August 27-28, 2015

Selectively permeable barrier between the cell
and the environment.

Selectively permeable barrier between the cell
and the environment.
What does ‘selectively permeable’ mean?

Selectively permeable barrier between the cell
and the environment.
What does ‘selectively permeable’ mean?
Only some materials can cross the
membrane
Selective permeability is necessary for the
cell to maintain the correct internal
environment for physiological functions.

Phospholipids
◦ Make up the majority of
the membrane
◦ Arranged in a bilayer,
with hydrophilic heads
outside, and
hydrophobic tails inside

Phospholipids
◦ Make up the majority of
the membrane
◦ Arranged in a bilayer,
with hydrophilic heads
outside, and
hydrophobic tails inside
Hydrophilic = ___________
Hydrophilic molecules are __________ like water.
Hydrophobic = ____________
Hydrophobic molecules are __________ like oil.

Phospholipids
◦ Make up the majority of
the membrane
◦ Arranged in a bilayer,
with hydrophilic heads
outside, and
hydrophobic tails inside
Hydrophilic = water loving
Hydrophilic molecules are polar like water.
Hydrophobic = water fearing
Hydrophobic molecules are nonpolar like oil.

Phospholipids
The structure of
phospholipids is the key
to their function!
Hydrophilic heads can interact with watery external
environment and watery cytoplasm.
Hydrophobic tails reduce the diffusion of water and
other charged or polar substances across the
membrane.

Cholesterol
◦ Makes the cell membrane more rigid
and less permeable to water

Proteins
◦ Act as enzymes, pores, carriers, and hormone
receptors, and structural elements

Glycoproteins and Glycolipids
◦ Glyco = sugar!
◦ Influence cell interactions (e.g. identifying cell as
‘self’) and molecule transport
Talk with a partner then share as a class

Scholar on the left answers …
◦ What are the 4 membrane components?
◦ Which component has most functions? Why?

Scholar on the right answers …
◦ Name 4 functions of membrane proteins
◦ Which two components are primarily responsible for
reducing fluid loss through the cell? What do those
components have in common?

____________ a dissolving agent (water, usually)

____________ substances dissolved in a solution

____________ watery environment outside cells

____________ lower solute concentration

____________ higher solute concentration

____________ equal solute concentration

Solvent: a dissolving agent (water, usually)

Solute: substances dissolved in a solution

Interstitial fluid: watery environment outside cells

Hypotonic: lower solute concentration

Hypertonic: higher solute concentration

Isotonic: equal solute concentration
Transport of materials across the cell
membrane can be characterized as passive or
active.
Transport of materials across the cell
membrane can be characterized as passive or
active.
Passive mechanisms require NO ENERGY from
the cell. ALL passive mechanisms transport
molecules down their concentration gradient.
Active mechanisms require energy from the
cell.
Diffusion is the net movement of molecules
down their concentration gradient. Results
from the random movement of molecules.
Diffusion animation

Simple Diffusion – diffusion directly across
the cell membrane or through membrane
pores. Only works for tiny OR non-polar
molecules.
Examples:

Simple Diffusion – diffusion directly across
the cell membrane or through membrane
pores. Only works for tiny OR non-polar
molecules.
Examples:
fats, fat-soluble
vitamins, O2, CO2, Cl-

Simple Diffusion – diffusion directly across
the cell membrane or through membrane
pores. Only works for tiny OR non-polar
molecules.
Examples:
fats, fat-soluble
vitamins, O2, CO2, ClOsmosis is simple
diffusion of water.

Facilitated diffusion - diffusion using a
protein carrier; used for large polar molecules
◦ Example: glucose
Filtration occurs when water and solutes are
pushed through a membrane by hydrostatic
(fluid) pressure.
Water and solutes move down pressure
gradient.
Process by which blood
is filtered in the kidney.
Wait 30 sec, then show answer with your fingers

What 2 things do all passive transport
mechanisms have in common?
1) Membrane proteins are always involved and no
energy is required
2) Membrane proteins are always involved and energy
is required
3) Molecules move down a gradient and no energy is
required
4) Molecules move down a gradient and energy is
required
Wait 30 sec, then show answer with your fingers

What 2 things do simple and facilitated
diffusion have in common?
1) Membrane proteins are always involved and no
energy is needed
2) Membrane proteins are always involved and energy
is required
3) Molecules move down their concentration gradient
and no energy is needed
4) Molecules move down their concentration gradient
and energy is required
How is each molecule transported? Show
1) Simple diffusion through lipids
2) Simple diffusion through protein pores
3) Facilitated diffusion using carrier proteins
a)
b)
c)
d)
Water
CO2
Glucose
Cl-
How is each molecule transported? Show
1) Simple diffusion through lipids
2) Simple diffusion through protein pores
3) Facilitated diffusion using carrier proteins
a)
b)
c)
d)
Water - 2
CO2 - 1
Glucose - 3
Cl- - 2
Use the picture to answer.
In which direction will ions diffuse?
1) into the cell
2) out of the cell
In which direction will
osmosis occur?
1) into the cell
2) out of the cell
Use the picture to answer.
In which direction will ions diffuse?
1) into the cell
2) out of the cell
In which direction will
osmosis occur?
1) into the cell
2) out of the cell
Active transport requires the use of energy (ATP)
to transport material across the cell.
Active transport is used for
◦ Solutes moving against the concentration gradient
- or ◦ Very large substances

Solute Pumping (aka active transport)
Membrane proteins (called solute pumps) use
ATP to carry solutes against their concentration
gradient.
Examples: amino acids and
most ions

Exocytosis - movement of materials out of the
cell by vesicle
Examples: hormones, neurotransmitters, mucus, some
wastes

Endocytosis – movement of materials into the
cell by vesicle

Endocytosis – movement of materials into the
cell by vesicle
◦ Phagocytosis (cell eating) –
white blood cells engulf bacteria, dead cells, and
foreign debris
◦ Pinocytosis (cell drinking) –
used to take up droplets of fats and dissolved
proteins
Animation
Many diseases are caused by malfunctions in
cell membrane transport.
Examples:
 Cystic Fibrosis: a Cl- channel is missing,
causing Cl- to build up within the cell
 Familial hypercholesterolemia – cholesterol
receptors on cell membrane missing, so
cholestrol builds up in the blood
 Burned tissue ‘weeps’ fluids, proteins, ions,
etc.
Draw a detailed picture of the cell membrane.
Include, and label:
 The structural components
 Phospholipids, cholesterol, membrane proteins,
glycoproteins, glycolipids

The transport mechanisms
 Simple diffusion, osmosis, facilitated diffusion, solute
pumping, exocytosis, pinocytosis, phagocytosis
When done, compare with a neighbor, but don’t add to
it.