molecules of life chp 2

nucleus

The dense central part of an atom containing protons and neutrons.

protons

A positively charged particle in the nucleus of an atom.

neutrons

An electrically neutral particle in the nucleus of an atom.

electron

A negatively charged particle that moves around the nucleus of an atom.

atomic number

The number of protons in the nucleus of an atom.

atomic mass

determined by the number of protons and neutrons.

isotopes

Atoms of the same element that have different numbers of neutrons.

ion

An electrically charged atom or molecule.

orbital

A region in space where an electron is present most of the time.

periodic table

The arrangement of the chemical elements in tabular form, organized by their chemical properties.

molecule

A substance made up of two or more atoms.

chemical bond

Any form of attraction between atoms that holds them together.

valence electrons

An electron in the outer shell of an atom, which can participate in the formation of a chemical bond.

molecular orbital

behavior of an electron in a molecule, extending over the entire molecule instead of just a single atom

covalent bond

A chemical bond formed by a shared pair of electrons holding two different atoms together.

double bond

A covalent bond in which covalently joined atoms share two pairs of electrons.

electronegativity

The propensity of atoms to attract electrons.

polar covalent bond

Bonds that do not share electrons equally.

nonpolar covalent bond

A covalent bond between atoms that have the same, or nearly the same, electronegativity.

ionic bond

A chemical bond in which two ions with opposite charges associate with each other due to their difference in electronegativity.

chemical reaction

The process by which molecules, called reactants, are transformed into different molecules, called products.

reactants

Any of the starting molecules in a chemical reaction.

products

Any one of the transformed molecules that result from a chemical reaction.

hydrophillic

“Water loving”; describes a class of molecules with which water can undergo hydrogen bonding.

hydrophobic

“Water fearing”; describes a class of molecules poorly able to undergo hydrogen bonding with water.

solvent

A liquid capable of dissolving a substance.

nonpolar

Describes compounds that do not have regions of positive and negative charge.

hydrophobic effect

The exclusion of nonpolar molecules by polar molecules,

Results in formation of cell membranes and the folding of proteins.

hydrogen bond

An electrostatic interaction between a hydrogen atom in one molecule and an electronegative atom in another molecule.

cohesion

Attraction between molecules; surface tension.

pH

measure of the concentration of protons in a solution, the difference in hydrogen ion concentration from basic to acidic

acidic

Describes a solution in which the concentration of protons is higher than the concentration of hydroxide ions; having a pH less than 7.

basic

Describes a solution in which the concentration of protons is lower than the concentration of hydroxide ions; having a pH greater than 7.

organic molecules

A molecule containing carbon atoms, usually in chains or rings.

isomers

Molecules that have the same chemical formula but different structures.

proteins

The key structural and functional molecule that does the work of the cell, providing structural support and catalyzing chemical reactions.

nucleic acids

A polymer of nucleotides that encodes and transmits genetic information.

carbohydrates

An organic molecule containing C, H, and O atoms that provides a source of energy for metabolism and that forms the starting point for the synthesis of other organic molecules.

lipids

store energy, act as signaling molecules, and are a component of cell membranes.

polymers

A complex molecule made up of repeated simpler units connected by covalent bonds.

amino acids

An organic molecule containing a central carbon atom attached to a carboxyl group, an amino group, a hydrogen atom, and a side chain.

building blocks (monomers) of proteins (polymers).

nucleotides

A constituent of nucleic acids, consisting of a 5-carbon sugar, a nitrogen-containing base, and one or more phosphate groups.

sugars

The simplest carbohydrate molecule; also called a saccharide.

functional groups

A group of one or more atoms that has particular chemical properties of its own, regardless of what it is attached to.

enzyme

A protein that functions as a catalyst to accelerate the rate of a chemical reaction; enzymes are critical in determining which chemical reactions take place in a cell.

α (alpha) carbon

In amino acids, the central carbon atom of each amino acid.

amino group

Covalently linked to the central carbon atom of an amino acid.

carboxyl group

an acidic functional group in organic chemistry, consisting of a carbon double-bonded to an oxygen and single-bonded to a hydroxyl group

R group

A chemical group attached to the central carbon atom of an amino acid, whose structure and composition determine the identity of the amino acid; also called a side chain.

side chain

A chemical group attached to the central carbon atom of an amino acid, whose structure and composition determine the identity of the amino acid

peptide bond

A covalent bond that links the carbon atom in the carboxyl group of one amino acid to the nitrogen atom in the amino group of another amino acid.

base

A nitrogen-containing compound that makes up part of a nucleotide.

pryimidine

In nucleic acids, any of the bases thymine, cytosine, and uracil, which have a single-ring structure.

cytosine, thymine and uracil

purine

In nucleic acids, either of the bases adenine and guanine, which have a double-ring structure.

guanine and adenine

phosphodiester bond

A bond that forms when a phosphate group in one nucleotide is covalently joined to the sugar unit in another nucleotide.

relatively stable and form the backbone of a DNA strand.

double helix

The structure formed by two strands of complementary nucleotides that coil around each other.

Structure of DNA

monosaccharide

a simple sugar

polysaccharide

A polymer of simple sugars.

Provide long-term energy storage or structural support

complex carbohydrates

A long, branched chain of monosaccharides.

glycosidic bonds

A covalent bond that attaches one monosaccharide to another.

triacylglycerol

A lipid composed of a glycerol backbone and three fatty acids.

fatty acid

used by the body for energy storage and as structural components of cell membranes

glycerol

A 3-carbon molecule with OH groups attached to each carbon.

saturated

Describes fatty acids that do not contain double bonds; the maximum number of hydrogen atoms is attached to each carbon atom

unsaturated

Describes fatty acids that contain carbon–carbon double bonds.

van der Waals forces

The attraction of temporarily polarized molecules that results from opposite charges.

steroids

lipids with a structure of four fused carbon rings.

hydrophobic and essential components of cell membranes and as powerful signaling molecules, including hormones.

phospholipids

forms a bilayer with their hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails facing inward