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BIOL243 > Theme 2B > Flashcards

Theme 2B Flashcards

Transcriptional and Post-Transcriptional Gene Regulation

1
Q

Transcriptional regulation of gene expression

A
  1. Initiation
  2. Elongation
  3. Termination
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2
Q

Differential expression of genome

A
  • when not all genes are being turned on
  • gives rise to different cell types and tissues
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3
Q

Organism’s phenotype is dependant on

A

cell number, type, and function

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4
Q

Every cell in an organism has an ____________

A

identical genome (DNA sequence)

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5
Q

Turning on a gene means going from ______ to __________________________

A

DNA; transcription

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6
Q

Structure and function of a gene

A

gene includes a promoter and transcriptional unit

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7
Q

Promoter

A

DNA sequence (includes TATA box) that specifies where transcription begins on chromosome

  • signal or landing spot for enzymes so location of specific gene can be identified
  • located immediately upstream or 5’ of the transcriptional starting point of the non-template or coding DNA strand
  • bound and recognized by transcriptional machinery
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8
Q

Transcriptional machinery

A

initiate transcription

  • RNA polymerase and transcription factors
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9
Q

Transcriptional unit

A

part of the gene that is copied into RNA

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10
Q

RNA polymerase: enzymes of transcription

A

synthesize RNA transcript in a 5’-3’ direction while reading DNA template in the 3’-5’ direction

  • does not need primer for initiation of RNA synthesis
  • unwinds and rewinds DNA helix during RNA synthesis
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11
Q

3 types of RNA polymerase

A

RNA polymerase I

RNA polymerase II

RNA polymerase III

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12
Q

RNA pol I

A

transcribes rRNA

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13
Q

RNA pol II

A

transcribes mRNA

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14
Q

RNA poly III

A

transcribes tRNA

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15
Q

Step 1: Transcriptional Initiation

A

transcriptional initiation is mediated by direct interaction of DNA-binding proteins to specific regulatory sequences of the gene (rate determining step)

2 types of processes:
- general transcriptional factors bind to promoter and recruite RNA poly II resulting in LOW BASAL LEVEL of transcription (gene expression = low)

  • transcriptional activator proteins bind to enhancer regions distant from promoter to cause DNA looping bringing mediator and RNA polymerase to promoter resulting in HIGH LEVEL of transcription
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16
Q

Step 2: Transcriptional Elongation

A

RNA pol moves along template DNA (3’ to 5’)

DNA is unwound in front of moving RNA poly and reannealed behind in the transcription bubble

Ribonucleotides are added to the 3’ end of the RNA transcription (synthesis continues 5’-3’)

growing RNA transcript is displaced from DNA template strand to allow reannealing back into double stranded DNA

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17
Q

Step 3: Transcriptional Termination

A

5- sequence in DNA template causes termination after transcribed into RNA

  1. Rho-independant termination
  2. Rho-dependant termination
  3. Cleavage & polyadenylation specifc factor
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18
Q
  1. Rho-independant termination
A

prokaryotes

terminator sequence in mRNA base pairs with itself to form G-C hairpin and causes RNA polymerase to stall and dissociate

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19
Q
  1. Rho-dependant termination
A

prokaryotes

terminator sequence in mRNA is recognized and bound by the Rho helicase which unwinds the RNA from template DNA and RNA polymerase

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20
Q
  1. Cleavage & polyadenylation specific factor
A

eukaryotes

poly-A sequence in mRNA signals the CPSF to cleave the completed mRNA transcript thereby separating it from RNA polymerase

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21
Q

When is the RNA molecule the longest during transcription

A

end of transcription as it reads more

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22
Q

When is the RNA molecule the shortest during transcription

A

start of transcription as it reads more as you go

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23
Q

In transcription, RNA molecules are _____________

single/double strands?

A

single strands

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24
Q

transcription occurs at _______ in the genome

A

selected locations

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25
Q

In transcription, synthesis of RNA occurs in __________ and copies vary throughout genome

A

multiple copies

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26
Q

In transcription, RNA poly does not need a _________ for initiation

A

primer

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27
Q

In transcription, RNA product does not remain ________ to the template DNA

A

base-paired

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28
Q

In transcription, synthesis of RNA occurs in the _________ direction

A

5’-3’

29
Q

In DNA replication, DNA molecules are

single/double stranded?

A

double stranded

30
Q

In DNA replication, replication occurs for the ___________

A

entire genome

31
Q

In DNA replication, genome is only replicated _____________

A

once/cell cycle

32
Q

In DNA replication, DNA poly requires __________ for initiation

A

primer

33
Q

In DNA replication, daughter strand remains ____________ with parental template strand

A

base-paired

34
Q

In DNA replication, synthesis of new DNA strand occurs in the ______ direction

A

5’-3’

35
Q

Posttranscriptional regulation of gene expression has 3 steps:

A
  1. 5’ capping
  2. 3’ polyadenylation
  3. splicing
36
Q

The ends of prokaryotic and eukaryotic mRNAs are __________

A

not translated

37
Q

Both 5’-UTRs and 3’-UTRs regulate

A

mRNA stability and translational efficiency

38
Q

5’-UTRs contain

A

ribosome binding stie (RBS) or Shine Dalgarno sequence in prokaryotes
&
Kozak box sequences in eukaryotes

that function in translational initiation

39
Q

Open reading frame (ORF)

A

region of mRNA that is translated and includes the start and stop codons at the borders

40
Q

The newly transcribed mRNA (pre-mRNA) undergoes processing in the ________ to produce ___________

A

nucleus ; mature translatable mRNA

41
Q
  1. 5’CAP
A

modified guanosine triphosphate is added to the 5’ end of the mRNA and acts as a ribosome binding site (attracts r to 5’) and protects mRNA from degradation

42
Q

Poly(A) tail

A

long string of adenine nucleotides added to the 3’ end of the mRNA by poly-A polymerase to protect the mRNA from being degraded & increase translational efficiency

43
Q

Introns are removed/spliced during ___________ to ____________b/c

A

pre-mRNA processing; produce translatable mRNA because they don’t contain codon

44
Q

If you remove poly (A), what enzyme degrades?

A

5’-3’ exoribonuclease

45
Q

The longer the poly-A, the more

A

stable

46
Q

Posttranscriptional processing from pre-mRNA to mRNA

A

newly-transcribed precursor mRNA (pre-mRNA) needs to be converted to a translatable mRNA because it cannot be yet translated into a protein

  • addition of 5’-CAP and poly-A tail
  • pre-mRNA has a mix of alternating coding segments and UTRs (exons) and non-coding segments (introns)
  • removal of introns by splicing to generate the open reading frame consisting of a continuous stretch of codons & URTs
  • mRNA is exported from nucleus into the cytoplasm to associate with ribosomes
47
Q

Why is removal of introns by splicing important?

A

if they are not removed, you won’t get functional protein

48
Q

Exons

A

coding segments and UTR

49
Q

Introns

A

non-coding segments

50
Q

mRNA splicing

A

removal of introns from pre-mRNA and joining of exons to make mature mRNA

51
Q

spliceosome

A
  • carries out splicing
  • made out of snRNA and splicing proteins
  • made up of five non-coding RNAs (snRNA) complexed to several proteins (small ribonucleoprotein particles/ snRNPs)
52
Q

Process of Splicing in 4 steps

A
  1. Spliceosome binds to intron-exon junctions
  2. Loops introns out of the pre-mRNA (lariat structure) bringing exons closer together
  3. Clip the intron at each exon boundary releasing the lariat structure
  4. Join adjacent exons together
53
Q

Alternative splicing

A

splicing can occur in different combinations to generate two or more different mRNAs from a gene, and several related protein products (isoforms)

  • different isoforms are made in diff tissues from the same gene, producing tissue-specific phenotypes
  • increases the number and variety of proteins that can be encoded by a genome
54
Q

Posttranscriptional regulation by RNA interference

A

found in all eukaryotes

microRNA transcribed by RNA Pol II; small interfering RNA also transcribed (siRNAs)

  • miRNA/siRNA precursors are cleaved to 21-23 bp double-stranded RNAs by the Dicer Rnase
  • these double stranded RNAs are substrates of RISC
  • likely evolved as an antiviral mechan9ism to destroy viral mRNA
55
Q

RISC

A

RNA induced-silencing complex

  • unwinds one of the RNA strands which attracts binding of complementary mRNA
56
Q

(Posttranscriptional regulation by RNA interference)

Binding of the mRNA to RISC interferes with ____________ or induces ___________

A

translation initiation; mRNA degradation (represses gene expression)

57
Q

Transcriptional regulation

A

control of mRNA synthesisT

58
Q

Transcription rate depends on the

A

speed of transcriptional initiation (promoter strength)

59
Q

Posttranscriptional regulation

A

processing of mRNA which affect- usually improves - its stability & translational efficiency

60
Q

Stability of mRNA depends on the presence of ____________ & _______________

A

5’-CAP & length of poly-A tail

61
Q

Expression level of a specific gene depends on the ___________, ____________, and it’s eventual _______

A

abundance of mRNA, nucleotide sequence, eventual translation

62
Q

Abundance of RNA depends on

A

rate of synthesis (transcription) and degradation of mRNA (posttranscriptional)

63
Q

More RNA = More

A

Protein

  • depends on RNA stability
64
Q

If the enhancer is deleted…

Level of gene regulation affected=
Gene expression increases/decreases
Molecular process affected =

A
  • transcription
  • decreases
  • RNA polymerase cannot initiate transcription (gene expression decreases)
65
Q

If polyadenylation of mRNA is increased…

Level of gene regulation =
Gene expression increases/decreases
Molecular process affected =

A
  • post-transcription
  • increased
  • enhanced mRNA stability & translation
66
Q

If 5’-CAP is removed…

Level of gene regulation =
Gene expression increases/decreases
Molecular process affected =

A
  • post-transcription
  • decreases
  • mRNA degradation accelerated, less efficiency in translation initiation
67
Q

If TATA box is deleted….

Level of gene regulation =
Gene expression increases/decreases
Molecular process affected =

A
  • transcription
  • decreases
  • formation of transcriptional initiation complex is hindered
68
Q

If siRNA synthesis is inhibited….

Level of gene regulation =
Gene expression increases/decreases
Molecular process affected =

A
  • post-transcription
  • increases
  • less mRNA degradation
69
Q

Review slide 20

A

BIOL243 (7 decks)

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