Organic macromolecules

Intro to organic molecules Organic molecules by definition contain carbon. Many organic molecules are made of chains, called polymers. –Polymers are large molecules made up of repeating molecular units. The repeated units are small molecules called monomers. –Some monomers have other functions of their own.

Cells join smaller organic molecules together to form larger molecules. These larger molecules, macromolecules, may be composed of thousands of atoms and weigh over 100,000 amu. The four major classes of macromolecules are: carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates

All are composed of carbon, hydrogen, and oxygen in a 1:2:1 ratio. All sugars are carbohydrates. Glucose is a monosaccharide. Sucrose (aka: table sugar) is a disaccharide. Starch and cellulose are polysaccharides.

Monosaccharides, particularly glucose, are a major fuel for cellular work. Energy is stored in their chemical bonds, which holds the carbons together. They also function as the raw material for the synthesis of other monomers, including those of amino acids and fatty acids. Fig. 5.4

Two monosaccharides can join with a glycosidic linkage to form a disaccharide via dehydration.  For example, maltose, malt sugar, is formed by joining two glucose molecules.  Sucrose, table sugar, is formed by joining glucose and fructose and is the major transport form of sugars in plants.

Starch is a storage polysaccharide composed entirely of glucose monomers. Plants store starch within plastids, including chloroplasts. Plants can store surplus glucose in starch and withdraw it when needed for energy or carbon. Animals that feed on plants, especially parts rich in starch, can also access this starch to support their own metabolism.

Fig. 5.8 Cellulose is a complex carbohydrate Plant cells are usually enclosed by a more or less rigid cell wall containing cellulose. Only a few algae as well as some protists have no cell wall.

Fats

Fats are made from mostly Carbon and Hydrogen, with a small amount of Oxygen. Lipid is another name for a fat. They are made from fatty acids and one glycerol unit.

Lipid structure

The major function of fats is energy storage. A gram of fat stores more than twice as much energy as a gram of a polysaccharide. Humans and other mammals store fats as long- term energy reserves in adipose cells. Fat also functions to cushion vital organs. A layer of fats can also function as insulation. This subcutaneous layer is especially thick in whales, seals, and most other marine mammals.

Phospholipids make up much of the cell membrane, which protects a cell.

Nucleic Acids

Nucleic acids are polymers of monomers called nucleotides. Nucleic acids include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Each nucleotide consists of three parts: a nitrogen base, a pentose sugar, and a phosphate group.

What is DNA? DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).

The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences. Did you know that human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people.

Draw this generalized diagram of how the information in DNA becomes a protein (AKA protein synthesis)

Proteins

All protein molecules contain Carbon, Hydrogen, Oxygen, and Nitrogen. Proteins are long chains of amino acids. There are a total of 20 amino acids.

Proteins are the most structurally complex molecules known. –Each type of protein has a complex three- dimensional shape or conformation. All protein polymers are constructed from the same set of 20 monomers, called amino acids. Polymers of proteins are called polypeptides. A protein consists of one or more polypeptides folded and coiled into a specific conformation.

Proteins are instrumental in about everything that an organism does. Proteins are responsible for implementing the instructions contained in DNA. –These functions include structural support, storage, transport of other substances, intercellular signaling, movement, and defense against foreign substances. –Proteins make up enzymes in a cell which regulate metabolism by selectively accelerating chemical reactions. Humans have tens of thousands of different proteins, each with their own structure and function.