February 10 - Membranes Flashcards
Membrane structure review
- Proteins (incl. transport proteins)
- Carbohydrate chains
- Phospholipids
Membrane Composition
Lipids
- phospholipids & sterols (ex. cholesterol)
- proteins, ex transport and receptor
- carbohydrates, ex. glycoproteins, glycolipids
Membrane Permeability
selective based on solute properties and membrane composition
permeability : phospholipids allow
hydrophobic and minute hydrophilic substances to cross
permeability : proteins allow
hydrophilic (polar and charged) substances to cross
how do large solutes cross the membrane
via endo/ exocytosis .. which requires energy
what does permeability to hydrophilic solutes rely on
- abundance of relevant transmembrane proteins
- whether said transmembrane proteins are active/ open (ex. gated channels)
Types of transmembrane transport
- simple diffusion
- facilitated diffusion
- active transport
- bulk transport
Simple diffusion
- molecules move down electrochemical gradients (^conc to low)
- phospholipids involved
- solutes that do this: hydrophobic molecules (ex. co2, o2, many lipids, i.e. steroids), small hydrophilic/ polar molecules, ex. H2O
- subcategory: osmosis
Osmosis
subcategory of simple diffusion that involves water molecules
facilitated diffusion
- moving down ecg
- macromolecules : transmembrane proteins (channels, carriers - uniport, symport, antiport)
- solutes: hydrophilic molecules (sugars, amino acids, ions)
Active Transport
- moving up ecg (exception in 2nd degree AT)
- macros: transmembrane protein (carriers), and ATP
- solutes: hydrophilic (sugars, AA, ions)
- subcategories : primary (direct ATP use) and secondary (atp used to set up gradient of some other solute)
Movement exception secondary active transport
there is cotransport of another solute down the gradient
Bulk Transport
macros: phospholipid bilayer and proteins (ex. receptor)
solutes: macros (ex. proteins, polysaccharides), whole cells/ parts of cells
subcategories: endocytosis and exocytosis
endocytosis
subcategory of bulk transport
- material moving into the cell
exocytosis
subcategory of bulk transport
- material moving out of the cell
transport proteins selectivity
- usually very selective
- selectivity depends on protein structure
insulin / liver example of change in membrane permeability
- insulin binds to receptor
- signal cascade
- exocytosis occurs
- glucose entry is permitted
summary of cell signalling
- reception - receptor + external stimulus
- transduction - relay molecules inside the cytoplasm
- response - activation of cellular response
passive transport
diffusion across a membrane without any energy investment
simple diffusion def.
the free movement off solutes down their concentration gradient across the plasma membrane
Passive transport
