Types of CellsNerve cells: surface is sensitive to stimuli.

Long extensions.Muscle cells: contain tiny fibers that slide

together forcefully. Elongated and threadlike.Red blood cells: contains hemoglobin that

attracts and releases oxygen.Gland cells: contains sacs that release a

secretion to the outside of the cell. Immune cells: recognize and destroy

“nonself” cells such as bacteria and cancer.

Cell StructureCytoplasm: gel like substance inside the cell. This

gel contains the cell organelles. Plasma membrane: the outer boundary of the cell.

Membranous organelles also have these membranes.Primary structure of a cell membrane is a double

layer of phospholipids molecules. Heads are hydrophilic (water loving)Tails are hydrophobic (water fearing)Double layer is called a bilayer. The bilayer allows the heads to face the water and the

tails to face away.

Fluid Mosaic ModelMolecules that comprise a cell membrane are

arranged in a sheet. Molecules are able to slowly float around the membrane like icebergs because it is fluid.

Membrane proteins have many different structural forms that allow them to serve various functions.

Some have a carbohydrate attached to their outer surface forming glycoprotein molecules which act as identifying markers.

Fluid Mosaic ModelMembrane channel proteins have openings

like gates in a fence that only allow certain kinds of molecules to pass through.

Other membrane proteins are receptors that can react to the presence of a hormone or other regulatory chemicals thereby triggering a change in the cell.

Cell OrganellesOrganelles: “little organs”. Two classifications:

Membranous organelles: organelles that are specialized sacs or canals made of a cell membrane.

Nonmembranous organelles: are not made of a membrane but of microscopic filaments or other nonmembranous material.

Cell OrganellesEndoplasmic reticulum: protein synthesis and

intracellular transportation. Rough ER: ribosomes are attached to the ER

and synthesize proteinsSmooth ER: synthesizes lipids, steroid

hormones and certain carbohydrates.

Ribosomes: site of protein synthesis. A cell’s “protein factory”. Nonmebranous.

Cell OrganellesGolgi Apparatus: synthesizes carbohydrates,

combines it with protein and packages the product as globules of glycoprotein. Membranous.

Lysosome: bags of digestive enzymes break down worn cell parts and ingest particles. A cell’s “digestive system”. Membranous.

Peroxisomes: contain enzymes that detoxify harmful substances. Membranous. Contain peroxidase and catalase.

Cell OrganellesMitochondria: ATP synthesis. A cell’s “power

plant”. Membranous. Centrosome: area of cytoplasm near the

nucleus that coordinates the building and breaking of microtubules in the cell. Nonmembranous. Plays an important role during cell division

when the “spindle” moves chromosomes around the cell.

NucleusNucleus is one of the largest cell organelles.

Houses the genetic code which in turn dictates protein synthesis. It’s membrane the Nuclear envelope consists of:Nucleoplasm: nuclear substanceNuclear pores: selectively permeable

Nucleolus: the most prominent structure visible in the nucleus. Plays an essential role in the formation of ribosomes. Synthesizes ribosomal RNA. Nonmembranous.

Cell ExtensionsCilia and Flagella: hair like extensions that

serve to move substances over a cells surface (cilia) or to propel sperm cells (flagella).

Microvilli: like tiny fingers crowded against each other. Cover surfaces where absorption is important.Example: epithelial cells that line the

intestines.

Cell FibersMicrofilaments: serve as “cellular muscles”. They

are thin, twisted strands of protein molecules and usually form bundles that lie parallel to the long axis of a cell.

Intermediate filaments: are twisted protein stands that are slightly thicker than microfilaments. Thought to form much of the supporting framework in many types of

cells.

Microtubules: are the thickest cell fibers. They are tiny, hollow tubes made of protein subunits arranged in spiral fashion. Called the “engines” of cells because they often move things around.

Cell ConnectionsGap Junctions: are formed when membrane

channels of adjacent plasma membranes adhere to each other. They form gaps or “tunnels”. This allows certain molecules to pass

directly from one cell to another. Example: heart muscle cells- allows for impluses to travel.

Tight Junctions: occurs in cells that are joined by “collars” of tightly fused membrane. This is important for tissues that need to control what gets past. Molecules can not penetrate this membrane. Example: lining of the intestines.

Desmosomes: are small “spot welds” that hold adjacent cells together. Example: adjacent skin cells are held together this way.