Lipids Overview and Types

Study Notes

Lipids are composed of carbon, hydrogen, and oxygen atoms, with a lower proportion of oxygen than carbohydrates.
Lipids are insoluble in water.
Learning objectives include defining lipids, stating their functions, explaining the types found in the human body, and describing their fate.
Lipids are used to synthesize triglycerides and phospholipids; they can also be broken down to produce ATP.
Lipids provide protection, insulation, and energy storage.
They are a major component of cell membranes, and are precursors to bile salts, vitamin D, and steroid hormones.
Lipids are critical for digestion and absorption of dietary fats.
Lipids help regulate calcium levels, metabolism, and responses to stress and maintain salt and water balance.

Fatty Acids: The simplest form, used in triglyceride and phospholipid synthesis and can be broken down for ATP production.
Saturated fatty acids have single covalent bonds between carbon atoms, are saturated with hydrogen atoms, and can cause atherosclerosis.
Unsaturated fatty acids have double covalent bonds, aren't completely saturated with hydrogen atoms, and have kinks in the carbon chain.
Monounsaturated fatty acids have one double bond (one kink).
Polyunsaturated fatty acids have more than one double bond (more than one kink).

Triglycerides are the most abundant lipids in the human body and diet.
A triglyceride is composed of one glycerol molecule and three fatty acid molecules.
Triglycerides form via dehydration synthesis.
Triglycerides can be solid or liquid at room temperature, depending on whether they contain saturated or unsaturated fatty acids.
Saturated fats are usually solid at room temperature (e.g., red meat, whole milk, butter, palm oil, coconut oil) and are linked to heart disease and colorectal cancer.
Unsaturated fats are usually liquid at room temperature (e.g., oils) and can help lower heart disease risk.
- Monounsaturated fats include olive oil, peanut oil, and canola oil.
- Polyunsaturated fats include corn oil, safflower oil, sunflower oil, soybean oil, and fish oil.

Phospholipids have a glycerol backbone with two fatty acid chains attached (tails) and a phosphate group and nitrogen-containing molecule attached to the head.
The tails are nonpolar (hydrophobic) and the head is polar (hydrophilic).
Phospholipids are the major components of cell membranes.

Steroids are lipids that do not contain fatty acids; they have a four-ring structure.
Cholesterol: crucial for cell membrane structure and a precursor for sex hormones.
Sex hormones (estrogen, testosterone): regulate reproductive functions.
Cortisol: maintains normal blood sugar levels.
Bile salts: help in lipid digestion and absorption.
Vitamin D: necessary for bone growth.

Eicosanoids: 20-carbon fatty acids (e.g., arachidonic acid).
- Prostaglandins and leukotrienes: modify responses to hormones, inflammatory responses, allergic reactions, affect body temperature, blood clotting, and more.
Fat-soluble vitamins: Beta-carotene converts to vitamin A; Vitamin D, E, K, and lipoproteins are other fat-soluble vitamins.