BIOCHEMISTRY C 785 Lipids Exam With Correct Answers. 2020

Which diet listed below would result in the production of ketone bodies in a healthy individual? A diet rich in protein and very low in fat A diet rich in carbohydrates and very low in fat A diet rich in carbohydrate ...

Which diet listed below would result in the production of ketone bodies in a healthy individual? A diet rich in protein and very low in fat A diet rich in carbohydrates and very low in fat A diet rich in carbohydrates and very low in protein A diet rich in fats and very low in carbohydrates Correct! Many of our cell- and tissue-types cannot use fatty acids as a fuel source for making ATP because they lack the capacity to carry out betaoxidation of fatty acids.When our only (or major) source of energy is fatty acids, the liver will do the job of breaking them down into acetyl CoA for those cells that cannot do it for themselves. However, owing to differences between the chemistry of the blood versus the chemistry of the insides of our cells, we cannot ship acetyl CoA through the bloodstream. Therefore, the liver will assemble the excess acetyl CoA it produces (from beta-oxidation of fatty acids) into the ketone bodies, acetoacetate and 3-hydroxybutyrate. You can think of ketone bodies as transport forms of acetyl units that can travel through the bloodstream and be taken up by those cells that cannot break down fatty acids. Those cells will convert the ketone bodies back to acetyl CoA and use that to keep their citric acid cycles going so they can keep making ATP and stay alive. This, after all, is the whole point of this exercise - to enable us to survive when our only energy source is fatty acids. Question 2 of 14 What stimulates beta-oxidation of fatty acids? The insulin signal Low blood lipid levels High blood glucose concentrations The glucagon signal Correct! Glucagon is the hormone that signals the hungry state. It tells us that our blood sugar level is too low and that we are fasting or starving and need energy. Thus, glucagon signaling switches cells (especially liver cells) to a program of releasing stored energy. It stimulates the breakdown of our storage molecules (glycogen, triglycerides, and fatty acids.) Question 3 of 14 If a person were eating an absolutely fat-free diet, which vitamins would he or she not get enough of? Vitamins A, B, C, and D Vitamins A, D, E, and K Vitamins A, C, D, and K Vitamins A, C, E, and K Correct! It is important to recall that there are just four fat-soluble vitamins. All the other vitamins that we need in our diet are water-soluble molecules. The fat-soluble vitamins are A, D, E, and K. If we consume no fats in our diet, we will have no source for these vitamins, since they come in along with the fat we consume. Question 4 of 14 What is a function of this molecule? Structure of a sterol molecule ©WGU It is a hormone. It is used to make nucleic acids. It is used to store energy. It is used to maintain membrane fluidity. Correct! In the membranes of our cells, cholesterol acts in a manner similar to antifreeze in our cars’ radiators. If we add antifreeze to our coolant, the coolant will freeze at a lower temperature and boil at a higher temperature than it otherwise would, all by itself. That is to say, antifreeze EXPANDS the range over which the coolant stays liquid. Cholesterol has the same effect on our cell membranes, expanding the range over which they remain fluid. The presence of cholesterol in our membranes means that they freeze at lower temperatures and melt at higher temperatures than they would without cholesterol. In fact, this function is so crucial that if we did not have any cholesterol, we would die. Luckily, we chordates (~vertebrates) can make all the cholesterol we need so we never need to eat any. Question 5 of 14 Which class of lipid is shown below? Lipid structure with three carbon-hydrogen chains linked to a polar group ©WGU Eicosanoid Cholesterol Triglyceride Phospholipid Correct! The correct answer is ‘triglyceride.’ The key to recognizing a triglyceride is to remember that a triglyceride has three (3) fatty tails attached to a backbone of glycerol. Those three fatty tails are what the “tri” in triglyceride refers to. The “glyceride”, obviously, refers to glycerol. In this course, the only molecules we encounter that have three fatty tails are the triglycerides. Question 6 of 14 If a fish raised in cold water were moved to much warmer water, how would it alter its membrane phospholipids? Membrane phospholipids would include the same fatty acids under either condition. Membrane phospholipids would include more shorter-chain, unsaturated fatty acids. Membrane phospholipids would include more longer-chain, saturated fatty acids. It would add more cholesterol to its membranes. Incorrect. The correct answer is ‘Membrane phospholipids would include more longer-chain, saturated fatty acids.’The key to this question is to understand the relationship between the physical/chemical properties of fatty acids and the fluidity of membranes. An important thing to understand about cell membranes is that they are fluid. They are neither solid nor liquid, really, but something in between, almost like a gel. This fluidity allows the things in the membrane, such as membrane proteins, cholesterol, and phospholipids to move around and this movement is essential for staying alive. If we were to suddenly move a goldfish (for example) from freezing water (0 degrees Celsius) to a summertime pond (say, 25 degrees Celsius), that would be a huge problem. This is because the membrane lipids that were appropriately fluid at 0 C will now be TOO liquid at the warmer 25 C. The same is true going the other way too. A membrane that was appropriately fluid at 25 C would suddenly ‘freeze-up’ and become too solid at 0 C. The bulk of the material that makes up our cell membranes are the fatty acids that are part of the phospholipids from which the membrane is made. We can get a good idea of how temperature will affect membrane fluidity if we remember how temperature affects fatty acid fluidity. A basic relationship you will want to remember is this: The longer a fatty acid molecule is, the higher its melting point. The more double bonds it has, the lower it’s melting point. What this means for membrane fluidity is this: When it’s warm outside, and we want our membrane not to get too “runny”, we want to make our phospholipids with more saturated, longer chain fatty acids. By contrast, when it is colder, we want to use more shorter-chain and unsaturated fatty acids in our phospholipids to keep our membrane from freezing solid. Question 7 of 14 What is the correct chemical formula of the following fatty acid? Fatty acid structure ©WGU CH3(CH2)3CH=CH(CH2)3CH=CH(CH2)3CH=CH(CH2)7COOH CH3(CH2)4CH=CH(CH2)4COOH CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH CH3CH2H=HCH2C=CCH2C=C(CH2)7COOH Correct! The given structure and formula match with 18 total carbons and three double bonds at the omega-3, omega-6, and omega-9 position. Question 8 of 14 Which molecule represents the structural formula CH3(CH2)5CH = CH(CH2)7COOH? Fatty acid structure (3)©WGU Fatty acid structure (1 )©WGU Fatty acid structure (2) ©WGU Fatty acid structure (4) ©WGU Correct! The given formula and structure match with a single double bond at the omega-7 position and 16 total carbons.