Chapter 15: Lipid Structure and Function Flashcards
What are many lipids made from?
fatty acids
What are some of the roles that lipids serve in the body?
- energy storage
- cell membranes
- endocrine signaling
Describe fatty acids
- consist of a carboxylic acid and a hydrocarbon tail 4-36 C long
- the most abundant fatty acids are unbranched chains of 12-20 carbons and are even numbered
- can covalently bond to proteins to tether proteins to biological membranes
Compare saturated to unsaturated fats
Saturated fats contain fully reduced methylene groups (maxed out on H) and are typically solid at room temp
Unsaturated fatty acids contain at least one double bond (makes a kinked shape). Monounsaturated have one double bond while polyunsaturated FA contain multiple double bonds. They are typically liquid at room temp
Why are saturated FAs solid and unsaturated FAs liquid at room temp?
Saturated FAs have regular packing and more extensive intermolecular interactions.
Unsaturated FAs have looser packing and fewer intermolecular interactions due to the branching in their tails
What is hydrogenation?
The commercial process of using H2 gas to reduce C to C double bonds.
This process raises the melting point of lipid mixtures and converts unsaturated fatty acids to saturated fatty acids.
It produces a semisolid mixture.
What are trans fats?
Fatty acids created by partial hydrogenation. They are associated with high rates of cardiovascular disease. They were ruled unsafe by the FDA in 2013, and have been found to increase levels of LDL while decreasing levels of HDL
What are waxes?
Molecules classified as lipids that contain long chain alcohols linked to long-chain fatty acids.
They have high melting points.
How much energy is released from the full oxidation of a triglyceride?
~ 38 kJ/g
How are dietary TGs packaged?
as chylomicrons
How are TGs synthesized in the liver packaged?
as VLDL particles (lipoprotein)
How are TGs released from adipose packaged?
as albumin
Describe the process of TG packaging to VLDLs in the liver.
- Triacylglycerol biosynthesis uses acetyl-CoA and proteins to generate palmitic acid in the cytosol
- palmitic acid is converted to triacylglycerols and exported as VLDL particles
- liver VLDL assembled in endoplasmic reticulum and Golgi body, then repackaged and exported to circulatory system
- liver cells synthesize cholesterol from acetyl-CoA, which is packaged into VLDL particles as cholesterol esters
- VLDL particles deliver triacylglycerols and cholesterol esters to tissues throughout the body
What are lipid droplets?
storage vehicles for newly formed triacylglycerols from adipocytes
they are surrounded by a phospholipid monolayer containing perilpin
How are triacylglycerols metabolized?
They are cleaved by lipases to generate free fatty acids and glycerol
Fatty acids can pass through the membrane on the luminal side of intestinal epithelial cells
How is the glucagon signaling pathway involved with fatty acid metabolism?
Glucagon signaling initiates a cascade resulting in fatty acid release to the bloodstream