Types of Cells
Nerve cells: surface is sensitive to stimuli. Long
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.
Cytoplasm: 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 Model
Molecules 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
Fluid Mosaic Model
Membrane 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
Organelles: “little organs”.
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
Endoplasmic reticulum: protein synthesis and
Rough ER: ribosomes are attached to the ER and
Smooth ER: synthesizes lipids, steroid hormones and
Ribosomes: site of protein synthesis. A cell’s “protein
Golgi 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
Peroxisomes: contain enzymes that detoxify harmful
substances. Membranous. Contain peroxidase and
Mitochondria: ATP synthesis. A cell’s “power plant”.
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.
Nucleus is one of the largest cell organelles. Houses
the genetic code which in turn dictates protein
synthesis. It’s membrane the Nuclear envelope
Nucleoplasm: nuclear substance
Nuclear pores: selectively permeable
Nucleolus: the most prominent structure visible in
the nucleus. Plays an essential role in the formation of
ribosomes. Synthesizes ribosomal RNA.
Cilia 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.
Microfilaments: 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
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.
Gap 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.