TG & Phospholipid Synthesis Flashcards
What is the form of fat we consume from diet?
Triglycerides
Another name for triglycerides
Triacylglycerols
Fat stored in body is in the form of ?
Triglycerides
Any excess carbons you take in from carbohydrates and/or proteins is used?
For synthesizing FA —> which go onto being incorporated into triglycerides and/or phospholipids
Why store more energy as triglycerides as opposed to glycogen?
Glycogen is water soluble and would cause excess weight leading to problems with mobility. TG are hydrophobic.
Also TG are most reduced form of carbon in nature
Energy stored in fat vs. carbohydrates
9 kcal/gram for fat
4 kcal/gram for carbohydrate
Other advantages/functions of TG (3)
- Insulation (efficient packing)
- Energy without nitrogen (as in the case of using proteins)
- Metabolic water is released when oxidize fatty acids
Structure of triglycerides
- Glycerol backbone + 3 fatty acid chains
- Ester bonds join hydroxyl groups from glycerol and carboxylic acid from fatty acids
- Makes molecule extremely hydrophobic
White adipose tissue cell
- Huge lipid droplet
- Very little cytoplasmic/organelle content
Where does synthesis of TG occur?
Liver
Glycerol-3-phosphate purpose
Need to be the backbone of triglycerides and phospholipids
Source of glycerol-3-phosphate
In liver: through glycolysis & glycerol kinase
In adipose tissue: only through glycolysis
Glycolysis as a source of glycerol-3-phosphate
Occurs in liver and adipose tissue
Glucose —> DHAP + NADH —> Glycerol-3-phosphate + NAD+
Another reason why glycolysis increases in fed state.
Other way liver can make glycerol-3-phosphate
Using the enzyme glycerol kinase
Takes glycerol from dietary triglycerides that were broken down during digestion
Glycerol + ATP —> Glycerol-3-phosphate + ADP
Esterification
Occurs in?
What happens?
- Occurs in endoplasmic reticulum
- Fatty acids are added to a glycerol backbone
Process of Esterification
Add fatty acyl-CoA to glycerol-3-phosphate —> make ester bond with the hydroxyl group on C-1 forming lysophosphatidate —> then attach another fatty acid to hydroxyl group on C-2 forming phosphatidate —> use H2O in a hydrolysis reaction to remove the phosphate forming diacylglycerol (DAG) —> phosphate comes off as inorganic phosphate —> add third fatty acid to form triacylglycerol
First FA added to glycerol backbone is usually? Second FA?
First FA —> Saturated
Second FA —> Unsaturated
Difference between phospholipid and triacylglycerol synthesis
Phospholipid synthesis requires an activation step
Triglyceride synthesis has NO activation step
Common intermediate for triglyceride and phospholipid biosynthesis
How make each?
Phosphatidate
To make triglyceride —> remove P and add third fatty acid
To make phospholipid —> keep P and add polar head group
Phospholipid biosynthesis requires ____________
Activation step with CTP
Can be done in 2 ways:
- Activate DAG
- Activate polar head group
Activation of diacylglycerol (DAG)
Phosphatidate + CTP —> CDP-diacylglycerol + PPi
- Keep original phosphate from phosphatidate
- Add one phosphate from CTP
- Eventually, CMP from CDP-diacylglycerol will come off and polar head group comes on
Activate polar head group done before?
Done before attachment to diacylglycerol
Step 1 of activating polar head group
- Ethanolamine + ATP —> phosphorylethanolamine + ADP
Added a phosphate group
Step 2 of activating polar head group
Phosphorylethanolamine + CTP —> CDP-ethanolamine + PPi
- Keep original phosphate from phosphatidate
- Add one phosphate from CTP
- Activation step
Step 3 of activating polar head group
CDP-ethanolamine + DAG —> phosphatidylethanolamine + CMP
Dietary and newly synthesizes triglycerides are transported to ?
Adipose tissue for storage
- cannot be stored in liver
Triglycerides have to be ____________ because?
Packaged as lipoproteins
hydrophobic
Carriers of most lipids in the body
Lipoproteins
Lipoprotein structure
- Monolayer of phospholipids on the outside
- Apolipoprotein wrapped outside outside too (each particle has diff protein)
- Interior is cholesterol ester
- Surface has unesterified cholesterol in b/t phospholipid fatty acid tails
Plasma lipoproteins concerning triglycerides
- Chylomicron
2. Very Low Density Lipoprotein (VLDL)
Chylomicron
Made where?
Function?
- Made in small intestine
- Transports dietary triglycerides to adipose tissue
VLDL
Made?
Function?
- Made in liver
- Transports newly synthesized triglycerides from liver to adipose tissue
Densities of plasma lipoproteins depends on
Primarily protein and lipid composition
More protein = higher density
Chylomicron density
Lowest density
86% TG, 2% protein
What happens when VLDL leaves the liver?
VLDL enters blood (in fed state) —> as VLDL gets near either adipose tissue or muscle the lining of the blood vessel which contains enzyme lipoprotein lipase attacks TG in the VLDL particle —> release glycerol and it goes back to the liver for reuse for reesterification
Lipoprotein lipase is activated by
Insulin
What happens to fatty acids in adipose tissue?
Fatty acids are taken up, reesterified into TG, and put into storage
Use glycerol-3-phosphate that comes from glycolysis
What happens to fatty acids in skeletal muscle?
Especially during endurance exercise, FA are major source for ATP generation
Oxidize FA to CO2 + H2O
Broken down into acetyl CoA which goes directly into TCA cycle and glycolysis is bypassed completely
Insulin’s effects on adipose tissue in fed state (2)
- Stimulates transport of glucose into adipose tissue
2. Activates lipoprotein lipase
What happens when glucose is taken up by adipose tissue in the fed state in response to insulin signaling?
Goes through glycolysis —> produces DAG —> from which you can take glycerol 3-phosphate to esterify the FA coming from either chylomicron or VLDL
What happens when insulin activates lipoprotein lipase?
Lipoprotein can attack both chylomicron and VLDL to release fatty acids
What happens to chylomicron when fatty acids are released?
Get a remnant which goes back to liver
What happens to VLDL once fatty acids are released?
Since released most of the FA that were part of the TG, particle is becoming heavier —> becomes IDL —> which becomes LDL
LDL
“Circulating cholesterol”
Contributes to atherosclerosis and heart attack when deposited in arteries and regulation fails
