Transcription Flashcards
(15 cards)
what is transcription ?
is the synthesis of RNA using the sequence of nucleotides contained in the dna and the law of complemenmtary base pairing .
what is gene expression :
the effects of the gene being carried out by the cell .
DNA must be first converted into RNA because :
1- RNA is single-stranded allowing it to exit the nucleus throughthe nuclear pores
2- the enzymes that use rna to make proteins(the ribosome) can only read rna .
vrai ou faux : many rna molecules are made from a single gene in DNA
vrai
what are the 3 steps of transcription:
1- initiation
2- elongation
3- termination
step 1 initiation :
what happend in this step :
1-RNA polymerase will first regognize and bind to the promoter.
2- the 2 dna strands will unwind only where the rna polymerase has bound to the DNA
what is a promoter ?
a sequence of DNA nucleotides found before the coding sequence of the gene that allows RNA polymerase to know where to start transcription .*Always contains the sequence of TATAAA(KNOWN AS THE TATA BOX)
in the first phase is it 5’ to 3’ or 3’ to 5’
3’ to 5’
step 2 in elongation :
1- rna polymerase sythesizes an rna strand using the nucleotide sequence in the DNA.Adds Rna nucleotides that are complementary to those found in the dna.
* 3’ to 5’ and reads the nucleotides sequences of only one strand of DNA called TEMPLATE STRAND .
2- The 2 strands making up the DNA double helix re attach to each other ,shortly after the rna polymerase passes
step 3 termination :
1- Rna polymerase eventually comes to a terminator in the dna.Once the terminator i reached :
2- the new rna strand is released,rna polymerase detaches from the DNA ,and the 2 dna strands re attach together
REGULATION OF TRANCRIPTION : Why is gene expression regulated ?
because not every cell need to make the protein encoded by a gene all the time.
- not every type of cell in a multicellular oranism needs the protein from evry gene
- even if a cell need a protein from a particular gene, it might not need it all the time .
REGULATION OF TRANCRIPTION :what is one of the main ways to regulate?
trought regulating if it can be transcribed into RNA
transcription is selective meaning what :
all of your 25000 genes are not being transcribed by every type of cell all at the same time .
how does the cell select which gene to transcribe ?
- proteins called transcription factors bind to the promoter or other nuleotide sequences around the promoter.
- this can either help RNA polymerase to bind to the promoter and transcribe the gene (an activator) or block it from binding and transcribing the gene (a repressor).
- whether it helps transcription to occur or block it depends on which transcription factor you are looking at and which gene it is acting.
dont forget to study the examples in page 154
