Metabolism 6 Flashcards
(23 cards)
What are fatty acids commonly stored in cells as?
Triacylglycerols
What are the cells that store fatty acids called?
Adipocytes
Saturated acids are typically
Solids
Unsaturated fatty acids typically liquids
3 sources of fats
- Diet
- De novo - biosynthesis in liver
- Storage depots in adipocytes
What can a lack of Bile salts cause?
Fats will pass through digestive tract undigested and unabsorbed. Will result in steatorrhea (fatty stool)
Where are biles produced?
Where are they stored?
Where are they secreted?
Produced in liver
Stored in gall bladder
Secreted into intestine
Bile salts have a hydrophobic and hydrophilic face. What does this allow them to do?
Allows them to interact with both solute and triacylglycerols
Hydrophobic face to triacylglycerols
Bile salts get Triacylglycerols into a soluble form. What does this allow?
Allows lipases to start breaking them down
Describe fat digestion and absorption.
- Pancreatic and gastric lipase results in formation of MAGS, DAGS and free fatty acids.
- These then associate with bile salts, cholesterol, lysophosphatidic acid and fat soluble vitamins to form mixed micelles.
- Micelles then absorbed by enterocytes lining the brush border of the small intestine.
- TAGs resynthesised and packaged into chylomicrons.
How can obesity be treated?
Orlistat - tetrahydrolipstatin (reduces fat absorption by 30%)
Where does B-oxidation occur (fatty acid oxidation)?
MITOCHONDRIA
Explain the process of B-oxidation.
- Fatty acids ——-> Acyl-CoA
ATP ———> AMP
This reaction occurs in the outer mitochondrial membrane
How does acyl-CoA get into the matrix?
- It is coupled with carnitine to form the carnitine shuttle. Forms acyl carnitine.
- Carnitine and acyl carnitine are moved to/from matrix via a translocase.
- Carnitine Acetyltransferase 2 then removes the acyl group from acyl carnitine and transfers it to a CoA, and carnitine is also reformed.
- Carnitine moves back across the membrane to cytoplasmic side.
Describe the B-oxidation cycle.
- Fatty acyl-CoA oxidised. FAD reduced to FADH2
- Molecule is then hydrolysed.
- Product then oxidised. NAD+ reduced to NADH
- Resultant molecules are one molecule of acetyl-CoA and acyl-CoA (2C shorter than usual)
- Acetyl-CoA kicked off by bringing in CoA, using B-ketothiolase.
- The original fatty acyl-CoA is shortened by 2C
(B-oxidation essentially removes 2C units at a time from Acyl-CoA which produces acetyl-CoA)
EACH CYCLE PRODUCES 1 NADH and 1 FADH2
Acetyl-CoA formed from B-oxidation can only enter the TCA cycle how?
If B-oxidation and carbohydrate metabolism are balanced.
BECAUSE OXALOACETATE IS NEEDED FOR ENTRY OF Acetyl-CoA INTO TCA CYCLE
What happens if fat breakdown predominates?
Acetyl-CoA forms:
- Acetoacetate
- D-3-hydroxybutyrate
- Acetone
These are all collectively called ketone bodies.
How many ATPs does one Acetyl-CoA produce?
12 ATP
Which 2 enzymes does fatty acid biosynthesis require?
- Acetyl-CoA carboxylase
2. Fatty acid Synthase (FAS)
Describe the lipogenesis process.
- Acetyl CoA ———> Malonyl CoA
2C —————————> 3C
Enzyme: Acetyl CoA carboxylase (requires 1xATP) - Malonyl (from malonyl CoA) transferred to acyl carrier protein (ACP). Forms malonyl-ACP.
- Acetyl from CoA species transferred to Acyl Carrier Protein (ACP) to form Acetyl-ACP
- Malonyl-ACP and acetyl-ACP condense to form 4C Acetoacyl-ACP (CO2 generated)
- Acetoacyl-ACP reduced to form D3-hydroxylacyl-ACP.
- D3-hydroxylacyl-ACP dehydrated to form Crotonyl-ACP.
- Crotonyl-ACP reduced to Butyryl-ACP (via enoyl-ACP reductase)
- Steps 4-7 repeat to give 16C palmitoyl-ACP, which is then hydrolysed to give Palmitoyl and ACP.
What enzyme is required for desaturation of fatty acids?
Fatty acyl-CoA desaturases
What are the 5 types of fatty acid dehydrogenase enzymes?
- 3-hydroxy
- Short
- Medium
- Long
- Very long
What happens after malonyl-ACP and acetyl-ACP join?
The resultant molecule undergoes reduction and dehydration through the following enzymes:
- Ketoreductase
- Dehydratase
- Enol Reductase
Which reducing agent does fatty acid synthesis use?
NADPH
