Lipids are a kind of compounds that are insoluble in water and can be extracted by nonpolar organic solvents such as ether, chloroform, benzene, etc., mainly including esters and their derivatives generated by the reaction of fatty acids with alcohols.

1. fat

Grease is triglyceride or triacylglycerol, which is the general name of grease. Generally, oil that is liquid at room temperature is called oil, and when it is solid, it is called fat.

Fat is synthesized by dehydration of glycerol and fatty acids. -OH in the carboxyl group of fatty acid combines with -H in the hydroxyl group of glycerol to lose one molecule of water, so glycerol and fatty acid form ester bonds and become fat molecules.

The three acyl groups in fat (the atomic groups left after hydroxyl groups are removed by inorganic or organic oxyacids) are generally different, and their sources are C 16, C 18 or other fatty acids. Fatty acids with double bonds are called unsaturated fatty acids, and those without double bonds are called saturated fatty acids. 、

Unsaturated fatty acids are less in animal fat and more in vegetable oil. Too much saturated fat in the diet will cause atherosclerosis, because both fat and cholesterol will deposit on the inner wall of blood vessels to form plaques, which will hinder blood flow and produce cardiovascular diseases. Because of this, there are deposits on the blood vessel wall, which narrows the blood vessels and makes obese patients prone to diseases such as hypertension.

Oils and fats are widely distributed, and there are a certain amount of oils and fats in the seeds of various plants, tissues and organs of animals, especially in the seeds of oil crops and subcutaneous adipose tissues of animals. Fat in human body accounts for about 10%~20% of body weight. There are many kinds of fatty acids in human body, and there are different arrangements and combinations when triglycerides are produced. Therefore, triglycerides exist in many forms.

Energy storage and energy supply are the most important physiological functions of fat. 1g fat can release 38kJ(9.3kcal) of energy when it is completely oxidized in vivo, which is more than twice the energy released by 1g glycogen or protein. Adipose tissue is a tissue specially used to store fat in the body. When the body needs energy, the fat stored in adipose tissue cells can be mobilized and decomposed to supply the body with what it needs. In addition, the fat in higher animals and human body can also reduce body heat loss, keep body temperature constant, reduce friction between internal organs and buffer external pressure.

Lipid (lipid)

Include phospholipids, glycolipids, cholesterol and cholesterol esters.

① Glyceryl phosphate is a lipid containing phosphoric acid, including glycerophosphate composed of glycerol and sphingomyelin composed of sphingosine. In animal brains and eggs, soybean seeds contain more phospholipids.

② Glycolipids are lipids containing sugar groups.

In addition, cholesterol, steroids and other substances mainly include cholesterol, cholic acid, sex hormones, vitamin D and so on. These substances play an important role in regulating the normal metabolism and reproductive process of organisms.

In addition, cholesterol is also the synthetic raw material of fatty acid salts, vitamin D3 and steroid hormones, and plays an important role in regulating the absorption of lipid substances, especially the absorption of fat-soluble vitamins (A, D, E, K) and the metabolism of calcium and phosphorus. These three lipids are important components of biofilm, which form a hydrophobic "barrier" to separate the water-soluble components of cells and divide cells into compartments such as organelles/nuclei, so as to ensure that multiple metabolic activities can be carried out at the same time without interfering with each other and maintain the normal structure and function of cells.

function

store energy

It is the best way to store energy, such as triglycerides of animals and oilseeds. By comparing the following data, we can draw a conclusion:

Comparison of two energy substances (sugar and lipid) in the body

Energy supply per unit weight: sugar 4. 1 kcal/g, fat 9.3 kcal/g.

Storage capacity: 1 glycogen or starch: 2 water, while fat is relatively pure and much smaller.

In the order of utilization: sugar is consumed first, and then lipid is consumed. So many weight loss/slimming principles, such as breaking the valley, all come from this.

Skeleton of biofilm

Liquid mosaic model of cell membrane: phospholipid diester layer, cholesterol, protein, glycolipid, glycerophosphate and sphingomyelin.

Electrical and thermal insulators

Animal adipose tissue has protective functions such as heat preservation and mechanical stress prevention, and vegetable wax can prevent water evaporation.

Electrical insulation: sheath cells of nerve cells, sheath of electric wires, and short circuit of nerves.

Insulation: keep warm in winter, penguins, polar bears, etc.

other

Signal transmission: steroid hormones.

Enzyme activator: lecithin activates β -hydroxybutyrate dehydrogenase.

Glycosyl carrier: Polyphenol phosphate is used as the carrier of carbonyl group when glycoprotein is synthesized.

Precursors of hormones, vitamins and pigments (terpenes, sterols).

Growth factors and antioxidants.

Participate in signal recognition and immunity (glycolipid).