KEY WORDS

MEANING

MICROSCOPIC OBSERVATIONS OF CELLS

pages 37-48

light microscope

Uses visible light to illuminate the specimen. Can be used to see an object as small as 0.2 um in diameter.

(Fig 3-2).

electron microscope

Uses a beam of electrons to illuminate the specimen. Can be used to see an object as small as 0.002 um in diameter.

(Fig 3-2).

prokaryotic cells

Lack a nucleus (ie bacteria).

eukaryotic cells

Contain a nucleus.

viruses

Nucleic acid molecule surrounded by a protein shell.

CELL COMPARTMENTS

pages 38-43

plasma membrane

Membrane surrounding the cell sur

face.

cell organelles

Membrane bound compartments that serve specialized functions within a cell. (Fig. 3-4).

nucleus

Spherical or oval structure near the center of a cell that contains the chromosomes which determine cell structure and function and heredity.

cytoplasm

The interior of the cell other than the nucleus.

cytosol

Fluid surrounding the organelles outside the nucleus.

intracellular fluid

All fluid inside the cell.

membrane structure

Cell membranes consist of a double layer of lipid molecules in which proteins are embedded.

phospholipids

The major membrane lipids. One end is charged and the other end is nonpolar. The polar regions are towards the surface and nonpolar regions toward the interior. (Fig. 3-6, 3-7)

cholesterol

A major lipid in plasma membranes. There is about one molecule of cholesterol for each phospholipid. Intracellular membranes contain very little cholesterol.

integral membrane proteins

Closely associated with the membrane lipids and cannot be extracted without disrupting the lipid bilayer. They have polar and non-polar regions. Some serve as channels for passage of ions or water. Others are involved in transmission of chemical signals.

peripheral membrane proteins

Located at the membrane surface where they are bound to the polar regions of the integral membrane proteins. Involved in cell shape and motility.

glycocalyx

carbohydrates in the plasma membrane.

fluid-mosaic model

The general membrane structure described above. (See Figs. 3-7, 3-8).

membrane junction

There exists a space of about 20 nm between cell membranes of adjacent cells. This space is filled with extracellular fluid (interstitial) and serves as a pathway for substances to pass between cells to and from blood.

desmosomes

A disc shaped region of concentrated protein holding two cell membranes together. Similar to a spot weld. (Fig. 3-9A).

tight junction

A membrane junction holding two cell membranes together so that no extracellular space occurs at this location. The tight junction forms a band around the entire cell. Most epithelial cells are bound by tight junctions. In the digestive tract this forms a barrier so that digested products pass through the cells of the gut wall rather than through the extracellular space between these cells. (Fig. 3-9B)

gap junction

Contains protein channels linking the cytoplasm of adjacent cells. This junction has small diameter protein channels (1.5 nm) that limit what can pass between the cells to small molecules and ions (Fig. 3-9C)

CELL ORGANELLES

pages 43-50n (Fig 3-4).

nucleus

An oval membrane bound organelle near the middle of the cell whose main function is storage, transmission and expression of genetic information used to synthesize proteins that determine the structure and function of the cell. (Fig. 3-4).

nuclear envelope

Barrier surrounding the nucleus consisting of two membranes.

nuclear pores

Pores in the nuclear envelope. Molecules that regulate genetic expression can move between these pores. (Fig. 3-10).

chromatin

A fine network of threads in the nucleus made up of DNA and protein. Chromatin is somewhat coiled. (Fig. 3-10).

chromosomes

Highly condensed chromatin that occurs when a cell divides.

nucleolus

A highly coiled structure in the nucleus containing RNA and protein. It assembles ribosomal subunits.

ribosomes

Composed of protein and RNA. Ribosomes use genetic information from mRNA and assemble amino acids into proteins. Ribosomes are free or bound to rough endoplasmic reticulum (RER). Proteins assembled on free ribosomes go into the cytosol. Proteins assembled in RER pass through RER lumen into the Golgi apparatus.

endoplasmic reticulum

An extensive network of membranes in the cytoplasm.

rough endoplasmic reticulum (granular)

RER has ribosomes bound to its surface and has a flattened appearance. RER is involved in the packaging of proteins secreted by cells or distributed to other organelles. (Fig. 3-11).

smooth endoplasmic reticulum (agranular)

Has no bound ribosomes and has a tubular appearance. It is a site of synthesis of lipid molecules and releases calcium ions involved in cell activities. (Fig. 3-11).

Golgi apparatus

Cup shaped membranous sacs associated with numerous vesicles. Sort proteins into these vesicles which are sent to other organelles or secreted out of the cell. (Fig. 3-12).

secretory vesicles

Vesicles that contain proteins secreted by the cell.

mitochondria

Round or elongated organelles with an inner and outer membrane. They produce ATP which the cell uses for energy. Cells requiring much energy may have 1000 mitochondria. (Fig. 3-13).

cristae

The inner folded membrane of mitochondria.

matrix

The inner compartment of mitochondria.

lysosomes

Single membrane organelle containing acidic fluid and digestive enzymes for breakdown of bacteria and cellular debris.

peroxisomes

Organelles that destroy toxic substances containing oxygen, particularly hydrogen peroxide.

filaments

These are used to form the cell's cytoskeleton and for cell movement. (Fig. 3-15).

microfilaments

The thinnest filaments. Composed of the protein actin. They make up the major portion of the cell cytoskeleton and can be rapidly assembled and disassembled to change cell shape.

intermediate filaments

Made up of several proteins. Most extensive in areas subject to mechanical stress.

muscle thick filaments

Found only in muscle. Composed of the contractile protein myosin.

myosin

Contractile protein involved in producing forces for cell movement.

microtubules

The thickest filaments. They have a helical arrangement of the protein tubulin. They are the most rigid if filaments and are found in nerve axons and dendrites to maintain their shape.

centrioles

Organelles that generate spindle fibers at the time of cell division. They are composed of microtubules.

cilia

Hairlike extensions on some epithelial cells. They have a central core of microtubules to move the cilia. An example of their use is in the airway where they sweep mucous and dust particles away from the lungs toward the pharynx (throat) to be swallowed.