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unicellular organisms that do not have nuclei


metabolic processes carried out by green plants and cyanobacteria, by which visible light is trapped and the energy used to convert CO2 into organic compounds


any of the membrane-enclosed structures within a eukaryotic cell


organisms whose cells contain their genetic material inside a nucleus


the theory that the eukaryotic cell evolved via the engulfing of one prokaryotic cellby another

cellular specialization

in multicellular organisms, the division of labor such that different cell types become responsible for different functions


a change in the genetic material not caused by recombination


a taxomic naming system in which species are given two names


the three monophyletic branches of life

model systems

small group of species that are the subject of extensive research; organism that adapt well to laboratory situations and findings from experiments on them can apply across a broad range of species


the complete DNA sequence for a particular organism or individual


the basic chemical unit in nucleic acids, consisting of a pentose sugar, a phosphate group, and a nitrogen-containing base


the fundamental hereditary material of all living organisms


long chain polymer of amino acids with twenty different common side chains


the maintenance of steady state, such as a constant temperature, by means of physiological or behavioral feedback responses

natural selection

the differential contribution of offspring to the next generation by different types belonging to the same population


a particular structure, physiological process, or behavior that makes an organism better able to survive and reproduce


any gradual change


a far-reaching explanation of observed facts that is supported by such a wide body of evidence, with no significant contradictory evidence, that is scientifically accepted as a factual framework

natural history

the characteristics of a group of organisms, such as how the organisms get their food, reproduce, behave, regulate their internal environments, and interact with other organisms


to assign numerical values to observations through measurement


a tentative answer to a question from which testable predictions can be generated

deductive logic

to make predictions based on the hypothesis

controlled experiment

an experiment in which a sample is divided into groups whereby experimental groups are exposed to manipulations of an independent variable while one group serves as an untreated control. the data from various groups are then compared to see if there are changes in a dependent variable as a result of the experimental manipulation


in a controlled experiment, a factor that is manipulated to test its effect on a phenomenon

comparative experiment

experimental design in which data from various unmanipulated samples or population are compared, but in which variables are not controlled or even necessarily indentified

null hypothesis

in statistics, the premise that any differences observed in an experiment are simply the result of random differences that arise from drawing two finite samples from the same population


quantified observations about a system under study


the smallest unit of chemical element


the centrally located compartment of eukaryotic cells that is bounded by a double membrane and contains the chromosomes


a subatomic particle outside the nucleus carrying a negative charge and very little mass


a subatomic particle with a single positive charge. the number of these determine its element


one of the three fundamental particles of matter, with mass slightly larger than that of a proton and no electrical charge


a substance that cannot be converted to simpler substances by ordinary chemical means

atomic number

the number of protons in the nucleus of an atom

Bohr model

a model for atomic structure that depicts the atom as largely empty space, with a central nucleus surrounded by electrons in orbits, or electron shells, at various distances from the nucleus

electron shells

the region surrounding the atomic nucleus at a fixed energy level in which electrons orbit


a chemical substance made up of two or more atoms joined by covalent bonds or ionic attractions

chemical bond

an attractive force stably linking two atoms


an electrically charged particle that forms when an atom gains or loses an electron


an ion with one or more positive charges


a negatively charged ion

ionic bonds

an electrostatic attraction between positively and negatively charged ions

covalent bond

chemical bond based on the sharing of electrons between two atoms


the tendency of an atom to attract electrons when it occurs as part of a compound

polar covalent pond

a covalent bond in which the electrons are drawn to one nucleus more than the other, resulting in an unequal distributions of charge

hydrogen bond

a weak electrostatic bond which arises from the attraction between the slight positice charge on a hydrogen atom and a slight negative charge on a nearby oxygen or nitrogen atom

heat of vaporization

the energy that must be supplied to convert a molecule from a liquid to a gas at its boiling point


the tendency of molecules to stick together


having an affinity for water


having no affinity for water

functional groups

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


a larger molecule made up of similar or identical subunits called monomers


a small molecule, two or more of which can be combined to form oligomers or polymers


a chemical reaction in which two molecules become connected by a covalent bond and a molecules of water is released


a chemical reaction that breaks a bond by inserting the components of water


organic compounds containing carbon, hydrogen, and oxygen in the ratio 1:2:1


a simple sugar; makes up oligosaccharides and polysaccharides

glycosidic linkages

bond between carbohydrate molecules through an intervening oxygen atom


a carbohydrate made up of two monosaccharides


a polymer containing a small number of monosaccharides


a macromolecule composed of many monosaccharides; ex. cellulose and starch


nonpolar, hydrophobic molecules that include fats, oils, waxes, steroids, and the phospholipids that make up biological membranes


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


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

fatty acid

a molecule made up of a long nonpolar hydrocarbon chain and a polar carboxyl group

saturated fatty acid

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

unsaturated fatty acid

a fatty acid whose hydrocarbon chain contains one or more double bonds


having both hydrophilic and hydrophobic regions


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


a structure that is two layers in thickness; most often referred to the phospholipid ______ of membranes

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 together

chemical reaction

the change in the composition or distribution of atoms of a substance with consequent alterations in properties


a chemical substance that enters into a chemical reaction with another substance


the molecules that result from the completion of a chemical reaction


the sum total of the chemical reactions that occur in an organism, or some subset of that total

potential energy

the energy of a state or position that is stored energy

kinetic energy

the energy of movement, the type of energy that does work

anabolic reactions

a synthetic reaction in which simple molecules are linked to form more complex ones; requires an input of energy and captures it in the chemical bonds that are formed

catabolic reactions

a synthetic reaction in which complex molecules are broken down into simpler ones and energy is released

laws of thermodynamics

laws derived from studies of the physical properties of energy and the ways energy interacts with matter

nucleic acids

a polymer made up of nucleotides, specialized for the storage, transmission, and expression of genetic information


the fundamental hereditary material of all living organisms.


an often single-stranded nucleic acid whose nucleotides use ribose rather than deoxyribose and in which the base uracil replaces thymine found in DNA


the basic chemical unit in nucleic acids, consisting of a pentose sugar, a phosphate group, and a nitrogen containing base


a substance that can accept a hydrogen ion in solution; in nucleic acids, the purine or pyrimidine that is attached to each sugar in the sugar-phosphate backbone


one of the two types of nitrogenous bases in nucleic acids; it pairs with a specific purine


one of the two types of nitrogenous bases in nucleic acids; each pairs with a specific pyrimidine


a five carbon sugar found in nucleotides and DNA


a five carbon sugar in nucleotides and RNA

phosphodiester linkage

the connection in nucleic acid strand, formed by linking two nucleotides

complimentary base pairing

The AT or AU, TA or UA, CG, and GC pairing of bases in double-stranded DNA, in transcription, and between tRNA and mRNA


when DNA sequences are copied into RNA


when the nucleotide sequence is used to specify a sequence of amino acids in a polypeptide chain

gene expression

the overall process of transcription and translation


the complete DNA sequence for a particular organism or individual


a unit of heredity


catalytic proteins that speed up biochemical reactions

defensive proteins

recognize and respond to substances or particles that invade the organism from the environment

hormonal and regulatory proteins

control physiological processes

receptor proteins

receive and respond to molecular signals from inside and outside the organism

storage proteins

store chemical building blocks for later use

structural proteins

provide physical stability and movement

transport proteins

carry substances within the organism

genetic regulatory proteins

regulate when, how, and to what extent a gene is expressed

amino acids

an organic compound containing both NH2 and COOH groups; proteins are its polymers

R group

the distinguishing group of atoms of a particular amino acid

disulfide bridge

the covalent bond between two sulfur atoms linking two molecules or remote parts of the same molecule

peptide linkage

the bond between amino acids in a protein; formed between a carboxyl group and amino group with the loss of water molecules

primary structure

the specific sequence of amino acids in a protein

secondary structure

localized regularities of structure, such as the alpha helix and the beta pleated sheet

alpha helix

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

beta pleated sheet

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

tertiary structure

the relative locations in three-dimensional space of all the atoms in the molecule; the overall shape of the protein


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

quarternary structure

the specific three-dimensional arrangement of protein subunits


a chemical substance that accelerates a reaction without itself being consumed in the overall course of the reaction; they lower the activation energy or a reaction

transition state

in an enzyme-catalyzed reaction, the reactive condition of the substrate after there has been sufficient input of energy to initiate the reaction

activation energy

the energy barrier that blocks the tendency for a chemical reaction to occur


the molecule or molecules on which and enzyme exerts catalytic action

active site

the region on the surface of an enzyme or ribozyme where the substrate binds, and where catalysis occurs

enzyme-substrate complex

an intermediate in an enzyme-catalyzed reaction; consists of the enzyme bound to its substrate


a carbon-containing molecule that is required for the action of one or more enzymes

prosthetic groups

distinctive, non-amino acid atoms or molecular groupings that are permanently bound to their enzymes

competitive inhibitor

a nonsubstrate that binds to the active sire of an enzyme and thereby inhibits binding of its substrate

noncompetitive inhibitor

a nonsubstrate that inhibits the activity of an anzyme by binding to a site other than its active site

allosteric regulation

regulation of the activity of a protein by the binding of an effector molecule to a site other than the active site

feedback inhibition

a mechanism for regulating a metabolic pathway in which the end product of the pathway can bind to an inhibit the enzyme that catalyzes the first committed step in the pathway


catalyze the same reaction but have different chemical compositions and physical properties

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