M3: Dietary Lipids L16 Flashcards
What are lipids?
Heterogeneous group of biological compounds, including fats, oils, steroids, waxes, that are relatively insoluble in water.
What are common properties of lipids?
- Relatively insoluble in water,
2. Soluble in non-polar solvents such as ether and chloroform
What are the functions of lipids?
- Energy Storage
- Important dietary components because of their high energy (It’s a chemical reserve of energy because you can generate ATP from their breakdown).
- Structural components of biomembranes
- Serve as thermal insulators in the subcutaneous tissues and around certain organs
- Signaling molecules (PI, Leukotrienes)
Ex of lipids that can serve as a signalling molecule is DAG, IP3, PIP2 - Hormone precursors
What is a micelle?
Micelles are lipid molecules that arrange themselves in a spherical form in aqueous solutions. The formation of a micelle is a response to the amphipathic nature of fatty acids, meaning that they contain both hydrophilic regions (polar head groups) as well as hydrophobic core (the long hydrophobic chain). Micelles form if the lipid concentration is high enough.
Why is the formation of lipid micelles in aqueous solutions favourable?
The ∆G of lipids with water is not favourable. The ∆G of a lipid associated with lipids is favourable. They will naturally form together. It is a more stable conformation.
What is a lipid bilayer?
Lipids, depending on their physical properties, will form a bilayer (instead of micelles for example). Ex: phospholipids
What is the difference between a vesicle and a micelle?
The difference between a vesicle and a Micelle is that vesicles have a hydrophilic core whereas micelles have a hydrophobic core.
Where are lipids found in the cell?
Lipids are found everywhere in the cell:
- Membranes (double or single layer)
- Fatty acids found in the mitochondria for Beta-oxidation
- Fatty acids found in cytosol due to fatty acid biosynthesis
- Biosynthesis of phospholipids and neutral lipids in the ER.
- In lipid storage droplets
What are the clinical consequences of Dyslipidemias?
- Hyperlipidemic: too many lipids in blood. This could happen to you for a short period of time after having a fatty meal. You should be able to go back to normal through clearance of the lipids by uptake of lipids into adipose tissue and/or in the liver.
- Accumulation of lipids in the joints or lower limbs
- Atherosclerotic cardiovascular disease can be due to accumulation of lipids in the arteries.
- Deposition of lipids under the skin.
Describe how Atherosclerosis can manifest.
Too much LDL or atherogenic lipoproteins (promotes the formation of fatty deposits in the arteries) accumulate under the intima of your arteries. Then macrophages come in, they try to solve the problem and get overwhelmed by too many lipids so they die and start forming a necrotic core. Then your blood vessel will try to repair on top of this which will build a necrotic core where you have an accumulation of lipids and dead cells.
In the heart: Eventually this thickening of the artery happens. If it happens in the coronary arteries, your heart muscle will lack oxygen and cells will start dying. At some point there will be de-synchronized pulses in your heart and it will stop.
In the brain: If atherosclerosis happens in the brain, the lack of oxygen can cause a stroke. The tissues would have to switch from aerobic glycolysis to anaerobic glycolysis which could last for a little bit but eventually the tissue will die.
What are the types of dietary lipids? Give examples for each.
- Purified lipids. Ex: oils and butter
2. Cellular lipids. Ex: Meats
What are purified lipids?
Fatty acids organized under the form of triglycerides. Triacylglycerol is a neutral lipid therefore, it does not mix with water. Ex: oil in water
What are cellular lipids?
- Cells can accumulate lipids in the form of Lipid droplets. These are composed of Triacylglycerol and cholesteryl esters which are neutral lipids.
- Cells can accumulate lipids in the form of membrane lipids. These are composed of Phospholipids, Sphingolipids, Glycolipids, and Cholesterol which are all amphipathic.
Describe a lipids journey from ingestion to absorption by liver.
- Dietary fat and cholesterol are ingested.
- Lipids get absorbed in the intestine and get re-secreted under the form of chylomicrons (lipoproteins).
- The chylomicrons will travel in the blood stream and associate with certain enzymes (ex: lipoprotein lipase [LPL]). They will become more mature by getting rid of some fatty acids that will be taken up by adipose tissues and muscle. They will then become chylomicron remnants.
- Chylomicron remnants taken up by liver and cleared out of the circulation. This is how you get rid of dietary lipids…by taking them up into the liver.
What are chylomicrons?
Chylomicrons have a mono layer of phospholipids and cholesterol at the surface. In the middle there are neutral lipids that are trying to avoid water (cholesterylester [CE] and triacylglycerol [TG]).
