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Genetics > CHAPTER 12 > Flashcards

CHAPTER 12 Flashcards

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1
Q

What is transcription in genetics?

A

Transcription is copying a DNA sequence into an RNA sequence, the first gene expression level.

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2
Q

What sequences define the beginning and end of a gene and regulate RNA synthesis?

A

DNA base sequences define the beginning and end of a gene and regulate RNA synthesis.

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3
Q

What is a promoter in gene transcription?

A

A promoter is a DNA sequence that promotes gene expression by directing the initiation of transcription. It is typically located upstream of the transcription start site.

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3
Q

What are the three stages of transcription?

A
  1. Initiation
  2. Elongation
  3. Termination
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4
Q

During transcription initiation, what happens at the promoter?

A

RNA polymerase binds to the promoter with the help of transcription factors, forming the open complex where DNA unwinds.

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5
Q

What happens during the elongation stage of transcription?

A

RNA polymerase slides along the DNA in the open complex to synthesize RNA, using the template strand in a 3’ to 5’ direction.

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6
Q

What is the role of sigma factor in bacterial transcription initiation?

A

Recognizes the -35 and -10 sequences in the promoter, facilitating the binding of RNA polymerase to the DNA.

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7
Q

Describe rho-dependent termination in bacterial transcription.

A

Rho-dependent termination requires the rho protein, which binds to the RNA and moves toward the RNA polymerase to release the transcript.

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8
Q

What is rho-independent termination?

A

Rho-independent termination involves a uracil-rich sequence and a stem-loop structure that causes RNA polymerase to dissociate from the DNA.

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9
Q

What is a consensus sequence in a promoter?

A

The most common promoter sequence results in high transcription levels; sequences deviating from it usually result in lower transcription.

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10
Q

Name the three types of eukaryotic RNA polymerases and their functions.

A
  1. RNA pol I: transcribes rRNA genes (except 5S rRNA)
  2. RNA pol II: transcribes protein-coding genes (mRNAs)
  3. RNA pol III: transcribes tRNA and 5S rRNA genes
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11
Q

What is the function of enhancers and silencers in transcription regulation?

A

Enhancers increase the transcription rate, while silencers decrease it; both regulatory elements affect RNA polymerase binding.

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12
Q

What is the role of general transcription factors in eukaryotic transcription?

A

-Assist RNA polymerase II in binding to the promoter
-Essential for the formation of the transcription initiation complex.

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13
Q

How does the allosteric model explain RNA polymerase II termination?

A

It suggests that RNA polymerase II destabilizes and dissociates from the DNA after passing the polyA signal.

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14
Q

RNA splicing

A

Removing introns from pre-mRNA and joining exons to produce a mature mRNA.

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15
Q

What modifications occur to eukaryotic pre-mRNA?

A
  1. Addition of a 5’ cap
  2. Polyadenylation (3’ polyA tail)
  3. Splicing to remove introns
16
Q

How are tRNA precursors processed?

A

tRNA precursors are cleaved at the 5’ and 3’ ends by exonucleases and endonucleases to produce mature tRNA.

17
Q

What is a ribozyme?

A

It is an RNA molecule with catalytic activity, such as RNaseP, which cleaves precursor tRNA.

18
Q

RNaseP (endonuclease)

A

Enzyme creates the correct 5’ end of tRNA

19
Q

What happens at the 3’ end of tRNA during processing?

A

A different endonuclease cuts the 3’ end, and RNaseD (exonuclease) removes 9 nucleotides from the 3’ end.

20
Q

tRNA nucleotidyltransferase

A

Enzyme adds CCA to the 3’ end of tRNA

21
Q

What are the three main splicing mechanisms?

A
  1. Group I intron splicing
  2. Group II intron splicing
  3. Spliceosome-mediated splicing.
22
Q

What is a common result in all splicing mechanisms?

A

Removal of the intron and covalent linkage of exon fragments.

23
Q

What is self-splicing, and which groups does it include?

A

Splicing that occurs without enzymes, by the RNA itself; includes Group I and Group II introns.

24
Q

What is the main difference between Group I and Group II self-splicing?

A

-Group I uses a free guanosine
-Group II uses the 2’ OH of adenosine to catalyze splicing

25
Q

Spliceosome

A

Structure assists pre-mRNA splicing in eukaryotes

26
Q

What components make up a spliceosome?

A

Several snRNPs (small nuclear ribonucleoproteins) containing small nuclear RNA and proteins.

27
Q

How does the spliceosome recognize intron-exon boundaries?

A

Through specific intron sequences and consensus sequences at the boundaries.

28
Q

Why is alternative splicing beneficial?

A

It increases polypeptide diversity and allows fewer genes to encode more proteins.

29
Q

Alternative Splicing

A

A process where pre-mRNA with multiple introns can be spliced in different ways to produce mRNA with various exon combinations.

30
Q

Constitutive Exons

A

Exons always found in the mature mRNA across all cell types, essential for protein structure and function.

31
Q

What is the 5’ cap on eukaryotic mRNA?

A

A 7-methylguanosine cap added during transcription.

32
Q

What role does the 5’ cap play in mRNA function?

A

-Aids nuclear export
-Translation Initiation
-Splicing

33
Q

What is polyadenylation, and where does it occur?

A

The addition of a polyA tail at the 3’ end of mRNA, enhancing stability.

34
Q

RNA Editing

A

Modifying the RNA base sequence post-transcription, which can add, delete, or change specific bases.

35
Q

Give an example of an RNA editing process.

A

Deamination, where an RNA nucleotide is chemically altered to a new form.

36
Q

How does the promoter differ between bacteria and eukaryotes?

A

Bacteria have −35 and −10 sequences, while eukaryotes often have a TATA box.

37
Q

How does termination differ in bacterial and eukaryotic transcription?

A

-Bacteria use ρ-dependent or ρ-independent termination
-Eukaryotes use the allosteric or torpedo model

38
Q

Does RNA capping occur in bacteria?

A

No, capping occurs only in eukaryotes.

Genetics (10 decks)

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