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MOLECULES GENES AND DISEASE > Transcription and translation > Flashcards

Transcription and translation 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
What is splicing?
-Introns in mRNA removed and exons ligased
25
Is splicing random?
- No | - It is sequence dependant; introns have 3 specific sequence sites, one at either end and one in the middle
26
What protein complex carries out splicing?
-A splisosome made of many proteins
27
Can splicing defects cause disease?
-Yes they can cause unstable or unreadable mRNA
28
What is a triplet codon?
-A three letter segment which denotes a protein
29
5'->3' translation produces a polypeptide in what direction?
-N'->C'
30
What is the start codon?
-AUG (methionine)
31
How many termination codons are there?
-3
32
Why is the genetic code described as degenerate?
-More than one codon can code for one a'a
33
Why do mutations in the 3rd position of a codon often have no effect?
- Due to the genetic code being degenerate | - Substitutions in the 3rd position of another nucleotide often codes for the same a'a
34
What are the three main types of RNA?
- mRNA - rRNA - tRNA
35
Why can mRNA copies of the same gene produce different proteins?
-Due to alternate splicing
36
Why can some mRNA molecules produce proteins with different half lives?
-Different extents of polyadenylation
37
What is mRNA?
-A copy of the gene of interest
38
What is rRNA?
-RNA which encodes for ribosomal subunits
39
Why are there only 4 types of rRNA?
-Only 2 ribosomal subunits
40
What is the structure of tRNA?
- A single strand of RNA which forms stem loops - The secondary structure forms the anticodon loop - Naturally uncharged and free
41
How do a'as bind to tRNA?
-A bond between the 3'-OH and the COOH of the a'a
42
What is a tRNA molecule with a bound a'a called?
-AminoacyltRNA
43
What is the anticodon loop?
-A loop of DNA which contains a complementary codon to the a'a it will bind
44
How does the anticodon bind an a'a?
-Recognition of the a'a codon is in a antiparallel fashion
45
What is nucleotide I and why does tRNA have it?
- Inosine - a derivative of purine | - Due to the genetic code being degenerative; I can bind to any of the 4 nucleotides
46
Why does I introduce a wobble base, and what does it allow?
- 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
Where does translation occur?
-In the cytoplasm
48
What is translation?
-The conversion of the mature mRNA molecule into a fully functioning protein
49
How are tRNA molecules activated?
-Activation occurs by the transfer of a molecule of ATP and the a'a onto the tRNA molecule catalysed by tRNA synthetase
50
Describe initiation of translation
- 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
Describe elongation of translation
- 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
Describe termination of translation
- 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
Can only one ribosome bind to one mRNA molecule?
-No, there can be many translating the same length of mRNA
54
List the differences of bacterial translation
- Simple promoter regions - Different transcription/translation factors - Couples transcription-translation - Different ribosomal subunits - Different transcription initiation mechanism - One RNApol/mRNA - Different RNApol
55
How can the differences in bacterial transcription/translation be used as an advantage?
-Allows drug targeting of bacterial cells without damage to mammalian cells during infection
56
What mutations can occur, causing disease, in areas outside the coding region?
- Promoter/enhancer regions - Splicing - Termination regions - Ribosome binding regions

MOLECULES GENES AND DISEASE (12 decks)

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