Translation BIT 220 Chapter 13

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TranslationBIT 220 Chapter 13

• Making protein from mRNA
• Most genes encode for proteins
• -some make RNA as end product

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Proteins
-Monomer Amino Acid 20 amino acids -peptides -pol
ypeptides -Structure of Amino Acid amino group
(NH2) carboxyl group (COOH) side group (R, for
radical group) -Figure 13.1 Acidic Basic Hydrop
hobic Hydrophilic -Amino acids are held
together by covalent bonds PEPTIDE BONDS -
Figure 13.2 - Termini Carboxy and Amino termini
of a protein
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Proteins Contd
-Structure Figure 13.3 1o - amino acid
sequence 2o - spatial relations amino acids 3o
- folding in 3D space 4o - association of 2 or
more peptides Dependent on properties of side
chains Ionic between acidic and
basic hydrophobic inside Figure 13.4 -
secondary structure - alpha and beta
helices Figure 13.5 - tertiary structure
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How is RNA Translated in Protein
CODONs nucleotide triplet which encodes for
amino acid AUG - start codon (translation) enc
odes methionine Three stop codons - UAA, UAG,
UGA
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Components of Translation
Figure 13.6 1. Ribosomes 3-5 RNA molecules 50
proteins 2. mRNA 3.60 tRNAs 4. Aminoacyl tRNA
synthetases (20) - so amino acids attached to
proper tRNA 5. Misc. Proteins
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Types of RNA
1.messenger RNA (mRNA) single chain copy of
gene that describes sequence in which aa should
bond together to for protein 2.transfer RNA
(tRNA) picks up appropriate aa and transfers it
to ribosome contains ANTICODON complementary to
mRNA codon 3.ribosomal RNA (rRNA) 4. Small
nuclear RNAs (snRNAs) - part of splicesomes,
excise introns from nuclear genes
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tRNA

• 1) Charging
• carboxyl group of amino acid is covalently
• bound to 3 end of tRNA molecule
• (acceptor stem)
• results in aminoacyl-tRNA
• 2) Anticodon

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Ribosomes
1. Organelles which serve as site of synthesis
of proteins 2. Meeting place for mRNA, tRNA,
amino acids 3. Exists as two units ie. E
coli 30S and 50S subunits 4. Combination of
50 RNA and 50 proteins 5. rRNA
genes -moderately repetitive sequences 6. Site
of transcription and assembly NUCLEOLUS -
organelle in nucleus
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Binding SitesFigure 3.14a
1. A Aminoacyl site incoming tRNA 2. P
peptidyl site holds growing polypeptide 3. E
exit site departing tRNA
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Translation-InitiationFigure 13.15http//www.ncc
.gmu.edu/dna/ANIMPROT.htm
1. rRNA of ribosome base pairs with the
Shine-Dalgarno (SDS) sequence of mRNA Figure
13.16 5 cap used in eukaryotes 2. Complex
looks for Start codon is AUG located 7 nt
downstream of SDS encodes methionine formylated
met this aa is sometimes cleaved interacts with
IF2 3.Charged tRNA molecule attached to
complementary mRNA, brings appropriate amino acid
(Methionine) 4. 50S ribosomal subunit joins
complex
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ElongationFigure 13.17
1.Second tRNA/amino acid sits on mRNA. Two
amino acids bond PEPTIDE bond PEPTIDYL
TRANSFERASE - helps grow chain 2.1st tRNA moves
to E site 5.Ribosome moves down mRNA
TRANSLOCATION 6.Next tRNA/amino acid
attached 7.Repeat

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Translation
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TranslationTermination
Figure 13.19 1.Release factors (termination
factors) recognize stop codon(s) UAG, UAA, UGA
(on mRNA) 2. Complex falls apart 3.Further
modifications to protein are made Met cleaved
frequently
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Genetic Code

• Genetic Code
• 1. Degenerate (Redundant)
• A. more than one codon designates an amino
  acid.
• B. Third base which is changed
• (wobbly base)
• C. This allows for mutations without deleterious
  effects.
• D.Leu, Ile, Val similar chemical properties
• one base difference
• 2. Universal
• 3. Non-Overlapping, without commas
• 4. Reading frame

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Genetic Code
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Prokaryotes vs Eukaryotes
Prokaryotes have no introns P have different
codon usage Ribosomes are different
(Streptomycin) P Transcription/Translation
simultaneous E Moves mRNA out of
nucleus Enzymes are different Promoters are not
interchangeable