Chapter 13 posted.pptx

Translation Overview • Translation – Components – Process • Initiation • Elongation • Termination • Inborn errors in metabolism • Protein structure Translation components 13-6 The ribosome 13-1 tRNA • RNA molecule with secondary structure • Contains “unusual” nitrogenous bases – example:...

Translation Overview • Translation – Components – Process • Initiation • Elongation • Termination • Inborn errors in metabolism • Protein structure Translation components 13-6 The ribosome 13-1 tRNA • RNA molecule with secondary structure • Contains “unusual” nitrogenous bases – example: Inosinic acid (I) • Pairs with U, C, or A • Allows GCU, GCC, GCA to all code for alanine – This is distinct from wobble 13-3 Charging tRNA • Process of loading an amino acid onto a tRNA • Enzyme and tRNA are specific for the amino acid 13-5 Translation 1) Initiation • mRNA binds to small subunit Amino acid – Prokaryotes: • Shine-Dalgarno sequence – Eukaryotes: • Kozak sequence – AUG codon • establishes reading frame • Initiatior tRNA binds to mRNA in P site – Prokaryotes: fmet – Eukaryotes: met • Large subunit binds – IFs are released 13-6 2) Elongation • Next tRNA enters “A” site • Peptide bond is formed • “P” site amino acid (met) released from its tRNA – Polypeptide is linked to next tRNA • tRNAs move: – “spent” (now uncharged) met tRNA moves to E site and exits ribosome – Next tRNA moves to P site – Note: polypeptide chain is attached to this tRNA • mRNA moves three bases • Next tRNA can now enter A site 13-7 2) Elongation • • • • • Next tRNA enters A site Peptide bond is formed tRNAs move mRNA moves Process is repeated until termination codon is read 13-7 3) Termination • UAG, UAA, or UGA (stop codons) • Release factors cleave the polypeptide chain from terminal tRNA • Ribosome disassociates 13-8 Polyribosomes 13-9 Inborn errors in metabolism • Demonstrate that proteins are important factors in heredity One gene:one polypeptide hypothesis (spores) 13-11 One gene:one polypeptide hypothesis 13-11 One gene:one polypeptide hypothesis 13-11 The amino acid a carbon H Amino group H O N C C H R Carboxyl group OH Side chain Amino acids • 20 different amino acids (R groups) • Four classes: – Nonpolar (hydrophobic) – Polar (hydrophililc) – Positively charged (basic) – Negatively charged (acidic) • Average polypeptide = 200 amino acids – 20200 = tremendous diversity! • Each amino acid ~110 Daltons (0.11kD) 13-14 Nonpolar, hydrophobic Polar, hydrophilic Polar, negatively charged (acidic) Polar, positively charged (basic) The polypeptide Protein structure • Primary: the amino acid sequence specified by the mRNA • Secondary: segments of a polypeptide that assume regular repeating configurations in space – a-helix – b-pleated sheet • Tertiary: three dimensional structure of an entire polypeptide chain • Quaterinary: 3D structure of multiple polypeptide chains (only applies to proteins of more than 1 subunit) Secondary structure • Proline: a-helix breaker 13-15 Tertiary structure Types of interactions: • Cysteine: can form disulfide bridges • Charged: Ionic bonds • Polar: Hydrogen bonds • Hydrophobic: “like dissolves like” General: • Hydrophilic amino acids towards outside • Hydrophobic towards inside Tertiary/Quaternary structure Tertiary Quaternary • Cysteine: can form disulfide bridges that stabilize these structures 13-16 Review • Translation – Ribosomes – tRNA – Steps in translation • Proteins – One gene:one enzyme hypothesis • Inborn errors of metabolism – Protein structure