Chapter 3 - Proteins, Carbohydrates, and Lipids

secondary structure

Of a protein, localized regularities of structure, such as the α helix and the β pleated sheet.

glycosidic linkages

Bond between carbohydrate (sugar) molecules through an intervening oxygen atom (-O-).

tertiary structure

In reference to a protein, the relative locations in three-dimensional space of all atoms in the molecule. The overall shape of a protein. (Contrast with primary, secondary, and quaternary structures.)

denatured

Loss of activity of an enzyme or nucleic acid molecule as a result of structural changes induced by heat or other means.

isomers

Molecules consisting of the same numbers and kinds of atoms, but differing in the bonding patterns by which the atoms are held together.

structural isomers

Molecules made up of the same kinds and numbers of atoms, in which the atoms are bonded differently.

phospholipid bilayer

The basic structural unit of biological membranes; a sheet of phospholipids two molecules thick in which the phospholipids are lined up with their hydrophobic "tails" packed tightly together and hydrophilic, phosphate-containing "heads" facing outward. Also called lipid bilayer.

peptide linkage

The bond between amino acids in a protein; formed between a carboxyl group and amino group (CO-NH⁻) with the loss of water molecules.

disulfide bridge

The covalent bond between two sulfur atoms (-S-S-) linking two molecules or remote parts of the same molecule.

R group (side chain)

The distinguishing group of atoms of a particular amino acid; also known as a side chain.

primary structure

The specific sequence of amino acids in a protein.

quaternary structure

The specific three-dimensional arrangement of protein subunits.

optical isomers

Two isomers that are mirror images of each other.

amphipathic

[Gk. amphi: both + pathos: emotion] Of a molecule, having both hydrophilic and hydrophobic regions.

glucose

[Gk. gleukos: sugar, sweet] The most common monosaccharide; the monomer of the polysaccharides starch, glycogen and cellulose.

hexoses

[Gk. hex: six] A sugar containing six carbon atoms.

hydrolysis reaction

[Gk. hydro: water + lysis: break apart] A chemical reaction that breaks a bond by inserting the components of water (AB + H₂O 〉 AH + BOH). (Contrast with condensation reaction.)

lipids

[Gk. lipis: fat] Nonpolar, hydrophobic molecules that include fats, oils, waxes, steroids, and the phospholipids that make up biological membranes.

monomers

[Gk. mono: one + meros: unit] A small molecule, two or more of which can be combined to form oligomers (consisting of a few monomers) or polymers (consisting of many monomers).

pentoses

[Gk. penta: five] A sugar containing five carbon atoms.

polymers

[Gk. poly: many + meros: unit] A large molecule made up of similar or identical subunits called monomers. (Contrast with monomer, oligomer.)

proteins

[Gk. protos: first] Long-chain polymer of amino acids with twenty different common side chains. Occurs with its polymer chain extended in fibrous proteins, or coiled into a compact macromolecule in enzymes and other globular proteins.

polysaccharides

A macromolecule composed of many monosaccharides (simple sugars). Common examples are cellulose and starch.

fatty acid

A molecule made up of a long nonpolar hydrocarbon chain and a polar carboxyl group. Found in many lipids.

α(alpha) helix

A prevalent type of secondary protein structure; a right-handed spiral.

chaperones

A protein that guards other proteins by counteracting molecular interactions that threaten their three-dimensional structure.

triglyceride

A simple lipid in which three fatty acids are combined with one molecule of glycerol.

monosaccharides

A simple sugar. Oligosaccharides and polysaccharides are made up of monosaccharides.

bilayer

A structure that is two layers in thickness. In biology, most often refers to the phospholipid bilayer of membranes.

glycerol

A three-carbon alcohol with three hydroxyl groups; a component of phospholipids and triglycerides.

fats

A triglyceride that is solid at room temperature. (Contrast with oil.)

oils

A tryglyceride that is liquid at room temperature. (Contrast with fat.)

β(beta) pleated sheet

A type of protein secondary structure; results from hydrogen bonding between polypeptide regions running antiparallel to each other.

phospholipids

A lipid containing a phosphate group; an important constituent of cellular membranes.

disaccharides

A carbohydrate made up of two monosaccharides (simple sugars).

functional groups

A characteristic combination of atoms that contribute specific properties when attached to larger molecules.

condensation reactions

A chemical reaction in which two molecules become connected by a covalent bond and a molecule of water is released (AH + BOH 〉 AB + H₂O.) (Contrast with hydrolysis reaction.)

ester linkage

A condensation (water-releasing) reaction in which the carboxyl group of a fatty acid reacts with the hydroxyl group of an alcohol. Lipids are formed this way

saturated fatty acids

A fatty acid in which all the bonds between carbon atoms in the hydrocarbon chain are single bonds-that is, all the bonds are saturated with hydrogen atoms. (Contrast with unsaturated fatty acid.)

unsaturated fatty acids

A fatty acid whose hydrocarbon chain contains one or more double bonds. (Contrast with saturated fatty acid.)

macromolecules

A giant (molecular weight>1,000) polymeric molecule. The macromolecules are the proteins, polysaccharides, and nucleic acids.

heat shock proteins (HSPs)

Chaperone proteins expressed in cells exposed to high or low temperatures or other forms of environmental stress.

carbohydrates

Organic compounds containign carbon, hydrogen, and oxygen in the ratio 1:2:1 (i.e., with the general formula CⁿH₂ⁿOⁿ). Common examples are sugars, starch, and cellulose.