Class Notes (810,512)
Canada (494,140)
BIOB10Y3 (39)

biob10 lec 16 notes

3 Pages
Unlock Document

University of Toronto Scarborough
Biological Sciences
Aarti Ashok

Transcription: tRNAs  50 different species of tRNA = transfer RNAs o Encoded by repeated DNA sequences o Internal promoter o Transcribed by RNA polymerase III o Lots of non-transcribed spacer sequences o tRNA coding sequences in tandemly repeated arrangement  tRNAs match up the sequence of nucleotides with the correct amino acid to be inserted into the protein that is encoded o matches up to the mRNA o each tRNA brings along an enzymatically attached amino acid Transcription: mRNAs  mRNAs are synthesized from precursors that are found in the nucleus: o radioactively label RNA nucleotides in cells (30min pulse) – pulse experiment, no chase o Lyse open the cell, extract the RNA and look to see where the radioactivity ended up OR o Wash out the radioactivity for 3 hours after the pulse = CHASE o Then lyse cells, extract RNA and look to see where the radioactivity ended up *30 min PULSE only -very large RNAs radioactive -found to be in nucleus -heterogeneous nuclear RNAs (hnRNAs) *30 min PULSE + 3 hour CHASE -hnRNAs not seen -smaller RNAs -found to be in cytoplasm =hnRNAs processed into smaller RNAs that are exported to the cytoplasm = mRNAs  All eukaryotic mRNA precursors are synthesized by RNA polymerase II o Enzyme has many different subunits  Requires the activity of various “general” transcription factors (GTFs) o Called general b/c their binding is required for transcription to initiate at many different promoters  Polymerase II recognizes promoter regions located 5’ of the transcription unit o b/w -24 and -32 is a specific promoter sequence known as the TATA box o Polymerase II and the transcription factors assemble here = preinitiation complex  TATA box is bound by a protein known as the TATA-binding protein = TBP  TBP binding is required for RNA polymerase II to initiate transcription at the right place  TBP binds in the minor groove of DNA and significantly alters its conformation o Bends the DNA  The assembly of the preinitiation complex occurs in a step-wise manner  TAFs = TBP association factors  TFIID (Transcription Factor 2 D) is a large complex of TBP and various TAFs  TFIIH assembles onto the complex once RNA Polymerase II is bound; 2 enzymatic functions: 1. Helicase – unwinds DNA 2. Kinase – phosphorylates Polymerase II  RNA Polymerase II assembled as part of the pre-initiation complex is not phosphorylated o it becomes heavily phosphorylated upon initiation of transcription o phosphorylated by TFIIH and other kinases o on serine residues in its C-terminal domain (CTD)  phosphorylation is thought to be the trigger that allows Polymerase II to escape the promoter and move down the DNA template  Once Polymerase II begins transcription, most GTFs are either left behind at the promoter (TFIID) are simply released from the complex (TFIIB) o TFIID can then initiate assembly of a preinitiation complex with another RNA Pol II molecule o additional rounds of transcription without the delay of assembly *NOT phosphorylated -preinitiation complex on promoter *phosphorylated -initiates transcription -elongation factors bound (SII, ELL) -PTEFb is another kinase that phosphorylates CTD once initiation begins Properties of mRNAs  they are found in the cytosol  they contain a sequence of nucleotides that will direct the order of amino acids in the proteins that they encode  they often contain untranslated regions (UTRs) that do not direct the incorporation of amino acids but play important regulatory roles o can be present on both 5’ and 3’ ends of the coding region  5’ terminii contain methylated guanosines = 5’ cap  3’ terminii contain 50-250 adenosines = poly (A) tail  They are transcribed from segments of DNA that are separated from one another along the template strand = introns spliced out Processing of mRNAs  There are 3 processing events that need to take place: 1. Addition of 5’ cap 2. Addition of a 3’ Poly(A) Tail 3. Splicing out of introns (fusing exons together)  5’ Capping
More Less

Related notes for BIOB10Y3

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.