Microbiology, part 24: Metabolism - Photosynthesis

Hi. I'm Cathy with Level Up RN. In this video, I will be discussing lipid and protein catabolism. And at the end of the video, I'm going to give you guys a little quiz to test your understanding of some of the key facts I'll be covering, so definitely stay tuned for that. And if you have our Level Up RN microbiology flashcards, go ahead and pull out your flashcard on lipid and protein catabolism so you can follow along with me. And of note, our flashcards are also available in digital format via Flashables, which offers personalized guided learning as well as progress tracking.

We previously talked about glucose catabolism and how a glucose molecule goes through glycolysis, the transition reaction, the citric acid cycle, and oxidative phosphorylation. However, microorganisms can also break down lipids and proteins into smaller molecules, which can then enter some of these same pathways. Let's first talk about the catabolism of lipids such as triglycerides and phospholipids. So triglycerides are an important type of lipid used by animals for long-term energy storage. They are composed of a glycerol and three fatty acids. A phospholipid is another important type of lipid that is a key component of cell membranes. Its structure is very similar to triglycerides, except for one of the fatty acids is replaced with a phosphate group.

To break down a triglyceride, lipase, which is an enzyme, removes the fatty acid chains from the glycerol backbone. So anytime you see ase at the end of a medical term, that means we are talking about an enzyme that is breaking down a substance. So lipase is an enzyme that breaks down a lipid. After lipase breaks the bond between glycerol and the fatty acid chains, glycerol is converted into glyceraldehyde 3-phosphate, which then enters glycolysis. The fatty acid chains are broken down in a process called beta oxidation. During this process, two carbon acetyl groups, as well as coenzyme A, are removed from the end of the fatty acid chain. And then that molecule can enter the citric acid cycle. Also, during beta oxidation, NAD+ and FADH are reduced to NADH and FADH2, and then those molecules can bring their electrons to the electron transport chain to help produce ATP.

Next, let's talk about protein catabolism. Proteins are broken down by proteases. So again, anytime you see ase, you know we're talking about an enzyme. So in the case of protease, we're talking about an enzyme that breaks down proteins. Extracellular proteases break down proteins into smaller peptides. These peptides are taken up by cells, and intracellular proteases break down the peptides into individual amino acids. The amino group is removed from the amino acid by enzymes in a process called deamination. The remaining deaminated amino acid gets processed into pyruvate or acetyl-CoA, or is shuttled into one of the intermediate steps of the citric acid cycle.

All right. It's quiz time, and I have three questions for you. Question number one, what is the name of the enzyme that helps to break down triglycerides by removing the fatty acid chains from the glycerol backbone? The answer is, lipase. Number two, what is the name of the enzyme that breaks down proteins into smaller peptides? The answer is, protease. Number three, during lipid catabolism, blank is the process in which two carbon acetyl groups are removed from the ends of the fatty acid chains? The answer is, beta oxidation.

All right. That's it for this video. I hope it was helpful. Take care, and good luck with studying.