Chapter 14: Transcription

Question 1

what is transcription?

Answer 1

the process of copying DNA into RNA

Question 2

what serves as the template strand whose information is transcribed into mRNA in bacteria?

Answer 2

either the coding strand (same sequence as the RNA) or the non-coding strand (complementary sequence)

Question 3

what are regulatory sequences in bacteria?

Answer 3

sites in DNA where regulatory proteins bind to control the rate of transcription

Question 4

what is the promoter sequence in bacteria?

Answer 4

site on DNA where RNA polymerase binds, signaling the beginning of transcription

Question 5

what is the terminator in bacteria?

Answer 5

region in the DNA where RNA synthesis is signaled to stop

Question 6

what is the ribosomal binding site in bacteria?

Answer 6

site for ribosome binding, translation begins near this site in the mRNA

Question 7

what is the start codon in bacteria?

Answer 7

the first amino acid in the polypeptide sequence, formylmethionine in bacteria and methionine in eukaryotes

Question 8

what are codons in bacteria?

Answer 8

3-nucleotide sequences within the mRNA that specify particular amino acids

Question 9

what are stop codons in bacteria?

Answer 9

codon that specifies the end of polypeptide synthesis

Question 10

what are the three steps of transcription in bacteria?

Answer 10

initiation: RNA polymerase binds to DNA
elongation: RNA polymerase synthesizes RNA
termination: RNA polymerase stops synthesizing RNA

Question 11

what happens during the initiation step in bacteria?

Answer 11

the promoter at the end of the DNA strand acts as a recognition site for transcription factors, the transcription factors then enable the sigma factor of the RNA polymerase to bind to the promotor forming a closed complex, after binding the DNA is denatured into a bubble (the open complex) and a short RNA strand is made within the complex and sigma factor is released, signaling the end of initiation

Question 12

what happens during the elongation step in bacteria?

Answer 12

RNA polymerase slides along the DNA in the open complex from 5’ to 3’ and synthesizes RNA

Question 13

what happens during the termination step in bacteria?

Answer 13

a terminator is reached at the end of the DNA strand that causes RNA polymerase and the RNA transcript to dissociate from the DNA

Question 14

what does each RNA polymerase transcribe in eukaryotes?

Answer 14

RNA polymerase I: transcribes all rRNA genes except 5S rRNA
RNA polymerase II: transcribes all protein-encoding genes and synthesizes all mRNAs
RNA polymerase III: transcribes all tRNA genes and the 5S rRNA gene

Question 15

what are the three components of the promotor for protein-encoding genes?

Answer 15

regulatory elements (sequences bound by general transcription factors), TATA box, and a transcriptional start site, the TATA box and the transcriptional start site comprise the core promotor

Question 16

what are the cis-acting elements and trans-acting factors?

Answer 16

cis-acting: DNA sequences that exert effects only over a particular gene, such as enhancers and silencers that either stimulate or reduce transcription
trans-acting: regulatory proteins that bind to cis-acting elements

Question 17

what proteins are required for basal transcription to occur at the promotor of structural genes in eukaryotes?

Answer 17

RNA polymerase II, 5 different general transcription factors (GTFs), and a protein complex called mediator

Question 18

what is a mediator in eukaryotes?

Answer 18

mediates interactions between RNA polymerase II and transcription factors, regulates the switch between transcriptional initiation and elongation

Question 19

what three functions do the subunits of spliceosomes carry out?

Answer 19

1. bind to an intron sequence and precisely recognize the intron-exon boundaries
2. hold the pre-mRNA in the correct configuration
3. catalyze chemical reactions that remove introns and covalently link exons

Question 20

what is alternative splicing and what is its biological advantage?

Answer 20

alternative splicing is the idea that pre-mRNA with multiple introns can be spliced different ways which generates mature mRNAs with different combinations of exons, meaning that more than one polypeptide can be derived from a single gene