Biochem Test 5
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Why do fats serve as a good source of energy storage?
- 1. Energy density is high.
- 2. They are insoluble so they don't impact osmolality.
- 3. They are hydrophobic, so they won't suck up water like glycogen will.
For the cell, what are 3 sources of fat?
- 1. Ingested fats
- 2. Stored fats
- 3. Produced fats, this occurs in the liver.
Describe bile salts:
Amphipathic cholesterol derivitives that help maximize the digestible surface area of triacylglycerols.
What do Lipases do?
Lipases cleave triacylglycerols into glycerol and 3 fatty acids.
What can be identified?
- a. Bile Salts
- b. Pancreatic Lipase
- c. Tryacylglycerol
Describe the caloric breakdown for a triacylglycerol.
- Glycerol ~ 5% total calories.
- 3 fatty acids ~ 95% total calories.
What happens to glycerol after it has been cleaved from a TAG by lipase?
- It is phophorylated and dehydrogenated into GAP in steps 5/6 of glycolysis.
- It goes on to produce 2 ATP and 1 Pyruvate.
Describe a Chylomicron:
Cholesterol, Apolipoprotieins, and phospholipids forma shell around triacylglycerols and cholesteryl esters.
After being broken down by lipases what happens to all the products (MAGs, DAGs, FAs, and glycerol)?
They are absorbed by the intestinal mucosa, and it is there that they are assembled into chylomicrons.
What are steps 1-2 in The removal of Fat from an adipocyte?
- 1. Hormone (Glucogon, Epinephrine) binds to receptor, active g-protine, Activates Adenylyl Cyclase.
- 2. Active AC pumps out cAMP, which activates protein Kinase A (PKA)
What are steps 3-4 in the removal of fat from adipocytes.
- 3,4. PKA phosphorylates A. Hormone Sensitive Lipase (HSL). B. Perilipin membrane border.
- The phosphorylated perilipin is destabilized, and HSL can move from out to in and begin breaking down the TAG lipid droplet.
What are steps 5-6 in the removal of fat from an adipocyte?
- 5. TAG is metablolized by P(HSL) and is moves to the cytosol as individual Fatty acids.
- 6. The FA's are moved to the blood stream where they are picked up and transported by Serum Albumin
What are steps 7-8 in the removal of fat from an adipocyte?
- 7. At a myocyte Serum Albumin releases the FA, which is brought into the cell by a FA transporter.
- 8. It then undergoes B-oxidation, TCA, and respritory chain to produce ATP and CO2
What happens to FAs once they enter the cytosol of the target cell?
In the cytosol they are converted to fatty acyl-CoA
Describe the action of the first enzyme when FA is converted into fatty acyl-CoA:
- The Carboxylate head of the Fatty acid is phosphorylated by ATP at P1 not P3 as usual. The resulting PP is immediately reduced into inorganic phosphate.
- This is done by fatty acyl-CoA synthetase.
Describe the action of the 2nd enzyme when FA is converted into fatty acyl-CoA:
- The Thiol group of CoA attacks the carbon. The e- jump up the C=O and then back down. Because of previous phosphorylation, the O-P is now strong leaving group.
- This is also done by fatty acyl-CoA synthetase
Where does FAO occur?
In the mitochondrial matrix
What is carnitine, and what does it do?
- Carnitine is the transporter "handle" that replaces S-CoA so that the FA can be transported past the 2 mitochondrial membranes into the mitochondrial matrix.
- It is pumped back out of the mitochondria after it is released from the FA.
What are the names for the 2 enzymes that participate in Carnitine mediated transport into the mitochondrial matrix?
- Carnitine acyltransferase 1 & 2.
- You should note that the Data suggests a tetrahedral intermediate.
Identify the alpha and beta positions:
What is generated by each cycle of FAO?
- 1 NADH = 2.5 ATP
- 1 FADH2 = 1.5 ATP
- 1 Acetyl CoA
What is the 1st Enzyme in FAO and what does it do?
What is the 2nd Enzyme in FAO and what does it do?
- Enoyl-CoA Hydratase
- Addition of water accross double bond.
What is the 3rd Enzyme in FAO and what does it do?
- Beta-Hydroxyacyl-CoA Dehydrogenase
- Forms the trans configuration
What is the 4th enzyme in FAO and what does it do?
- Acyl-CoA Acetyltransferase.
- Pops up, down, and off x2
- Cuts between Alpha and Beta and preps for repeat of 1-4.
Be able to calculate the stoicheometry of a long chain fatty acid.
What will the enzymes do to an unsaturated fatty acid when the double bond is not idealy placed?
- The enzymes pause FAO until the double bond is isomerized to the alpha-beta (2,3) trans form.
- Then it will procede.
- This is the principle for both monounsaturated and polyunsaturated fatty acids.
What happens to odd numbered fatty acids as they undergo beta-oxidation?
- They procede like normal until the final propionyl-CoA (3C-SCoA) is reached.
What is the similarity between the mitochondrial inner membrane and the thilakoid space?
The enzymes required for the actions are contained inside the membranes.
Describe the key features of the chlorophylls a and b.
- They are pigments.
- They have long hydrocarbon tails, so they are integrated into the membrane.
- They are constructed similar to heme, but with Mg in the center instead of Fe.
What wavelengths do chlorophylls a and b absorb?
Describe Excitons incorporating HOMO's and LUMO's.
- An electron pair starts off in the HOMO. the EM radiation enters and and kicks 1 electron up to the LUMO.
- The Electron that is kicked up, and the hole it left behind constitute the Exciton.
- The Electron has a negative charge, the hole has a positive charge, so the net is neutral.
How do photosystems act as light antennas?
- The array of pigments create and transfer excitons down to the center, aka reaction center.
- The photochemical reaction center converts the energy it receives from the exciton into a separation of charge. This initiates an electron flow.
Describe how a photochemical reaction center separates charge:
- An exciton arrives from an antenna molecule and excites the middle electron to it's lumo.
- The LUMO is energetically equivalent to the next energy levels HOMO, so the electron shares that position.
- The lowest energy level electron donates an electron and fills the electron hole, that the 1st electron left behind.
- This results in a Net negative charge on top and a net positive charge at the bottom.
Describe what is meant by the Z-scheme:
- Photosystem 2 kicks up an electron, and as it falls it pumps 2 H+ into the thylakoid space.
- Photosystem 1 then takes the electron back up, and as it falls, it eventually reduces NAD+ to NADH.
What is the mytochondrial analogue for Photosystem 2?
What is the mitochondrial equivilant for cytochrom b6f?
Describe the non-cyclic nature of photosynthesis:
In the absence of NADH, the Electron will continue through PS1, through FN-oxoreductase, and create the final NADH.
Describe the cyclic nature of photosynthesis:
In excess NADH, The electron pass through PS1 to FD. Then it will cycle back to cytochrome b6f complex and pump in an extra 2 H+ into the thylakoid space.
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