Transcript Membrane TXPT2

Membrane
Transport:
Passive & Active
See 81-85 in your book
See the handout
What is the difference between
passive and active transport?
Passive Transport #1: Diffusion
Passive Transport #2: Osmosis
Passive Transport #3:
Passive Transport #4: Ion Channels
Active Transport #1: Membrane/Ion Pumps
Active Transport #2: Endocytosis
Active Transport #3: Exocytosis
Key Definitions
• Homeostasis: maintaining the internal
conditions of the cell
• Equilibrium: an equal amount of solutes
on both sides of a membrane
• Potential energy vs. Kinetic energy
• Concentration gradient
Passive Transport #1: Diffusion
• Movement of molecules from
area of [high] to [low]
• Caused by kinetic energy; molecules
simply colliding.
• Ability to diffuse depends
Size
Polarity: like dissolves like
Electric charge: opposites attract
Passive Transport #1: Diffusion
• Examples of diffusion:
– CO2 and O2 are nonpolar. They can dissolve
in lipids and diffuse across membrane
– Small molecules can diffuse; what does this
mean for large molecules like glucose?!
Passive Transport #2: Osmosis
• The diffusion of water
• Solution = solute in a solvent
• Water = “Universal Solvent”
• Direction of osmosis
– Shortcut: Water flows to area of
higher solute concentration.
Osmosis: Definitions of
Solutions
• Hypotonic: Solution with lower [solutes]
• Hypertonic: Solution with high [solutes]
• Isotonic: Solution with equal [solutes]
• Pay attention to how a cell maintains
equilibrium!
(Pause to practice analyzing situations)
How Do Cells Deal With
Osmosis?
• Isotonic? Vertebrates on land. Most sea
organisms
• Most freshwater organisms are in hypotonic
environments (esp if unicellular)
– Where is water constantly moving?
– Contractile vacuoles: to pump water out
(NOTE: This requires energy!)
Multicellular organisms will get rid of solutes
instead
How Do Plants Deal With
Osmosis?
Generally, plants live in hypotonic environments.
Turgor pressure: pressure that membrane exerts
agains the cell wall as the cell fills with water.
BUT
Plants in hypertonic environments LOSE water
Turgor pressure is….
Cell membrane ….
This is PLASMOLYSIS (--> WILTING)
See page 83 in your book
How Do Animals Deal With
Osmosis?
Some cells cannot withstand changes caused by
osmosis.
(No cell walls, no contractile vacuoles, no solute
pumps*)
In hyptertonic solutions, what happens?
In hypotonic solutions, what happens?
CYTOLYSIS
See page 83 in your book
(Red blood cells)
Passive Transport #3:
• If molecules are large or not lipid soluble
• Carrier proteins change shape, shield the
molecule from nonpolar region of membrane
– Specific to each molecule: glucose; each amino
acid
Passive Transport #4: Ion
Channels
• Ions like K+, Na+, Ca2+, Cl- are not lipid soluble
• Specific to each ion: Basic Ion Channel
• Some are “gated”
– Membrane stretching
– Electrical signals
– Chemical signals
Check out this potassium channel
Active Transport: What’s so
special about active transport?
• Solute moves from [LOW] to [HIGH]
• Like going uphill, or upstream, this
requires energy
– “Up the concentration gradient”
(Keep in mind the osmosis issues
that require active transport)
Active Transport #1: Membrane
Pumps a.k.a. Na-K Pump
Acts like a carrier protein BUT ATP is needed to
fuel the activity
Animal cells need Na outside and K inside
The ATP changes the shape of the protein…
Basic Ion Pump
How The Pump Works
*Important for creating gradients leading to membrane
potential aka voltages
Active Transport #2:
Endocytosis
• To transport things INTO the cell.
• Phagocytosis: transport large particles or
whole cells, bacteria and viruses (Cell eating)
• Pinocytosis: transport solutes or fluids (cell
drinking)
• Membrane folds in and forms a vesicle
• Some vesicles fuse with lysosomes, which
digest the contents.
Paramecium! Neutrophils!
Macrophages!
Active Transport #3:
Exocytosis
• Reverse of endocytosis
• To release large molecules made by the
cell…
– Proteins can be made by the ribosomes on
rough ER, then packaged into vesicles by
Golgi apparatus, and secreted
– Endocrine system is a good example
– To get rid of waste
Paramecium Performing Exocytosis
Membrane Transport
Passive Transport #1: Diffusion
Passive Transport #2: Osmosis
Passive Transport #3:
Passive Transport #4: Ion Channels
Active Transport #1: Membrane/Ion Pumps
Active Transport #2: Endocytosis
Active Transport #3: Exocytosis