Download Transport-cell membrane

Why is the cell membrane so
important???
Names!
• Cell membrane
• Plasma membrane
• Selectively permeable
membrane
• Semi permeable membrane
Functions of the Cell Membrane
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Protects the cell
Regulates what goes in and out of cell
Helps to communicate with other cells
Creates attachments between cells
Dynamic!
**Maintains HOMEOSTASIS in the cell**
Structure of the Cell Membrane
• Phospholipid bilayer –
double layered sheet
– Properties of the lipids
determine the properties of
the membrane:
• Hydrophobic (“waterfearing”) = tails
• Hydrophilic (“water-loving”)
cluster together = heads
Heads DO touch water, tails
DO NOT touch water
Fluid Mosaic Model
dev. By Singer & Nicolson 1972
• Proteins move within layers of lipids w/I viscous
fluid
– Transport
– Structure
• Hydrogen bonds can form between water and
phospholipid heads inside and outside of cell
Types of Membrane Proteins
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Glycoproteins
Receptor proteins
Recognition proteins
Enzymatic proteins
Attachment proteins
Transport proteins
*KNOW THE FUNCTIONS! (pg. 84 in textbook)*
• The more double bonds there are in the tails the more fluid
the membrane
• Incr. in temp. causes membr. To be more fluid (because
mol. Move faster)
• Decr. Temp. (mol. Move slower -> less fluid)
Selectively Permeable
• Some substances can pass, others cannot pass
– Most substances can pass
– Substances that are too big or charged cannot
cross the bilayer
• Therefore, cells need different means of
TRANSPORT to move these substances into
and out of the cell
REVIEW
(review slide)
REVIEW
• Head region of the lipid are polar molecules so
they are attracted to water
• Tails region of the lipid are nonpolar they
repel water.
• These molecular properties form the
separation of inside and outside the cell.
Vocabulary Terms
• Solution- mixture in which one or more
substances are UNIFORMLY distributed in
another. “homogenous solution”
• Solute- what gets dissolved.
• Solvent- what does the dissolving.
• Ex. salt water:
– salt is solute
– water is solvent.
• Ex. Ice tea
– Mix is solute
– Water is solvent
Passive Transport
• Requires NO energy!!
• Movement from a high
concentration to a low
concentration!
Passive Transport
• 1. diffusion
• 2. osmosis
• 3. facilitated diffusion
• 4. diffusion through ion
channels
Diffusion
Diffusion
• Individual particles continuously move in
random directions
• Molecules moving from a greater
concentration to a lower concentration
• Ex: perfume, air freshener
• Simple diffusion – substances pass through
the membrane with no outside aid
– Ex. substances: Oxygen, Carbon Dioxide, water
and lipid soluble molecules
Diffusion
Molecules are in constant motion
they will continue to move until
equilibrium is reached.
Outside cell
inside cell
Equilibrium !
O2
O2
O2
O2
O2
O2
High
Concentration
Low
Concentration
Diffusion video:
http://highered.mcgrawhill.com/sites/00724958
55/student_view0/chapt
er2/animation__how_dif
fusion_works.html
Vocabulary
• Concentration gradient: difference
in concentrations (amount of solute)
• Equilibrium: particles/molecules are
equal on both sides of membrane
More diffusion -> “equilibrium”!!
Describe how oxygen and carbon dioxide move into and out
of the lungs and extremities. Page 4 molecular workbench “diffusion,
osmosis, active transport”
Osmosis
Osmosis
• Diffusion of WATER from a high
concentration to a low
concentration across the cell
membrane
• Water moves DOWN its
concentration gradient until
http://highered.mcgrawequilibrium
is reached
hill.com/sites/0072495855/student_view0/chapter2/a
nimation__how_osmosis_works.html
water
membrane
6
sugar solution
There are as many water molecules on the right as there are
on the left but many of them are attached to sugar molecules
and are not free to move.
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Because there are more freely moving water molecules on
the left, more diffuse through the pores of the membrane from
left to right than from right to left.
Iso – Hyper – Hypotonic Solutions
Vocabulary
• Isotonic: concentration inside and
outside of cell are the same  no net
diffusion
• Hypertonic: when concentration of solute
outside of cell is greater, water moves out
of cell (shrink) (High solute, Low water)
• Hypotonic: concentration of solute inside
of cell is greater, water moves into cell
(burst) (Low solute, High water)
Osmosis in animal cells
There is a greater concentration of
free water molecules outside the
cell than inside
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so water diffuses into the cell
by osmosis
and the cell swells up
Where is there more water?
Out of the cell
Which way will it move?
Into the cell
Type of Solution?
Hypotonic Solution
Where is there more water?
Equal
Which way will it move?
No net movement
Type of Solution?
Isotonic Solution
Where is there more water?
In the cell
Which way will it move?
Out of the cell
Type of Solution?
Hypertonic Solution
Plasmolysis
Plants!
• Plasmolysis = cell shrinks away from cell
wall due to water loss ex: drought (low rain
fall) causing plants to wilt
• Turgid: swollen
• Turgor pressure the rigidity of plant cells
when they contain enough water so that
the cell membrane exerts pressure on the
cell wall.
• Can tell turgor pressure is low when plant
wilts
Osmosis: the diffusion of water as seen in
class.
• Size of a cell membrane can change as the
amount of water inside changes in response
to external conditions change.
Cells surrounded by “plain water”
Cells surrounded by “salt” water
Facilitated Diffusion
Facilitated Diffusion
• Uses specific protein pores in the cell membrane to
move certain “large” molecules from high
concentration to low concentration.
• Used for transport of water soluble molecules
(hydrophillic). Ex: ions, amino acids (small proteins),
and sugars
• Carrier Protein - protein recognizes substance>changes shape->delivers substance to inside of the
cell
• Aquaporins – allow water to cross at a fast rate via
faciliated diffusion
http://highered.mheducation.com/sites/0072495855/stude
nt_view0/chapter2/animation__how_facilitated_diffusion_
works.html
Ion Channels
Ion channels
• Allows ions Ca2+ and Cl- to enter cell
• Some are open all the time
• Others are gated and will open when
– Cell membrane stretches
– Electrical signals
– Chemical signals
Active Transport
• REQUIRES ENERGY!
• Movement from a LOW
concentration to a
HIGH concentation!
Active Transport
• 1. Sodium Potassium Pump
• 2. Endocytosis
• 3. Exocytosis
Active Transport
Sodium Potassium Pump
• pumps to keep ions in balance
• 3 Na+ out for every 2 K+ in
• This creates a build up of Na+ outside cell
and K+ inside cell forming a net electrical
charge across the membrane
• Allows for nerve impulses
• Contraction of muscles
• 1/3 of all energy in animal cells goes to
running this pump even as we sleep!
Endocytosis
Endocytosis
• Take in external fluid, macromolecules and
other large particles.
• Forms “vesicle” some fuse with
lysosomes (digestion) others fuse with
membrane of other organelles.
• 2 Types: a) pinocytosis – cell drinking
fluid
•
b) phagocytosis – cell eats
Exocytosis
opposite of endocytosis!!