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BIOL243 DNA, Inheritance and Evolution > Theme 2B > Flashcards

Theme 2B Flashcards

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1
Q

What is transcription?

A

The process by which information coded in sequential DNA bases is transferred to a complementary RNA strand

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2
Q

Machinery used for making an RNA transcript of a gene is:

A

to be used for gene expression, not cell division

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3
Q

What do RNA polymerases do?

A

Catalyze the assembly of nucleotides into an RNA strand

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4
Q

What is a promoter?

A

The control sequence for transcription, specifically the DNA sequence (TATA box) that specifies where transcription begins

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5
Q

Where is the promoter located?

A

Upstream of the 5’ transcriptional start point of the coding DNA strand

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6
Q

The promoter is recognized by?

A

RNA polymerase and transcription factors that initiate transcription

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7
Q

What is the transcription unit?

A

Section of the gene that is copied into an RNA molecule

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8
Q

Steps of Initiation (Type 1)

A
  1. Transcription factors bind to the promoter in the TATA box area
  2. TFs recruit RNA polymerase II (mRNA). Combo of TFs and RNA polymerase II = transcription initiation complex
  3. DNA is unwound in front of RNA polymerase II to expose the template strand. RNA synthesis begins and TFs are released.
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9
Q

Steps of Elongation

A
  1. RNA polymerase II moves along, unwinding and adding (3’ end) new RNA nucleotides to the transcript in the 5’-3’ direction.
  2. Behind the Pol II, the DNA strands reform into the double helix
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10
Q

Steps of Termination (generally)

A
  1. RNA molecule is released from the template DNA, RNA polymerase II leaves the DNA, the helix reforms. Creates pre mRNA
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11
Q

What are the three types of RNA polymerases?

A
  1. RNA polymerase I (rRNA)
  2. RNA polymerase II (mRNA)
  3. RNA polymerase III (tRNA)
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12
Q

Initiation (Type 2)

A

Transcriptional activator proteins bind to the enhancer regions distant from the promoter to cause DNA looping. Brings mediator and RNA polymerase to the promoter, resulting in a high level of transcription

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13
Q

Rho-independent Termination (prokaryotes)

A

Terminator sequence in mRNA base pairs with itself to form G-C hairpin and causes RNA to stall and detach

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14
Q

Rho-dependent Termination (eukaryotes)

A

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

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15
Q

Cleavage and Polyadenylation Specific Factor (eukaryotes)

A

Poly-A sequence in mRNA signals the CPSF to cleave the completed mRNA transcript and separates it from RNA polymerase

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16
Q

What is pre-mRNA?

A

Translated RNA strand with all introns and exons still included

17
Q

What is 5’ capping?

A

5’ cap added to pre-mRNA soon after RNA polymerase II begins transcription. Cap is connected to the rest of the chain via 3 phosphate groups. Stays attached as pre-mRNA is processed. Protects the mRNA from degradation and is where ribosomes attach at the start of translation.

18
Q

What are UTRs and what do they do?

A

They are two untranslated regions at the 5’ and 3’ ends of the transcriptional unit. They regulate mRNA stability and translation efficiency.

19
Q

What is the ORF?

A

The opening reading frame is the region of mRNA that is translated.

20
Q

What are the post-transcriptional modifications?

A
  1. 5’ capping
  2. Poly-A tails
  3. Intron splicing
21
Q

What are poly-a tails?

A

A long string (50-250 nucleotides) of adenine nucleotides added to the 3’ end of the mRNA to protect against degradation and for translational efficiency.

22
Q

What are introns?

A

Non-protein-coding intervening sequences that interrupt the protein-coding sequence.

23
Q

What are exons?

A

Amino-acid sequences that are retained in finished mRNAs that are expressed

24
Q

What is mRNA splicing?

A

Occurs in the nucleus, removes introns from pre-mRNAs and joins exons together

25
Q

What is the spliceosome?

A

A complex that carries out splicing, made up of five non-coding RNAs (snRNAs) complexed to several proteins (small ribonucleoprotein particles/snRNPs)

26
Q

Steps of Splicing

A
  1. Bind to intron-exon junctions
  2. Loop introns out of the pre-mRNA bringing exons closer together
  3. Clip the intron at each exon boundary releasing the lariat (loop) structure
  4. Join adjacent exons together
27
Q

What is alternative splicing?

A

Splicing in different combinations to generate 2 or more different mRNAs from a gene = different protein isomers (used in different tissues). Increases the number and variety of proteins encoded by the genome.

28
Q

What are activators?

A

Regulatory proteins that play a role in the positive regulatory system that controls the expression of one or more genes. They bind to the promoter-proximal elements and interact with the general TFs at the promoter to stimulate transcription initiation.

29
Q

What are the two major groups of small regulatory RNAs?

A

microRNA (miRNA) and short interfering RNAs (siRNA)

30
Q

How are miRNAs and siRNAs made?

A

Transcription for miRNA and/or foreign origin only for siRNA. They cleave to 21-23 bp double-stranded RNAs

31
Q

What is RISC and what does it do?

A

RNA induced-silencing complex unwinds one of the RNA strands which attracts binding of the complementary mRNA. This interferes with translation initiation or induces mRNA degradation (represses gene expression)

32
Q

What does the abundance of RNA depend on?

A

Rate of synthesis (transcription) and degradation of mRNA (post-transcriptional)

33
Q

What does the deletion of the enhancer cause?

A

Decreased gene expression, affects RNA polymerase b/c it cannot initiate transcription, is regulated transcriptionally

34
Q

What does increased polyadenylation of mRNA cause?

A

Increased gene expression, enhanced mRNA stability, and translation, is regulated post-transcriptionally

35
Q

What does removal of the 5’ cap cause?

A

Decreased gene expression, degradation accelerated, less efficiency in translation initiation, regulated post-transcriptionally

36
Q

What does deletion of the TATA box cause?

A

Decreased gene expression, the formation of transcriptional initiation complex is hindered, regulated transcriptionally

37
Q

What does inhibition of siRNA synthesis cause?

A

Increased gene expression, less mRNA degradation, regulated post-transcriptionally

BIOL243 DNA, Inheritance and Evolution (9 decks)

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