METABOLISM, THE SYNTHESIS OF NUCLEICACIDS AND PROTEINSI. Nucleic Acid Structure:A. Nucleic acids: Bipolymeres: Consist of:Pentose phosphate chains Nitrogenous bases:Two types of nitrogenous bases:Purines:AdenineGuanine Pyrimidines:Thymine (DNA only)CytosineUracil (RNA only)Form linkages with pentose sugars:Nucleoside:Base + 5 Carbon sugar Nucleotide: Base + 5 Carbon sugar + PO4:Phosphate group (PO4):Combines with two different five carbon sugars: Forms backbone of nucleic acid molecule:B. DNA Structure:Long moleculesComposed of two polynucleotide chainsCoiled together - double helix Backbone: Alternating deoxyribose and PO4 groups:Held together by hydrogen bonding between bases:Strands are complementary: Adenine always pairs with Thymine: Two hydrogen bondsGuanine always pairs with Cytosine:Three hydrogen bondsB3621Differences between specific DNA molecules due to difference in base sequence C. RNA STRUCTURE:Long molecules:Single stranded molecule:Contains: Five carbon sugar:RibosePyrimidine:UracilCan coil back on itself:Base pairing occurs:Forms hair-pin shaped structuresHelical organization Three kinds:Messenger RNA (mRNA)Transfer RNA (tRNA)Ribosomal RNA (rRNA)II. Organization of DNA in cells:A. Prokaryotic cells:Closed circle: Twisted into supercoiled DNAAssociated with basic proteins:Not associated with histonesBasic proteins:Organized bacterial DNA into coiled chromatin-like structureB. Eukaryotic cells:More highly organized:Linear:Associated with histones: Small basic proteins rich in: Lysine ArginineArranged in nucleosomesIII. DNA ReplicationB3622A. Replication pattern varies between prokaryotic and eukaryotic cells:B. General stepsTwo strands of double helix:UnwindSeparate - helicaseFree nucleotides move inLine up along the two parental strands via base paringLinked together by DNA polymerases:750 -1000 bases/second IV RNA transcription:A. DNA not direct template for protein sequence: Transfers information to RNA RNA is transcribed from DNA B. All RNA molecules have same backbone structure:Ribose alternating with phosphate:C. Differences in RNA molecules:Due to the differences in the order of bases connected to the sugar phosphate backbone:Any possible sequence of: Adenine UracilCytosineGuanine D. Single DNA strand is template for RNA synthesis:Base sequence of RNA complementary to base sequence of DNA template:E. RNA bases form H bonds with bases of DNA molecule: Ribose sugar phosphate backbone zipped up by RNA polymeraseRNA polymerase must bind to promoter before transcription can startPromoter: Region in DNA where RNA polymerase must bind before it can make the linkage between ribonucleotides and phosphateF. Messenger RNA (m RNA): Directs amino acid sequence in proteinsTemplate for protein synthesisTranscribed from a specific gene which codes for a specific protein: Specific gene contains: Series of codons: B3623Sequence of three bases coding for an single amino acid: Genetic codeAfter transcription:mRNA associates with a ribosomeV. Protein Synthesis:A. Translation:Synthesis of protein using an RNA templateAmino acid activation:Amino acid attached to transfer RNA: tRNA = Adaptor molecule:Modifies amino acids so that they can combine with a mRNA codonSmall - 60 - 70 nucleotides long Contain anticodon: Three bases complementary to the codon in RNAAt least one specific tRNA for each amino acidAmino Acetyl tRNA Synthetase:Links amino acids to tRNAsSpecific enzyme for each amino acidOccurs only on surface of ribosomesRibosome:Orients the AA-tRNA combination and mRNA so that genetic code can be read:Have specific surfaces that bind mRNA and tRNA B. Prokaryotic ribosomeComposed of 2 separate subunits:Subunits separate when not actively synthesizing protein30s unit contains: 21 different kinds of protein16s RNA 50s unit contains: 32-34 kinds of proteinRNA:23s RNA 5s RNA Combined units = 70s C. Eukaryotic ribosomeComposed of 2 separate subunits:B3624Subunits separate when not actively synthesizing protein:40s unit contains: 32 different kinds of protein 18s RNA 60s unit contains: 40 kinds of protein RNA:28s RNA 5s RNA Combined units = 80s D. Initiation of protein synthesis requires:Initiation complex: Consists of: 30s ribosome mRNA N-formylmethionyl-tRNA Must be formed before protein synthesis starts:Combines with 50s subunit to form functional ribosomeInitiation of protein synthesis is complex:Insures that protein synthesis starts at the correct location:At the beginning of a gene At the correct codonAt the correct base in the codon E. Elongation of the polypeptide Chain:50s subunit has two special sites involves in the elongation of the polypeptide chain:Acceptor (A) site: Place where new tRNA-aa attach to 50s subunitPeptidyl (P) site: Place where growing polypeptide chain held by a tRNAPeptidyl transferase: Part of the 50s ribosome Makes peptide bond between adjacent amino acidsF. Protein synthesis continues until a termination (nonsense) codon is reached:Termination Codons:UAAUAG B3625UGACode for no amino acidStop polypeptide elongationG. Protein synthesis requires more energy than any other synthetic process in the cell:Four ATP molecules per peptide