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Protein Synthesis and Function: Chapter 3 Central Dogma Central Dogma of the transfer of biological information. DNA RNA protein Nucleic acid sequence must be translated into an amino acid sequence. PROTEIN SYNTHESIS Protein Translation tRNA mRNA: template Ribosomes: peptidyl transferase tRNA: adaptors Acceptor end CCA terminus T loop T stem D stem Anticodon stem D loop Variable loop Anticodon loop Protein Translation Amino-acyl tRNA synthetases specifically attach amino acids to tRNAs. amino acid + ATP aminoacyl-AMP + PPi aminoacyl-AMP + tRNA aminoacyltRNA + AMP Protein Translation Protein Translation Protein Translation— Termination Termination of the amino acid chain is signaled by one of three nonsense, or termination codons, UAA, UAG, or UGA which are not charged with an amino acid. Termination or release factors trigger hydrolysis of the finished polypeptide from the final tRNA. Initiation of Translation (Protein Synthesis) Attachment of Preinitiation Complex Scanning mRNA for AUG rRNA and Proteins of Ribosomes Ribosomes are composed of both proteins and rRNA Confer some of the specificity of these complex interactions Ribosomal Subunits Solving the Genetic Code Four nucleotides must code for 20 amino acids. 41 = 4, 42 = 16, 43 = 64, 44 = 256 George Gamow Solving the Genetic Code Synthetic RNAs UUUUUUUUU = phe-phe-phe GGGGGGGGG = gly-gly-gly CCCCCCCCC = pro-pro-pro AAAAAAAAA = lys-lys-lys Marshall Nirenberg and Johann Matthaei Solving the Genetic Code Synthetic RNAs of defined sequence UCUCUC = ser-leu-ser-leu Gobind Khorana Three nucleotides = 1 codon = 1 amino acid The Genetic Code: Redundancy And Wobble Structure of an Amino Acid Amino Acids Nonpolar Alanine, Ala, A Isoleucine, Ile, I Leucine, Leu, L Methionine, Met, M Phenylalanine, Phe, F Tryptophan,Trp, W Valine, Val, V Polar Asparagine, Asn, N Cysteine, Cys, C Glutamine, Gln, Q Glycine, Gly, G Proline, Pro, P Serine, Ser, S Threonine, Thr, T Tyrosine, Tyr, Y Negatively Charged (Acidic) Aspartic acid, Asp, D Glutamic acid, Glu, E Positively Charged (Basic) Arginine, Arg, R Histidine, His, H Lysine, Lys, K Amino Acid Structures Isoelectric Point (pI) Amino acids are neutral at a pH, which is their isoelectric point (pI). Peptide Bonds Amino acids are joined together by C-C-N- linkages or peptide bonds to make proteins. Amino terminus Carboxy terminus INITIATION OF PROTEIN SYNTHESIS TRANSFER OF GROWING CHAIN Transfer Of Growing Chain Termination Of Chain Location Of Translation Machinery ENDOPLASMIC RETICULUM Microscopic series of tunnels Involved in transport and storage Two types of ER: Rough ER (RER) Smooth ER (SER) ENDOPLASMIC RETICULUM Rough endoplasmic reticulum (RER) Originates from the outer membrane of the nuclear envelop Extends in a continuous network through cytoplasm Rough due to ribosomes Proteins are synthesized and shunted into the ER for packaging and transport First step in secretory pathway Smooth Endoplasmic Reticulum (SER) Closed tubular network without ribosomes Functions in nutrient processing synthesis and storage of lipids, etc. Rough Endoplasmic Reticulum (RER) OVERVIEW OF SYNTHESIS POLYRIBOSOMES Protein Structure Primary: amino acid sequence Secondary: Intrachain folding beta-pleated sheets alpha helices Protein Structure Four levels of structure Primary Secondary Alpha helix, beta pleated sheet, random coil Tertiary Quatanary Primary Structure: Amino Acid Sequence Secondary Structure: Alpha Helix, Beta-pleated Sheet, or Random Coil Amino Acid Content Determines Protein Structure and Function. Extracellular domains (charged, glycosylated) Cell membrane Intracellular domains (hydrophilic) Transmembrane domains (hydrophobic) Protein Structure Tertiary: further folding, loss of which denatures protein Quaternary: protein–protein interaction for function. Monomers form multimers. Dimer Trimer Tetramer Protein Function Enzymes Transport Storage Motility Structural Defense Regulatory Conjugated Proteins Lipoproteins–lipid Glycoproteins–carbohydrate Metalloproteins–metal atoms Non-amino acid portion–nonprotein prosthetic group MODIFICATION OF PROTEINS MODIFICATION OF PROTEINS MODIFICATION OF PROTEINS POST TRANSLATIONAL MODIFICATION OF PROTEINS PROCESSING OF INSULIN Golgi Apparatus Consists of a stack of flattened sacs called cisternae Closely associated with ER Transitional vesicles from the ER containing proteins go to the Golgi apparatus for modification and maturation Condensing vesicles transport proteins to organelles or secretory proteins to the outside Golgi Apparatus Golgi Apparatus Transport Process MULTIPLE CONTROL POINTS Summary Proteins are made of combinations of 20 amino acids. Protein structure and function depends on the amino acid content and organization. A gene is defined, in part, by an open reading frame that contains the genetic code. In the genetic code, three nucleotides code for each amino acid. Proteins are translated from mRNA by peptidyl transferase activity in the ribosome, using tRNA as adaptors.