Unit 1: Chemistry of Life

21 terms. Say what each one means, then open the card to check.

• Polar molecule

  A molecule with an uneven share of electrons, so one end carries a partial negative charge and the other a partial positive charge.

  Example. In water, oxygen pulls shared electrons closer, so the oxygen end is slightly negative and the hydrogen ends are slightly positive.

• Hydrogen bond

  A weak attraction between a partly positive hydrogen atom and a partly negative atom, such as oxygen or nitrogen, in another molecule or in another part of the same large molecule.

  Example. The slightly positive hydrogen of one water molecule is drawn to the slightly negative oxygen of the water molecule next to it.

• Cohesion

  The tendency of molecules of the same substance to stick to each other, which in water comes from hydrogen bonds.

  Example. A column of water is pulled up through a tall tree because each water molecule tugs on the ones below it.

• Adhesion

  The attraction between molecules of one substance and a different surface, such as water clinging to glass or cell walls.

  Example. Water creeps up the inside of a thin glass tube because it is attracted to the polar glass surface.

• High specific heat

  Each gram of water must absorb a lot of energy to warm by one degree, because much of the energy first goes into breaking hydrogen bonds.

  Example. A large lake warms only slowly on a hot afternoon, so the fish living in it face small temperature swings.

• Carbon skeleton

  The chain or ring of carbon atoms that forms the frame of an organic molecule; each carbon can make four covalent bonds.

  Example. Glucose is built on a six-carbon frame, and the atoms attached to that frame give glucose its properties.

• Nitrogen in biomolecules

  Nitrogen is a building element of proteins, in every amino acid, and of nucleic acids, in every nitrogenous base.

  Example. A plant grown in soil with too little nitrogen makes less protein and grows slowly with pale leaves.

• Phosphorus in biomolecules

  Phosphorus is found in phosphate groups, which are part of nucleic acids, phospholipids and ATP.

  Example. A bacterium that cannot get phosphate cannot build new DNA, so it stops dividing.

• Monomer and polymer

  A monomer is a small subunit; a polymer is a long chain of many monomers joined by covalent bonds.

  Example. Glucose is a monomer, and starch is a polymer made of hundreds of glucose units linked together.

• Dehydration synthesis

  A reaction that joins two monomers with a covalent bond and releases one molecule of water for each bond formed.

  Example. Joining two amino acids forms a peptide bond and gives off one water molecule.

• Hydrolysis

  A reaction that breaks the covalent bond between two monomers by adding a molecule of water.

  Example. In the gut, enzymes use water to split the starch in bread into single glucose molecules.

• Saturated fatty acid

  A fatty acid whose carbon chain has only single bonds, so the chain is straight and packs tightly with others.

  Example. Butter is solid at room temperature because its straight, saturated chains pack closely together.

• Phospholipid

  A lipid with a hydrophilic phosphate head and two hydrophobic fatty acid tails, the main part of cell membranes.

  Example. In water, phospholipids line up in two layers with tails pointing inward, away from the water.

• R group

  The side chain that differs among the 20 amino acids; its size, charge and polarity give each amino acid its properties.

  Example. An amino acid with a charged R group is hydrophilic, while one with a hydrocarbon R group is nonpolar.

• Peptide bond

  The covalent bond formed by dehydration synthesis between the carboxyl group of one amino acid and the amino group of the next.

  Example. A chain of 50 amino acids is held together by 49 peptide bonds.

• Primary structure

  The order of amino acids in a polypeptide, which sets how the chain will fold.

  Example. Two proteins with the same 300 amino acids in a different order would fold into different shapes.

• Tertiary structure

  The overall 3D shape of one polypeptide, held by interactions among R groups such as hydrogen bonds, ionic bonds and hydrophobic clustering.

  Example. In a protein dissolved in the cytoplasm, nonpolar R groups tend to cluster in the core, away from water.

• Denaturation

  A loss of a protein's folded shape, and so its function, caused by conditions such as high heat or extreme pH.

  Example. Egg white turns from clear to white when cooked because heat unfolds its proteins.

• Nucleotide

  The monomer of nucleic acids: a five-carbon sugar, a phosphate group and a nitrogenous base.

  Example. A DNA nucleotide might hold deoxyribose, a phosphate and the base guanine.

• Antiparallel strands

  The two strands of DNA run in opposite directions, one 5' to 3' and the other 3' to 5'.

  Example. If one strand reads 5' ATG 3' from left to right, its partner reads 3' TAC 5' in the same direction.

• Complementary base pairing

  In DNA, adenine pairs with thymine and guanine pairs with cytosine, held by hydrogen bonds; in RNA, uracil replaces thymine.

  Example. A DNA strand reading AGCT pairs with a strand reading TCGA.