4What are proteins? Polymers of amino acids Amino acid structure: Amino Carboxylgroup groupVariable group ↑
5What are proteins? There are 20 different amino acids. The R group (called a “side chain”) is different for each amino acid.
6A few A.A. side chains: Glycine: H Alanine: CH3 Serine: CH2OH Tryptophan:
7A few A.A. side chains:Only cysteine and methionine contain sulfur atoms in their side chains. These atoms can form “cross bridges” (aka disulfide bonds)In General, side chains can be:Polar Non-polarBulky -- SmallPositively chargedNegatively charged
8Amino AcidsEssential A.A.’s must be supplied by the diet, cannot be synthesized by organism.Non-essential A.A.’s can be synthesized by organism.
9We like to bond Links between amino acids are called peptide bonds. Dehydration synthesis (joining by removal of H2O)Carboxyl group of 1 A.A. links to amino group of another A.A.Peptidyl transferase is the ribosomal enzyme responsible.
11Levels of structure Primary Structure Secondary Structure The sequence of amino acids(ex: valine, proline, cysteine…)Secondary StructurePortions of the polypeptide form standard shapes:Alpha helixBeta pleated sheet
14Levels of structure Tertiary structure Quaternary structure Unique folds and bends due to attraction of charges and polar A.A.sSulfur cross-bridgesQuaternary structureTwo or more polypeptides combine as functional protein
15TranscriptionInformation encoded in DNA is converted to mRNA by transcription.RNA is different from DNA:Ribose versus DeoxyriboseUracil (U) versus Thymine (T)Single-stranded versus double-stranded
16Transcription Occurs on an Open Reading Frame (ORF). An ORF is a sequence of DNA that gets transcribed:START codon many codons for A.A.’s Stop Codon
17Transcription Both strands of DNA contain genes (ORFs) Strand with the same base sequence as mRNA is the sense strand (coding strand).Complimentary strand is the antisense strand (anticoding)Antisense strand is the template for mRNA
27Translation mRNA is read from 5’ to 3’ 3 Bases make up a codon Every codon codes for either an amino acid or STOPRibosome has 3 sites for tRNA binding: A site (Amino-acyl), P site (peptidyl), E site (exit).
29Process of Translation: 1. A “loaded” tRNA pairs with its codon at the A site.2. A peptide bond forms between the amino acid and the previous a.a. chain as the tRNA moves to the P site.3. The tRNA shifts to the E site and “exits”, to be reloaded.