Initiation
promoter
contains the start codon
In eukaryotes transcription factors mediate the binding of RNA polymerase
Transcription initiation complex
contains the TATA box
Elongation
RNA polymerase moves down DNA growing the pre-mRNA from 3' end
Termination
Bacteria
transcribed terminator ends transcription
part of DNA sequence
Eukaryotes
RNA polymerase II transcribes for polyadenylation signal (AAUAAA)
10-35 nucleotides downstream proteins release mRNA strand
RNA processing
5' cap
a 5' form of guanine is added to 5' end
Poly- A tail
at 3' end 50-250 more adenine nucleotides are added
both ends of the primary transcript are altered
RNA splicing
introns are taken out by spliceosome
exons are the coding segments of mRNA
iniatation
Structure of Ribosome
large and small ribosomal subunit made from ribosomal RNA (rRNA)
one binding site for mRNA
three binding sites for tRNA
P Site: hold the tRNA carrying the growing polypepetide chain
A site: holds the tRNA carrying the next amino acid
E site: discharges tRNA
Structure of tRNA
anticodon: the particular nucleotide triplet that base pairs to a specific mRNA codon
aminoactyl-tRNA synthestasaes
helps tRNA grab the correct amino acids
mRNA binds to the small ribosomal subunit and the initiator tRNA
start codon initiates the start of translation
attachment of large ribosomal subunit, completing the translation initiation complex
Elongation
mRNA is moved through ribosome in one direction 5' end first
polyribosomes (polysomes) multiple ribosomes translate a mRNA at the same time
Termination
stop codon in mRNA reaches A site
on sn mRNA, the triplet grouping of ribonucleotides used by the translation machinery during polypeptide synthesis
Triplet codon
a genetic information system in which a series of three-nucleotide- long words specifies a sequence of amino acids for a polypeptide chain