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Life’s Guardian…
Cell Membranes
…their Structure & Function
How do things enter and
leave living cells?
How does carbon dioxide
and other waste products
Do cells drink
and eat? leave our cells?
How does oxygen
How do nutrients get into our cells?
enter our cells?
How do white blood cells
engulf foreign invaders?
All living cells are surrounded by
an extracellular fluid (ECF).
Besides other organisms, there
are many chemicals in the ECF.
SMALL
HYDROPHOBIC
MOLECULES
O2 , CO2 , N2 ,
LARGER UNCHARGED
POLAR MOLECULES
amino acids, glucose,
benzene
nucleotides
H2O , alcohols
IONS
SMALL UNCHARGED
N+ , Na+ , HCO 3- , K+, POLAR MOLECULES
Ca2+ , Cl - , Mg 2+
Solutions where the water is the
solvent such as the ECF and blood
are called aqueous solutions.
solvent
Solution
A solution is a combination of a
solvent with one or more solutes.
solvent
Solution
solute
If this solution was blood the solvent
would be called plasma and the solute
would be red and white blood cells.
An organism's chemical processes
are carried out inside cells and/or it’s
organelles.
Biochemical reactions require raw
materials from outside the cell and
generate waste products inside that
the cell must discharge back into its
environment.
In order to do this and remain alive a
cell must maintain
CHEMICAL HOMEOSTASIS.
Homeostasis is the maintenance of a
steady state or balance within the
cell or organism.
The PLASMA MEMBRANE plays a
major role in the maintenance of
homeostasis as it determines what
enters and leaves the cell.
Life’s Hangout
Plasma membrane
Embedded
Proteins
Phospholipids
Gk: phil – loving phob – fear
Life’s Hangout
Phospholipids
hydrophillic or
water loving head
hydrophobic or
water fearing end
~75-95% of the cell’s
plasma membrane
Life’s Hangout
Embedded Proteins
Carrier proteins that
regulate transport
and diffusion
~5-25%
of that
the cell’s
Marker
proteins
identify
the cell
to
plasma
membrane
other cells
And receptor proteins
that allow the cell to
receive instructions
Life’s Hangout
Embedded Proteins
Embedded proteins provide the cell with a
pore for the passive transport of solute
particles.
Diffusion
concentration
gradient
Life’s Hangout
Embedded Proteins
Carrier proteins provide the cell with a
means of active transport.
facilitated diffusion
concentration
gradient
Life’s Hangout
Embedded Proteins
Symport carrier proteins provide the cell
with a means of two-way diffusion.
Sodium-Na+
Active Transport
concentration
ATP
gradient
Glucose
Life’s Hangout
Embedded Proteins
Marker proteins extend across the
plasma membrane and serve to
identify the cell. The immune system
uses these proteins to tell friendly
cells from foreign invaders.
Life’s Hangout
Embedded Proteins
Receptor proteins are used in
intercellular communication. In this
animation a hormone binds to the
receptor. This
causes the receptor
protein to release a
chemical signal to
perform a specific
action.
Life’s Hangout
Embedded Proteins
The passive transport of solvent
molecules like water is called ….
A
B
concentration
gradient
Life’s Hangout
Review
Cells are essentially a selectively
permeable sack of particles
dissolved in water with larger
complex structures suspended in
the resulting solution.
For this reason, it is important to know
what a solution is before attempting to
understand how cells respond to
changes in their environments.
Simple Diffusion