Key Terms

active transport

form of transport across the cell membrane that requires input of cellular energy

amphipathic

describes a molecule that exhibits a difference in polarity between its two ends, resulting in a difference in water solubility

anaphase

third stage of mitosis (and meiosis), during which sister chromatids separate into two new nuclear regions of a dividing cell

anticodon

consecutive sequence of three nucleotides on a tRNA molecule that is complementary to a specific codon on an mRNA molecule

autolysis

breakdown of cells by their own enzymatic action

autophagy

lysosomal breakdown of a cell’s own components

cell cycle

life cycle of a single cell, from its birth until its division into two new daughter cells

cell membrane

membrane surrounding all animal cells, composed of a lipid bilayer interspersed with various molecules; also known as plasma membrane

centriole

small, self-replicating organelle that provides the origin for microtubule growth and moves DNA during cell division

centromere

region of attachment for two sister chromatids

centrosome

cellular structure that organizes microtubules during cell division

channel protein

membrane-spanning protein that has an inner pore which allows the passage of one or more substances

checkpoint

progress point in the cell cycle during which certain conditions must be met in order for the cell to proceed to a subsequence phase

chromatin

substance consisting of DNA and associated proteins

chromosome

condensed version of chromatin

cilia

small appendage on certain cells formed by microtubules and modified for movement of materials across the cellular surface

cleavage furrow

contractile ring that forms around a cell during cytokinesis that pinches the cell into two halves

codon

consecutive sequence of three nucleotides on an mRNA molecule that corresponds to a specific amino acid

concentration gradient

difference in the concentration of a substance between two regions

cyclin

one of a group of proteins that function in the progression of the cell cycle

cyclin-dependent kinase (CDK)

one of a group of enzymes associated with cyclins that help them perform their functions

cytokinesis

final stage in cell division, where the cytoplasm divides to form two separate daughter cells

cytoplasm

internal material between the cell membrane and nucleus of a cell, mainly consisting of a water-based fluid called cytosol, within which are all the other organelles and cellular solute and suspended materials

cytoskeleton

“skeleton” of a cell; formed by rod-like proteins that support the cell’s shape and provide, among other functions, locomotive abilities

cytosol

clear, semi-fluid medium of the cytoplasm, made up mostly of water

diffusion

movement of a substance from an area of higher concentration to one of lower concentration

diploid

condition marked by the presence of a double complement of genetic material (two sets of chromosomes, one set inherited from each of two parents)

DNA polymerase

enzyme that functions in adding new nucleotides to a growing strand of DNA during DNA replication

DNA replication

process of duplicating a molecule of DNA

electrical gradient

difference in the electrical charge (potential) between two regions

endocytosis

import of material into the cell by formation of a membrane-bound vesicle

endoplasmic reticulum (ER)

cellular organelle that consists of interconnected membrane-bound tubules, which may or may not be associated with ribosomes (rough type or smooth type, respectively)

exocytosis

export of a substance out of a cell by formation of a membrane-bound vesicle

exon

one of the coding regions of an mRNA molecule that remain after splicing

extracellular fluid (ECF)

fluid exterior to cells; includes the interstitial fluid, blood plasma, and fluid found in other reservoirs in the body

facilitated diffusion

diffusion of a substance with the aid of a membrane protein

flagellum

appendage on certain cells formed by microtubules and modified for movement

G₀ phase

phase of the cell cycle, usually entered from the G₁ phase; characterized by long or permanent periods where the cell does not move forward into the DNA synthesis phase

G₁ phase

first phase of the cell cycle, after a new cell is born

G₂ phase

third phase of the cell cycle, after the DNA synthesis phase

gene

functional length of DNA that provides the genetic information necessary to build a protein

gene expression

active interpretation of the information coded in a gene to produce a functional gene product

genome

entire complement of an organism’s DNA; found within virtually every cell

glycocalyx

coating of sugar molecules that surrounds the cell membrane

glycoprotein

protein that has one or more carbohydrates attached

Golgi apparatus

cellular organelle formed by a series of flattened, membrane-bound sacs that functions in protein modification, tagging, packaging, and transport

helicase

enzyme that functions to separate the two DNA strands of a double helix during DNA replication

histone

family of proteins that associate with DNA in the nucleus to form chromatin

homologous

describes two copies of the same chromosome (not identical), one inherited from each parent

hydrophilic

describes a substance or structure attracted to water

hydrophobic

describes a substance or structure repelled by water

hypertonic

describes a solution concentration that is higher than a reference concentration

hypotonic

describes a solution concentration that is lower than a reference concentration

integral protein

membrane-associated protein that spans the entire width of the lipid bilayer

intermediate filament

type of cytoskeletal filament made of keratin, characterized by an intermediate thickness, and playing a role in resisting cellular tension

interphase

entire life cycle of a cell, excluding mitosis

interstitial fluid (IF)

fluid in the small spaces between cells not contained within blood vessels

intracellular fluid (ICF)

fluid in the cytosol of cells

intron

non-coding regions of a pre-mRNA transcript that may be removed during splicing

isotonic

describes a solution concentration that is the same as a reference concentration

kinetochore

region of a centromere where microtubules attach to a pair of sister chromatids

ligand

molecule that binds with specificity to a specific receptor molecule

lysosome

membrane-bound cellular organelle originating from the Golgi apparatus and containing digestive enzymes

messenger RNA (mRNA)

nucleotide molecule that serves as an intermediate in the genetic code between DNA and protein

metaphase

second stage of mitosis (and meiosis), characterized by the linear alignment of sister chromatids in the center of the cell

metaphase plate

linear alignment of sister chromatids in the center of the cell, which takes place during metaphase

microfilament

the thinnest of the cytoskeletal filaments; composed of actin subunits that function in muscle contraction and cellular structural support

microtubule

the thickest of the cytoskeletal filaments, composed of tubulin subunits that function in cellular movement and structural support

mitochondrion

one of the cellular organelles bound by a double lipid bilayer that function primarily in the production of cellular energy (ATP)

mitosis

division of genetic material, during which the cell nucleus breaks down and two new, fully functional, nuclei are formed

mitotic phase

phase of the cell cycle in which a cell undergoes mitosis

mitotic spindle

network of microtubules, originating from centrioles, that arranges and pulls apart chromosomes during mitosis

multipotent

describes the condition of being able to differentiate into different types of cells within a given cell lineage or small number of lineages, such as a red blood cell or white blood cell

mutation

change in the nucleotide sequence in a gene within a cell’s DNA

nuclear envelope

membrane that surrounds the nucleus; consisting of a double lipid-bilayer

nuclear pore

one of the small, protein-lined openings found scattered throughout the nuclear envelope

nucleolus

small region of the nucleus that functions in ribosome synthesis

nucleosome

unit of chromatin consisting of a DNA strand wrapped around histone proteins

nucleus

cell’s central organelle; contains the cell’s DNA

oligopotent

describes the condition of being more specialized than multipotency; the condition of being able to differentiate into one of a few possible cell types

organelle

any of several different types of membrane-enclosed specialized structures in the cell that perform specific functions for the cell

osmosis

diffusion of water molecules down their concentration gradient across a selectively permeable membrane

passive transport

form of transport across the cell membrane that does not require input of cellular energy

peripheral protein

membrane-associated protein that does not span the width of the lipid bilayer, but is attached peripherally to integral proteins, membrane lipids, or other components of the membrane

peroxisome

membrane-bound organelle that contains enzymes primarily responsible for detoxifying harmful substances

phagocytosis

endocytosis of large particles

pinocytosis

endocytosis of fluid

pluripotent

describes the condition of being able to differentiate into a large variety of cell types

polypeptide

chain of amino acids linked by peptide bonds

polyribosome

simultaneous translation of a single mRNA transcript by multiple ribosomes

promoter

region of DNA that signals transcription to begin at that site within the gene

prophase

first stage of mitosis (and meiosis), characterized by breakdown of the nuclear envelope and condensing of the chromatin to form chromosomes

proteome

full complement of proteins produced by a cell (determined by the cell’s specific gene expression)

reactive oxygen species (ROS)

a group of extremely reactive peroxides and oxygen-containing radicals that may contribute to cellular damage

receptor

protein molecule that contains a binding site for another specific molecule (called a ligand)

receptor-mediated endocytosis

endocytosis of ligands attached to membrane-bound receptors

ribosomal RNA (rRNA)

RNA that makes up the subunits of a ribosome

ribosome

cellular organelle that functions in protein synthesis

RNA polymerase

enzyme that unwinds DNA and then adds new nucleotides to a growing strand of RNA for the transcription phase of protein synthesis

S phase

stage of the cell cycle during which DNA replication occurs

selective permeability

feature of any barrier that allows certain substances to cross but excludes others

sister chromatid

one of a pair of identical chromosomes, formed during DNA replication

sodium-potassium pump

(also, Na⁺/K⁺ ATP-ase) membrane-embedded protein pump that uses ATP to move Na⁺ out of a cell and K⁺ into the cell

somatic cell

all cells of the body excluding gamete cells

spliceosome

complex of enzymes that serves to splice out the introns of a pre-mRNA transcript

splicing

the process of modifying a pre-mRNA transcript by removing certain, typically non-coding, regions

stem cell

cell that is oligo-, multi-, or pleuripotent that has the ability to produce additional stem cells rather than becoming further specialized

telophase

final stage of mitosis (and meiosis), preceding cytokinesis, characterized by the formation of two new daughter nuclei

totipotent

embryonic cells that have the ability to differentiate into any type of cell and organ in the body

transcription

process of producing an mRNA molecule that is complementary to a particular gene of DNA

transcription factor

one of the proteins that regulate the transcription of genes

transfer RNA (tRNA)

molecules of RNA that serve to bring amino acids to a growing polypeptide strand and properly place them into the sequence

translation

process of producing a protein from the nucleotide sequence code of an mRNA transcript

triplet

consecutive sequence of three nucleotides on a DNA molecule that, when transcribed into an mRNA codon, corresponds to a particular amino acid

unipotent

describes the condition of being committed to a single specialized cell type

vesicle

membrane-bound structure that contains materials within or outside of the cell