Chapter 12: 12.1 Fat Metabolism Flashcards
What initiates fat breakdown/metabolism?
Epinephrine/glucagon
Fat can be used for ATP through…
Catabolism, Mobilization, and Oxidation
What is fat mobilization also known as?
β adrenergic signalling
Describe:
Steps in Fat mobilization
- Hormone binds GCPRs on adipose cells
- Signal transduction: Gα-GTP, adenylate cyclase, cAMP production, PKA activation
- Hormone sensitive lipase is activated by PKA
- TAGs converted to glycerol and 3 fatty acids
Where are how are fatty acids activated?
In the cytoplasm
* Activated through the addition of a CoA (traps them in the cell)
What is fatty acid activation performed by?
Acyl-CoA synthetase
In fatty acid activation:
Acyl-CoA moves into the ————- —— where ————– occurs
- Mitochondrial matrix
- Beta-oxidation
In fatty acid activation:
How does Acyl-CoA move into the mitochondrial matrix?
- Passes through the outer membrane through porins
- Passes through the inner membrane via carnitine shuttle
How many steps does beta oxidation occur through?
Occurs in 4 steps
Describe:
The steps of beta oxidation
- Acyl CoA dehydrogenase: Double bond formation in the fatty acid chain (FADH2 produced)
- Hydratase: Adds water across the bond, introducing a hydroxyl group
- Dehydrogenase: Converts hydroxyl group to ketone group (NADH produced)
- Thiolase: Cleaves acetyl-CoA from the fatty acid chain and leaves the fatty acyl-CoA with two less carbons
What can a 16-carbon CoA yield?
8 acetyl CoA + 7 NADH + 7 H+ + 7 FADH2
True or False:
Beta oxidation yields more ATP than glucose
True
What is the limitations of the Citric Acid Cycle?
Limited by oxaloacetate (derived from pyruvate)
What does “hitting the wall” during exercise mean?
When no more glycogen is available
* ATP production from fat is limited by oxaloacetate
How many stages does fatty acid synthesis occur in? State them
3 stages:
1. Mitochondrial acetyl-CoA gets exported to the cytoplasm
2. Acetyl-CoA carboxylase (ACC) converts acetyl-CoA to malonyl-CoA
3. Fatty Acid Synthase (FAS) converts malonyl-CoA into fatty acid chains
In fatty acid synthesis:
In the first stage:
* How is acetyl-CoA exported to the cytoplasm?
* Why?
Exported to the cytoplasm through the Citrate-Malate-Pyruvate Shuttle
* Acetyl-CoA cannot pass through the mitochondrial inner membrane
In fatty acid synthesis:
In stage 2:
* It is a ——— and ——— step
* Uses —
- Regulated, committed
- ATP
In fatty acid synthesis:
In stage 2, what are the 2 reactions that occur to convert acetyl-CoA to malonyl-CoA?
- Carboxylation of biotin with ATP
- Transfer of carboxyl group to acetyl-CoA
In fatty acid synthesis:
In stage 2, describe the regulation of ACC
- Activated by citrate
- Inhibited by phosphorylation and palmitoyl-CoA
In fatty acid synthesis:
In stage 2, what does malonyl-CoA inhibit?
Inhibits carnitine acyltransferase 1 during beta oxidation
In fatty acid synthesis:
In stage 3, describe FAS
A large dimer with 10 active sites
In fatty acid synthesis:
In stage 3, describe ACP
Acyl Carrier Protein
* Contains a phosphopantetheine group
In fatty acid synthesis:
In stage 3, list the reactions that malonyl-CoA undergoes to be converted into fatty acid chains
(5 points)
- Acetyl-CoA and malonyl-CoA bind to the ACP which condeses them to β-keto-acyl-ACP and CO2 is released
- Two redox reaction occur through β-ketoacyl reductase (KR) and β-enoyl reductase (ER)
- H2O is released by dehydratase (DH)
- Chain accepts 2 more carbons from malonyl-CoA
- Thioesterase (TE) adds an H2O to the fatty acid and releases it from the ACP
To generate a 16 carbon chain, what is required?
- 7 cycles of FAS
- 1 acetyl-CoA and 7 malonyl-CoA
- ACC requires 7 ATP and FAS uses 14 NADPH
In fatty acid synthesis:
Where does elongation of the 16 carbon chain occur?
ER
In fatty acid synthesis:
What happens in denaturation?
Desaturases introduce double bonds within the first 9 carbons
* Anything past the 9th carbons comes from diet (omega 6 and omega 3)
What do desaturases require to work?
NADPH and O2
In fatty acid synthesis:
Where does triacylglyceride formation occur?
In liver and adipose tissue
In fatty acid synthesis:
Describe triacylglyceride formation
- Phosphatidate is converted to diacylglycerol by phosphatase
- Diacylglycerol acyltransferase converts diacylglycerol to triacylglycerol
