Chapter 4 Cell Structures

ATP

(adenosine triphosphate) main energy source that cells use for most of their work

mitochondria

(singular = mitochondrion) cellular organelles responsible for carrying out cellular respiration, resulting in the production of ATP, the cell's main energy-carrying molecule

nucleus

cell organelle that houses the cell's DNA and directs the synthesis of ribosomes and proteins

eukaryote

cell that has a membrane-bound nucleus and several other membrane-bound compartments or sacs

ribosome

cellular structure that carries out protein synthesis

nucleoid

central part of a prokaryotic cell in which the chromosome is found

gap junction

channel between two adjacent animal cells that allows ions, nutrients, and low molecular weight substances to pass between cells, enabling the cells to communicate

plasmodesmata

channel that passes between the cell walls of adjacent plant cells, connects their cytoplasm, and allows materials to be transported from cell to cell

organelle

compartment or sac within a cell

intermediate filaments

cytoskeletal component, composed of several intertwined strands of fibrous protein, that bears tension, supports cell-cell junctions, and anchors cells to extracellular structures

nucleolus

darkly staining body within the nucleus that is responsible for assembling the subunits of the ribosomes

nuclear envelope

double-membrane structure that constitutes the outermost portion of the nucleus

central vacuole

large plant cell organelle that regulates the cell's storage compartment, holds water, and plays a significant role in cell growth as the site of macromolecule degradation

desmosome

linkages between adjacent epithelial cells that form when cadherins in the plasma membrane attach to intermediate filaments

flagella

long, hair-like structure that extends from the plasma membrane and is used to move the cell

lysosome

organelle in an animal cell that functions as the cell's digestive component; it breaks down proteins, polysaccharides, lipids, nucleic acids, and even worn-out organelles

plasma membrane

phospholipid bilayer with embedded (integral) or attached (peripheral) proteins, and separates the internal content of the cell from its surrounding environment

microtubule organizing center

structure found in eukaryotic cells from which microtubules emerge. MTOCs have two main functions: the organization of eukaryotic flagella and cilia and the organization of the mitotic and meiotic spindle apparatus, which separate the chromosomes during cell division.

chromosome

structure within the nucleus that is made up of chromatin that contains DNA, the hereditary material

thylakoid

A flattened membrane sac inside the chloroplast, used to convert light energy into chemical energy.

endosymbiosis

A theorized process in which early eukaryotic cells were formed from simpler prokaryotes.

cristae

Infoldings of the inner membrane of a mitochondrion that houses the electon transport chain and the enzyme catalyzing the synthesis of ATP.

stroma

The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.

peroxisome

small, round organelle that contains hydrogen peroxide, oxidizes fatty acids and amino acids, and detoxifies many poisons

unified cell theory

a biological concept that states that all organisms are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells

cytoplasm

entire region between the plasma membrane and the nuclear envelope, consisting of organelles suspended in the gel-like cytosol, the cytoskeleton, and various chemicals

golgi apparatus

eukaryotic organelle made up of a series of stacked membranes that sorts, tags, and packages lipids and proteins for distribution

tight junction

firm seal between two adjacent animal cells created by protein adherence

cytosol

gel-like material of the cytoplasm in which cell structures are suspended

endomembrane system

group of organelles and membranes in eukaryotic cells that work together modifying, packaging, and transporting lipids and proteins

extracellular matrix

material (primarily collagen, glycoproteins, and proteoglycans) secreted from animal cells that provides mechanical protection and anchoring for the cells in the tissue

centrosome

membrane-bound sac, somewhat larger than a vesicle, which functions in cellular storage and transport

vacuole

membrane-bound sac, somewhat larger than a vesicle, which functions in cellular storage and transport

microfilaments

narrowest element of the cytoskeleton system; it provides rigidity and shape to the cell and enables cellular movements

cytoskeleton

network of protein fibers that collectively maintain the shape of the cell, secure some organelles in specific positions, allow cytoplasm and vesicles to move within the cell, and enable unicellular organisms to move independently

chloroplast

plant cell organelle that carries out photosynthesis

exocytosis

process of passing bulk material out of a cell

chromatin

protein-DNA complex that serves as the building material of chromosomes

smooth endoplasmic reticulum

region of the endoplasmic reticulum that has few or no ribosomes on its cytoplasmic surface and synthesizes carbohydrates, lipids, and steroid hormones; detoxifies certain chemicals (like pesticides, preservatives, medications, and environmental pollutants), and stores calcium ions

rough endoplasmic reticulum

region of the endoplasmic reticulum that is studded with ribosomes and engages in protein modification and phospholipid synthesis

cell wall

rigid cell covering made of cellulose that protects the cell, provides structural support, and gives shape to the cell

nucleoplasm

semi-solid fluid inside the nucleus that contains the chromatin and nucleolus

endoplasmic reticulum

series of interconnected membranous structures within eukaryotic cells that collectively modify proteins and synthesize lipids

cilia

short, hair-like structure that extends from the plasma membrane in large numbers and is used to move an entire cell or move substances along the outer surface of the cell

vesicle

small, membrane-bound sac that functions in cellular storage and transport; its membrane is capable of fusing with the plasma membrane and the membranes of the endoplasmic reticulum and Golgi apparatus

endocytosis

type of active transport that moves substances, including fluids and particles, into a cell

prokaryote

unicellular organism that lacks a nucleus or any other membrane-bound organelle

microtubules

widest element of the cytoskeleton system; it helps the cell resist compression, provides a track along which vesicles move through the cell, pulls replicated chromosomes to opposite ends of a dividing cell, and is the structural element of centrioles, flagella, and cilia