Membrane Transporters and Osmosis Flashcards
What is the structure of the plasma membrane?
Bi-layered (two layers of phospholipids)
Phophate group (head) + 2 chains of fatty acids (lipid tails)
What is the function of the plasma membrane?
Allows cells to interact with watery environment but remain resistant
Selective permeability
- Permeable to lipid-soluble substances
- Impermeable to charged molecules
What are the different body fluid compartments?
Intracellular fluid (plasma membrane) Interstitial fluid (blood vessel) Plasma Extracellular fluid (ECF = plasma + interstitial fluid)
What is osmosis?
Water movement through a semipermeable membrane
Passive transport to equalise the concentration of a solution
Size of solute particles does not influence osmosis
What is osmotic pressure and hydrostatic pressure?
Osmotic pressure is created by concentration difference of dissoled substances between two sides of a bio-membrane
Hydrostatic pressure is achieved when movement of water stops
What is passive movement across a biological membrane?
Movement that follows the concentration gradient (high to low) and does not require energy
Driving forces = concentration gradient (diffusion/facilitated diffusion) and electrical potential (charged particles ONLY)
What is active transport across biological membranes?
Movement against the concentration gradient (low to high) that requires energy to achieve
Also includes endocytosis and exocytosis
What’s the difference between diffusion and facilitated diffusion?
Diffusion = PASSIVE movement across membranes of solute to form equilibrium
Facilitated diffusion = Diffusion of substances that CANNOT cross the lipid bilayer due to size / charge / polarity. This movement still follows the concentration gradient but is aided by carrier proteins
What are the different functions of membrane proteins?
Transport proteins Enzymes Intercellular junctions Cell-to-cell recognition Receptors Adhesion to extracellular matrix
What are channels?
Membrane proteins that allow passive movement of solutes through a membrane following the concentration gradient (ions = ion channels, water = aquaporins)
They can be specific or non-selective
How are gated channels different from channels and what are some examples?
Some channels are open or closed in response to local changes unlike regular channels
- Ligand-gated = responds to a signal molecule that can be external or internal
- Voltage-gated = respond to alterations in membrane potential
- Mechanical stretch = open according to cell movement
What are pumps?
A form of active transport (against concentration gradient)
Catalyse is the hydrolysis of ATP to ADP, therefore requires energy
IMPORTANT FOR CONTROLLING MOVEMENT OF WATER
What are carrier / transporter proteins?
Method for facilitated diffusion OR active transport
They bind a specific molecule and transfer it across the membrane
When bound, will undergo conformational changes, altering affintiy of binding site (remember haemoglobin the O2 carrier)
What are the three types of carrier / transporter proteins?
Uniporter = only one substance Symporter = binding of more than one Antiporter = exchange
What is exocytosis?
A method of active transport in which vesicles containing material for export are released
Typically used for secretion of hormones or waste removal
