Lipids Flashcards
Lipids are
heterogenous organic molecules that exist in a few different forms and have several purposes
Give 3 functions of lipids
- a stored form of energy
- a structural component of cell membranes
- needed as enzyme cofactors
- used in hormones
- used for the synthesis of Vitamins A, D, E and K
- used as signalling molecules
What are the major lipid classes?
- fatty acids
- triacylglycerides
- phospholipids
What are fatty acids?
Hydrocarbon chains with a carboxylic group at one end
- can be saturated or unsaturated
- nomenclature defines which is which
What are the four types of fatty acids?
Essential fatty acids - must be obtained from plants
Good fats - high in polyunsaturated fatty acids
Bad fats - high in saturated fatty acids
Really bad fats - trans fatty acids
Give an example of an essential fatty acid
- Linoleic acids
- A-Linoleic acids
Give an example of a good fat
Plant oils e.g. sunflower oil
Give an example of a bad fat
Stearic acid
Give an example of a really bad fat
Margarine
Essential fatty acids must be obtained via
our diet, since humans cannot introduce double bonds beyond carbon nine
What are triacylglycerides?
Esters of fatty acids and glycerol - water insoluble
- coalesce into droplets in water
- major component of adipose tissue
- act as insulation and dietary fuel
What are phospholipids?
Glycerol bonded to two fatty acids and a phosphate group
- amphipathic
- form basic structure of the cell membrane
What is the main dietary lipid?
Triglycerols
Where does most digestion of triglycerols take place? Through the use of what?
Small intestine
pancreatic enzymes, emulsification by bile salts and peristalsis
Most triglycerols are digested by ___ into ___
pancreatic lipase
monoacylglycerol and two fatty acids
Cholesterol esters are broken down to
cholesterol and a fatty acid
Phospholipids are hydrolysed to
a fatty acid and lysophospholipid
Mixed micelles release their contents when they
approach the brush border
The intestinal cells repackage ___
into ___
which are released ___
TAG, fatty acids and cholesterol esters
chylomicrons
into the blood via the lymphatic system
When lipids reach the tissues, TAG is hydrolysed to ___
by ___
fatty acids and glycerol
lipoprotein lipase
The resulting free fatty acids are used for ___
or ___
energy
re-esterified into TAG for storage
Free fatty acids are transported in lipoproteins in a complex with
serum albumin
Fats are also transported in
high and low density lipoproteins
LDLs carry
cholesterol from the liver to other tissues
HDLs
pick up cholesterol from tissues and bring it back to the liver for elimination
The beta-oxidation pathway degrades ___
to form ___
fatty acids two carbons at a time
Acetyl CoA, NADH and FADH2
The beta-oxidation pathway occurs in the
mitochondrial matrix
What are the three stages of the beta-oxidation pathway?
- activation
- transport
- degradation
What happens in the activation stage of the beta-oxidation pathway?
The fatty acids are activated to form fatty acyl CoA in the cytoplasm
What happens in the transport stage of the beta-oxidation pathway?
- carnitine shuttle transfers long chain fatty acyl CoA from the cytoplasm to inside the mitochondrion
- carnitine is a non-essential amino acid
- carnitine fatty-acyl transferase is inhibited by malonyl CoA, used in fatty acid synthesis
- therefore synthesis and degradation cannot occur simultaneously
What happens in the degradation stage of the beta-oxidation pathway?
- fatty acyl CoA is dehydrogenated to form FADH2 and another intermediate
- this intermediate is then hydrated
- the resulting intermediate is dehydrogenated again to form NADH
- finally, thiolysis occurs to form Acetyl CoA that feeds into the CAC
Each beta-oxidation cycle forms
- 1 Acetyl CoA
- 1 NADH
- 1 FADH2
- Carbon species 2 carbons shorter than the original
No fatty acid is
gluconeogenic
During fasting or starvation, glucose supplies run low and so excess Acetyl CoA from fat metabolism can be made into
ketone bodies
What cells can use ketone bodies?
- cardiac muscle cells
- skeletal muscle cells
- brain cells during times of starvation
Ketogenesis occurs in the
liver
What is also produced in ketogenesis?
Acetone (but is expelled during expiration)
What are the main ketone bodies?
Acetoacetate
3-Hydroxybutarate
