AP Biology - Key Terms & Phrases

Adhesion

The force that draws molecules of different substances together.

Cell membrane

A phospholipid bilayer with embedded proteins that surrounds a cell and controls the movement of materials into and out of the cell.

Cohesion

The force of attraction that draws molecules of the same substance together.

Evaporative cooling

The loss of heat through absorption of energy into an evaporating substance.

Heat of vaporization

The amount of energy, or heat, it takes to boil a substance.

Homeostasis

An organism's maintenance of constant internal conditions.

Hydrogen bond

A type of strong polar attraction between an atom that strongly attracts electrons (in other words, an electronegative atom) and a hydrogen atom that already has a covalent bond with another electronegative atom.

Hydrophilic

Able to dissolve in water.

Hydrophobic

Unable to dissolve in water.

Passive Transport

The movement of molecules across a membrane without an energy expenditure.

Polar

Having an unbalanced arrangement of charge.

Solute

The substance that is dissolved in a liquid to make a solution.

Solvent

The liquid that a substance is dissolved in to make a solution.

Surface area

The total area of the exterior surface of a solid figure.

Example: The surface area of a pyramid equals the sum of the area of its square base and the areas of its four triangular faces.

Surface-area-to-volume ratio

The ratio of the surface area of an object to its volume; often expressed as the fraction: SA/V.

Surface tension

The attraction among molecules at the surface of a liquid. It creates a skin-like barrier between air and underlying liquid molecules.

Volume

The enclosed space of an object or mass.

5’ cap

A sequence of seven modified bases added to the 5' end of a eukaryotic mRNA transcript and that is recognized by the ribosome.

Amino Acids

Small organic molecules that link with other amino acids in long chains to form proteins. Each amino acid contains an amino group, a carboxylic acid group, and a side chain.

Anticodon

A sequence of three bases at one end of a tRNA molecule that match up to their complementary bases on mRNA.

Codon

A three-nucleotide sequence of an mRNA molecule that codes for a specific amino acid or the start or stop of the polypeptide.

Elongation

The growth of a protein molecule during translation, or of an RNA molecule during transcription.

Exons

In eukaryotes, sequences of a gene that are not removed during RNA processing and hence are expressed as a part of the polypeptide sequence.

Gene Expression

The process by which the information in a gene is translated into functional molecules in the cell, either RNA or protein.

Initiation

First step of transcription; RNA polymerase binds to the promoter and a transcription initiation complex is formed.

Initiation Complex

In translation, the combination of the small ribosomal subunit, the start tRNA, and other initiation facors on the mRNA molecule.

Introns

In eukaryotes, sequences of a gene that are removed from mRNA during processing.

Messenger RNA (mRNA)

An RNA transcript that is subsequently translated (after processing in eukaryotes) into a polypeptide.

Plasmids

Circular DNA molecules common in prokaryotes that are often used as vectors for recombinant DNA.

Point Mutation

A mutation that changes a single base on a strand of DNA.

Poly-A tail

A long sequence of modified adenine nucleotides added to the 3' end of a eukaryotic mRNA molecule during processing after transcription that assists in its export from the nucleus.

Primary Structure

The sequence of amino acids in a protein.

Promoter

A sequence of bases that binds with RNA polymerase, located upstream of a gene to be transcribed.

Ribosomal RNA

A type of RNA molecule that has an enzymatic function and contributes to the structure of the ribosome.

RNA Polymerase

An enzyme that polymerizes a complementary RNA sequence from a DNA sequence.

Start Codon

The sequence of bases AUG, which codes for the amino acid methionine and indicates the beginning of protein assembly.

Stop Codon

A sequence of three bases on mRNA that do not code for an amino acid and therefore indicate the stop of translation.

Termination

The ending processes of transcription of an RNA molecule from DNA, or of translation of a polypeptide from mRNA.

Tertiary Structure

The three-dimensional structure of a protein formed by folding of the polypeptide, largely in response to interactions with hydrophobic and hydrophilic regions of the molecule and sometimes stabilized by disulfide bonds.

Transcription

The process by which the sequence of a DNA molecule is copied to a sequence of an RNA molecule.

Transfer RNA (tRNA)

An RNA molecule that has a specific anticodon sequence, binds a specific amino acid, and acts as the translator between an mRNA sequence and a polypeptide sequence.

Transformation

The alteration of a genotype and phenotype through the uptake of environmental DNA.

Translation

The process by which an mRNA sequence is translated into a sequence of amino acids in a polypeptide.

abiotic

Nonliving.

catalyst

A substance that enables a chemical action to occur more quickly without being used up as a reactant.

endosymbiosis

A type of symbiosis ("living together") in which one organism lives inside the body or cells of another.

evo-devo

An abbreviation signifying the study of the evolution of development and the relationships between species using their developmental characteristics.

gene expression

The process by which the information in a gene is translated into functional molecules in the cell, either RNA or protein.

homeobox

A highly conserved (present in plants, animals, and fungi) DNA sequence coding for protein regions that bind DNA and are thus involved in regulating transcription and usually control genes affecting anatomical development.

homeotic genes

Regulatory genes that affect development of significant regions of an animal or plant body in response to the position of the cell in the embryo

homologous structures

Anatomical structures that bear a similarity to another structure because of shared ancestry.

hox genes

A group of homeobox genes that code for regulatory proteins that are expressed in different parts of the developing embryo and signal to developing tissues their location within the embryo.

molecular switches

Regulatory molecules that turn gene expression on or off.

primordial soup

The name given to Earth's pre-oceans containing the precursors to biological molecules.

protobionts

Sacs of nucleic acids and other molecules surrounded by a simple membrane. A precursor to the first cells.

protocells

An early membrane bound cell-like structure with minimal functions including growth and the ability to replicate and evolve.

relative dating

Estimating the age of an object by comparing it to something else.

ribozymes

RNA enzymes.

vestigial structure

A type of homologous structure that has been greatly reduced by selection and is nonfunctional.

ancestral character

A character that is found in extant taxa and the common ancestor of those taxa.

clade

A related group of organisms with a common ancestor. determined by the presence or absence of traits.

cladogram

A diagram that shows the relationships among organisms.

convergent evolution

Evolution toward a common or similar character state.

derived character

A character that is found in a clade of organisms, but that is not shared by all of them.

gel electrophoresis

A laboratory technique used to separate biological molecules by size and charge. The technique is based on the movement of the molecules through an agarose gel in an electric field.

ingroup

A taxon under study in a phylogenetic study.

Maximum likelihood

A statistical method for estimating the parameters of a population from a sample; in phylogenetics, the method can be used to estimate the relationships among taxa.

monophyletic

Having a common ancestor

outgroup

In a cladogram, the species in a group that shares the fewest traits with the other organisms.

paraphyletic

Consisting of a single ancestral species and some, but not all, of its descendants.

phylogenetic tree

A chart representing the evolutionary relationships among organisms; it is also called an evolutionary tree. The points where two branches diverge represent a common ancestor of the organisms that lie at the ends of the branches.

phylogeny

The evolutionary history of a set of taxomonic groups; the science of discovering evolutionary history.

polymerase chain reaction (PCR)

A method for making a large number of copies of a DNA fragment.

primers

Short segments of DNA that serve as the starting point for DNA synthesis.

prokaryotes

One-celled organisms that do not have a membrane-enclosed nucleus.

restriction enzymes

Proteins that cut DNA at specific sequences; typically used in recombinant DNA technology.

taxon

A taxonomic group.

GMO

An organism that has had its genetic make-up altered by genetic engineering.