L14/15: Genes, Transcription Flashcards
(30 cards)
What is the central dogma?
- genetic information is transferred from DNA to RNA to protein
- DNA is copied in mRNA and mRNA is translated into a polypeptide
- but some RNAs are not translated into protein.
What are the three types of RNA molecules?
- rRNA
- tRNA
- mRNA
What is the role of rRNA?
- they are integrated with ribosomal proteins.
- they are not translated. single strands of RNA assembled w/ proteins
What is the role of mRNA?
- translated into a polypeptide chain in protein synthesis
What is the role of tRNA?
- Folded into the secondary structure as a tRNA for translation.
- not translated
Which RNA molecules are stable?
- rRNA and tRNA are considered to be “stable”
- strands of RNA either bind w/ proteins (rRNA) or fold to form secondary structures, which protest the RNA from degradation
Which RNA molecule is unstable?
- mRNA is considered to be “unstable”
- RNases are present everywhere.
- These enzymes in (and out) of the cell degrade RNA easily as it is single-stranded
What is a gene?
- A transcription unit
- i.e. the sequence of DNA that produces an RNA transcript.
What does a gene contain?
- A promoter
- the complete sequence of a “transcript” (RNA)
- a terminator sequence
What is the coding region?
- the region b/w the promoter and terminator
- the sequence that codes for amino acids
In which direction do polymerases read genes?
- 3’ - 5’ direction on the template strand (depends where promoter is located)
What is the coding strand?
- The opposite, anti-parallel strand to the template.
What is the comparison of transcription in eukaryotes and bacteria?
EUKARYOTES:
- transcription takes place in the nucleus
- RNA transcript is processed (spliced) and exported to the cytoplasm
BACTERIA:
- transcription and translation occur in the cytoplasm (same place and time)
- RNA is not processed
What is the direction of transcription?
- RNA polymerase reads the template 3’ to 5’
- Newly synthesized RNA is made 5’ to 3’
What is the overall process of transcription?
- RNA polymerase synthesizes RNA
What are the 3 basic steps of transcription?
- RNA pol. binds to a region called a promoter
- transcription starts at the +1 site/transcription start site (transcribes the first base/nucleotide)
- transcription stops after RNA pol. passes through a region called the terminator.
What is the promoter sequence in bacteria?
- promoter sequence has 2 key sequences: -10 box and -35 box (“box” = short sequence)
- comprised of 40-50 base pairs and have two regions
Where is the -10 box found?
- found 10 bases upstream from the transcription start site ( +1 site) and consists of the sequence 5’-TATAAT-3’
Where is the -35 box found?
- found 35 bases upstream from the transcription start site (+1 site)
What is the promoter sequence in eukaryotes?
- promoter sequence is called the TATA box (i.e. a TATA repeat sequence 5’-TATAAT-3’)
Where is the transcription start site for eukaryotes?
- 25 bases downstream from the TATA box
How is transcription initiated in bacteria?
- sigma factor + RNA pol. = holoenzyme
- the orientation of the sigma/RNA pol. relative to the -35 box and -10 box is important; the RNA pol. complex “knows” which direction to move along the strand
- the ability to bind tightly to the promoter is a level of control
What is a TBP?
-TATA Binding Protein that initiates transcription by helping RNA pol. to bind
How is transcription initiated in eukaryotes?
1) TBP and general transcription factors (and activators) bind to the promoter to recruit the binding of RNA pol. (referred to the basal transcription complex)
2) Transcription starts at the transcription start site ( +1 site for bacteria, ~25 bases downstream from TATA sequence for eukaryotes)
3) termination (termination sequence is copied into RNA as transcription stop after the terminator is copied)
