Cellular Transport Notes
(Text 7.2 p 175-178 &
8.1 p 194-200)
Definitions

Cell membranes are completely
permeable to water.

The environment the cell is exposed to can
have a dramatic effect on the cell.

Solutions are made of solute and a solvent

Solvent - the liquid (water) into which the
solute is poured and dissolved.
Definitions

Solute: substance that is dissolved or
put into the solvent (water).
Common cell solutes include salts, sugars,
some minerals (iron ions and calcium ions)
and protons (electrons from acids).
 Eg. Sodium chloride dissolved in water
makes a saline solution. The sodium
chloride is the solute. The water is the
solvent.

Concentration



amount of solute per unit volume of
solution.
expressed in mass/volume (g/100ml percentage), ppm (parts per million), and
moles/volume (molarity).
The greater the mass or moles per unit
volume, the more concentrated the
solution.
Concentration Gradient


Difference in concentration between solute
molecules from area high concentration to
area of low concentration.
The greater the difference the faster the
rate of diffusion and vice versa

i.e. the steeper the hill
Cellular Membrane
Structure and
Function
All cells have a cell membrane
Chiefly responsible for maintaining
homeostasis inside a living cell using different
methods to transport molecules in and out of
the cell.
TEM picture of a real cell membrane.
Cellular Membrane
Structure and
Function



TEM picture of a real cell membrane.
Too much water can burst the cell
Too many wastes can poison the cell
The cell cannot tolerate any great variations
in ion conditions.
Jobs of the Cell
Membrane
TEM picture of a real cell membrane.
1. Provides protection and support for the cell
2. Regulate the exchange of substances (gases and
ions)
3. Communicates with other cells
4. Identification (proteins and carbohydrates on its
surface)
http://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdf
http://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdf
Polar heads love
water & dissolve
Fluid Mosaic
Model of the
cell membrane
Non-polar tails
hide from water
Carbohydrate cell
markers
Proteins
Membrane
movement
animation
Fluid Portion
Lipid Bilayer
- 2 phospholipid layers
a. Phosphate head is
polar (hydrophilic –
water loving)
b. Fatty acid tails nonpolar (hydrophobic –
water fearing)
c. Proteins embedded in
membrane
Phospholipid
Lipid Bilayer
Cell Membrane Pores
a.
b.
Selectively permeable: Allows some
molecules in and keeps other molecules out
The structure helps it be selective!
Pores
Lipid Bilayer
Outside of cell (interstitial)
Proteins
Transport
Protein
Animations
of membrane
Go to structure
Section:
Carbohydrate
chains
Phospholipids
Inside of cell (cytoplasm)
http://www.goldiesroom.org/AP%20Biology/AP%20Lecture%20Notes%20pdf/LN014--Ch05--Cell%20Transport.pdf

The different components of a plasma
membrane are integral proteins, peripheral
proteins, glycoproteins, phospholipids,
glycolipids, and in some cases cholesterol,
and lipoproteins.

Construction of the Cell Membrane Learning Activity
detailed cell membrane animation

Proteins Embedded in Membrane
Serve Different Functions

Transport Proteins


Channel Proteins


regulate movement of substance
form small openings for molecules to diffuse
through like water
Carrier Proteins

binding site on protein surface "grabs" certain
molecules and pulls them into the cell
animation
Gated Channels

similar to carrier proteins, not always "open"—
eg. Bind and pull in calcium ions when
needed. This requires cell energy—active
transport.
Receptor Proteins

molecular triggers that set off cell
responses (such as release of
hormones or opening of channel
proteins)

e.g. The junction between nerve cells
requires the transmission of
neurotransmitters between synaptic
gaps—these chemicals bind onto receptor
proteins.

Recognition Proteins - ID tags, to identify
cells to the body's immune system (called
antigens)
TRANSPORT MECHANISMS
1.
2.
PASSIVE TRANSPORT
ACTIVE TRANSPORT
1.
2.
ENDOCYTOSIS
EXOCYTOSIS
Types of Cellular Transport


Passive Transport
doesn’t use energy
1. Diffusion
2. Facilitated Diffusion
3. Osmosis
Active Transport
uses energy
1. Protein Pumps
2. Endocytosis
3. Exocytosis
•Transport Animations
Weeee!!!
high
low
This is
gonna be
hard
work!!
high
low
Passive Transport (p 198)
cell uses no energy
molecules move randomly
Molecules spread out from an area of
high concentration to an area of low
concentration.






i.e. down a concentration gradient
(High  Low)
Passive Transport Animation
3 Types of Passive Transport
1.
2.
3.
Diffusion – high conc. to low conc.
Facilitative Diffusion – diffusion with
the help of transport proteins
Osmosis – diffusion of water
1. Diffusion
Animation
 random movement of particles
from an area of high
concentration to an area of low
concentration.
(High to Low)
 Diffusion continues until all
molecules are evenly spaced
(equilibrium is reached)
 Note: molecules will still move around
but stay spread out.
http://bio.winona.edu/berg/Free.htm
1. Diffusion
2. Facilitated Diffusion
 diffusion that is enabled
by proteins (channel or
carrier proteins) which
bind onto required
molecules so that they
flow into the cell.
Transport Proteins are
specific – they “select”
only certain molecules
to cross the membrane
Transports larger or
charged molecules

A
B
Facilitated
diffusion
(Channel
Protein)
Diffusion
(Lipid
Bilayer)
Animation: How Facilitated Diffusion Works

http://bio.winona.edu/berg/Free.htm
Carrier Protein
2. Facilitated Diffusion
Cellular Transport
from an area of
Glucose
molecules
High
High Concentration

Cell Membrane
Low Concentration
Through a 
Go to
Section:
Transport
Protein
Protein
channel
Low
Channel Proteins
animations
3. Osmosis
Animations
Diffusion of water
through a selectively
permeable membrane
 From high to low
concentrations

•Water moves freely
through pores.
•Solute (green) too
large to move
across.
3. Osmosis
Factors Affecting Rate of Diffusion
1. Size


small molecules can slip through
phospholipids bilayer easier than large
molecules
very large molecules may not be able to
diffuse at all
2. Concentration



the greater the concentration gradient (bigger range) the
quicker a material diffuses (makes the molecules want to
move faster) – think of a crowded room
3. Temperature
In general as temperature increases – molecules move
faster which translates into faster diffusion
4. Polarity of molecules

Water-soluble (polar) molecules will not
easily move through the membrane
because they are stopped by the middle
water-insoluble (nonpolar) layer
5. Surface Area

As a cell’s size increases its volume increases
much quicker than it’s surface area.


If cell size is doubled, it would require 8 times
more nutrients and have 8 times s much waste.
SA only increases by a factor of 4 – not enough
surface area through which nutrients and wastes
could move.


If you double individual lengths (1 cm to 2 cm) the
surface areas increases 4 times, and the volume
increases 8 times.
Cell would either starve or be poisoned (waste
products)
Cells divide before they come too large to
Active Transport

Involves moving molecules "uphill" against
the concentration gradient, which requires
energy.

Uses carrier protein molecules as receptors.
One may transport calcium ions another glucose
molecules.
 Hundreds of these types of protein molecules.
 Each one changes shape to accommodate a
specific molecule.

(Low  High)
2. Active Transport (cont’d)

Their activity can be stopped from
transporting molecules with inhibitors
(unfortunately, these are usually poisons)
which:


either destroy the membrane protein
or just plug it up
(e.g. for your neurons – tetanus &
botulinum-B secrete a poison that
suppress the Na/K pump)


Three types:
active transport animation
http://www.biology4kids.com/files/cell2_activetran.html
1. Protein Pumps
Sodium
Potassium Pumps
• transport proteins that
require energy to do
work
• Example: Na+/K+
pumps are important
in nerve responses.
Protein changes
shape to move
molecules: this
requires energy!
Sodium-Potassium Pump

Pumps out 3 sodium atoms for ever 2
potassium atoms taken in against gradient
in the cell.
ATP and the Na/K Pump
Animation: How the Sodium Potassium Pump Works
The H+/K+ ATPase


The parietal cells of your stomach (lining) use
this pump to secrete gastric juice.
These cells transport hydrogen ions (H+) from a
concentration of about 4 x 10-8 M within the cell
to a concentration of about 0.15 M in the gastric
juice (giving it a pH close to 2).


Recall: pH – power of the H+ ion
Small wonder that parietal cells are stuffed with
mitochondria and use huge amounts of energy
as they carry out this three-million fold
concentration of protons.
The H+/K+ ATPase
3. Exocytosis


Endocytosis &
Exocytosis
animations
Moves large, complex molecules such as
proteins out of the cell membrane.
Large molecules, food, or fluid droplets are
packaged in membrane-bound sacs called
vesicles.
Cell changes shape – requires energy
 Ex: Hormones or wastes released from cell
 Transport Animations

2. Endocytosis

taking bulky material into a
cell
• Uses energy
• Cell membrane in-folds
around food particle
• “cell eating”
• forms food vacuole &
digests food
• This is how white blood
cells eat bacteria!
Endocytosis

Endocytosis moves large particles (huge
molecules or molecular conglomerates)
into a cell.
endo & exocystosis animations
Phagocytosis
Phagocytosis is another type of endocytosis
used for massive transport.
Cell membrane extends out forming
pseudopods (fingerlike projections) that
surround the particle.
 Membrane pouch encloses the material &
pinches off inside the cell making a vesicle.
 Vesicle can fuse with lysosomes(digestive
organelles) or release their contents in the
cytoplasm
Animation: Phagocytosis
HowStuffWorks "Phagocytosis"


Used by ameba to feed & white blood
cells to kill bacteria.
Known as “killer cells"

Pinocytosis is another type of
endocytosis



Cell membrane surrounds fluid droplets
Fluids taken into membrane-bound vesicle
Known as “cell drinking”
•Exocytosis is used to remove
large products from the cell
such as wastes, mucus, & cell
products such as hormones
and antibodies.
•Exocytosis is the process
used by our memory cells
(white blood cells that produce
antibodies to fight infection).
•It is also used by our gland
cells to secrete hormones
when needed.
•Phagocytosis
animation
In Summary
Essential Biochemistry - Membrane Transport
Transport Flowchart
Transport of Materials
Across a Membrane
Active
Ion Endocytosis
Exocytosis
Pump
Pinocytosis Phagocytosis
Passive
Simple
Osmosis Facilitated
Diffusion
Diffusion
Osmosis and Tonicity


Tonicity is a relative term
Water molecules are so small, and there is
so much of it, that the cell can’t control it’s
movement through the cell membrane.
Osmosis
Animations for
isotonic, hypertonic,
and hypotonic
solutions

Hypotonic Solution
Hypotonic: The solution has a lower concentration of
solutes and a higher concentration of water than
inside the cell. (Low solute; High water)
Result: Water moves from the solution to inside the
cell): Cell Swells and bursts open (cytolysis)!
Osmosis
Animations for
isotonic, hypertonic,
and hypotonic
solutions

Hypertonic Solution
Hypertonic: The solution has a higher concentration
of solutes and a lower concentration of water than
inside the cell. (High solute; Low water)
shrinks
Result: Water moves from inside the cell into the
solution: Cell shrinks (Plasmolysis)!
Osmosis
Animations for
isotonic, hypertonic,
and hypotonic
solutions

Isotonic Solution
Isotonic: The concentration of solutes in the solution
is equal to the concentration of solutes inside the cell.
Result: Water moves equally in both directions and
the cell remains same size! (Dynamic Equilibrium)
What type of solution are these cells in?
A
B
C
Hypertonic
Isotonic
Hypotonic
Plant and Animal Cells put into
various solutions
How Organisms Deal with
Osmotic Pressure

Paramecium
(protist) removing
excess water
video
•Salt water fish pump salt out of their specialized gills so
they do not dehydrate.
•Animal cells are bathed in blood. Kidneys keep the
blood isotonic by remove excess salt and water.
•Blood brain barrier allows some substances into the
brain, but screens out toxins and bacteria
• Allows water, CO2, glucose, AA’s, alcohol, &
antihistamines
• HIV and bacterial meningitis can also cross this
barrier
How Organisms Deal with
Osmotic Pressure

Paramecium
(protist) removing
excess water
video
•Bacteria and plants have cell walls that prevent them from overexpanding. In plants the pressure exerted on the cell wall by the
central vacuole is called tugor pressure. (bike tire analogy)
•A protist like paramecium has contractile vacuoles that collect
water flowing in and pump it out to prevent them from overexpanding.