21 - Lecture Guide

Review of Lecture 21 Questions to think about…. The molecules known as ketone bodies are ACETON, ACETOACETATE, and BETA-HYDROXYBUTYRATE. Under what conditions do liver mitochondria synthesize acetoacetate and ?-hydroxybutyrate from some of the acetyl CoA formed from fatty acids? UNTREATED DIABETES OR DURING STARVATION, ACETYL-COA IS CONVERTED INTO KETONE BODIES via the enzyme HMG-CoA synthase AS AN ENERGY SOURCE TO THE BRAIN. One important thing to mention is that since the kerb cycle requires acetyl-coa as a starting point with oxaloacetate, the acetyl-coa no longer feeds into the kerb cycle because kerb cycle intermediates are no longer produced. Is there any biochemical basis for the statement that going on a carbohydrate-free diet can lead to a life-threatening situation? Yes… although carbohydrates are converted into fats and can be converted into amino acids, essential amino acids still need to be ingested. Our bodies cannot synthesis this special group of compounds. Release of fatty acids for energy production is inhibited by insulin. In diabetics who lack insulin, massive amounts of fatty acids are released from adipose tissue. This and other factors lead to an acceleration of fatty acid oxidation. Can fatty acid oxidation proceed indefinitely? What are the consequences? There is a little to how much fat can be taken up by cells and is also dependent on the amount of epinephrine. In order for fatty acid oxidation to proceed indefinitely, you would need an indefinite supply of acetyl-coa, carnitine, essential regulatory enzymes, etc. Therefore, no, it cannot proceed indefinitely. Be able to compare and contrast fatty acid synthesis, polyketide synthesis and non-ribosomal peptide synthesis. FATTY ACID SYNTHESIS POLYKETIDE SYNTHESIS NON-RIBOSOMAL SYNTHESIS ENZYME USED FATTY ACID SYNTHASE POLYKETIDE SYNTHASE NON-RIBOSOMAL SYNTHASE TYPE In bacteria, type II iterative; in eukaryotes; type I iterative Could be Type I modular/iterative, II modular Type I, modular PROTEIN CARRIER ACYL CARRIER PROTEIN [ACP] via phosphopantethiene arm ACYL CARRIER PROTEIN [ACP] via phosphopantethiene arm PEPTIDYL CARRIER PROTEIN [PCP] via phosphopantethiene arm MODIFICATIONS THE ADDITION OF DOUBLE BONDS VIA DESATURASES AND ELONGATION PASSED 18 CARBONS VIA ELONGASE GLYCOSYLATION, OXYGENATION, METHYLATION, Dehydration, epimerization CYCLIZATION, ACYTLATION (METHYL GROUP ADDED) CHAIN INITIATION, STARTER UNITS ACETYL-COA ACETYL, MALONYL, PROPIONYL, benzioyl MANY OTHERS AMINO ACIDS AS MONOMERS ELONGATING UNITS MALONYL-COA MALONYL-COA OR METHYLMALONYL-COA Doesn’t apply, it’s modular; if anything: amino acids TERMINATING ENZYME THIOESTERASE THIOESTERASE THIOESTERASE PRODUCTION ASSEMBLY LINE PRODUCTION OF COMPLEX MOLECULES, NOT IN FIXED ORDER. CHEMISTRY BOTH CONVERT SHORT-CHAIN ACYL-S-COA THIOESTERS INTO LONG-ACYL-CHAIN PRODUCTS Discuss the energetic costs of converting 2 acetyl-CoA to the ketone body 3-hydroxybutyrate in the liver and then converting the 3-hydroxybutyrate back to 2 acetyl-CoA in the muscle. OTHER LECTURE What is the difference between a Type I and Type II FAS? TYPE I FAS SUGGESTS THAT THE CATALYTIC AND CARRIER PROTEIN DOMAINS OF THE ENZYME ARE GATHERED IN CIS AS PART OF A LARGE, MULTIDOMAINAL SUBUNIT TYPE II FAS SUGGESTS THAT THE CATALYTIC AND CARRIER PROTEIN DOMAINS ARE SCATTERED AS SEPARATE SUBUNITS, IN TRANS, WHERE THEY RAPIDLY ASSOCIATE TRANSIENTLY AND DISSOCIATE IN EACH CATALYTIC CYCLE. Be sure to understand that shuffling of modules of PKs and NRPs can result in the creation of entirely new products. Type I modular/processive polyketide synthase, since each new short-chain monomer added to the growing acyl chain polymer is conducted by a different module and that each module carries a specific monomer, shuffling of these modules will result in a different product. Moreover, because these synthases perform similar biosynthetic reactions, the genes of one absolutely known polyketide synthase can be used to find polyketide synthase genes in other organisms simply by matching the DNA. Therefore, cloned genes of one polyketide synthase can be mixed and match with polyketide genes of other organisms to produce hybrid secondary metabolites. BECAUSE OF SIMILAR BIOSYNTHETIC REACTIONS, CLONED GENES FOR ONE POLYKETIDE CAN BE USED TO ISOLATE GENES FOR OTHER POLYKETIDES. FOR THIS REASON, YOU CAN MIX AND MATCH POLYKETIDE SYNTHASE GENES TO PRODUCE HYBRID ANTIBIOTICS. What are polyketides? Give one example used in class. Type I processive/modular includes erythromycin (S. erythraea) which is an antibiotic, rifamycin, and rapamycin (immunosuppresent, anti cancer) Type I iterative includes lovastatin which is an anti-cholesterol agent. POLYKETIDES ARE SECONDARY METABOLITES PRODUCED BY MULTIDOMAINAL SUBUNITS THAT SERVE AS ANTIBIOTICS, ANTI-CHOLESTEROL DRUGS, VIRULENCE FACTORS, AND IMMUNOSUPPRESANTS (ANTI-CANCER). POSSESS DIVERSE STRUCTURE AND FUNCTION. Give an example of a NRP antibiotic discussed in class. Cyclosporin (contains D-ala) PENICILIN G IS PRODUCED BY A TRIMODULAR NRP PRODUCED BY L-ALPHA AMINOADIPATE, CYSTEINE, AND VALINE. THE MAIN ENZYME INVOLVED IN THIS REACTION IS ACV SYNTHETASE which produces LLD-AVC tripeptide and then the enzyme IPN-synthase to produce isopenicillin, and then acyl transferase to add phenylacetate. REQUIRES THE AMINO ACIDS TO BE IN ‘D’ FORM BECAUSE IT IMPARTS STABILITY IN THE PRESENCE OF PROTEASES