The Structure and Function of Macromolecules (Proteins have many…
The Structure and Function of Macromolecules
Most macromolecules are polymers, built from monomers
A polymer is a long molecule consisting of many similar or identical building blocks linked by covalent bonds.
The repeated units are small molecules called monomers.
Monomers are connected by covalent bonds that form through the loss of a water molecule. This reaction is called a condensation reaction or dehydration reaction.
In hydrolysis, bonds are broken by the addition of water molecules. A hydrogen atom attaches to one monomer, and a hydroxyl group attaches to the adjacent monomer.
Carbohydrates serve as fuel and building material
The simplest carbohydrates are monosaccharides, or simple sugars.
Carbohydrates include sugars and their polymers.
Two monosaccharides can join with a glycosidic linkage to form a disaccharide via dehydration.
Polysaccharides are polymers of hundreds to thousands of monosaccharides joined by glycosidic linkages.
Starch is a storage polysaccharide composed entirely of glucose monomers.
Glycogen is highly branched like amylopectin.
Cellulose is a major component of the tough wall of plant cells.
Chitin is similar to cellulose, except that it contains a nitrogen-containing appendage on each glucose monomer.
Lipids are a diverse group of hydrophobic molecules
The unifying feature of lipids is that they all have little or no affinity for water.
A fat is constructed from two kinds of smaller molecules: glycerol and fatty acids.
In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride.
If the fatty acid has one or more carbon-carbon double bonds formed by the removal of hydrogen atoms from the carbon skeleton, then the molecule is an unsaturated fatty acid.
A saturated fatty acid is a straight chain, but an unsaturated fatty acid has a kink wherever there is a double bond.
Phospholipids have two fatty acids attached to glycerol and a phosphate group at the third position.
Steroids are lipids with a carbon skeleton consisting of four fused rings.
Cholesterol, an important steroid, is a component in animal cell membranes.
Proteins have many structures, resulting in a wide range of functions
Most important, protein enzymes function as catalysts in cells, regulating metabolism by selectively accelerating chemical reactions without being consumed.
Polymers of proteins are called polypeptides.
A protein consists of one or more polypeptides folded and coiled into a specific conformation.
Amino acids are organic molecules with both carboxyl and amino groups.
Amino acids are joined together when a dehydration reaction removes a hydroxyl group from the carboxyl end of one amino acid and a hydrogen from the amino group of another. The resulting covalent bond is called a peptide bond.
The primary structure of a protein is its unique sequence of amino acids.
Quaternary structure arises when two or more polypeptides join to form a protein.
Tertiary structure is determined by interactions among various R groups.
Typical secondary structures are coils (an alpha helix) or folds (beta pleated sheets).
Nucleic acids store and transmit hereditary information
A gene consists of DNA, a polymer known as a nucleic acid.
There are two types of nucleic acids: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).
A nucleic acid strand is a polymer of nucleotides.
The nitrogen bases are rings of carbon and nitrogen that come in two types: purines and pyrimidines.
The pentose joined to the nitrogen base is ribose in nucleotides of RNA and deoxyribose in DNA.
Genomics and proteomics have transformed biological inquiry and applications
Biologists can now analyze and compare whole genomes of different species (an approach called genomics) and large sets of proteins (proteomics).