Lipids - Theory
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Define a lipid
An organic substance (carbon containing) which is poorly soluble in water, but which is soluble in organic solvents or oils
Where do we find lipids? (3)
Found in cell membranes Stored in adipocytes - distributed through the body Fat sores
What are two major fat stores in humans
Subcutaneous Internal (visceral/retroperitoneal)
What are the two types of internal fat
Visceral Retroperitoneal
Comment on the recommended ratio between internal and external lipid
Young healthy person should have 2 litres of internal fat out of a total 20 litres
Realistically how much internal fat do women have?
3 litres of internal fat for a total of 37 litres
Realistically how much internal fat do men have
5 litres out of 35 litres
Realistically how much internal fat do men have
5 litres out of 35 litres
List the four types of lipids found in plasma
Steroids Triacylglycerols Fatty acids Bioactive lipids
List the three types of steroid lipids found in circulation
Cholesterol Estrogen Testosterone
Give five examples of fatty acids found in circulation
Palmitate Oleata Linoleate Linolenate Docosahaeneoate
List five bioactive lipids found in circulation
Prostaglandins Eicosanoids Plasmalogens Isoprostanes Leukotrienes
What are triacylglycerols composed of?
Three acyl chains joined to one glycerol molecule by ester linkages
Write about cholesterol
A 27 carbon sterol molecule Rigid nucleus and flexible 8 carbon side chain
Describe the absorption of lipids (4)
Lipids enter the enterocyte at the lumenal side Lipids are processed within the enterocyte and loaded onto transport particles called chylomicrons These are secreted from the basolateral side of enterocyte into the lymph These pass through the lymph system and enter the systemic circulation at the thoracic duct
What can happen to body fluids after ingestion of a high fat meal? (2)
They can become opaque Lipemic serum
Lipids are hydrophobic and cannot dissolve in the blood plasma, we need some way to get them through the blood, how do we do this?
Through the use of lipoproteins These act as taxi caps - transporters to carry lipids through circulation
What are lipoproteins
Complexes of protein and lipids
What are lipoproteins composed of (3)
Cargo lipids - sequestered in the hydrophobic core Amphiphatic phospholipids - these form a layer around the lipid cargo and allow the particle to dissolve in circulation Apolipoproteins - these define the properties of the lipoprotein
Classify Lipoproteins (5)
Chylomicron and chylomicron remnant (1000nm/largest) Very Low Density Lipoprotein Intermediate Density Lipoprotein Low Density Lipoprotein High Density Lipoprotein (10nm)
What is considered the good type of lipoprotein
HDL
Why do lipoproteins exist (2)
They act as a biochemical mechanism for distribution of hydrophobic cargo in an aqueous environment Transport of cholesterol, TAGs, Fat-soluble vitamins, xenobiotics, phytochemicals, pharmaceuticals
What are the two systems of lipoprotein metabolism?
Distribution of exogenous lipids Distrubition of endogenous lipids
What is the common structure in all lipoproteins?
Outer monolayer of amphiphatic lipids Inner cargo of highly hydrophobic lipids e.g. TAGs Integral and peripheral proteins (apolipoproteins)