Week 1: transport across membranes Flashcards
Primary vs secondary active transport?
Both:
- Transport molecules AGAINST conc. gradient
- Often work together
1
- uses ATP hydrolysis directly to power transport (e.g. using carrier proteins).
2
- uses ion conc. gradient established by ATP hydrolysis as to use electrochemical gradient to counter conc. gradient.
What are the key types of movement across the cell membrane?
Passive: no energy needed
- Osmosis
- Diffusion
- Facilitated transport
Active: uses energy
- Primary active transport
- Secondary active transport
Endo/exocytosis
- Endocytosis
- Pinocytosis
- Receptor-mediated endocytosis
Signal transduction
What is pinocytosis?
Pinocytosis (“cellular drinking”) is a type of endocytosis that takes up fluids across the plasma membrane.
- Affects small molecules, non-specific
What are the main types of membrane proteins? What are they used for?
- Transport proteins => Facilitated transport
- Signalling proteins => signal transduction
- Joining cells => intercellular joining
- Enzymes => enzymatic activity (active site exposed to external substances
What are the two main types of transport protein involved in facilitated transport/diffusion
Transport proteins in facilitated diffusion/transport:
+ Carrier protein (changes conformationally)
+ Channel protein (provides gateways x membrane)
What are the two main types of transport protein involved in facilitated transport/diffusion
Transport proteins in facilitated diffusion/transport:
+ Carrier protein (changes conformationally)
+ Channel protein (provides gateways x membrane)
What are the characterisitics of bilayer permeability?
Lipid bilayer is variably permable depending on solute, which allows osmosis and diffusion.
- MOST permeable to small hydrophobic (non-polar uncharged) molecules (e.g. O2, CO2, N2). Quite fast crossing allowed
- LEAST permeable to larger or hydrophilic molecules; ions (regardless of size) or polar uncharged molecules. Either slow and relatively imperable or essentially impermeable.
Diffusion vs osmosis?
Both:
- Passive (no energy needed)
- Levels out extremes of gradient
- Stop when equilibrium is reached
- Fairly slow
Diffusion:
- Solutes move across membrane to area of lower conc.
- For molecules that CAN cross membrane
(small, non-polar)
- Occurs at level of specific solute type (e.g. conc. of Na+ doesn’t affect diffusion of K+)
Osmosis:
- Solvent moves across membrane to area of higher conc.
- For molecules that CAN’T cross membrane (large or polar)
- Needs selectively/semi-permeable membrane so solute can’t cross + fluid can
- Driven by TOTAL solute conc. so composition doesn’t matter (Na+ conc. and K+ BOTH affect change from osmosis).
Facilitated transport vs diffusion?
Diffusion is generally the movement of solute towards low conc. areas across the membrane. Diffusion often plays a role in facilitated diffusion.
Facilitated diffusion is when this happens using transport proteins specifically (e.g. diffusion but through channel protein. Same process but made faster). Facilitated transport can also mean using ATP in active transport. Facilitated transport acts on hydrophilic and large molecules that can’t simply cross the plasma membrane.
How do contractile vacuoles relate to osmosis?
Contractile vacuoles can control water levels in the cell which can trigger changes in overall cell water content as it has to increase or decrease to restore equilibrium relative to outside
Isotonic vs hypotonic vs hypertonic? Relative to outside.
Isotonic: solute conc. equivalent either side
Hypotonic outside: lower conc. outside (water wants to flood cell)
Hypertonic outside: higher conc. outside (water wants to leave cell, shrivelling it up)
How do cells regulate the conc. of larger or polar molecules?
Conc. of larger + polar molecules can’t be controlled through diffusion across membrane because the membrane is (relatively) impermable to them, so controlled by…
- osmosis
- Facilitated diffusion (can recognise specifics)
- endo/exocytosis
What is a symport protein?
Symport proteins move two types of ion in the same direction. Can be useful in creating electrochemical gradient changes to power 2ndary active transport.
Example of 1 and 2 active transport working together?
Na+ and K+ pumped into cell against conc. gradient, (inside: high K+ low Na+, outside: low K+ and high Na+), maintaining +ve charge inside and -ve charge outside. This electrochemical gradient of + and - charge then drives 2 active transport of glucose against conc. gradient towards higher conc. inside
Example of 1 and 2 active transport working together?
Na+ and K+ pumped into cell against conc. gradient, (inside: high K+ low Na+, outside: low K+ and high Na+), maintaining +ve charge inside and -ve charge outside. This electrochemical gradient of + and - charge then drives 2 active transport of glucose against conc. gradient towards higher conc. inside
