Lipid Biochemistry and Pathogen Identification PDF

Triglycerides: Long-term energy storage in animals. Made of glycerol and three fatty acids. Phospholipids: Form cell and organelle membranes in all organisms (except archaea). Similar to triglycerides but have a phosphorylated head group instead of one fatty acid. Breakdo...

Triglycerides: Long-term energy storage in animals. Made of glycerol and three fatty acids. Phospholipids: Form cell and organelle membranes in all organisms (except archaea). Similar to triglycerides but have a phosphorylated head group instead of one fatty acid. Breakdown Process: Both triglycerides and phospholipids are broken down by releasing fatty acids (and/or phosphorylated head groups) from the glycerol backbone. Enzymes: ○ Lipases break down triglycerides. ○ Phospholipases break down phospholipids. Certain microbes (like Staphylococcus aureus and Cryptococcus neoformans) use these enzymes to harm host cells and obtain energy. Products of Lipid Catabolism: Resulting products are glycerol and fatty acids. Glycerol: ○ Can be converted to glycerol-3-phosphate and then to glyceraldehyde 3-phosphate, entering glycolysis. Fatty Acids: ○ Go through β-oxidation, which removes two-carbon acetyl groups, producing NADH and FADH2 for ATP generation via oxidative phosphorylation. ○ Acetyl groups enter the Krebs cycle, producing CO2 and more NADH and FADH2. Other Lipids: Certain pathogens (like Mycobacterium tuberculosis) can degrade cholesterol, aiding their virulence. Cholesterol's side chains can be easily removed; however, the fused rings require a multistep enzymatic process for degradation, producing pyruvate for the Krebs cycle. Definition: Proteins are broken down by microbial enzymes called proteases. Extracellular Proteases: Cut proteins at specific amino acid sequences. Break proteins into smaller pieces called peptides for cell uptake. Pathogen Identification:  Certain pathogens produce specific extracellular proteases. Example: ○ Gelatinase: Produced by Proteus and Serratia; used to differentiate them from other gram-negative bacteria. ○ When grown in gelatin broth, gelatinase prevents gelatin from solidifying when chilled. Caseinase: Breaks down casein (milk protein). ○ Found in Pseudomonas aeruginosa, used to distinguish it from other gram-negative bacteria. ○ When grown on skim milk agar, caseinase creates a clear zone around growth. Further Breakdown: After uptake, peptides are further broken down into amino acids by intracellular proteases. Amino acids can be deaminated (removal of amino group). Remaining molecules enter the transition reaction or Krebs cycle.