Lipids
| English | Chinese | Pinyin |
|---|---|---|
| triglyceride | 甘油三酯 | gān yóu sān zhǐ |
| glycerol | 甘油 | gān yóu |
| fatty acid | 脂肪酸 | zhī fáng suān |
| ester bond | 酯键 | zhǐ jiàn |
| hydrophobic | 疏水 | shū shuǐ |
| saturated | 饱和 | bǎo hé |
| unsaturated | 不饱和 | bù bǎo hé |
| phospholipid | 磷脂 | lín zhī |
| bilayer | 双层 | shuāng céng |
Energy stored, membranes built
- Lipids are the fats and oils — the body's long-term energy store.
- They do not mix with water, and that single fact explains what they do.
- One special lipid builds every cell membrane.
Triglycerides 甘油三酯
- A triglyceride is one glycerol 甘油 joined to three fatty acids 脂肪酸 by ester bonds 酯键 (each bond forms by condensation, so three waters are removed).
- It is non-polar and hydrophobic 疏水 — it will not mix with water.
- Fatty acids are saturated 饱和 (no C=C double bonds, straight, usually solid fats) or unsaturated 不饱和 (one or more double bonds, kinked, usually liquid oils).
A triglyceride: glycerol joined to three fatty acids by ester bonds
- Step through it below to watch the three ester bonds form.
Building a triglyceride
Watch one glycerol join three fatty acids. Each ester bond forms by condensation, removing one water — three bonds, three waters.
A triglyceride is made from:
A triglyceride = 1 glycerol + 3 fatty acids, joined by ester bonds (each forms by condensation).
Glycerol joins each fatty acid by an ______ bond, formed by condensation.
Three ester bonds form, removing three water molecules in total.
Match each fatty acid type to its feature.
Saturated chains have no C=C and pack tightly (solid); unsaturated chains kink at each C=C, so they stay liquid.
Put the formation of a triglyceride in order.
Each ester bond forms by condensation; three bonds release three water molecules.
Why fat is a great energy store
- It releases about twice the energy per gram as carbohydrate.
- It is insoluble, so it stays put and has no osmotic effect.
- It stores no extra water, so it adds little mass.
- Under the skin it also gives insulation and protects organs.
One reason triglycerides are good long-term energy stores is that they:
Lipids release ~2× the energy per gram of carbohydrate, are insoluble, and store no water.
Phospholipids 磷脂 and the bilayer 双层
- A phospholipid is a triglyceride with one fatty acid replaced by a phosphate group.
- This gives it two ends: a hydrophilic ("water-loving") polar phosphate head and two hydrophobic fatty-acid tails.
- In water the heads face out and the tails hide inside — forming the bilayer that makes every cell membrane.
Phospholipids line up with their water-loving heads out and water-hating tails in, forming a bilayer
A phospholipid forms membranes because it has:
The polar head is attracted to water and the non-polar tails avoid it, so phospholipids arrange into a bilayer.
In a phospholipid bilayer, the hydrophobic tails point inward and the hydrophilic heads face the water.
Correct — heads face the watery surroundings on both sides; tails meet in the middle, away from water.
You've got it
- triglyceride = 1 glycerol + 3 fatty acids joined by ester bonds (condensation)
- saturated = no C=C (solid fats); unsaturated = has C=C double bonds (liquid oils)
- great energy store: ~2× energy/gram, insoluble, no water, insulation
- phospholipid = hydrophilic head + hydrophobic tails → forms the membrane bilayer