Video for Fats, Oils and Your Diet:
Introduction
Lipids comprise of a large group of diverse biological molecules in terms of structure and function.
1. Commonly Rich in Lipids:
1.1 Fats
- Butter, cheese, cream, whole milk
- Usually of animal origin
- Properties: greasy, slippery, soft, solid at room temperature
1.2 Oils
- Olive oil or seed oil, corn, nuts
- Usually of plant origin
- Properties: exhibit many of the properties of animal fats, usually in the form of liquid at room temperature
1.3 Cholesterol
2. Common Properties in all Lipids:
They are insoluble in water as they have high levels of hydrophobic atoms, carbon and hydrogen in their structure. They also have low level of polar (hydrophilic) atoms, such as oxygen and nitrogen.
Explanation: Structure and Functions
3.1 Triglycerides
- Most abundant: Lipids in animals and major dietary lipids ingested from animals and plants
- Also called triacylglycerol or lled triacylglycerol or triacylglyceride (TAG)
- Has two parts: a glycerol molecule whose hydroxyl groups are covalently linked through ester bonds with the carboxyl groups of three fatty acids, which may be same or different
Figure 1. Formation of triglyceride when a glycerol molecule is linked to three fatty acid molecules through ester bonds
- Fats or oils = triglycerides = glycerol and fatty acids (glycerol has ester bonds)
- Fatty acid consisted of a linear non-polar hydrocarbon chain, with an acidic polar group (carboxyl group) at the end:
– Length variable, over 100 fatty acids known to occur naturally
– Simplest lipids: building blocks for complex lipids
– Weak acids: pH 5.0 to 6.8
– Amphipathic
Figure 2. Basic structure of a fatty acid molecule
- Most common ones in biological systems have an even number, ranging from 14 to 20 carbon atoms
3.2 Saturated and Unsaturated Fatty Acids
Figure 3. Structure of a saturated Figure 4. Structure of an fat molecule unsaturated fat molecule
| Property | Saturated fats | Unsaturated fats |
| Degree of saturation | Triglycerides with only saturated fatty acid chains | Varying degrees of unsaturated fatty acid chains |
| Molecular structure | Linear | Has kinks at double bonds |
| Molecular packing | Structures allows molecules to be packed regularly and tightly | Structure makes packing of molecules irregular and tight |
| Melting point | Due to compact molecular packing, melting point is high. At room temperature, fats like butter and lard remain solid | Due to loose molecular packing, melting point is low. At room temperature, fats such as mustard oil, olive oil and other vegetable oils remain in liquid state |
| Origin | Fats of animal origin are mostly solid at room temperature due to saturated fatty acid content | Plant oils are liquid because they contain high proportions of unsaturated fatty acids
Palm oil and coconut oil are 2 exceptions because they contain mostly saturated fatty acids |
3.3 Partially Hydrogenated Fats
- Hydrogenation reduces the number of C=C bonds to C-C bonds; hydrogen is added across the double bond. A metal catalyst is required
Figure 5. Hydrogenation of an unsaturated C=C bond
- The number of double bonds in the fatty acid decreases, and it is transformed from an oil to a semi-solid fat
- The hydrogenation can be controlled to yield products with desired melting point, softness and spreadability
3.4 Cholesterol
- Lipids that do not carry the glycerol backbone, found in all animal cell membrane
- Has a hydroxyl polar head group, which can interact with the other polar head groups of the other lipids
- It has a hydrophobic tail that consists of a series of rings and this part is embedded inside the hydrophobic region of the bilayer
- Its association with the membrane lipid bilayer allows cholesterol to play an important role in the regulation of membrane fluidity
- It is also the precursor (starting material) for the synthesis of a series of steroid hormones, including testosterone and estrogens
Estrogen: 
Figure 6. Structure of estrogen
Cholesterol:
Figure 7. Structure of cholesterol
- High levels of blood cholesterol is associated with atherosclerosis
- Complicated by how the cholesterol is carried in bloodstream:
HDL: high density lipoprotein
LDL: low density lipoprotein
- LDL carry the cholesterol from intestines and liver to the rest of the body, while HDL carry excess cholesterol to liver
- The ratio of HDL:LDL is important
References
- Christopher K. Mathews, Kensal E. van Holde, Dean R. Appling and Spencer J. Anthony-Cahill. Pearson, 2012. Biochemistry, 4th Edition (International Edition).
- David L. Nelson and Michael M. Cox. W.H.Freeman & Co Ltd, 2008. Lehninger Principles of Biochemistry (5th Edition).