Cell Transport Flashcards
What is the structure of the cell membrane
Fluid mosaic of lipids and proteins
What is the consequence of this structure
It is consequently a selectively permeable membrane which means different substances cross the membrane via
1) Passive Transport
2) Active Transport
3)Bulk Transport
Phospholipids
- Phospholipids are the most abundant lipids in the plasma membrane
- contain hydrophobic and hydrophilic regions.
*Making the cell membrane Amphipathic. The amphipathic nature of phospholipids results in the formation of a bilayer in water
The Fluidity of Membranes
- The lipid membrane must be fluid in order to function
- Phospholipids in the plasma membrane can move within the bilayer
- As temperatures cool, membranes switch from a fluid state to a solid state.
- Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids
Membrane Proteins and Their Functions
Proteins embedded in the lipid bilayer determine most of the membrane’s specific functions
The 6 major functions of embedded proteins
a) Transport
b) Enzymatic Activity
c)Signal Transduction
d)Cell-Cell Recognition
e)Intercellular joining
f) Attachment to the Cytoskeleton
Membrane structure results in
selective permeability
- A cell must exchange its materials with its surroundings, a process controlled by the plasma membrane.
- Plasma membranes are selectively permeable,
regulating the cell’s molecular traffic - Two components affect permeability:
1) Lipid bilayer
2) Transport proteins
The Permeability of the Lipid Bilayer
- Hydrophobic molecules ( non-polar) can pass
through the lipid bilayer rapidly - eg.
- Hydrophilic molecules (polar) do not
cross the membrane easily - eg.
Hydrophobic nonpolar O2, CO2 and hydrocarbons
Hydrophilic ions and polar sugars, water, Na+, K
Transport Proteins
- allow passage of hydrophilic substances
across the membrane - Two main types:
1) Channel, have a hydrophilic channel
that certain molecules or ions can be used as a
tunnel
2) Carrier proteins, bind to molecules and
change shape to shuttle them across the
membrane
Passive transport is the diffusion of a substance across a membrane with no energy investment
Diffusion is the tendency of molecules to spread out evenly into the available space
* Although each molecule moves randomly, diffusion of a population of molecules may have a net movement in one direction
* At dynamic equilibrium, as many molecules cross one way as cross in the other direction
Concentration gradients
Substances diffuse down their concentration gradient
* No work must be done to move substances down a concentration gradient
* Diffusion across a biological membrane is
passive because it requires no work to make it happen
Osmosis
The diffusion of water across a selectively permeable membrane
* Water diffuses across a membrane from the
region of lower solute concentration to the
region of higher solute concentration.
Tonicity
The ability of a solution to cause a cell to gain or lose water
Osmoregulation
The control of water balance is a necessary adaptation for life in such environments
* The unicellular Paramecium, which is hypertonic to its pond water environment, has a contractile that acts as a pump
Water Balance of Cells with Walls
- Cell walls help maintain water balance
- A plant cell in a hypotonic solution swells until the wall opposes uptake; the cell is now turgid (firm)
- In an isotonic environment, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt
- In a hypertonic environment, plant cells lose
water; the membrane pulls away from the wall,
a usually lethal effect called plasmolysis.
