Fundamentalsscribe: Hillary Carney

FundamentalsScribe: Hillary Carney

Thursday September 3, 2009Proof: Jake Nolen

Dr. Weikhart LIPID SYNTHESIS Page1 of 4

1. Review/Introduction [S3]:
2. So we learned about lipids yesterday. We talked about ingestion, transport, storage, and a little pathology and the use of these lipids as fuels and now we are going to talk about biosynthesis.
3. Going to focus on fatty acid synthesis and cholesterol synthesis. Might get to steroid hormones later. Not going to look at sphingolipids, bile acids or steroid hormones.
4. Read from slide.

1. Fatty Acid Synthesis [S4]
2. We have a large variety of fatty acids. These are taken in and stored and broken down for specific cell needs. Why do cells go through the process of making them?
3. In developed nations the need for synthesis of fatty acids isn’t really critical. In fact, we get too much.
4. The process does occur and in two different ways: De novo—making long chain fatty acids from precursor substances like acteyl-coA, and then there is carbon lengthening of palmitic acid in the formation of some double bonds--limited amount

1. De Novo Synthesis [S5]
2. De novo comes from 2-carbon units. One is important in developing fetus and in countries with decreased fat in their diet.
3. Side effects of de novo? Because glucose is used to produce 2 carbon units like acetyl coA, these 2 carbon units that are not used are converted to fatty acids in a one-way process. Do not convert them back to glucose because the machinery isn’t there.
4. All extra glucose that is not used is converted to lipids in a sedentary person.

1. Tissue Sites of Action [S6]
2. Primary liver and secondarily in fat tissue.
3. Goes from cytosol to mitochondria back to cytosol- this assumes that glucose is the source of fatty acid synthesis.
4. What the compounds are: Glucose to pyruvate (meyerhauf pathway) from there to acetyl coA then toCitrate (intermediate for transport) back to acetyl coA and then to fatty acids.

1. Part I: What is needed for Synthesis and where it comes from [S7]
2. Interesting chart. Numbered in red to give you a pathway to get through the woods. Start at glucose at the bottom. From there go to pyruvate by the normal metabolic pathway. Then it gets from cytosol into mitochondrial matrix. Then goes to oxaloacetate to acetyl coA, and here it can go into the TCA cycle, but often times if there is an excess it goes to citrate and citrate is transported back into the cytosol. And then from there goes on to the synthesis of fatty acids
3. Notice that fatty acids can be broken down and re-formed into fatty acids again.
4. Primary means that this occurs is from glucose for the synthesis of fatty acids.

1. Part II: Formation of Malonyl-CoA [S8]
2. 3 carbon fatty acid from.
3. In synthesizing fatty acids you really need acetyl-coA and a 3 C equivalent called malonyl-CoA. To prime this process of making fatty acids you have to make malonyl-CoA on an enzyme called acetyl coA carboxylase. Two active sites on this ezyme: a biotin carboxylase, and a carboxyltransferase, and also Biotin carboxyl carrier protein.
4. Unique mechanism. Have swinging molecule of biotin, which goes back and forth like a clock. Will pick up a carbon dioxide which happens to be bound to a phosphate group on the carboxylase enzyme. It’s going to swing captured CO2 so it binds to acetyl CoA. The phosphate comes from ATP and ATP powers this whole reaction.

1. Notes on Formation [S9]
2. Read from slide.
3. Powered by the hydrolysis of ATP.
4. This enzyme also happens to be the rate-limiting enzyme of fatty acid synthesis. This is the enzyme that makes it go.
5. Allosteric enzyme. Has many sites for activation and inhibition. Have to have substances that will speed up the reaction and slow it down. Insulin promotes this reaction and epinephrine and glucagon inhibit.
6. The relative supply of energy which is acetyl coA activates it while Pulmatate (which is what we’re trying to make) will slow it down.
7. If you have lots of Pulmatate, it communicates to the cell that “we don’t need anymore.”
8. The activity is controlled by the sum of all of the activators and inhibitors.

1. Part III: General Scheme of De NovoSynthesis of Fatty Acids [S10]
2. We need the precursors acetyl CoA and malonyl CoA. Notice that we need 7 molecules of malonyl CoA compared to only one of the acetyl CoA. These will be bound to acyl carrier protein. And they’re going to go on this “Christmas tree” ball of an enzyme called Fatty acid synthase, which is a complex of six different enzymes in multiple copies. And out of the bottom will come palmitoyl CoA or palmetic acid, which is the final product.
3. All the reactions starting with acetyl Co A are in the cytoplasm. Because of this we have to be careful of the “solubility problem.” Way to solveis to put all the enzymes together in a complex so the intermediates only have a short distance to travel to make the next product in this reaction pathway.

1. Part IV Fatty Acid Synthesis Structure [S11]
2. [pointing at picture] The little red stars are the active sites for the enzyme. The acyl carrier protein is going to act as a carrier for the malonyl and the acetyl CoA, and it is going to move from one active site to the next. Like hummingbird going from one flower to the next. In this case the acyl carrier protein is delivering the incompletely formed malonyl-coA to be processed to one enzyme site to the next and the next.
3. Notice he’s labeled the acyl carrier protein and the thioesterase on the picture, but these locations are not known with certainty.
4. Thioesterase is the final enzyme in this process.
5. You can think of this whole process as this back and forth motion going from one active site to the next processing the malonyl CoA into the next product in the reaction.

1. Priming the Pump- the Acyl Carrier Protein Domain [S12]
2. This acyl carrier protein binds to both the acetyl and the malonyl groups. Looking at acetyl coA here [pointing at picture] being transferred over to acyl carrier protein. Notice that they have this pentethenyl group (uncommon) so it’s very easy for it to leave by means of an interesting enzyme known as malonyl coA-acetyl coA- ACP transacylase (MAT). MAT is the first enzyme involved in this complex to get the malonyl-CoA into the active area of the enzyme.

1. The First Cycle of Synthesis [S13]
2. There are many cycles of synthesis; every cycle adds a two carbon unit to the growing fatty acid. What we are looking at here is the first cycle. Each cycle will be a repeat of everything that went before it. Only 5 enzymes shown here.
3. There is a 6th reaction that releases everything at the end of the reaction. Notice the kind of things that are going on [refer to picture]: Acyl ACP and Malonyl ACP get together with MAT in a Condensation reaction (kind of synthesis reaction) going to kick off some CO2 and give you acetoacetyl ACP. Now we have a 4 carbon unit.
4. Next it goes on as a reduction reaction and a dehydration reaction and then another reduction reaction giving you Butylryl ACP, the final 4 carbon unit. Will repeat until get a 16 carbon unit. Each one of these gets recycled.
5. You do have to know how these reactions occur. What they start with and the product of each reaction. He will ask you about this. Don’t have to know the enzymes, but need to know what is happening to the molecule. Know the big picture and the intermediates (will be on the board exams).

1. Subsequent Cycles and Release[S14]
2. Overall sequence of what is going on. Enzyme complex—gray color.
3. At the end get palmitic acid which is going to be released by the final enzyme.

1. Comparison of Fatty Acid basic metabolic Mechanisms[S16]
2. A good comparison between fatty acid degradation and synthesis. You can see how similar and somewhat dissimilar they are. For example B-oxidation takes place in the mitochondrial matrix and Fatty acid degradation takes place in the cytosol. Study on your own.

1. Fatty Acid Synthesis [S17]
2. Diet common to developed nations don’t really have need but it still occurs in two ways: de novo and carbon lengthening.
3. Carbon lengthening--Additional processing of palmitic acid (C-16 fatty acid) occurs as well as the formation of some double bonds. Once palmitic acid is formed we can do some more with it.

1. Chain Lengthening and double-bond formation [S18]
2. Read from slide.
3. Lengthening usually limited to 2 carbons so you get C-16 and C-18. No C-17 because odd number fatty acids are uncommon.
4. Some single unsaturated fatty acids can also be formed: palmitoleic acid, steric acid, and oleic acid. These three commonly occur in their ester forms in fat cells.
5. He won’t ask you about the bottom portion of this slide (FA elongases)

1. Getting Longer Chain [S19]
2. Read slide.
3. PUFA’s=polyunsaturated fatty acid. The presence and use of PUFAs represent a disconnect for higher life forms. They can’t make these. Must have starting material that comes from the diet.
4. To get to these longer chains you have to have either alpha linoleic or alpha linolenate as starting fatty acids. Essential because we can’t make them. The linoleic and linolenate must be used to make fatty acids like arachidonate fatty acid which is 20 carbons longs and has 4 double bonds. These are examples of omega 6 FA’s. The alpha linoleic is an example of an omega 3 FA. We can get omega 3 FA’s from nuts or fish.

1. PUFA’s and products [S20]
2. Need to know a couple things about the PUFAs, what are some things formed? Ex. Arachidonic acid.
3. Arachidonate actually carried as a phospholipid in cell membranes. Is released by an enzyme (green) called phospholipase A2 from the membrane.
4. NEED TO KNOW ABOUT PHOSPHOLIPASE A2—what it does.PHOSPHOLIPASE A2 BREAKS ARACHIDONATE AWAY FROM PM PHOSPHOLIPIDS
5. Arachidonate acid goes on to form a lot of interesting products that are called prosteglandins: leukotrienes and similar kinds of short term influential hormones. Example of fats being turned into hormones.
6. A lot of these products can cause inflammation. Inhibitors for phospohlipase alpha-2 for example and prostaglandin synthesis can cause decrease in inflammation.
7. NSAIDs(Non-steroidal anti-inflammatory drugs) and corticosteroids can lessen inflammation.. So each one of these drugs, class referred to as eicosinoids, serve as short acting local hormones. Aspirin is one example of a NSAID.
8. Read from slide.

1. Notes on the Pathways to eicosanoid synthesis [S21]
2. Read from slide.

1. Another PUFA [S22]
2. Omega 3 fatty acid. He prefers the name cervonic acid.
3. Read from slide.
4. Important thing about this enzyme: It has a very high degree of unsaturation. It has 6 double bonds and makes the fatty acids desirable to membranes that need a lot of flexibility. Flexibility allows for complex conduction processes required in nervous tissue and even in visual transduction. 22% of the proteins in the retina are made from cervonic acid.

1. Points to Note about Fatty Acid synthesis [S23]

1. Read from slide. Fatty acid synthesis doesn’t seem to serve humans with the best efficiency for a couple of reasons: If we happen to take in a lot of carbs that aren’t used will make fatty acids and that occurs when glucose isn’t used to make ATP.
2. Read Slide.
3. PUFA is any fatty acid with two or more double bonds –GOOD QUESTION. Minimum carbon length of 18.

1. Synthesis of Cholesterol [S24]
2. Molecule is very important because it’s an important component of the plasma membrane structure and is a precursor for lipid digestion in the form of bile salts. Lipid soluble vitamins like Vitamin D. and steroid hormones. Couldn’t live without this molecule. Read from slide.

1. We Obtain Cholesterol from Two Sources: Diet and Synthesis [S25]
2. It’s the synthetic route that can cause problems. Dietary cholesterol can be controlled. Don’t have control over cholesterol synthesis.

1. Sites of Origin of Synthesis [S26]
2. Starts with acetyl CoA. Goes through a stage called the commitment stage. First product is mevalonate acid. Then goes through a building block formation to give you activated isoprene. Isoprene could be dangerous but is always bound to something. Individual isoprene units are assembled by a condensation process to give you this intermediate (points to picture). If you separate each of the dotted lines you will have isoprene.
3. Intermediate called squalene (Latin for shark—where it was first isolated). Finally a cyclization process goes on and we get cholesterol itself.
4. This diagram is way over simplified. Know general.

1. Why should biosynthesis of cholesterol be studied? [S27]
2. We need to know because the control of cholesterol synthesis is important.
3. HMG-CoA Reductase is important. Intermediate is mevolante. Studies researched inhibitors for this enzyme.
4. Found that a group of compounds called statins could inhibit.

1. Steps in Synthesis of Cholesterol [S28]
2. Read slide

1. Inhibitors for HMG-CoA Reductase [S29]
2. Read slide

1. Example of an Inhibitor--Lipitor [S30]
2. This portion (yellow block) has a very similar structure to hydroxyl-methyl intermediate shown here. What happens is lipitor binds at active site and the active site in this location is almost the same as the intermediate (blue).
3. Magenta is NADP (coenzyme). Co-enzyme in green. Hydroxy-methyl glutamate is in blue.
4. Building block and Condensation Stages [S31]
5. Read slide
6. LDL Receptor [S32]
7. This is important. LDL receptor defect can prevent cholesterol from being taken up into the cells. Two places defect can occur:
8. sequence mistakes in the binding domain—fail to release cholesterol
9. problem with c-terminal domain—failure in pit formation to invaginate
10. also possible that receptor protein delivery mechanism from Golgi to plasma membrane is deficient
11. Summary [S33-35]
12. Read on your own. Good study guide.