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Cell and Molecular Biology > Eukaryotic Transcription and The Genetic Code > Flashcards

Eukaryotic Transcription and The Genetic Code Flashcards

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1
Q

How many RNA polymerases do eukaryotes have

A

3 RNA polymerases

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2
Q

What are RNA polymerase I and III responsible for transcribing

A

rRNA and tRNA

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3
Q

What is RNA polymerase II responsible for transcribing

A

mRNA

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4
Q

What happens when the TATA-binding proteins bind to the TATA box

A
  • it induces bending in DNA and distorts DNA
  • allowing for the recruitment of transcriptional factors + RNA polymerase
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5
Q

What are general transcription factors

A

proteins required for the initiation of transcription at the promoter

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6
Q

Why is chromatin remodelling needed

A

to allow the TATA box (promoter region) to be accessible for transcription so that general transcription factors can bind

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7
Q

What is the role of transcription Factor II H

A

helps to separate the strands for RNA polymerase II

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8
Q

How are DNA strands separated (eukaryotic transcription)

A
  • transcription factor II H (made up of helicase) unwinds DNA
  • using the energy obtained by hydrolysing ATP
  • creates the transcription bubble
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9
Q

Outline how RNA polymerase II escapes the promoter

A
  1. transcriptional factor II H (2 kinases) phosphorylates at the C terminal of protein
  2. this allows RNA polymerase to disengage from general transcription factors and elongate the RNA transcript
  3. transcription factor II D remains bound to continue to initiate transcription
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10
Q

What are the 3 post transcription modifications needed

A
  • capping
  • splicing
  • polyadenylation
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11
Q

What is the function of the 5’ capping function

A

it protects the RNA transcript from degradation + enables nuclear export

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12
Q

why does transcription take longer in eukaryotes

A

Introns are numerous and longer than exons as a result mRNA transcription takes longer in eukaryotes than in bacteria

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13
Q

Explain what splicing is

A

the removal of introns

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14
Q

Why does splicing occur

A

introns need to be removed so that only exons are left remaining because they code for proteins

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15
Q

When does splicing occur

A

After the 5’ end has been capped

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16
Q

what are isoforms

A

different versions of a protein that are encoded by the same gene due to alternative splicing

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17
Q

Does splicing result in different proteins being made from the same gene

A
  • Yes
  • splicing can generate diversity in gene expression
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18
Q

What is alternative splicing

A

it allows cells to produce isoforms from a single gene by selectively including or excluding different exons during mRNA post-transcription

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19
Q

where does splicing occur

A

in the spliceosome (complex protein responsible for cutting RNA transcripts)

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20
Q

What is the spliceosome made of

A

snRNAs

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21
Q

What is spinal muscular atrophy (SMA)

A

a genetic disease caused by a loss of SMN1 that decreases motor neuron survival

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22
Q

How is SMA caused

A

due to mutation in transcription (splicing) and produces a non-functional protein

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23
Q

What is the Function of poly-A tail

A

helps to provide stability to the mRNA and to promote translation

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24
Q

What is the purpose of post-transcriptional modifications?

A
  • increased stability
  • prevention of breakdown by exonucleases
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25
Q

How is a poly-A tail made

A

Poly-A polymerase will bind to the 3’ end of the transcript and add around 200 adenines

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26
Q

Define mRNA

A

a type of RNA molecule that carries the genetic information from DNA to the ribosome, where it is used to make proteins

27
Q

What is the importance of codons

A

The use of 3 nucleotides enables to code for all amino acids

28
Q

What is an anticodon

A

the codons attached to the tRNA

29
Q

What is the function of tRNA

A

carries amino acids to mRNA

30
Q

What is the wobbling effect

A

a tRNA molecule can recognise more than one codon because the third base of the anticodon can wobble

31
Q

What is an advantage of the wobbling effect

A

it minimises the damage caused by a misreading of the code, the same protein is going to be produced

32
Q

What is so special about inosine

A

any of the 3 bases (A, U, C) can be matched with it

33
Q

why is it that if there is a change in the DNA sequence it will most likely have a minimal impact

A

Most amino acids can be coded by more than one codon

34
Q

Does the mitochondria genome differ from the universal genetic code

A

Yes

35
Q

What is point mutation

A

It is where there is a change in the sequence of a gene

36
Q

What are examples of point mutations

A

substitutions, insertions and deletions

37
Q

What is a silent mutation + why

A
  • does not result in a change in the amino acid
  • cause: wobbling effect and redundancy
38
Q

What is a missense mutation

A
  • a change in nucleotide which then changes the amino acid that is coded
39
Q

Does a silent mutation usually happen in the first nucleotide + why

A
  • no
  • first 2 bases of codon have precise pairing
40
Q

Does a missense mutation usually happen in the first nucleotide + why

A
  • yes
  • first 2 bases of codon have precise pairing –> change in amino acid
41
Q

What is a conservative missense mutation

A

if the amino acids have similar properties

42
Q

What is a non-conservative missense mutation

A
  • if the amino acid doesn’t have similar properties
  • change structure of protein
43
Q

What are nonsense mutations

A

they introduce a stop codon in the middle of the sequence

44
Q

What is the consequence of a nonsense mutation

A
  • protein is truncated
  • non-functional
45
Q

What is a frameshift mutation

A

a genetic mutation caused by a deletion or insertion in a DNA sequence that shifts the way the sequence is read

46
Q

What is the consequence of a frameshift mutation

A
  • change amino acid coded
  • change protein structure
  • protein will be non-functional
47
Q

Why can silent point mutations be bad

A

if a mutation changes the codon to one that is rare it can slow down translation because the ribosome has to wait longer for the tRNA to bring the right anticodon/amino acid

48
Q

What is amino acid activation

A

amino acids attach themselves to tRNA via activation

49
Q

What happens at the A site of ribosome

A

carries the new amino acid to be added to the polypeptide chain

50
Q

What happens at the P site of ribosome

A

formation of peptide bonds between amino acids –> polypetide chain

51
Q

What happens at the E site of ribosome

A

tRNA is ejected

52
Q

Outline the structure of a ribosome

A
  • small subunit + large subunit
  • made up of proteins and RNA
53
Q

How many Aminoacyl-tRNA Synthetase are there

A

20 (one for each amino acid)

54
Q

Outline characteristics of Aminoacyl-tRNA Synthetase

A
  • recognises anti-codon of tRNA
  • each synthetase has a specific affinity for each amino acid
  • have editing functions to check and correct if the wrong amino acid has been added to the tRNA
55
Q

How many codons are there

A

64 codons

56
Q

What are UTRs

A

untranslated regions of the mRNA

57
Q

True or False:
tRNA recognise stop codons

A

False
stop codons do not have corresponding tRNA molecules that deliver amino acids to the ribosome.

58
Q

How does amino acid activation occur

A
  • amino acid reacts w/ ATP = aminoacyl-AMP (activated amino acid)
  • aminoacyl-AMP is transferred to tRNA via aminoacyl-tRNA synthetase
59
Q

What are the characteristics of aminoacyl-tRNA synthetase

A
  • recognise the anti-codon of tRNA
  • has specific affinity for each amino acid
  • has editing functions and checks + corrects if the wrong amino acid has been added
60
Q

Outline the structure of ribosomes

A
  • has the APE sites
  • has small + large subunits
61
Q

What are ribosomes made of

A

RNA and protein

62
Q

What is the main function of ribosomes

A

synthesise polypetide chains

63
Q

What is the function of ribozyme

A

help join RNA molecules and form mature RNA molecules

64
Q

What is a ribozyme

A

a type of RNA molecule that can act as an enzyme

Cell and Molecular Biology (8 decks)

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