Transcription and Translation Flashcards
What is transcription?
RNA syntheissed from DNA template
RNA copy of the sense strand of DNA is formed by the enzyme RNA polymerase - reads the anti-sense strand and complement RNA created in 5’ to 3’ direction - identical base pair sequence to the sense strand of DNA
How is transcription initiated?
RNA polymerase enzyme recognizes and binds to promoter sequence.
Located immediately upstream of transcirption start site
RNA polymerase attaches to other proteins or transcription factors to forma n initiation complex
What is at the 5’ end and 3’ end of mRNA
5’ end - methylated guanosine cap - triphosphate bridge - requried for translation by ribosome
3’ end - poly A tail - large numbers of adenine residues - prevents 3’ end being degraded and signal for mRNA to be exporeted from nucleus
What is splicing?
Removal of junk intron sequences from mRNA to leave coding exon sequences which can be translated
What does lack of a polyA tail in mRNA indicate?
More rapid turnover
What is translation?
Synthesis of polypeptides using a sequence of mRNA
How many codons are there?
64 (4^3)
four bases, amino acids coded by groups of three bases
61 amino acid codons and three STOP codon
What are stop codons
UAA
UAG
UGA
Stop the translation process
Where does translation occur?
Ribosome - complexes of RNA and protein
Two unequal subunits 30S and 50S
What is the anticodon
tRNA carry a triplet sequence (anticodon) that is complementary to the codon on the mRNA
tRNA carries specific amino acids to the site of protein synthesis
What is the signal peptide sequence?
Hydrophobic amino acid seuqence of 18-30 amino acids that directs non-cytoplasmic polypeptides into the ER lumen - for further modification
