is when the R groups are very different, so the 2 3 structure changes

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21
Q

What is a nonsense mutation

A

When the incorrect base leads to synthesis of a stop mutation

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22
Q

Describe the different frameshift mutations

A

Insertion; nucleotide is added
Deletion; nucleotide is removed
Leads to a completely different amino acid sequence

23
Q

How is DNA repaired?

A

By excision, repaired by exonucleases
DNA polymerase will resynthesise incorrect DNA
Any incorrect DNA will get cut out by enzymes, the DNA ligase will seal the gaps

24
Q

What happens if DNA is broken?

A
  • Broken ends are polished and resealed rapidly by DNA ligase

Or

  • broken sequence gets combined with correct sequence on sister chromatid (gets used as a template). This is a slower process
25
Q

What does polycysteronic mean

A

When the same mRNA can code for multiple proteins (prokaryotes)

26
Q

How can DNA be damaged?

A

UV light, ionising radiation, toxic chemicals, oxygen species

27
Q

How do thymine diners arise?

A

UV light exposure

28
Q

What are introns and extrons?

A

Introns are non coding DNA
Extrons are coding DNA

29
Q

What are control elements?

A

Promoter, bind to pre initiator complex

30
Q

What are distil control elements?

A

Enhancers, bind to repress or proteins

31
Q

Name the stages of transcription

A

Initiation
Elongation
Processing
Termination

32
Q

What is the function of RNA polymerase 1

A

Makes pre rRNA

33
Q

Describe the 1st step of initiation

A

RNA polymerase 2 binds to the template strand is the pre initiation complex

34
Q

What is the purpose of chromatin remodelling in the initiation step

A

Allows chromatin to unwind, exposing the promoter so RNA polymerase can bind to it and initiate transcription

35
Q

What is the TATTA box

A

The recognition site on the promoter

36
Q

What occurs at the TATTA Box

A

bind proteins binds to promoter, leading to a chain reaction of recruiting transcription factors. Starting with TBP..
this bundle of transcription factors creates a bundle of proteins that signals RNA polymerase to bind to the promoter.
Creates the transcription initiation factor

37
Q

Describe the Elongation step

A

RNA Polymerase 2 opens the DNA and produces m RNA in the 5’ 3’ direction using the antisense strand as a template ].

38
Q

How is the mRNA processed?

A

Introns are removed and exons are spliced together
The 5’ end is capped with a GTP nucleotide to prevent degradation and promote translation and intron removal (Granyltranferase enzyme)
The 3’ end is tailed with an adenine molecule.Polyadenylation )
This indicates that it’s is mature mRNA

39
Q

What removes introns

A

Spliceosome

40
Q

What allow polyadenylation

A

Poly-A Polymerase
Adds 100-250 adenine to the tail to stabilise it

41
Q

Why do you need to process the mRNA?

A

Different cells have different needs, so require different genes switched on or off to code for certain proteins

42
Q

What is the mRNA start codon?

A

AUG Methionine

43
Q

What are the stages of translation?

A

Initiation: assembly or ribosome, tRNA, mRNA
Elongation; addition of amino acids to the chain
Termination: Stop codon causes protein complex to dissociate

44
Q

What are the different areas of the ribosome?

A

Peptidyl-tRNA
aminoacyl-tRNA
exit

45
Q

What is the purpose of the wobble position?

A

The 3rd base in the amino acid codon is less critical when binding to the anticodon binding site as the majority of the amino acids are .recognised by the 1st 2 bases

46
Q

What molecules recognises the tRNA molecule with the appropriate amino acid?

A

Aminoacyl tRNA synthases

47
Q

What are the ribosomal subunits?

A

30s small
50s large

48
Q

Outline the initiation step of translation

A

The 30s ribosomal subunit binds to the 5’ cap on the mRNA
Ribosome moves in the 3’ direction
TRNA binds to the codon at the anticodon binding site
50s subunit aligns next to the tRNA molecule at the P site

49
Q

Outline the elongation stage of translation

A

The 2nd tRNA molecule pairs with the mRNA codon at the A site
The amino acid at the P site forms a peptide bond with the amino acid on the A site
The tRNA at the P site is deacylated so the a on the A site carries the polypeptide chain
The deacylated tRNA molecule to the E site, and the tRNA at the A moves to the P site and this continues

50
Q

Outline the stages of the termination stage of translation

A

Once a stop codon is reached the tRNA recruits a release factor.
The polypeptide chain is released and the ribosome dissociates into the 2 subunits

51
Q

describe the process of splicing

A

snRNP proteins bind to the 5’ and 3’ end of the intron in the preRNA
U1, u2, u3, u4, u5 come together to form the lariat structure which cleaves the mRNA.
the exons are joined by EJC (exon junction added)

52
Q

what is 5’ capping

A

adding GTP to the 5’ end by guanyltransferase to prevent degredation by exonucleases

53
Q

what is 3’ capping

A

the end of the gene has a repeating AAUAAA polyadenylation signals

Poly-A-polymerase adds 110 to 250 adenine nucleotides to form a poly A tail to stabalise the transcript

Cells and Genes SF1 (11 decks)

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