Translation BIT 220 Chapter 13

Transcription

1 Translation BIT 220 Chapter 13 Making protein from mrna Most genes encode for proteins -some make RNA as end product

2 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 Termini Carboxy and Amino termini of a protein

3 Proteins Cont d -Structure Figure o - amino acid sequence 2 o - spatial relations amino acids 3 o - folding in 3D space 4 o - association of 2 or more peptides Dependent on properties of side chains Ionic between acidic and basic hydrophobic inside Figure secondary structure - alpha and beta helices Figure tertiary structure

4 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

5 Components of Translation Figure 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

6 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

7 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

8 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

9 Binding Sites Figure 3.14a 1. A: Aminoacyl site incoming trna 2. P: peptidyl site holds growing polypeptide 3. E: exit site departing trna

10 Translation-Initiation Figure rrna of ribosome base pairs with the Shine- Dalgarno (SDS) sequence of mrna Figure 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

11 Elongation Figure Second trna/amino acid sits on mrna. Two amino acids bond PEPTIDE bond PEPTIDYL TRANSFERASE - helps grow chain 2.1 st trna moves to E site 5.Ribosome moves down mrna TRANSLOCATION 6.Next trna/amino acid attached 7.Repeat

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13 Translation

14 Translation Termination Figure 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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16 Genetic Code Genetic Code 1. Degenerate (Redundant): A. more than one codon designates an amino acid. 2. Universal 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 3. Non-Overlapping, without commas 4. Reading frame

17 Genetic Code

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19 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