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Cell Membrane: Structure, Function, and Materials Movement - Prof. Thomas E. Rachow, Study notes of Physiology

An overview of the cell membrane, its composition, and its role in controlling the movement of materials into and out of the cell. Topics include the fluid-mosaic model, lipid bilayer, phospholipids, proteins, passive and active channels, diffusion, facilitated diffusion, osmosis, tonicity, and active transport. The document also covers exocytosis and endocytosis, specifically phagocytosis and pinocytosis.

Typology: Study notes

Pre 2010

Uploaded on 08/08/2009

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Cell Membrane-Structure and
Function
BIO 250
Living things are composed of cells
and cell products (extracellular)
Cells are the basic unit of structure
They are the basic unit of function
They vary in size, shape and function
Shape related to function
RBC shape gives large surface area for gas
exchange
Nerve cell (neuron) has long threadlike fiber to
communicate over long distance
Adult human has about 75 trillion cells.
Cell membrane
Separates outside from inside cell
Selectively permeable
Composed primarily of phospholipids and
p
roteins with some carbohydrates,
cholesterol and ions
Plays a role in intercellular communication
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Cell Membrane-Structure and

Function

BIO 250

Living things are composed of cells

and cell products (extracellular)

‹ Cells are the basic unit of structure

‹ They are the basic unit of function

‹ They vary in size, shape and function

‹ Shape related to function

  • RBC shape gives large surface area for gas

exchange

  • Nerve cell (neuron) has long threadlike fiber to

communicate over long distance

‹ Adult human has about 75 trillion cells.

Cell membrane

‹ Separates outside from inside cell

‹ Selectively permeable

‹ Composed primarily of phospholipids and

proteins with some carbohydrates,

cholesterol and ions

‹ Plays a role in intercellular communication

Back

Back

Back

Movement of Materials Through

Membranes

‹ Involve physical or physiological processes

‹ Gradients typically present

‹ Several processes involved

Diffusion

‹ Random motion of solutes in a solution

‹ Involves concentration gradient

  • Concentration gradient is a measure of the difference in concentration of a solute in a solvent between two points divided by distance between the two pointsdivided by distance between the two points.

‹ Factors affecting speed of diffusion

  • Concentration of molecules
  • Particle size and weight
  • Temperature

Diffusion through a leak channel

Facilitated Diffusion

‹ Scattering of molecules

‹ Involves concentration gradient

‹ Involves a cell membrane

‹ Involves specific protein carrierp p

‹ Does not require expenditure of energy by cell

Osmosis

‹ Involves diffusion of water

‹ Through a selectively permeable membrane

‹ Requires a concentration gradient

‹ Water diffuses through membrane from

side with high water concentration to side

with lower water, OR

‹ Water diffuses through membrane from

side with low solute concentration to side

with higher solute.

Colloid Osmotic Pressure (COP)

‹ Interstitial fluid is returned to blood by osmotic pressure of blood proteins. ‹ Filtration and COP are opposing forces ‹ Forces are not balanced

Exo- and Endocytosis

‹ More massive materials can be moved

‹ Exocytosis

‹ Endocytosis

Phagocytosis/Pinocytosis

‹ Particulate matter can brought into the cell

by endocytosis.

‹ Cells that regularly “eat” material from

outside are called phagocytes (cells that eat)id ll d h ( ll h )

‹ If the material brought into the cell by

endocytosis is soluble material the process

is called pinocytosis (pino- to drink)