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MC Biochem 1 > Chpt 29: Transcription > Flashcards

Chpt 29: Transcription Flashcards

1
Q

Types of RNA

A
  • ribosomal RNA-rRNA
  • transfer RNA-tRNA
  • messenger RNA-mRNA
  • small nuclear RNA-snRNA
  • micro RNA-miRNA
  • small interfering RNA- siRNA
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2
Q

Transcription of Genes

A

Genes may or may not be transcribed depend on the needs of particular cell type

  • expressed=Turned on
  • unexpressed=Turned off
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3
Q

Gene

A
  • discrete functional unit of DNA
  • when expressed/transcribed can produce a functional product
    a) rRNA, tRNA, snRNA
    b) mRNA- translated into polypeptide sequence
  • open reading Frame
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4
Q

tRNA

A

transfer RNA

  • small single stranded ribonucleotides
  • adaptor between RNA and protein
  • at least one tRNA per amino acid
  • folds into clover leaf or L shape due to intramolecular Hydrogen Bonding between complementary base pairs

Post transcriptional modifications
-bases modified to produce 3’ end CCA (not encoded in DNA) which is an attachment site for amino acids

Anticodon:

  • 3 nucleotide sequence specifies amino acid attachment to 3’end
  • will H-bond to the complementary base seq on mRNA called CODON
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5
Q

rRNA

A

ribosomal RNA

  • single stranded ribonucleotide
  • incorporated into ribosome
  • folds due to intramolecular H-bonds of complementary base pairs to form complex structure
  • Size differs between prokaryotes and eukaryotes
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6
Q

Eukaryotic vs Prokaryotic rRNA

A

Prokaryotic rRNA-
70s ribosome divides into 50S and 30S subunits
-50s large ribosome subunit contains 23S and 5s rRNA
-30s small ribosome subunit contains 16S rRNA

Eukaryotic rRNA:
80S ribosome divides into 60S and 40S subunits
-60S large ribosome subunit contains 28S, 5.8S, and 5S rRNA
-40S small ribosome subunit contains 18S rRNA

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7
Q

mRNA

A

Messenger RNA

1) single stranded ribonucleotide
- in a heterogenous population the mRNA size varies by length of gene (protein encoded)
2) NO intramoleculer H-bonds

Translated into protein sequence

  • read by ribosome and broken up into codons
  • anticodons of tRNA bind to codon of mRNA during translation
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8
Q

Prokaryotic mRNA and eukaryotic mRNA

A

BOTH have 5’ and 3’ UTR-untranslated regions that doesn’t encode protein

Prokaryotes
-Polycistronic- encode multiple polypeptide chains

Eukaryotes

  • monocistronic-encode single polypeptide chain
  • process in the nucleus and capped, polyaddenylated, and spliced
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9
Q

snRNA

A

Small Nuclear RNA-EUKARYOTES ONLY

  • small ribonucleotides
  • involved in splicing (spiceosome)
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10
Q

RNA polymerase

A

synthesizes RNA in the 5’ to 3’ direction complementar to DNA template

  • antiparallel to DNA template
  • does not synthesize primers for replication

Requires:

  • DNA template
  • ribonucleoside triphosphate-A, U, G ,C
  • Mg 2+ (2)
  • NO primer needed because synthesis begins de novo at +1 nucleotide
  • NO nuclease acitivity because Error rate is 1mistake/ 10^4/5 base pairs
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11
Q

Prokaryotic RNA polymerases

A

Single RNA polymerase

-multiple subunits

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12
Q

Eukaryotic RNA polymerases

A

Three RNA polymerases with multiple subunits
RNA poly I
-synthesizes pre 45S rRNA as single transcript which contains 18S, 5.8S and 28S rRNA
-functions in nucleolus’
-insensitive to alpha amanitin

RNA poly II

  • synthesizes pre-mRNA and snRNA
  • functions in nucleoplasm (outside the nucleolus)
  • strongly inhibited by alpha aminitin
  • contains a C-terminal domain called the CDT consisting of multiple repeats of YSPTSPS consensus sequence

RNA poly III

  • synthesizes tRNA and 5.0S rRNA
  • functions in nucleoplasm
  • sensitive to high concentrations of alpha amanitin
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13
Q

Three stages of Transcription

A

Initiation

  • identificaiton of promotor
  • unwinds region surrounding promotor

Elongation
-RNA polymerase synthesizes RNA

Termination
-detects termination signals

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14
Q

Promotor

A

conserve “consensus” nucleotide sequences

-identified by sigma factors

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15
Q

RNA polymerase Active Site

A

Growing RNA chain provides 3’ OH

-RNA poly provides three conserve Asp residues which bind 2 Mg2+ ions

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16
Q

Prokaryotic RNA polymerase structure

A 
Holoenzyme (core enzyme + sigma factor)
Core enzyme-RNA synthesis
-2 alpha subunits
-1 beta subunit
-1 beta prime subunit
-1 omega subunit

Sigma Factor-identifies promotor
-different sigma factors identify different promotors

Termination Rho factor
-some require Rho some don’t

17
Q

Prokaryotic Initiation step

A

Holoenzyme binds to Promotor

18
Q

Prokaryotic Promotors

A

1) -10 Sequence
- Pribnow or TATA box
- 5’ TATAAT 3’

2) -35 sequence

19
Q

UP element

A

Upstream element

  • found in only high expressed genes
  • 40 to 60 nucleotides 5’ from transcriptional start site
  • Binds alpha subunit of RNA polymerase
20
Q

Consensus Sequence

A

a nominal sequence inferred from multiple imperfect example

-average

21
Q

Types of Sigma Factors

A 
FOR PROKARYOTES
Sigma 70-Most genes
Sigma 32- Heat shock
Sigma 28- Stationary phase, stress
Sigma 54-Nitrogen metabolism
-adds specificity to RNA polymerase
-Serves as a switch; Quickly changes gene expression in response to environmental conditions
22
Q

Prokaryotic Elongation Step

A

HOLOenzyme synthesizes RNA complementary to DNA template
-sigma factor is released after addition of first nucleotide (usually purine)
0Topoisomerase I and II relax supercoiling ahead of unwinding of helix
-unwound regions is called transcriptional bubble

23
Q

Naming the DNA strands

  • template
  • coding
A

Template=noncoding=antisense (-) strand
-strand read by RNA polymerase-complementary to mRNA seq

Coding= Sense (+) strand
-DNA strands with same sequence as mRNA except U subs for T

24
Q

Prokaryotic Termination step

A

RHO dependent termination
-Requires Rho factor

Rho independent termination
Requires 2 features
1)DNA sequences must contain a palindrome 
-RNA transcript forms stable hairpin 
2) 3' to hairpin
-RNA contains stretch of U's
-lower melting temp
25
Q

Rho factor

A

ATP dependent RNA-DNA helixase activity

-hydrolyzes ATP which unwinds RNA-DNA complex

26
Q

Localization of Transcription

-Eukaryotes vs prokaryotes

A

Prokaryotic cells

  • Transcripton and translation occur in cytoplasm
  • Transcription and translation may be couples

Eukaryotic cells:

  • Transcription occurs in the nucleus
  • Translation occurs in the cytoplasm
27
Q

Post Transcriptional modifications?

A

ONLY OCCUR IN EUKARYOTIC CELLs

  • capping-attachment of 7-methylguanisine at 5’ end
  • polyadenylation- addition of adenine to 3’
  • splicing-removal of introns

MC Biochem 1 (30 decks)

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