Membranes Flashcards
What are membranes made out of?
Phospholipid bilayer
What are the properties of membranes?
Dynamic, flexible, insulating, selective permeability and act as binding sites for chemical recognition
What provides membranes with flexible properties?
Fatty acids
What provides membranes with insulating properties?
Hydrocarbon tails
What does dynamic mean?
Always being made and destroyed depending on the needs of the cell
What type of cell has the most protein?
Mitochondria
What are the 2 types of membrane proteins?
Integral and Peripheral
What is a peripheral membrane protein?
A protein that can be removed without disturbing the membrane. It is non-amphiphatic and its binding sites are on the IC side of the membrane. They can act as enzymes and are important for cell size and motility
What is an integral membrane protein?
A protein that can’t be removed without disturbing the membrane. It is amphipathic and its has the same orientation as the phospholipids and may span the membrane. They can act as channels, carriers, enzymes and receptors
Why do membrane proteins act as channels?
Allows ions to cross the membrane
Why do membrane proteins act as carriers?
Allows substances to be transported across the membrane
Why do membrane proteins act as enzymes?
To provide binding sites on the membrane surface
Why do membrane proteins act as receptors?
To provide recognition sites for chemicals
Where does diffusion occur?
Between compartments
What is the process of diffusion?
Movement form high -> low concentrations
What are the requirements for diffusion?
Permeable to the membrane, small, uncharged and lipophilic (hydrophobic)
What helps diffusion?
Large surface area, high permeability and high concentration gradient
What are protein channels?
They are trans-membranous IMPs that act as an aq route for the diffusion of ions
How does water pass thorough the membrane?
Through aquaporins which are always open
What is the name of changels that are not always open?
Gated
What are the 2 types of gated channels?
Voltage and Ligand
What are ligand gated channels?
When a certain chemical binds to the channel, its configuration changes which causes the channel to open/close
What is an example of a ligand gated channel?
ACh receptors
What is a voltage gated channel?
Channels open/close due to a change in electrical potential which causes a change in configuration
What is an example of a voltage-gated channel?
Na+ in nerve cells
How are electrochemical gradients formed?
Generated by the membrane potential. The inside of the cell is -ve due to a separation of charge across cell membranes
What is an electrochemical gradient needed for?
Ion diffusion
What uses carrier mediated transport systems?
Ions that can’t cross the channel and uncharged molecules e.g. glucose
What are the 2 ways that carrier mediated transport systems work?
Facilitated diffusion and active transport
What do carrier mediated proteins contain?
Binding sites for ions that can’t pass through the channel and uncharged molecules
What is the process by which carrier mediated proteins operate?
They bind to the solute which causes a change in configuration which exposes the site on the other side of the membrane. This allows the solute to diffuse into the cell and then the protein returns to its normal shape
What is facilitated diffusion?
The process by which solutes are transported down their concentration gradient, with no direct energy source needed
What is active transport?
The process by which substances move against their concentration gradients. ATP is required and it is caused by ATP synthase. An electrogenic pump is used which creates a net -ve charge. This takes up 40% or resting body energy
What is released by active transport?
3x Na+
In active transport, what is taken up by each molecule of hydrolysed ATP?
2x K+
What is osmolarity?
The measure of solute concentration
What is the osmolarity of 1M of glucose?
1 osmole/L
What is the osmolarity of 1M of NaCl?
2 osmole/L
What determines tonicity?
Cell volume, which depends on the concentration of non-penetrating solutes on either side of the membrane
What is a hypertonic solution?
ECF has a higher tonicity than ICF, which causes cells to shrink as water leaves the cell by osmosis to compensate
What is a hypotonic cell?
ICF has a higher tonicity than ECF, which causes the cells too swell as water enters the cell
What is an isosmotic solution?
A solution with equal numbers of both penetrating and non-penetrating solutes on either side of the membrane
What is an isotonic solution?
A solution with equal numbers of non-penetrating particles on either side of the membrane
What is the process of endocytosis?
The membrane is turned inside out then a vesicle forms around the target substance. The vesicles then separate from the membrane on the cytoplasmic side and migrate within the cell to its destination
What is exocytosis?
The opposite of endocytosis
