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Semester 1 - Molecule, Genes and Disease > Session 5 - Transcription and Translation > Flashcards

Session 5 - Transcription and Translation Flashcards

1
Q

Define transcription

A

The process by which DNA is transcribed into an RNA message

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2
Q

What are the four stages of transcription

A

Initiation, Elongation, Termination and Splicing

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3
Q

What occurs at initiation stage of transcription? (4)

A
  • Intitiation code is recognised 5’TATA3’
  • Transcription factors (regulating proteins) bind at this code, upstream of the fene
  • RNA polymerase is attracted and starts mRNA production
  • RNA polymerase ‘separates’ the DNA strands for the RNA nucleotides to bind
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4
Q

What does RNA polymerase do during process of elongation?

A

Travels along template stand, picking up base pairs and copying them onto a complimentary RNA strand.

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5
Q

How long does process of elongation continue?

A

Until genetic sequence is ‘transcribed’ onto the mRNA molecule

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6
Q

What two things happen at termination stage of transcription?

A

Methyl-guanine ‘cap’ added to 5’ end

Polyadenylation occurs

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7
Q

How is the methyl-guanine ‘cap’ added to mRNA, and what is its function?

A

Methyl-guanine bonded with 5’ - 5’ triphosphate linkage to stabilise the mRNA

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8
Q

What is polyadenylation of mRNA and what is its function?

A

The addition of lots of adenine nucelotides added at the 3’ end of mRNA. Improves stability.

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9
Q

What happens during splicing, and how does this process occur?

A

Introns are removed. Endonucleases remove introns within polynucleotide and exonucleases degrade polynucleotide for 5’ or 3’ end.

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10
Q

Define translation

A

The process by which the RNA message is translated into amino acid code

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11
Q 
Answer following for mRNA
What type of polymerase used?
Wht percent of all RNA does it make up?
How many different kinds are there?
How many copies of each present?
A

RNA polymerase II
-2%
100,000s of kinds
A few copies of each present

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12
Q 
Answer following for rRNA
What type of polymerase used?
Wht percent of all RNA does it make up?
How many different kinds are there?
How many copies of each present?
A

RNA polymerase I
>80%
Few kinds
Many copies of each

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13
Q

Answer following for tRNA
What type of polymerase used?
Wht percent of all RNA does it make up?
How many different kinds are there?

A

RNA polymerase III
15%
100 kinds
Very many copies of each

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14
Q

What is Ribosomal RNA used for?

A

To bind to mRNA and provide the location for tRNA

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15
Q

What is the differnce between eukaryotic and prokaryotic ribosomes?

A

Eukaryotes - Ribosome 80s (made up of 60s and 40s subunits)

Prokaryotes 70s - (made up of 50s and 30s subunits)

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16
Q

How is the genetic code read in a ribosome?

A

In triplets, with no overlapping and no gaps

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17
Q

What is meant by saying that DNA is degenerate?

A

Some amino acids can be coded for by several different codons

18
Q

When is tRNA uncharged, and what is it referred to when it is charged?

A

When no amino acid is bound to it. Is referred to as an aminoacyl-tRNA when amino acid bound and it is charged

19
Q 
Give following for DNA replication
Enzyme
Activated substance
Template
3 stage process?
A

DNA polymerase
dNTPs
DNA
yes

20
Q 
Give following for making mRNA (transcription)
Enzyme
Activated substance
Template
3 stage process?
A

RNA polymerase
NTPs
DNA
yes

21
Q 
Give following for making a polypeptide (translation)
Enzyme
Activated substance
Template
3 stage process?
A

ribosome
Amino acid
mRNA
yes

22
Q 
Outline following for ribosomes in prokaryotes
Number of rRNAs
Protein number
Subunits
Size of ribosome
A

3 rRNAs
56 proteins
30s, 50s
70s

23
Q 
Outline following for ribosomes in eukaryotes
Number of rRNAs
Protein number
Subunits
Size of ribosome
A

4 rRNAs
82 proteins
40s, 60s
80s

24
Q

Name three stages of translation

A

Initiation
Elongation
Termination

25
Q

What occurs at initiation stage of TRANSLATION

A
  • 40s subunit of ribosome binds with Met-tRNA attached binds at the 5’ cap end of the mRNA
  • the 60S subunit then binds and elongation occurs
26
Q

What starting codon must be recognised for translation to begin? What amino acid does it code for? What is the anticodon found on tRNA?

A

5’ AUG, which is a specific codon to one amino acid - methionine. 5’ CAU is the anticodon required.

27
Q

What are the two ribosomal sites at which tRNA binds, and what goes where?

A

P site - For the site holding the peptide chain

A site - for the site accepting the tRNA

28
Q

What are the first two steps in the process of translational elongation, and what do they require?

A

1 - Met-tRNA occupies the P site

2-Another aminoacyl-tRNA enters the ribosome to occupy the A site (requires GTP)

29
Q

What are the third and fourth steps of translational elongation?

A

3- Methionine forms a peptide bond with the next aminoacyl - tRNA, making original tRNA in the P sit now uncharged
4 - The uncharged tRNA now leaves and the ribosome translocates (moves along)

30
Q

What is the binding of two amino acids catalysed by?

A

Peptidyl Transferase

31
Q

How does the termination of translational elongation occur?

A

Requires a stop codon to be read on the mRNA.

32
Q

Give three stop codons, and explain why they halt process of translation

A

5’UAA, 5’UAG and 5’UGA.
No tRNAs that can bind to these codons, so the peptide and tRNA are hydrolysed and release the protein into the cytoplasm.

33
Q

Define the term “gene”

A

A unit of heredity and a length of DNA on a chromosome that contains the code for a protein (or RNA) as well as sequences necessary for its expression, such as promoter and terminator sequences and introns

34
Q

What are the three major reactions involved in the processing of Eukaryote processing

A

Capping, polyadenylation and splicing

35
Q

What is the 3’ molecule in a DNA triplet called a wobble position

A

Change in third base more likely to cause change in amino acid

36
Q

What does 5’ to 3’ template provide?

A

N to C polypeptide chain extension

37
Q

Give three features of DNA triplet code

A

Degenerative
Non overlapping
Read in 5’ to 3’ prime direction

38
Q

What can substitutions in genetic code lead to?

A

Different primary amino acid sequence, which can affect the tertiary structure of a protein

39
Q

What can be a large effect of a single base substitution?

A

Can occur in a stop codon, leading to longer polypeptide chain that will be malfunctional

40
Q

Give the nine key differences between mammalian and bacterial gene expression

A 
Prokaryotes have
- Simpler promoters
- Different transcription factors
- Single RNA polymerase
- Coupled transcription - translation
- No post-transcriptional processing
- Short lived mRNAs
- Simpler ribosomes
(exploited by attacking 30s subunit
- Distinctive translation initiation mechanism
-Different translation factors
41
Q

What does the severity of a mutation depend on?

A

The amount of difference in the protein caused

42
Q

How can mutations outside the coding region affect gene expression?

A

Mutations to promoter regions where transcription facts bind can affect gene expression, to either constituively activate or deactivate it

Semester 1 - Molecule, Genes and Disease (9 decks)

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