TRANSCRIPTION DNA à mrna
Central Dogma
Animation DNA: The Secret of Life (from PBS) http://www.youtube.com/watch? v=41_ne5ms2ls&list=pl2b2bd56e908da696&index=3 Transcription http://highered.mcgraw-hill.com/sites/0072507470/student_view0/ chapter3/animation mrna_synthesis transcription quiz_1_.html Translation http://highered.mcgraw-hill.com/sites/0072507470/student_view0/ chapter3/animation how_translation_works.html
Gene The segment of DNA that is transcribed into RNA Also called a transcription unit
Stages of Transcription Initiation Elongation Termination
Promoter Nucleotide sequence Located upstream of the gene Where RNA polymerase (RNAP) first binds to starts transcribing Composed of an AT rich region Why is this region rich in A & T? Hint: DNA is double stranded
Transcription Initiation RNAP recognize and bind to promoter Key element in promoter is TATA box in eukaryote. DNA unwinds at the front of RNAP
Defining the strands Coding strand = sense strand = DNA strand that is not being copied (contains same sequence as new RNA except Tà U) Noncoding strand = antisense strand = template Transcript = newly synthesized RNA
Practice In this diagram identify the following: Transcript Template strand Coding strand Sense strand Antisense strand Label the 5 and 3 end on each strand
Transcription Elongation RNAP unwinds DNA exposing 10-20 bases Uses template strand to add complementary RNA nucleotides Direction of transcription: downstream from 5 à 3 of the transcript
Transcription Elongation RNA transcript separates from template as RNAP continues elongation DNA helix reforms behind RNAP Many RNAP can transcribe simultaneously
Transcription Elongation
Transcription Termination Termination sequence: signals end of transcription Prokaryote: transcription ends immediately at signal Eukaryote: RNAP continues for hundreds of nucleotides past termination signal at 10-35 nucleotide past signal pre-mrna is released
Transcription Termination
RNA Processing Precursor mrna = primary transcript: Pre-mRNA need additional modification before it become mrna RNA processing only occurs in eukaryotes
RNA Processing Post-transcriptional modification: Capping: 5 cap Polyadenylation: Poly A tail Splicing: intron excision
Post-Transcriptional Modification: Capping Soon after transcription 5 cap is added 5 cap Modified guanine added to 5 end Function: Protect mrna from degradation Signals ribosome attachment
Post-Transcriptional Modification: Polyadenylation PolyA tail 50-250 adenine added to 3 end Added by poly-a polymerase Function Protect mrna from degradation Facilitate export of mrna from nucleus
RNA Processing: Splicing Splicing: removal of introns Introns: intervening (noncoding) sequences, interspersed between exons Removed by splicesome Exons: coding sequences, expressed Introns are removed Exons are joined together 3D animation: http://www.dnalc.org/view/16933-3d-animation-of-dna-to-rna-to-protein.html
Splicing Video General intro to splicing: http://www.dnalc.org/view/16939-rna-splicing.html Splicing mechanism: 3D animation - http://www.dnalc.org/view/16938-3d-animation-of-rna-splicing.html http://highered.mcgraw-hill.com/olc/dl/120077/bio30.swf
Intron Function Regulatory role Alternative splicing: single gene encode more than one kind of polypeptide depending on which segments are treated as exons
Prokaryotic versus Eukaryotic protein synthesis Video: http://highered.mcgrawhill.com/olc/dl/120077/ bio25.swf
HW Questions Which enzymes in DNA replication mimic the function of RNAP in initiation and elongation? Why would promoters have a higher abundance of A-T than G-Cs? Why is post-transcriptional modifications not necessary in prokaryotes? Summarize in a chart, all the differences between prokaryotes and eukaryotes in transcription