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Translation
BIT 220 Chapter 13
Making protein from mRNA
Most genes encode for proteins
-some make RNA as end product
Proteins
-Monomer Amino Acid
20 amino acids
-peptides
-polypeptides
-Structure of Amino Acid
amino group (NH2)
carboxyl group (COOH)
side group (R, for radical group)
-Figure 13.1
Acidic
Basic
Hydrophobic
Hydrophilic
-Amino acids are held together by covalent bonds
PEPTIDE BONDS - Figure 13.2
- Termini
Carboxy and Amino termini of a protein
Proteins Cont’d
-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
How is RNA Translated
in Protein
CODONs
nucleotide triplet which encodes for amino acid
AUG - start codon (translation)
encodes methionine
Three stop codons - UAA, UAG, UGA
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
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
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
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
Binding Sites
Figure 3.14a
1. A: Aminoacyl site
incoming tRNA
2. P: peptidyl site
holds growing polypeptide
3. E: exit site
departing tRNA
Translation-Initiation
Figure 13.15
http://www.ncc.gmu.edu/dna/ANIMPROT.htm
1. rRNA of ribosome base pairs with the ShineDalgarno (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
Elongation
Figure 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
Translation
Translation
Termination
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
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
Genetic Code
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