Unit 4 - Membranes Flashcards
Structure
Describe membrane phospholipid structure.
(4 sections)
- polar head
- phosphate
- 3-C glycerol
- fatty acid chain
Structure
Which end faces the water?
polar end
Structure
Describe movement of phospholipids.
- spins/rotates in place
- can swap within leaflets
Structure
Describe how temperature affects fluidity.
- transition temeperature (Tm) is where a membrane can become a fluid or gel
- if above Tm, membrane is fluid, more movement
- if below Tm, membrane is gel-like
Structure
What factors affect Tm?
- Length of fatty acid chains: longer chains = higher Tm
- Double bonds: more double bonds = lower Tm
- Amount of sterol: e.g. cholestorol prevents phase changes
Structure
Describe homeo viscous adaptations
Adapting to lower temperatures:
* shorter fatty acid chains
* more double bonds
Structure
Describe the location of proteins in membranes.
Proteins are transmembrane, spanning across both leaflets
Structure
Describe protein movement.
- Proteins move within the membrane
- orientation is maintiained
Structure
Describe how epithelial cells prevent protein movement.
- tight junctions prevent proteins from the top to cross into the bottom/sides of the cell
Structure
Describe membrane carbohydrates
- sugars attatch to proteins
- they attatch to non-cysotsolic side
Structure
Describe 4 steps of membrane formation.
- Fatty acids in cytosol, creating phospholipids
- Phospholipids attatch to the cytosolic side in ER
- Phospholipids cross leaflets to even out
- In golgi, flippase move phospholipids between leaflets to sort them out
Structure
Describe distribution of phospholipids and cholestorol between leaflets.
- phospholipids are distributed unevenly
- cholestorol is always even on both sides
Transport
Name 3 ways substances can enter a cell.
- Directly through lipid bilayer
- Membrane proteins
- Engulfing
Transport
Describe water movment across a membrane.
- moves in both directions
- moves from low concentration of solutes to high until equilibirum (osmosis)
Transport
Hypotonic Solution
- lower concentration of solutes
- water moves into cell
- ideal for plants
Transport
Hypertonic Solution
- higher concentration of solutes
- water moves out of cell
Transport
What molecules can freely cross bilipid membrane?
small, uncharged, polar/non-polar moleculres
Transport
Compare channel and carrier proteins.
- channels can allow anything to pass as long as it can fit and open
- carriers have a particular binding-site, transports molecules one at a time
Structure
Which phospholipids are moved to the cytosolic leaflet by flippase?
PS and PE
Transport
Describe ion channels.
- highly selective based on size and charge
- allows ions to move along concentration/electrical gradient
- can move ions in both directions
Describe the 3 ways ion channels open/close
- voltage gated: inside of membrane becomes positively charged
- ligand-gated: ligand binds to a site on channel
- mechanically-gated: pressure opens/closes the channel
transport
Describe carrier proteins
- has a binding site that flips at random
- molecules pass through diffusion one at a time
- moves along gradient
- binding site can be blocked by inhibitors that fit in binding site
Transport
What are the two types of transports that go against a gradient?
Active Transport and Coupled Transport
(co-transport)
Transport
Describe active transport
uses (releases) enegry to move ions against their concentration gradients
Describe the Na-K ATPase
- ATP pump that moves sodium into cell and potassium out
- 3 Na per 2 K
- coupled reaction: ATP to ADP
Transport
What is the significance of the Na+ gradient?
Transports glucose, amino acids and other molecules to cell, useful for co-transport
Transport
What is coupled transport?
two substances (usually a molecule and ion) are transported across a membrane simultaneously
Transport
What is a symport?
a molecule and ion move in the same direction across membrane
Transport
What is an antiport?
a molecule and ion move in opposite directions across membrane
Transport
In which direction does the ion usually move?
The ion usually moves along its gradient to create a driving force for the coupled molecule
Transport
Describe glucose-sodium symport
- occurs in intesntinal epithelium cell
- Na+ moves along gradient and glucose moves against graidient into the cell
- Na-K ATPase continues to move sodium out of cell to maintain gradient
Transport
Describe proton-driven symport in plant cells.
- co-transport occurs with H+ ions
- there is an H+ gradient
- H+ ATPase is used to maintain gradient
Transport
What mutation relating to membrane transport could occur?
- transporters are proteins, coded by DNA
- a mutation in an important transporter is very bad
