Transcription Transcription describes the process of synthesizing RNA from DNA RNA is synthesized in the 5 to 3 direction just like DNA This means that it is read in the 3 to 5 direction Transcription Process Before RNA is synthesized it needs to know where to bind to in order to start and these are called transcription factors These transcription factors recognize specific sequences on the DNA called cis acting elements An example of these elements is a promoter Promoters affect the accuracy and amount of transcription that occurs Promoter regions include a TATA box GC box and CAAT box which are all located on the coding strand Once the transcription factors bind the cis acting elements then the RNA Polymerase binds to the strand The double stranded DNA molecule separates into two strands the template stand and the non template or coding strand The template strand is the one that the complementary bases are added to The coding strand is the one that is identical to the new RNA strand Each RNA polymerase makes a different form of RNA Polymerase I transcribes ribosomal RNA rRNA polymerase II transcribes messenger RNA mRNA and polymerase III transcribes transfer RNA tRNA RNA Processing Capping and Polyadenylation Capping occurs when GTP is added to the 5 end of mRNA This helps protect the mRNA and marks the starting point of translation Polyadenylation occurs when a polyA tail is added to the 3 end of mRNA This helps protect the mRNA from degradation Splicing RNA is made up of introns and exons Introns do not code for anything so they are removed Exons do code for proteins so once the introns are removed they are joined together Splicing can either occur through self splicing where the RNA slices itself or in a complex called a splicesome Translation The process of making proteins out of the three RNAs Initiation or the G Cap Elongation The small ribosome unit recognizes the ribosome binding site on the mRNA The small ribosome tRNA and mRNA come together at a start codon by initiation factors and then the large ribosome binds with all of these to complete an initiation complex Codon Recognition an elongation factor helps to extend the amino acid chain by bringing the appropriate aminoacyl tRNA tRNA plus amino acid Peptide bond formation the peptidyl transferase activity of ribosomes moves the start codon over and binds it with a new amino acid through peptide bond Translocation The mRNAs and corresponding tRNAs are H bonded so that the mRNA moves along when the tRNA is translocated through the ribosome Termination Protein Processing The elongation continues until the stop codon on the mRNA is reached A release factor binds to this codon and h2o is added separating the polypeptide chain from the tRNA and ribosome Polypeptide chain travels to the Golgi apparatus There they are processed Ex Disulfide bonds are formed chemical modification to amino acid side chains glycosylation of protein residues and cleaving of the amino terminal to activate protein or remove a target signal