CHAPTER 17 gene to protein George Beadle and Edward Tatum were able to demonstrate the relationship between genes and enzymes by studying mutants of a bread mold, Neurospora Beadle and Tatums hypothesis has been restated as one gene-one polypeptide

Cracking the genetic code The first codon was deciphered in 1961 by Marshall Nirenberg of the National Institute of Health (NIH)  He synthesized an mRNA by linking only uracil- bearing RNA nucleotides The artificial mRNA (poly U) was translated into a polypeptide containing a string of only one amino acid, phenylalanine.

The genetic code is shared nearly universally among living organisms.  For example, the RNA codon CCG is translated into proline in all known organisms.

Transcription initiation 17.7 Cast: members of transcription initiation complex a) transcription factors – proteins which attach to upstream promoter to mediate RNA polymerase II attachment *first one goes to TATA box of promoter b) RNA polymerase (II) - unwinds DNA and adds RNA nucleotides in 5’ to 3’

ELONGATION RNA polymerase II unwinds DNA and exposes DNA nucleotides as it adds RNA nucleotides to growing mRNA strand (about 60 per second) Several RNA polymerase II often follow each other to transcribe many mRNA strands at once

TERMINATION Termination signal (AAUAAA) on mRNA (downstream) signals RNA polymerase II to terminate transcription At around 10 to 35 nucleotides past the termination signal, the pre-mRNA is cut free RNA polymerase II may go on past this!

mRNA processing 5’ Cap - Guanosine triphosphate added to 5’ end by enzymes in nucleus a) protects against degradation b) aids in ribosome attachment

3’ poly A tail - 50 to 250 adenine nucleotides added to 3’ end by enzymes in nucleus a) same functions as 5’ cap b) also may assist with exit from nucleus

SPLICING pre-mRNA RNA splicing – removal of introns so that only exons remain (exons = mRNA that exits nucleus (includes leader and trailer )) Roberts and Sharp 1977 RNA polymerase II transcribes whole transcription unit (DNA that is transcribed), but many nucleotides need to be spliced to form true mRNA from primary transcript mRNA (pre mRNA)

Splicing Cast: A)small nuclear RNA (snRNA) and other proteins form a snRNP (snurp) small nuclear ribonucleoproteins B) Spliceosome – several snRNP’s form this complex- this is where coding regions of introns are targeted for cutting. Cuts and pastes.

Ribozymes- RNA molecules functioning as enzymes *all biological catalysts are proteins? No

Alternative Splicing importance/?

tRNA anatomy Aminoacyl tRNA synthetase types (why?) -requires ATP to unite tRNA with proper amino acid

W o bb l e tRNA 3 rd base mRNA U pairs with A or G I (inosine) “ “ U, C, A

Ribosome anatomy rRNA + proteins *rRNA is most abundant RNA * two subunits compose eukaryotic ribosome Prokaryotic ribosomes are unique Importance?

TRANSLATION I.Initiation mRNA + small subunit + initiator tRNA + large subunit (requires GTP) = translation initiation complex *initiation factors required too!

II.Elongation codon recognition (2 GTP) peptide bond formation translocation (GTP)

E P A E= exit site P= middle, tRNA with polypeptide chain = also holds initial tRNA during initiation A= arrival site

0 -amino XXX 3’ ACU -anticodon 5’ 5’ xxxxxxxx UGAxxxxxxxxxxxxxxxxxxx-mRNA3’

III.Termination release factor binds to stop codon water is added to hydrolyze polypeptide chain from tRNA in P site

Point mutations I.Substitutions a) silent mutation- does not alter protein b) missense mutation – wrong amino acid in place of correct one – usually affects protein function c) nonsense mutation- random formation of premature stop codon

II.Insertions/deletions a) frameshift mutations

ONE GENE  one polypeptide or RNA molecule