Lipid (1): Fat, Oil, Triglyceride Structure and Function

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Fats are an important lipid in organisms and also the common organic substance in daily life. They’re water insoluble but soluble in organic solvents. Carbon, hydrogen and oxygen are three elements that make up fat where the oxygen content is low and carbon and hydrogen content is very high. Having more calories than sugar makes them ideal for energy storage.

Fats are also known as triglycerides that have one glycerol and three fatty acids. These three fatty acids may be identical or dissimilar. The hydroxyl group is located in every carbon in glycerol. The fatty acid chain has one carboxyl group in its end, and rest part is hydrocarbon chain. Ester bond formed by dehydration of hydroxyl and carboxyl groups links them together. Carbon number is almost even in nature world because they are synthesized from the two-carbon unit called acetyl CoA. These number ranges from 12-24, and 16 or 18 are most common.

Saturated and Unsaturated Fat

They’re classified into further according as whether they contain carbon-carbon double bond. If hydrocarbon chains don’t contain a double bond, or they have as many hydrogen atoms as possible, they are called saturated fat. The tightly arranged straight fatty acid give saturated fat a relatively high melting point. Hence, saturated animal fats are solid at room temperature, such as lard or butter. Some plants are also rich in these fats, such as coconut and palm.

When there are double bonds in their hydrocarbon chains or the hydrogen atoms aren’t saturated, these types of fats are called unsaturated. The bend caused by double bonds inhibits their hydrocarbon chains from packing closely. A lower melting point allows them to be liquid at room temperature, such as vegetable oils and fish fats.

Unsaturated fatty acids are divided further according to double bond quantity. Monounsaturated fatty acid that’s rich in olive, avocado, sunflower and canola oils has only one double bond. Another type is polyunsaturated fatty acids that contain multiple double bonds. The more bends make hydrocarbon tails arrange more loosely. Since our body can’t synthesize them, they must be supplemented from diet like corn, soy, safflower oil and deep-sea fish.

Fat and Health

The proportion of energy-dense carbon-hydrogen bonds is high in fats. so they release more energy when fully oxidized, a little more than twice as much energy as sugars. Saturated fats store slightly more calories than unsaturated fats. The unstable double bond of unsaturated fats can react with some strong oxidants easily. Oils are more susceptible to spoilage in air than fats. One of the most important functions is to destroy free radicals in your body. Their antioxidant properties make them a good dietary supplement that keep away high blood pressure, diabetes, heart disease and fight against aging. Peanuts, sesame seeds, salmon and tuna are all rich in these.

However, heart disease, obesity, high blood pressure, diabetes and certain cancers will knock at the door when you eat too much fat every day. WHO recommends that daily fat intake should only be 15 to 30% of total energy. For a person with a daily energy requirement of approximately 2000 kilocalories, only 300 to 600 kilocalories should come from fat or about 33 to 67 grams fat.

Frequently Asked Questions

What is the role of fats other than storing energy?

Other functions include keeping you warm, cushioning you from impact and facilitating absorption of fat-soluble vitamins.

Fat doesn’t easily transfer heat and plays an important role in keeping body temperature, especially in frigid zone. The polar bear or whale have a more than 10cm fat layer beneath their skin. These subcutaneous fats serve as quilts that wrap around their body to keep heat from losing too quickly.

Their loose structure means less density and cushion impact effectively. The fats around organs protect them from shock and damage.

Lipophilic vitamins should be dissolved in fats for absorption. Insufficient fats in food will lead to inadequate intake of vitamins A, D, E and k, which hinders growth, development and life activities. Omega-3 and omega-6 fatty acids are essential for organic synthesis and must be obtained from food. Consuming more sea fish help supplement these fatty acids.

Why can fat insulate heat?

There are three ways to transfer heat: convection, radiation, and conduction. Fat is an opaque solid, so it doesn’t generate convection like a liquid and infrared radiation can’t penetrate it. Heat conduction requires transferring kinetic energy from one molecule to another through collisions. If the molecules are very closely packed, such as in solid metal, kinetic energy is efficiently transferred to the target molecule efficiently. However, fat has a very fluffy structure with large gaps between molecules, and the very large mass of fat molecules makes it difficult to increase translational velocity after collision. Most of kinetic energy will be converted into potential energy for vibration rotation of atoms in fat molecules. This’s why fat is difficult for heat transferring and it’s thermal insulating.


Anec  > Biology > Material in life

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