archaeon
member of a group of single-celled organisms that lack a nucleus but are more closely related to eukaryotes than to bacteria
bacterium
a microscopic prokaryote
cell
smallest unit of life
chloroplast
organelle found in cells of plants and some other organisms that captures the energy from sunlight and converts it into chemical energy
chromosome
long, threadlike structure composed of DNA and proteins that carries the genetic information of an organism; becomes visible as a distinct entity when a plant or animal cell prepares to divide
cytoplasm
contents of a cell that are contained within its plasma membrane but, in the case of eukaryotic cells, outside of the nucleus
cytoskeleton
System of protein filaments in the cytoplasm of a eukaryotic cell that gives the cell shape and the capacity for directed movement. Its most abundant components are actin filaments, microtubules, and intermediate filaments.
cytosol
contents of the main compartment of the cytoplasm, excluding membrane-enclosed organelles such as the ER and mitochondria. The cell fraction remaining after membranes, cytoskeletal components, and other organelles have been removed.
electron microscope
Instrument that illuminates a specimen using beams of electrons to reveal and magnify the structures of very small objects, such as organelles and large molecules.
endoplasmic reticulum
labyrinth membrane enclosed compartment in the cytoplasm of eukaryotic cells where lipids and proteins are made
eukaryote
A cell that contains a nucleus and membrane bound organelles
evolution
process of gradual modification and adaptation that occurs in living organisms over generations
fluorescence microscope
Instrument used to visualize a specimen that has been labeled with a fluorescent dye; samples are illuminated with a wavelength of light that excites the dye, causing it to fluoresce.
genome
The total genetic information carried by all the chromosomes of a cell or organism
golgi apparatus
membrane enclosed organelle in eukaryotic cells that modifies the proteins and lipids made in the endoplasmic reticulum and sorts them for transport to other sites
homologus
describes genes, chromosomes, or any structures that are similar because of their common evolutionary origin, can also refer to similarities between protein sequences or nucleic acid sequences
micrometer
millionth of a meter
microscope
instrument for viewing extremely small objects. Some use a focused beam of visible light and are used to examine cells and organelles. Others use a beam of electrons and can be used to examine objects as small as individual molecules.
mitochondrion
Membrane-enclosed organelle, about the size of a bacterium, that carries out oxidative phosphorylation and produces most of the ATP in eukaryotic cells.
model organism
A living thing selected for intensive study as a representative of a large group of species.
nucleus
in biology, refers to the prominent, rounded structure that contains the DNA of a eukaryotic cell. in chemistry, refers to the dense, positively charged center of an atom.
organelle
a discrete structure or subcompartment of a eukaryotic cell that is specialized to carry out a specific function
photosynthesis
the process by which plants, algae, and some bacteria use the energy of sunlight to drive the synthesis of organic molecules from carbon dioxide
plasma membrane
the protein containing lipid bilayer that surrounds a living cell
prokaryote
major category of living cells distinguished by the absence of a nucleus, includes the archaea and the eubacteria.
protein
macromolecule build from amino acids that provides cells with their shape and structure and performs most of their activities
protozoan
A free-living, nonphotosynthetic, single-celled, motile eukaryote.
ribosome
large macromolecular complex, composed of RNAs and proteins, that translates a messenger RNA into a polypeptide chain
lysosome
membrane enclosed organelle that breaks down worn-out proteins and organelles and other waste materials, as well as molecules taken up by endocytosis; contains digestive enzymes that are typically most active at the acid pH found inside these organelles
peroxisomes
small membrane enclosed organelle that contains enzymes that degrade lipids and destroy toxins
acid
a molecule that releases a proton when dissolved in water; the dissociation generates hydronium ions, thereby lowering the pH
amino acid
small organic molecule containing both an amino group and a carboxyl group; it serves as a building block of proteins
atom
the smallest particle of an element that retains the properties of that element
atomic weight
the mass of an atom relative to the mass of a hydrogen atom; equal to protons + neutrons in the nucleus
ATP
activated carrier that serves as the principal carrier of energy in cells; a nucleoside triphosphate composed of adenine, ribose, and 3 phosphate groups
Avogadro's number
6.022 x 10^23; one mole
base
molecule that accepts a proton when dissolved in water; also used to refer to the nitrogen-containing purines or pyrimidines in DNA/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
chemical group
a combination of atoms, such as a hydroxyl group or an amino group, 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
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
electron
a negatively charged subatomic particle that is found in the space outside the nucleus of an atom
electronegativity
the tendency of an atom in a molecule 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
hydrolysis
chemical reaction that involves cleavage of a covalent bond with the accompanying consumption of water; the reverse of condensation
hydronium ion
the form taken by a proton (H+) in aqueous solution
hydrophillic
water loving, polar
hydrophobic
water fearing, nonpolar
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 help-s to fold proteins
inorganic
not composed of carbon atoms
ion
an atom carrying an electrical charge (either + or -)
ionic bond
interaction formed when one atom donates electrons to another; this transfer of e- causes both atoms to become charged
lipid
an organic molecule that is insoluble in water but dissolves readily in nonpolar organic solvents; typically contains long hydrocarbon chains or multiple rings.
lipid bilayer
thin pair of closely juxtaposed sheets, composed mainly of phospholipid molecules, that forms the structural basis for all cell membranes
macromolecule
Polymer built from covalently linked subunits; includes proteins, nucleic acids, and polysaccharides with a molecular mass greater than a few thousand daltons.
molecular weight
sum of the atomic weights of the atoms in a molecule; unitless number
molecule
group of atoms joined together by covalent bonds
monomer
small molecule that can be linked to others of a similar type to form a larger molecule (polymer)
noncovalent bond
Chemical association that does not involve the sharing of electrons; singly are relatively weak, but can sum together to produce strong, highly specific interactions between molecules. Examples are hydrogen bonds and van der Waals attractions.
nucleotide
The basic building block of nucleic acids, such as DNA and RNA; made up of nitrogenous base, a sugar, and a phosphate group.
organic molecule
chemical compound that contains carbon and hydrogen
pH scale
concentration of hydrogen ions in a solution, expressed as a logarithm. An acidic solution with pH 3 will contain 10^-3 hydrogen ions
polar
in chemistry, describes a molecule or bond in which e- are distributed unevenly
polymer
long molecule made by covalently linking multiple identical or similar subunits
proton
Positively charged particle in the nucleus of an atom
subunit
A monomer that forms part of a larger molecule, such as an amino acid residue in a protein or a nucleotide residue in a nucleic acid. Can also refer to a complete molecule that forms part of a larger molecule. Many proteins, for example, are composed of m
sugar
A substance made of carbon, hydrogen, and oxygen with the general formula (CH2O)n. A carbohydrate or saccharide. The "sugar" of everyday use is sucrose, a sweet-tasting disaccharide made of glucose and fructose.
van der waals attraction
Weak noncovalent interaction, due to fluctuating electrical charges, that comes into play between two atoms within a short distance of each other.
acetyl coA
Activated carrier that donates the carbon atoms in its readily transferable acetyl group to many metabolic reactions, including the citric acid cycle and fatty acid biosynthesis; the acetyl group is linked to coenzyme A (CoA) by a thioester bond that rele
activated carrier
A small molecule that stores energy or chemical groups in a form that can be donated to many different metabolic reactions. Examples include ATP, acetyl CoA, and NADH.
ADP
nucleoside diphosphate produced by hydrolysis of the terminal phosphate of ATP
activation energy
energy must be acquired by a molecule to undergo a chemical reaction
anabolism
set of metabolic pathways by which large molecules are made from smaller ones
biosynthesis
An enzyme-catalyzed process by which complex molecules are formed from simple substances by living cells; also called anabolism.
catabolism
set of enzyme catalyzed reactions by which complex molecules are degraded to simpler ones with release of energy
catalyst
a substance that accelerates the rate of a chemical reaction by lowering activation energy; enzymes are this in cells
cell respiration
Process by which cells harvest the energy stored in food molecules; usually accompanied by the uptake of O2 and the release of CO2.
coupled respiration
linked pair of chemical reactions in which free energy released by one reaction serves to drive the other reaction
diffusion
process by which molecules and small particles move from one location to another by random, thermally driven motion
entropy
thermodynamic quantity that measures the degree of disorder in a system
enzyme
a protein that catalyzes a specific chemical reaction
equilibrium
state in which the forward and reverse rates of a chemical reaction are equal so that no net chemical change occurs
equilibrium constant, K
For a reversible chemical reaction, the ratio of substrate to product when the rates of the forward and reverse reactions are equal.
free energy, G
energy that can be harnessed to do work, such as driving a chemical reaction
free energy change, delta G
in a chemical reaction, the difference in free energy between reactant and product molecules; a large negative value of delta G indicates that the reaction has a strong tendency to occur
metabolism
the sum total of the chemical reactions that tak eplcae in the cells of a living organism
oxidation
removal of electrons
reduction
addition of electrons
standard free energy change, delta G knot
the free energy change measured at a defined concentration, temp, and pressure
subtrate
a molecule on which an enzyme acts to catalyze a chemical reaction