Transcription Flashcards

1
Q

What is the role of RNA polymerase in transcription and what are its key components?

A

Role: enzyme that catalyzes the formation of new RNA

Key components include:
- Multiple subunits that
form the complex
enzyme
- The sigma subunit
(sigma factor) that
positions RNA
polymerase at the site
of transcription initiation

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2
Q

RNA pol I vs II vs III

A

I : transcribes rRNA genes,

II : transcribes mRNA and miRNA, protein coding

III : transcribes tRNA

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3
Q

What is a promoter in transcription?

A

the DNA sequence that RNA polymerase binds to in order to initiate transcription.

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4
Q

Key features of Promoter in Transcription

A

-1. Two sets of sequences upstream (5’) of the transcription start site (+1)

  1. The -10 and -35 regions where the sigma factor binds
  2. A consensus sequence that many genes share
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5
Q

RNA Pol Bacteria vs Eukaryotes

A

Bac: only utilized RNA pol I

Euk: has three versions of RNA pol with respective functions I, II, & III

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6
Q

How is there cell diversity if all genetic info is identical?

A

behavior of cells is determined not just by what genes are inheriteded, but by what genes are expresses at certain times —> regulation of gene expression

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7
Q

Bacterial Transcription Initiation

A

Multistep:

  1. Sigma factor guides RNA Pol to bind to DNA ( -10 and -35 regions)
  2. Sigma protein assists RNA pol to read start signals from DNA
  3. DNA unwinds and becomes single stranded DNA (ssDNA)
  4. Transcription begins and joined free nucleotides together
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8
Q

BAC transcription- Elongation

A

RNA POl continues to unwind the DNA in the 3’ to 5’ direction while winding in the 5’ direction

Elongation continues until RNA pol reaches termination signal (typically GC rich invertes repeat followed by several A residues)

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9
Q

BAC transcription - termination

A

RNA Pol reaches termination signal

The RNA formed from transcription of the term site will form stem-loop structure

After transcription of these residues, the RNA is released from RNA pol and will dissociate from DNA template

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10
Q

Types of RNA

A

Associated with protein-coding genes
–> Messenger RNA
(mRNA)
Used for regulation of gene expression in eukaryotes
–> Micro RNA (miRNA)
–> Long non-coding RNA
(lncRNA)
Associated with RNA processing, translation, and protein transport
–> Ribosomal RNA (rRNA)
–> Transfer RNA (tRNA)
–> Small nuclear RNA
(snRNA)
–> Small cytoplasmic RNA
(scRNA)

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11
Q

General Transcription factors

A

proteins that bind to DNA to activate the transcription of genetic information into messenger RNA

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12
Q

TATA box

A

The TATA box is a DNA sequence that’s important for transcription, the process of producing RNA from DNA

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13
Q

Euk Transcription Initiation

A
  • 5 general transcription factors are required AT minimum for formation of the transcription complex and initiation of transcription
    1. A general transcription factor binds to the promoter
    2. This binding recruits a second general transcription factor
    3. RNA polymerase II binds to this complex WITH a third factor
    4. Two more factors are added forming the “preinitiation complex”
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14
Q

Euk transcription Elongation

A
  1. RNA polymerase leaves the promoter region after synthesizing 9–10 RNA nucleotides
  2. Unzip DNA
  3. Add Nucleotides
  4. Move histones
  5. Form base pairs
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15
Q

Euk transcription- Termination

A

Less is known about this process

  1. A specific residue in the CTD is phosphorylated which creates a binding site for an RNA endonuclease
  2. The RNA endonuclease will recognize and cleave a non-coding sequence after the mRNA, freeing it
  3. An exonuclease will degrade the remaining RNA sequence and cause RNA polymerase II to dislodge from the DNA
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16
Q

mRNA processing steps

A
  1. the initial product of transcription is pre-mRNA
  2. happens as mRNA is being transcribed
  3. addition of a 5’ cap
  4. addition of a poly-A-tail (polyadenylation)
17
Q

Spliceosomes

A

consist of a variety of proteins and several small RNAs that recognize the splice sites
The RNAs of the spliceosome also catalyze the splicing reaction

18
Q

The Functional and Evolutionary Importance of Introns

A

Some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during splicing

–> Provides a mechanism for tissue-specific and developmental regulation of gene expression