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Anatomy and Physiology
Chapter 3: The Cell
Cell Theory
 Cells are the building blocks of all plants and
animals.
 Cells are produced by the division of pre-existing
cells.
 Cells are the smallest units that perform all vital
physiological functions.
 Each cell maintains homeostasis at the cellular
level.
 Homeostasis at the tissue, organ, system, and
organism levels reflect the combined and
coordinated actions of many cells.
Cells
 Basic structural and functional unit of living
organisms.
 Cytology – study of cell structure and
function.
 Classes of Cells:
– Sex cells – sperm and oocytes (eggs)
– Somatic cells – body cells
Plasma Membrane
 Defines the extent of the cell and acts as a
fragile barrier between the inside and
outside of the cell.
 Exceedingly thin, but stable, structure
composed of a phospholipid bilayer with
protein molecules dispersed throughout.
 Impermeable to water soluble molecules –
semi-permeable.
Phospholipid Bilayer
 Polar, phospholipid heads are hydrophilic.
– Form inner and outer portions of the membrane
that comes in contact with the external cell
environment and the cytoplasm of the cell.
 Non-polar, fatty acid tails are hydrophobic.
– Form the inner portion of the membrane,
between two layers of polar phospholipid heads;
doesn’t come in contact with any water at all.
 Glycoproteins serve as cell surface markers.
Membrane Proteins
 Integral
– firmly inserted into the lipid membrane.
– Act as receptors for hormones and other
chemical messengers.
– Act as transmembrane proteins which have
transport functions such as ion channels / pores
or carrier molecules.
– Consist of a hydrophobic and hydrophilic region
also.
Membrane Proteins
 Peripheral
– Not embedded in the membrane, but are
attached to integral proteins exposed to the
surface.
– Some are enzymes.
– Some lead to cell shape changes associated
with cell division.
– Some are responsible for muscle cell
contraction.
Membrane Protein Functions
 Transport of molecules as carrier proteins
and channels.
 Two types of channels:
– “Leaky” – water and ions move through all the
time.
– Gated – open and close to regulate ion
passage.
Membrane Protein Functions
 Enzymes
 Receptor Cells
 Cell adhesion – anchor cell to structure or
other cells.
 Attachment to cytoskeleton – holds plasma
membrane to internal proteins; gives cell a
shape.
 Recognition – allows body to recognize
foreign invaders (glycolipids)
Glycocalyx
 “Sticky” carbohydrate rich area of the cell
plasma membrane.
 Also contains glycoproteins
 Binds adjacent cells together.
 Lubricates and protects cell membrane.
 Locomotion of specialized cells – white
blood cells.
Plasma Membrane Functions
 Isolation
 Sensitivity to changes in cellular
environment.
 Structural support.
 Regulation of exchange with environment
(semipermeable / selectivity permeable)
Factors that Effect
Membrane Permeability




Size of Particle
Electrical Charge of Particle
Shape of Particle
Lipid Solubility
Passive Transport
 No net energy expended.
 Occurs down a concentration
gradient from an area of high
concentration to an area of low
concentration without using ATP.
 Diffusion
– Simple Diffusion – implies no
barrier to movement; occurs
because of molecular collisions.
 Oxygen and carbon dioxide
exchange
 Water and other small
molecules (glucose)
– Filtration Diffusion – under
pressure; hydrostatic pressure
forces water across a
membrane, transporting small
molecules with it.
– Facilitated Diffusion –
substance coupled to a carrier
molecule; may be an integral
membrane protein.
 Carriers are highly specific
 Saturation limits amount of
molecules that can be moved
 May be regulated by the
binding of cofactors and
coenzymes.
– Example – glucose + insulin –
uptake occurs 7-10X faster.
Factors Affecting Diffusion
 Distance – the larger the distance between the
molecule and the cell membrane, the longer
diffusion takes.
 Size of Gradient – the larger the concentration
factor, the faster diffusion occurs.
 Molecular Size – smaller molecules diffuse faster.
 Temperature – increasing temperature increases
diffusion rates.
 Electrical Forces – like charges repel each other,
while opposite charges attract each other.
Tonicity
 Ability of a solution to change the tone or shape of
cells by altering their internal water volume.
– Isotonic  solute in = solute out; no NET movement of
water.
– Hypertonic  number of solute particles is larger
outside the cell than inside the cell; net movement of
water is out; cause cell to crenate.
– Hypotonic  number of solute particles is smaller
outside the cell than inside the cell; net movement is
into the cell; causes the cell to burst.
Passive Transport
 Osmosis – diffusion of water through a
semipermeable membrane from an area of
high water content to an area of low water
concentration.
 Osmotic Pressure – indication of force of
water movement into a solution as a result
of solute concentration.
Active Transport Processes
 Movement of particles using energy (ATP);
not concentration dependent.
– Solute / Ion Pumps
 proteins in the plasma membrane that move ions
selectively in or out of the cell
 creates a polarized membrane
 Sodium – Potassium Pump
– Sodium ions and potassium ions must be recaptured and
moved back to their original starting points. Each ATP used
moves 3 sodium and 2 potassium back.
Active Transport Processes
 Bulk Transport – movement of large particles by
means of vesicles.
– Method:
 Molecule comes in contact with the membrane
 Membrane surrounds molecule and takes it into the cell.
 Membrane pinches off, freeing the vesicle.
– Three Types:
 Phagocytosis – large particles in
 Pinocytosis – liquid particles in
 Exocytosis – Moving material out of the cell
Membrane Specializations
 Microvilli – minute, finger-like extensions of
the plasma membrane that increases the
cell surface area; contains a core of actin
(protein).
 Cilia – hair-like projections that move
substances along the surface of the cell.
Membrane Junctions
 Tight Junctions – protein molecules fuse
together; forming impermeable junctions.
 Glycocalyx
 “Tongue in groove” fit of adjacent plasma
membranes.
 Gap Junctions – allow direct passage of
chemicals between adjacent cells through
hollow cylinders.