Overview
This lecture covers two major categories of biochemistry: carbohydrates and lipids, focusing on their structures, storage, and biological significance.
Carbohydrates
- Carbohydrates are one of the four major biochemistry categories; the others are proteins, lipids, and nucleic acids.
- Simple sugars (monosaccharides) like deoxyribose and ribose are part of DNA and RNA backbones.
- Disaccharides include sucrose (table sugar), maltose (two glucose molecules), and lactose (milk sugar).
- Polysaccharides are polymers made of many glucose molecules.
- In animals, polysaccharides are stored as glycogen, mainly in liver and muscle tissues.
- Liver glycogen serves the whole body, especially the brain; muscle glycogen is for muscle use.
- Glycogen storage depends on recent physical activity and caloric intake.
Lipids and Triglycerides
- Lipids (fats) are another major biochemistry category, primarily stored as triglycerides.
- Triglycerides consist of one glycerol molecule and three fatty acids.
- Fatty acids have a carboxyl group (C=O and CO) and can be saturated (hydrogenated) or unsaturated.
- Fatty acid metabolism involves beta oxidation, removing two carbons at a time to form acetyl-CoA for the Krebs cycle.
- Fatty acid chains usually have even numbers of carbons, with the last carbon called omega.
- Omega-3 and omega-6 fatty acids are named according to the position of the first double bond from the omega end.
- Omega-3 is essential for human health and must be obtained from the diet, mainly from green leafy vegetables and plant membranes (also from fish, which get it from plants).
- The human brain contains about one-third omega-3 fatty acids.
Membranes and Cholesterol
- Phospholipids form cell membranes with polar heads and fatty acid tails.
- Cholesterol, a type of steroid, fits between phospholipids in membranes and serves as the precursor for all steroid hormones and vitamin D.
Key Terms & Definitions
- Carbohydrates — Biomolecules including sugars and polymers like glycogen; provide energy and structural support.
- Disaccharide — A carbohydrate formed by joining two monosaccharides (e.g., sucrose, maltose, lactose).
- Polysaccharide — A large carbohydrate made by linking many monosaccharides (e.g., glycogen).
- Glycogen — Animal polysaccharide for energy storage, mainly in liver and muscles.
- Triglyceride — A fat molecule made of glycerol plus three fatty acids.
- Fatty acid — A long hydrocarbon chain with a carboxyl group; building block of lipids.
- Omega-3 fatty acid — An essential fatty acid with a double bond three carbons from the omega end.
- Phospholipid — Major membrane component with a polar head and two fatty acid tails.
- Cholesterol — A steroid molecule integral to membranes and precursor for steroid hormones.
Action Items / Next Steps
- Review the structure and functions of carbohydrates and lipids.
- Prepare for further discussion on energy metabolism and glycogen regulation in future chapters.