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Unformatted text preview: Translation
http://genome.imim.es/courses/Madrid04/exercises/ensembl/images/ribosome.jpg 1 Last time
✤ Proteins that affect gene transcription: Transcription Factors
✤ Classes (types) Anatomy of a transcription factor How speciﬁc transcription factors work ✤ ✤ ✤ Post transcriptional regulation: mRNA stability
✤ The role of the Poly A tail RNA interference (RNAi)
2 ✤ Translation
✤ from mRNA to proteins
✤ quick review: features of proteins ✤ Important components of translation machinery
✤ tRNA ✤ ribosomes ✤ Revisiting translation (with some detail) elongation, termination ✤ Initiation, 3 Translation
Process by which information in mRNA is translated to amino acid sequence 4 5 Finding the Rosetta Stone
INPUT (RNA) UUU UUU, etc AAA AAA, etc OUTPUT (aa) Phenylalanine Lysine 61/64 combinations code for amino acids What do the last 3 codons code for? STOP (UAA, UGA, UAG) AUG codes for START and for Methionine. Marks start of reading frame…..
en.wikipedia.org 6 The Start codon (AUG) determines reading frame
3 possible reading frames, only ONE is correct (usually).
the bad cat ate the red rat (English) aug uua ccc uua aua ccg uga (RNA) heb adc ata tet her edr ugu uac ccu uaa uac cgu Stop codon! no stop codon! 7 The key to the genetic code Note that the code is both redundant and unambiguous
8 A protein ‘refresher’ N C 9 10 Four levels of protein structure
primary secondary tertiary quaternary (not all proteins) 11 Important components of translation machinery
a bit more detail on tRNA and ribosomes http://biology.unm.edu/ccouncil/Biology_124/Images/RNAtranslation.jpeg 12 tRNA - the translator
tRNA binds codons in mRNA, and carry associated amino acid 13 Features of tRNA
stem loops modiﬁed bases anti-codon acceptor stem inosine
14 There are ~45 tRNAs
✤...but there are 61 codons coding for 20 amino acids. How does this work?
✤ the third base wobble. 15 Third base wobble
Sometimes the 3rd base in the codon doesn’t matter too much - “relaxed pairing”
Leucine codons: Glycine codons: CUU GGU CUC GGC CUA GGA CUG GGG (UUA) (UUG) inosine Wobble ‘rules’ in Fig. 13.14
16 tRNAs are ‘charged’ with a speciﬁc amino acid charged amino acid
Aminoacyl-tRNA synthetase attaches a speciﬁc amino acid to tRNA
17 Ribosomes carry out translation http://www.emc.maricopa.edu/faculty/farabee/BIOBK/ribosome.gif 18 A closer look at ribosomes
2 subunits Protein + RNA RNA is catalytic tRNA occupy 3 ‘slots’
19 Closer look at subunits 20 tRNAs ﬁt into 3 slots in large subunit 21 Translation in bacteria
✤ assembly of proteins ✤ Elongation
✤ protein synthesis ✤ Termination
✤ dissociation of translation machinery
22 Initiation (bacterial)
step 1 23 The Shine-Dalgarno sequence 9nt sequence of mRNA that binds 16S rRNA in ribosome!
24 Initiation (bacterial)
step 2 step 3 25 Eukaryotic initiation G C C (A/G) C C A U G G Kozak’s Rules (start consensus sequence)
26 Elongation (bacterial)
new tRNA comes in aa chain transfered to tRNA in A site
27 Elongation (bacterial)
tRNA in E site leaves 28 Termination (bacterial)
stop! 29 Polyribosomes 30 Summary
✤ mRNA sequence is translated into amino acid sequence
✤ Amino acids are joined by peptide bonds, and contain R groups, which give them speciﬁcity ✤ tRNA is the ‘translator’ molecular, binding mRNA codons and carrying speciﬁed amino acid Ribosomes (lg/sm subunit) are composed of both protein and RNA (catalytic) Initiation, Elongation and Termination are the three stages of translation
31 ✤ ✤ Ungraded problems
✤ ✤ Look over Chapter 13 S2, S4, S5 Try Chapter 13: C1, C2, C7, C10, C14, C23, C28 32 Next Time
Gene mutation 33 ...
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