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Cell Biology and Genetics > Gene expression > Flashcards

Gene expression Flashcards

1
Q

What is transcription?

A

Producing mRNA using DNA

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2
Q

Where does transcription occur?

A

Nucleus

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3
Q

What are the stages of transcription?

A

Inititation

Elongation

Termination

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4
Q

What happens in initiation of transcription?

A

Transcription factor binds to promoter site

RNA polymerase is recruited

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5
Q

What is a common sequence in the promoter site of genes in eukaryotes?

A

TATA

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6
Q

What is the base in front of RNA polymerase marked as?

A

+1

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7
Q

What is the direction of the +1 base called?

A

Downstream

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8
Q

What direction does RNA polymerase move along the DNA strand in?

A

3’ to 5’

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9
Q

What makes RNA polymerase move along the DNA strand 3’ to 5’?

A

The binding of the transcription factor sets the direction

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10
Q

What happens in elongation of transcription?

A

RNA polymerase reads DNA strand 3’ to 5’
forms pre-mRNA 5’ to 3’

RNA processing

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11
Q

What is the DNA strand that RNA polymerase reads called?

A

DNA template strand/non-coding strand

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12
Q

What reaction occurs repeatedly in elongation of transcription?

A

(rNMP)n + rNTP —–> (rNMP)n+1 + PPi

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13
Q

What is the purpose of RNA processing?

A

Convert pre-mRNA into mature mRNA

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14
Q

What are the different processes involved in RNA processing?

A

Capping

Tailing

Splicing

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15
Q

What happens in capping?

A

At 5’ end of pre-mRNA

methylated guanine is added by 5’-5’ linkage

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16
Q

What is the purpose of capping?

A

Protect mRNA against degradation by exonucleases

Role in translation???????

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17
Q

What happens in tailing?

A

At 3’ end of pre-mRNA

many A bases are added on

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18
Q

What is the enzyme repsonsible for tailing?

A

polyA polymerase

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19
Q

What is the purpose of tailing?

A

Protect mRNA against degradation by exonucleases

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20
Q

What happens in splicing?

A

Introns are splices out of pre-mRNA

exons are joined together

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21
Q

What enzyme is responsible for splicing?

A

Spliceosome enzyme complexes

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22
Q

What is alternative splicing?

A

Refers to how some introns can be kept, some exons removed
or exons joined together in different order
to create a new protein

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23
Q

What are introns?

A

Base sequences that are not expressed

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24
Q

What are exons?

A

Base sequences that are expressed

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25
Q

What happens in termination of transcription?

A

Termination sequence in pre-mRNA is recognised

cleaved by endonuclease

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26
Q

What is the name of the DNA strand that mRNA resembles?

A

Coding strand

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27
Q

Where does translation occur?

A

Cytoplasm

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28
Q

What organelle is responsible for translation?

A

Ribosomes

29
Q

What is a polyribosome?

A

Multiple ribosomes translating mRNA at same time

30
Q

What are ribosomes made up of?

A

rRNA

Proteins

31
Q

What type of ribosome is present in prokaryotes? What are its subunits?

A

70S ribosomes

50S and 30S subunits

32
Q

What type of ribosome is present in eukaryotes? What are its subunits?

A

80S ribosomes

60S and 40S subunits

33
Q

What are the types of RNA?

A

ribosomal RNA, rRNA

messenger RNA, mRNA

transfer RNA, tRNA

34
Q

Are there more types of mRNA or tRNA or rRNA?

A

More types of mRNA
then tRNA
least types of rRNA

35
Q

Are there more copies of mRNA or tRNA or rRNA?

A

More copies of tRNA
then rRNA
least copies of mRNA

36
Q

What are the features of the genetic code?

A

Triplet code

Degenerate

Non-overlapping

37
Q

What is the triplet code?

A

3 nucleotide bases code for 1 amino acid

38
Q

What is the adapter molecule of the genetic code?

A

tRNA

39
Q

What is meant by the genetic code being degenerate?

A

More than one triplet code

can all code for the same amino acid

40
Q

What is meant by the genetic code being non-overlapping?

A

Each base belongs to one triplet code only

not more than one

41
Q

5’ to 3’ mRNA produces a polypeptide chain in what order?

A

N to C

42
Q

What is the structure of tRNA?

A

Clover leaf shape

Stem loops

Anti-codon

43
Q

What are stem loops?

A

Anti-parallel RNA

Base pairs formed in the middle

44
Q

What is an anti-codon?

A

Three bases at a specific point on the tRNA molecule

45
Q

What does the anticodon do?

A

Recongises mRNA codon with complementary base sequence

base pairs form

46
Q

How do some mRNA codons code for the same amino acid?

A

Third base in anticodon/mRNA codon is wobble base

can form base pairs with multiple bases

47
Q

What may be at the 3’ end of the tRNA molecule?

A

Amino acid

48
Q

What is tRNA called when there is no amino acid at the 3’ end? And when there is an amino acid?

A

No amino acid - uncharged tRNA

Amino acid present - amino acyl tRNA

49
Q

What is amino acid activation?

A

Refers to adding amino acid to tRNA molecule 3’ end

50
Q

What happens in amino acid activation?

A

ATP is hydrolysed to release energy

this energy is used to combine amino acid to tRNA 3’ end

51
Q

What is the enzyme responsible for amino acid activation?

A

Amino acyl tRNA synthetase

52
Q

What are the stages of translation?

A

Inititation

Elongation

Termination

53
Q

What happens in initiation of translation?

A

Ribosome recruited to 5’ cap of mRNA

Methionyl tRNA recruited to 5’ cap

54
Q

How is the ribosome recruited to the 5’ cap of mRNA in initiation of translation?

A

Requires energy

55
Q

What does methionyl tRNA recognise?

A

Start codon AUG

56
Q

What happens in elongation of translation?

A

Ribosome moves along mRNA

tRNA molecules enter and leave ribosome

Polypeptide chain grows

57
Q

What direction does the ribosome move along the mRNA?

A

5’ to 3’

58
Q

Where do tRNA molecules leave the ribosome from?

A

P site

59
Q

Where do tRNA molecules enter the ribosome into?

A

A site

60
Q

How does the polypeptide chain grow in elongation of translation?

A

Peptidyl transferase moves amino acid from tRNA in P site to tRNA in A site
forms peptide bond between the two
and hence a polypeptide chain

61
Q

What is required for elongation of translation?

A

Requires energy

62
Q

What happens in termination of translation?

A

Stop codon enters A site

polypeptide chain is hydrolysed off tRNA at its C terminus

63
Q

What does UTR stand for?

A

Untranslated region

64
Q

Where are UTRs located?

A

5’ and 3’ end of mRNA

65
Q

What is meant by a gene being expressed?

A

Gene is switched on

the protein it codes for is produced

66
Q

Why are there many types of mRNA?

A

Because there are lots of genes

Alternative splicing

67
Q

Why are there few copies of mRNA?

A

Because many ribosomes can translate one mRNA molecule producing lots of protein molecules from it

68
Q

Why are there few types of rRNA?

A

All have same function

Cell Biology and Genetics (32 decks)

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