Chapter 2 Flashcards
acid
A molecule that releases a proton when dissolved in water;
this dissociation generates hydronium (H3O+) ions, thereby
lowering the pH.
amino acid
Small organic molecule containing both an amino group
and a carboxyl group; it serves as the building block of
proteins.
atom
The smallest particle of an element that still retains its
distinctive chemical properties; consists of a positively
charged nucleus surrounded by a cloud of negatively
charged electrons.
atomic weight
The mass of an atom relative to the mass of a hydrogen
atom; equal to the number of protons plus the number of
neutrons that the atom contains
ATP
Activated carrier that serves as the principal carrier of
energy in cells; a nucleoside triphosphate composed of
adenine, ribose, and three phosphate groups. (See Figure
2–26.)
Avogadro´s number
The number of molecules in a mole, the quantity of
a substance equal to its molecular weight in grams;
6.0221409 × 10^23
base
Molecule that accepts a proton when dissolved in water;
also used to refer to the nitrogen-containing purines or
pyrimidines in DNA and RNA
buffer
Mixture of weak acids and bases that maintains the pH of a
solution by releasing and taking up protons.
chemical bond
A sharing or transfer of electrons that holds two atoms
together. (See also covalent bond and noncovalent
bond. )
chemical group
A combination of atoms, such as a hydroxyl group (–OH) or
an amino group (–NH2), with distinct chemical and physical
properties that influence the behavior of the molecule in
which it resides
condensation reaction
Chemical reaction in which a covalent bond is formed
between two molecules as water is expelled; used to build
polymers, such as proteins, polysaccharides, and nucleic
acids.
conformation
Precise, three-dimensional shape of a protein or other
macromolecule, based on the spatial location of its atoms
in relation to one another.
covalent bond
Stable chemical link between two atoms produced by
sharing one or more pairs of electrons
DNA
Double-stranded polynucleotide formed from two separate
chains of covalently linked deoxyribonucleotide units.
It serves as the cell’s store of genetic information that is
transmitted from generation to generation
electron
Negatively charged subatomic particle that occupies space
around an atomic nucleus (e–)
electronegativity
The tendency of an atom to attract electrons
electrostatic attraction
Force that draws together oppositely charged atoms.
Examples include ionic bonds and the attractions between
molecules containing polar covalent bonds
fatty acid
Molecule that consists of a
carboxylic acid attached to
a long hydrocarbon chain.
Used as a major source of energy during metabolism and as
a starting point for the synthesis of phospholipids
hydrogen bond
A weak noncovalent interaction
between a positively charged
hydrogen atom in one molecule
and a negatively charged atom,
such as nitrogen or oxygen, in another; hydrogen bonds are
key to the structure and properties of water
hydrolysis
Chemical reaction that involves cleavage of a covalent
bond with the accompanying consumption of water (its –H
being added to one product of the cleavage and its –OH to
the other); the reverse of a condensation reaction.
hydronium ion
The form taken by a proton (H+) in aqueous solution.
hydrophilic
Molecule or part of a molecule that readily forms hydrogen
bonds with water, allowing it to readily dissolve; literally,
“water loving.”
hydrophobic
Nonpolar, uncharged molecule or part of a molecule
that forms no hydrogen bonds with water molecules and
therefore does not dissolve; literally, “water fearing.”
hydrophobic force
A noncovalent interaction that forces together the
hydrophobic portions of dissolved molecules to minimize
their disruption of the hydrogen-bonded network of water;
causes membrane phospholipids to self-assemble into a
bilayer and helps to fold proteins into a compact, globular
shape
