Chapter 14: Transcription Flashcards
exam 1 material
what is transcription?
the process of copying DNA into RNA
what serves as the template strand whose information is transcribed into mRNA in bacteria?
either the coding strand (same sequence as the RNA) or the non-coding strand (complementary sequence)
what are regulatory sequences in bacteria?
sites in DNA where regulatory proteins bind to control the rate of transcription
what is the promoter sequence in bacteria?
site on DNA where RNA polymerase binds, signaling the beginning of transcription
what is the terminator in bacteria?
region in the DNA where RNA synthesis is signaled to stop
what is the ribosomal binding site in bacteria?
site for ribosome binding, translation begins near this site in the mRNA
what is the start codon in bacteria?
the first amino acid in the polypeptide sequence, formylmethionine in bacteria and methionine in eukaryotes
what are codons in bacteria?
3-nucleotide sequences within the mRNA that specify particular amino acids
what are stop codons in bacteria?
codon that specifies the end of polypeptide synthesis
what are the three steps of transcription in bacteria?
initiation: RNA polymerase binds to DNA
elongation: RNA polymerase synthesizes RNA
termination: RNA polymerase stops synthesizing RNA
what happens during the initiation step in bacteria?
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
what happens during the elongation step in bacteria?
RNA polymerase slides along the DNA in the open complex from 5’ to 3’ and synthesizes RNA
what happens during the termination step in bacteria?
a terminator is reached at the end of the DNA strand that causes RNA polymerase and the RNA transcript to dissociate from the DNA
what does each RNA polymerase transcribe in eukaryotes?
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
what are the three components of the promotor for protein-encoding genes?
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
what are the cis-acting elements and trans-acting factors?
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
what proteins are required for basal transcription to occur at the promotor of structural genes in eukaryotes?
RNA polymerase II, 5 different general transcription factors (GTFs), and a protein complex called mediator
what is a mediator in eukaryotes?
mediates interactions between RNA polymerase II and transcription factors, regulates the switch between transcriptional initiation and elongation
what three functions do the subunits of spliceosomes carry out?
- bind to an intron sequence and precisely recognize the intron-exon boundaries
- hold the pre-mRNA in the correct configuration
- catalyze chemical reactions that remove introns and covalently link exons
what is alternative splicing and what is its biological advantage?
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
