Transcript Cell Membrane and Transport PowerPoint

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
• 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
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
• Molecules moving from a greater
concentration to a lower concentration
• Ex: perfume
• Simple diffusion – substances pass
through the membrane with no outside aid
– Ex. substances: Oxygen, Carbon Dioxide,
water and lipid soluble molecules
Vocabulary
• Concentration gradient: difference
in concentrations (amount of solute)
• Equilibrium: particles/molecules are
equal on both sides of membrane
More diffusion -> “equilibrium”!!
Osmosis
Osmosis
• Movement of WATER from
a high concentration to a
low concentration across
the cell membrane
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)
• Hypotonic: concentration of solute
inside of cell is greater, water moves
into cell (burst)
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
• Turgor Pressure = cell wall
sustains shape, otherwise would
explode
Facilitated Diffusion
Facilitated Diffusion
• Carrier Protein –
-protein recognizes substance->changes
shape->delivers substance to inside of
the cell
• Facilitated Diffusion: water soluble
molecules (hydrophillic). Ex: ions,
amino acids (small proteins), and
sugars
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 like 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
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b) phagocytosis – cell eats
Exocytosis
opposite of endocytosis!!