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MOLECULES GENES AND DISEASE > Transcription and translation > Flashcards

Transcription and translation Flashcards

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Organic Chemistry 101 flashcards
0
Q

Where does transcription occur?

A

-In the nucleus

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1
Q

What is transcription?

A

-The first stage in protein synthesis where an mRNA copy is made of a gene of interest from DNA

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2
Q

What chromatin can be transcribed?

A

-Euchromatin

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3
Q

Why does transcription require ATP?

A

-In order to start the process once all the transcription factors and enzymes have made the transcriptional complex

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4
Q

What are the three stages of transcription?

A
  • Initiation
  • Elongation
  • Termination
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5
Q

What is a promoter?

A

-A recognition sequence of nucleotides on a length of DNA which would initiate transcription when recognised by appropriate transcription factors

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6
Q

Can genes only be in one direction on DNA?

A

-Can be in both directions as the double strands of the alpha helix are antiparallel

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7
Q

What is the benefit of having a number of promoters?

A

-Different genes have different promoter regions in order for different genes to be activated in response to different stimuli

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8
Q

What is the ubiquitous region in all promoters of cells?

A

-TATAAA box

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9
Q

At what position is the TATAAA box located in eukaryotes?

A

–30

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10
Q

How does the TATAAA box initiate transcription?

A
  • Transcription factors recognise and bind to the TATAAA box
  • This binding to the promoter region causes the recruitment of RNApolymerase
  • RNApolymerase then moves along the length of DNA until it reaches the start codon
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11
Q

What is position +1 in transcription?

A

-The location at which RNApolymerase reaches the start codon

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12
Q

Anything upstream from +1 is…

Anthing downstream from +1 is…

A
  • Negative

- Positive

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13
Q

What is the benefit of having regulatory sequences upstream of the TATAAA box?

A

-Allows other transcription factors to regulate gene expression

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14
Q

How can regulatory sequences 1000s bp away from the TATAAA box influence transcription?

A
  • 3D folding of the protein allows interaction, either through direct interaction or between the regulatory region and a mediator
  • Enhancers, inhibitors, activators etc
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15
Q

How does elongation occur in transcription?

A
  • DNA helix unwinds itself
  • RNApol reads the 3’->5’ strand in order to produce an mRNA copy of the gene of interest in a 5’->3’ strand
  • Phosphodiester bonds join ribonucleotides to make a copy of the gene
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16
Q

What is an ORF in mRNA?

A

-The section of mRNA which codes for protein

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17
Q

How does termination of transcription occur?

A
  • RNApol reaches the end of the coding region of the gene and dissociates from DNA
  • Specific exonucleases recognises sequence in capped nascent mRNA and cuts free from RNApol
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18
Q

What is an nuclease, endonuclease and exonuclease?

A
  • Nuclease-> enzyme which degrade nucleic acids
  • Endonuclease->cuts within the polynucleotide; can be specific recognising sequences or non-specific making random cuts
  • Exonuclease-> degrades polynucleotides from the 5’ or 3’ end
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19
Q

What are the three processes which result in RNA maturation?

A
  • Capping
  • Tailing
  • Splicing
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20
Q

What is capping?

A
  • The immediate addition of 5’ cap when mRNA synthesis has begun
  • Methylated guanine 5’-5’ phospho linkage
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21
Q

What is the function of the 5’ cap?

A
  • Stops degradation of the polynucleotide

- Plays a role in translation

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22
Q

What is tailing?

A

-The addition of multiple adenines by polyA polymerase

23
Q

What is the function of tailing?

A

-A very long polyA tail (approx 200n) protects the 3’ end of mRNA from 3’specific exonucleases

24
Q

What is splicing?

A

-Introns in mRNA removed and exons ligased

25
Q

Is splicing random?

A
  • No

- It is sequence dependant; introns have 3 specific sequence sites, one at either end and one in the middle

26
Q

What protein complex carries out splicing?

A

-A splisosome made of many proteins

27
Q

Can splicing defects cause disease?

A

-Yes they can cause unstable or unreadable mRNA

28
Q

What is a triplet codon?

A

-A three letter segment which denotes a protein

29
Q

5’->3’ translation produces a polypeptide in what direction?

A

-N’->C’

30
Q

What is the start codon?

A

-AUG (methionine)

31
Q

How many termination codons are there?

A

-3

32
Q

Why is the genetic code described as degenerate?

A

-More than one codon can code for one a’a

33
Q

Why do mutations in the 3rd position of a codon often have no effect?

A
  • Due to the genetic code being degenerate

- Substitutions in the 3rd position of another nucleotide often codes for the same a’a

34
Q

What are the three main types of RNA?

A
  • mRNA
  • rRNA
  • tRNA
35
Q

Why can mRNA copies of the same gene produce different proteins?

A

-Due to alternate splicing

36
Q

Why can some mRNA molecules produce proteins with different half lives?

A

-Different extents of polyadenylation

37
Q

What is mRNA?

A

-A copy of the gene of interest

38
Q

What is rRNA?

A

-RNA which encodes for ribosomal subunits

39
Q

Why are there only 4 types of rRNA?

A

-Only 2 ribosomal subunits

40
Q

What is the structure of tRNA?

A
  • A single strand of RNA which forms stem loops
  • The secondary structure forms the anticodon loop
  • Naturally uncharged and free
41
Q

How do a’as bind to tRNA?

A

-A bond between the 3’-OH and the COOH of the a’a

42
Q

What is a tRNA molecule with a bound a’a called?

A

-AminoacyltRNA

43
Q

What is the anticodon loop?

A

-A loop of DNA which contains a complementary codon to the a’a it will bind

44
Q

How does the anticodon bind an a’a?

A

-Recognition of the a’a codon is in a antiparallel fashion

45
Q

What is nucleotide I and why does tRNA have it?

A
  • Inosine - a derivative of purine

- Due to the genetic code being degenerative; I can bind to any of the 4 nucleotides

46
Q

Why does I introduce a wobble base, and what does it allow?

A
  • I at the 5’ end of the anticodon introduces more space at the 3’ end of the anticodon
  • This allows unusual base pairing between nucleotides; if the wobble is large enough G can bind to U
47
Q

Where does translation occur?

A

-In the cytoplasm

48
Q

What is translation?

A

-The conversion of the mature mRNA molecule into a fully functioning protein

49
Q

How are tRNA molecules activated?

A

-Activation occurs by the transfer of a molecule of ATP and the a’a onto the tRNA molecule catalysed by tRNA synthetase

50
Q

Describe initiation of translation

A
  • Cap binding proteins recognise the mature mRNA molecule
  • Met, tRNA and the 40s subunit bind to the mRNA
  • tRNA becomes activated as the complex moves downstream and recognises the start codon
  • 60s ribosomal subunit and translational factors bind
  • GTP, initiation factors and cap binding proteins released
  • Fully functional ribosome ready for translation
51
Q

Describe elongation of translation

A
  • Ribosome has P and A site
  • P site occupied by met-tRNA and A site free
  • Binding of next aminoacyl-tRNA complementary to next codon
  • Peptide bond formed between P and A site via peptidyltransferase
  • Ribosome moves along; second a’a now occupies P site and cycle begins again
52
Q

Describe termination of translation

A
  • Stop codon recognised by uncharged tRNA-lookalike molecule
  • tRNA-lookalike physically moves the releasing factor
  • Releases new polypeptide chain and mRNA molecule
  • tRNA binds -OH group to terminate growth
53
Q

Can only one ribosome bind to one mRNA molecule?

A

-No, there can be many translating the same length of mRNA

54
Q

List the differences of bacterial translation

A
  • Simple promoter regions
  • Different transcription/translation factors
  • Couples transcription-translation
  • Different ribosomal subunits
  • Different transcription initiation mechanism
  • One RNApol/mRNA
  • Different RNApol
55
Q

How can the differences in bacterial transcription/translation be used as an advantage?

A

-Allows drug targeting of bacterial cells without damage to mammalian cells during infection

56
Q

What mutations can occur, causing disease, in areas outside the coding region?

A
  • Promoter/enhancer regions
  • Splicing
  • Termination regions
  • Ribosome binding regions

MOLECULES GENES AND DISEASE (12 decks)

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