Understanding Lipids, Carbohydrates, Proteins, and Nucleic Acids
Lipids: An Overview
What are lipids and what do they do? Lipids are molecules insoluble in water and less dense than it.
There are two major types: triglycerides and cholesterol esters.
Animals use them as long-term energy reserves, for insulation, and as protective tissues. Plants store them in seeds and fruits.
Triglycerides
Glycerol + 3 fatty acids
Fatty acids may be:
- Saturated (butyric, stearic, palmitic)
- Unsaturated:
- Monounsaturated: oleic
- Polyunsaturated: linoleic, linolenic, Omega-3, Omega-6
There are also trans fatty acids produced by partial hydrogenation of polyunsaturated fats.
Cholesterol
Cholesterol ester = fatty acid + cholesterol
Three types: HDL, LDL, VLDL
“Good” and “bad” cholesterol are needed to form cell membranes, vitamin D, and bile acids.
Lipids are involved in the formation of atheromas.
Digestion and Utilization
Enzymes break down lipid molecules into monoglycerides, fatty acids, and cholesterol. Lipids contribute 9.3 kcal/g (more than twice the amount from carbohydrates).
Carbohydrates: Functions and Types
Carbohydrates function as a power source (for all living things), supporting tissue (in plants), and outer sheaths (in insects and crustaceans). They are also involved in RNA and DNA.
Types of Carbohydrates
- Monosaccharides: pentoses (ribose, deoxyribose) and hexoses (glucose, fructose, galactose)
- Disaccharides (union of two monosaccharides): sucrose, lactose, maltose
- Polysaccharides (mono-n junction): cellulose, starch, glycogen, chitin
Digestion and Utilization
Monosaccharides are absorbed directly into the intestinal villi. The rest are broken down by hydrolysis under the action of enzymes into monosaccharides.
Glucose enters the bloodstream and is oxidized in cells or transformed into glycogen by the action of the hormone insulin.
Glycogen is hydrolyzed by the hormone glucagon. Monosaccharides are a source of energy for immediate use.
Proteins: Structure and Function
What are proteins and what do they do? Proteins are very large macromolecules formed by joining amino acids.
- They form tissues and organs.
- They are involved in the immune system.
- They catalyze reactions (enzymes).
- They regulate metabolism (hormones).
Amino Acids
Amino acids are essential components.
- Only 20 are sufficient to form proteins in living organisms.
- Humans require 8 essential amino acids.
- Amino acids are formed by an amino group, a carboxyl acid, and a radical.
Digestion and Utilization
Digestion involves breaking the long chain to release amino acids. These are used to form tissue (anabolism) or for energy (catabolism).
Biological value: quality of amino acids (absorption and number of essential amino acids).
Nucleic Acids: DNA and RNA
What are nucleic acids and what functions do they perform? They are fundamental components of all living things. RNA and DNA are found in the nucleus of cells, allow the formation of proteins, and are responsible for hereditary mechanisms. They are complex molecules formed by nucleotide unions through hydrogen bonds.
Nucleotides
Nucleotides are building blocks.
They consist of three parts:
- A phosphate group.
- A pentose: ribose (RNA) or deoxyribose (DNA).
- A nitrogenous base: RNA (adenine, cytosine, guanine, or uracil); DNA (adenine, cytosine, guanine, and thymine).
RNA is a single-stranded molecule, much smaller than DNA. The ribose of each nucleotide is attached to the phosphate of the next. Each of the bases is linked to the pentose.
RNA is involved in the manufacture of proteins through mRNA (messenger RNA) and tRNA (transfer RNA).
DNA is the longest and most complex molecule known. It consists of a double helix with a common axis. The bases in each chain are linked by hydrogen bonds: A-T (double bond) and C-G (triple bond). DNA is involved in cell division through replication of the double strand and encodes the information for the synthesis of proteins made by RNA.