Inside the Cell

actin filament

protein fibers that play a role in movement of cell and organelles

adenosine triphosphate (ATP)

one of the principal chemical compounds that cells use to store and release energy

adhesion junction

junction between cells in which the adjacent plasma membranes do not tough but are help together by intercellular filaments attached to buttonlike thickenings


a sticky, gelatinous substance around the cell wall; allows cells to stick together or to the host cell

cell theory

idea that all living things are composed of cells, cells are the basic units of structure and function in living things, and new cells are produced from existing cells

cellular respiration

process that releases energy by breaking down glucose and other food molecules in the presence of oxygen

cell wall

a thin membrane around the cytoplasm of a cell


one of two tiny structures located in the cytoplasm of animal cells near the nuclear envelope


material present in the cytoplasm of all eukaryotic cells, important during cell division; the microtubule-organizing center.


organelle found in cells of plants and some other organisms that captures the energy from sunlight and converts it into chemical energy


long strands of DNA found in the eukaryotic cell nucleus; condense to form chromosomes


a threadlike body in the cell nucleus that carries the genes in a linear order


A hairlike structure arranged in tightly packed rows that projects from the surface of some cells.

conjugation pili

in a bacterium, elongated, hollow appendage used to transfer DNA to other cells


inner foldings of the inner membrane of mitochondria


a jellylike fluid inside the cell in which the organelles are suspended


network of protein filaments within some cells that helps the cell maintain its shape and is involved in many forms of cell movement

endomembrane system

the collection of membranes inside and around a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles; includes the smooth and rough endoplasmic reticulum, the Golgi apparatus, lysosomes, and vacuoles

endoplasmic reticulum

a cell structure that forms a maze of passageways in which proteins and other materials are carried from one part of the cell to another

eukaryotic cell

cell with a nucleus (surrounded by its own membrane) and other internal organelles

extracellular matrix (ECM)

the substance in which animal cells are embedded, consisting of protein and polysaccharides synthesized and secreted by cells.


a short, hairlike appendage of a prokaryotic cell that helps it adhere to the substrate or to other cells; also known as an attachment pilus.


a lash-like appendage used for locomotion (e.g., in sperm cells and some bacteria and protozoa)

gap junction

A type of intercellular junction in animal cells that allows the passage of material or current between cells.

Golgi apparatus

stack of membranes in the cell that modifies, sorts, and packages proteins from the endoplasmic reticulum


the smallest particle that is capable of carrying out photosynthesis; the functional unit of a chloroplast


a vesicle that buds from the Golgi apparatus, contains digestive enzymes that break down large molecules


the extracellular substance that gives connective tissues their strength and flexibility. can be solid, semisolid, or liquid


straight, hollow tube of proteins that gives rigidity, shape, and organization to a cell


an organelle containing enzymes responsible for producing energy

motor protein

a protein that interacts with cytoskeletal elements and other cell components, producing movement of the whole cell or parts of the cell.

nuclear envelope

a double membrane that surrounds the nucleus in the cell

nuclear pore

opening in the nuclear envelope that permits the passage of proteins into the nucleus and ribosomal subunits out of the nucleus


shaped like or having the appearance of a nucleus


the site where DNA is concentrated when it is in the process of making ribosomal RNA


the control center of the cell


a specialized part of a cell

plasma membrane

thin outer boundary of a cell that regulates the traffic of chemicals between the cell and its surroundings


a cell-to-cell junction in plants that connects the cytoplasm of adjacent cells

prokaryotic cell

a type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles.


small particle in the cell on which proteins are assembled; made of RNA and protein

rough ER

ER (endoplasmic reticulum) that is dotted with ribosomes


a functionally specialized substance (especially one that is not a waste) released from a gland or cell

smooth ER

that portion of the endoplasmic reticulum that is free of ribosomes.


dense fluid within the chloroplast


limits cell size


a membrane system found within chloroplasts that contains the components for photosynthesis

tight junction

a type of intercellular junction in animal cells that prevents the leakage of material between cells

transport vesicle

a tiny membranous sac in a cell's cytoplasm carrying molecules produced by the cell


cell organelle that stores materials such as water, salts, proteins, and carbohydrates


a membrane bound sac that contains materials involved in transport of the cell.