Sec 6- Membranes Flashcards
Unit II- Life of a Cell
What are plasma membranes made of?
Phospholipids and proteins
Membrane Proteins
- Membrane proteins that interact with molecules outside of the cell are called receptors.
- They are improtant for cell-to-cell signaling.
- Viruses can take advantage of these receptors and bind to (and enter) our cells.
What is the function of membrane proteins?
- Anchor the cell to the ECM
- Transport substances across the membrane
- Catalyze enzymatic reactions near the cell surface
- Receive information from other cells in the form of chemical or electrical signals
- Serve as identification tag
What is the movement of molecules across the Plasma Membrane?
For metabolism to work, a cell must keep its internal composition stable- even when conditions outside are greatly different.
What is selective permeability?
Membrane property that allows some substances, but not others, to cross.
- Nonpolar, small molecules easily cross
- Ions and/or large molecules can’t cross
What is concentration?
The number of molecules or per unit volume of a fluid.
What is the concentration gradient?
Difference in concentration of a substance between adjoining regions of fluid.
What is passive transport?
Substance moving down its concentration gradient drives it across a cell membrane.
- Requires no direct energy input
- Diffusion (including osmosis)
- can be through the phospholipids directly or through a transport protein (pore)
- Molecules will move down it’s own concentration gradient until equilibrium is reached.
- This movement is independent of other molecules and their concentration gradients.
What is active transport?
A transport protein use energy, usually from ATP, to pump a substance across a cell membrane against its concentration gradient (pump).
What is diffusion?
Molecules and ions tend to follow their own concentration gradient and fdiffuse into an adjoing region in which they are less concentrated.
- net movement of molecules from a region of higher concentration to a region of lower concentration
What is diffusion rate?
How quickly a particular solute diffuses through a particular solution depends on various factors:
1. size
2. temp
3. steepness of the conc. gradient
4. solvent density
5. pressure
6. distance travelling
- Diffusion rate across a membrane is also influenced by:
1. solubility (nonpolar vs polar/ion)
2. surface area of membrane
3. thickness of membrane
Osmosis
Net diffusion of water molecules across a selectively permeable membrane between two fluids with different water concentrations.
- Passive transport
- water molecules tend to diffuse in response to its own concentration gradient
What is tonicity?
Describes relative concentrations of solutes in fluids separated by a selectively permeable membrane.
- Hypertonic solution
- Hypotonic solution
- Isotonic solution
What is a hypertonic solution?
Has a higher concentration of solute/stuff.
Has a low concentration of water.
What is a hypotonic solution?
Has a lower concentration of solute.
Has a high concentration of water.
What is an isotonic solution?
Has an equal concentration of solute/stuff.
Has an equal concentration of water.
What is osmosis?
Osmosis is the diffusion of water across a membrane from the region with a higher water concentration (low solute concentration = hypotonic) toward the region with a lower water concentration (high solute concentration = hypertonic).
Osmosis will continue until the two fluids are isotonic.