Lipid Metabolism 1
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What enzyme hydrolyzes triacylglycerids to form a free fatty acid? Is this enzyme activated by phosphorylation or dephosphorylation
Lipase: TAG --> DAG + FFA (repeat until resulting in glycerol + FFA).
Activated by phosphorylation from PKA
How do high levels of free fatty acids affect the fatty acid mobalization?
High levels of FFA inhibit the cyclase and the lipase.
How do FFA dissolve in the blood?
non covalent interaction with serum albumin
What reactions do CAT 1 and CAT 2 catalyze? Where are these enzymes located
CAT 1 (outer membrane): fatty acyl coA+ carnatine --> fatty acyl carnitine + coASH
CAT 2 (inner membrane) fatty acyl carnitine + co ash --> fatty acyl co A + carnitine
Locations of fatty acid activation for very long chain, long chain, medium chain, and short chain fatty acids
- >24C very long chain = peroxisomes
- 12-22C long chain = cytosol
- 6-10C medium chain = mitochondria
- <6 short chain = mitochondria
How do short and medium chain fatty acids get into the mitochondria?
Diffuse through lipid bilayer--not translocase required.
These are activated in the mitochondria via fatty acyl coA synthetase.
Process of liberating an Acetyl coA from fatty acetyl coA
1. oxidize between beta and alpha carbon to form double bond in trans formation (FAD -> FADH2)
2. Add water across double bond
3. Reduce (dehydrogenate) to creat a carbonyl on beta carbon (FAD -> FADH)
4. Cleave off acetyl coA by thiolytic reaction, resulting in a fatty acyl co A that has been reduced by 2 carbons + acetyl coA.
ATP per cleavage = 5
Enzymes of B oxidation
- 1. oxidize w/ acetyl co A dehydrogenase
- 2. hydrate with hydratase
- 3. oxidize with L beta hydroxyacyl co A dehydrogenase
- 4. thiolytic cleavage (release acetyl co A) with thiolase
How many ATP would you get from B oxidation of a 16C fatty acid (palmitate)
7 cleavages X 5 ATP = 35 ATP
8 acetyl co A for CAC X 12 ATP per round = 96 ATP
In a odd number carbon beta oxidation, what is the name of the last molecule?
propyl co A
How many ATP equivelents are used to activate a free fatty acid to fatty acyl co A?
2 ATP equivelents.
It's a 2 step reaction where a phosphate is cleaved off in each step.
What does the enzyme 2,4 dienol co A reductase do?
Uses NADPH to reduce conjugate double bonds in poly unsaturated fatty acids during beta oxidation.
Reduces to one double bond.
Isomerase then puts bond in correct position.
What step does a unsaturated fatty acid skip in beta oxidation
Skips the "creation" of a double bound--so does not reduce FAD to FADH2.
Is there ATP production from B oxidation of very long chain fatty acids?
No--this process occurs in peroxisomes which do not have mitochondria.
Oxidation occurs until 8 carbons, and then fatty acid can be transproted to the mitochondria for further B oxidation.
Zellwegers syndrom inhibits the breakdown of what?
Very long chain fatty acids.
Zellwegers = inabillity to make peroxisomes
(also presented in section 1, w/ inability to myelinate)
Where are ketone bodies made?
Mitochondria matrix in the liver
Can the liver use ketone bodies as a source of energy?
What are ketone bodies?
Water soluble derivities of fatty acids derived from condensation of acetyl-coA's.
How are beta hydroxybuterate and acetone formed from acetoacetate?
hydroxybuterate = acetoacetate is reduced by NADH to convert carbonyl to hydroxyl group
acetone = acetoacetate is decarboxylated to form acetone. Not a source of eneryg for body, exhaled through lungs.
Why would a patient have sweet smelling breath?
From an over production of ketone bodies (specifically form acetone).
This occurs in uncontrolled type 1 diabetes..
What enzymes convert 2 acetyl co As to ketone bodies?
- 1. Thiolase
- 2. HMG CoA synthetase
- 3. HMG co A lyase
Result = acetoacetate
Step 1 of ketone body synthesis
Thiolase 2 acetyl co A together, eliminate coash
Step 2 of ketone body synthesis
Add Acetyl CoA and eliminate coASH to form HMG coA
Step 3 of ketone body formation
Get rid of another coASH to form acetoacetate
Can fatty acids cross the blood brain barrier? Can ketone bodies?
No, fatty acids can't cross BBB. Yes, ketone bodies can cross BBB
Why are the productio of ketone bodies "glucose sparing"?
Ketone bodies can cross the BBB. This means during fasting/starving, liver has to do less gluconeogenisis to keep brain "fed".
Related to ketone bodies, what is one way NAD+ is regenerated in the liver?
Through conversion of acetoacetate to beta hydroxybutyrate.
Does the brain get a larger benefit from using acetoacetate or from using beta hydroxybuterate?
Betahydroxybuterate becase to convert this to glucose in the brain, the first step is do oxidize the hydroxyl group , resulting in generation of 1NADH = 3ATP in ETC.
How do you synthesize acetyl co A from b-hydroxybutyrate?
B hydroxybuterate is oxidzed for form NADH and acetoacetate.
acetoacetate accepts acetyl coA from succinyl co A (from CAC).
thiolase leaves teh 2 acetyl groups apart from each other to generate 2 acetyl co A molecules.
When production of ketone bodies is high, but not change in pH.
Example: Adkins diet, startving
When the production of ketone bodies is high AND there is a change in blood pH
examples: uncontrolled type 1 diabetes
How does ketone body production spare amino acids?
By providing a source of energy to the brain and other tissues that takes some stress off gluconeogenisis.
Gluconeogenisis requires amino acids or pyruvate.
Are fatty acids gluconeogenic?
FFA can be broken down to acetyl co A, which cannot be converted back to pyruvate in PDH (irreversable reaction).
Exception: The last cleavage of a FFA may result in a 3 carbon propionyl co A
What vitamin does propionyl co A carboxylase need, and what reaction does it carry out?
Propionyl co A + ATP + "CO2" --> methylmalonyl co A + ADP + P1
Next part of reaction is a mutase containing vitamin b12=biotin
end result is succinyl co A
(similiar to pyruvate carboxylase)
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