Lecture 2: Membrane Transport Mechanisms Flashcards
What is the difference between kinetic energy and thermal energy?
Kinetic energy is the energy of the molecular movement in a system, while internal energy is more of a measurement of the total energy of the system (Heat + kinetic?)
Define and describe diffusion
Diffusion is the frenzied random movement of free molecules in solution…. Net diffusion occurs across a barrier (i.e., more molecules moving one way than the other) if there is a driving force (a concentration gradient or, for charged molecules, a potential gradient) and if the barrier is permeable.
Describe the characteristics of osmosis
- Diffusion is the Movement of particles from a region of high concentration to a region of low concentration.
- Osmosis can be defined as the movement of a Solvent from a region of high concentration to a region of low concentration across a semipermeable membrane.
- To living organisms and the cell, the solvent is water, so osmosis is the movement of water from a region of high concentration to a region of low concentration across a semipermeable membrane –essentially a cell membrane.
What is osmotic pressure?
What is the Van Hoff definition for osmotic pressure
Water’s osmotic attempts to reach equilibrium causes a disproportionate amount of water to accumulate on one side.
Osmotic pressure depends on the concentration of osmotically active particles
What is the formula for Osmotic pressure?
pi = G * C * R * T
Where pi = osmotic pressure G = # of particles in a solution C = Concentration R = Gas Constant T = Absolute Temperature
Effective osmotic pressure = (osmotic pressure) * (sigma = reflection coefficient from 0(permeable) to 1(impermeable))
What is able to pass through the membrane of cells without the need for channels or energy?
Oxygen, carbon dioxide, nitrogen, alcohols can diffuse readily across a biphospholipid layer.
These move in and out based on concentration (diffusion), charge, and pressure differences
What factors of the cell membrane effect the diffusion rate across the membrane?
- Oil/water partition coefficient (Lipid solubility)
- Size of solute
- Membrane thickness
Give the equation for measuring diffusion across a cell membrane
J = -PA(C1 - C2) * The (-) is only relevant if the concentration is moving from high to low, which it almost always is J = Flux(Flow) in mmol/sec P = Permeability in cm/sec C = Concentration in mmol/Liter
Describe facilitated diffusion
- Requires uniporter carrier proteins
- Occurs down an electrochemical gradient.
- A uniporter has binding sites that are alternately available on either side of the membrane.
- Carrier mediated transport establishes stereospecificity.
- L and D amino acids would have completely different required carriers.
Structurally similar solutes may compete for transport sites on carrier molecules. - Has a Vmax
- Used by glucose and amino acids (All cells have GLUT, which receives glucose)
Describe active transport
- Movement of particles against a concentration/electrochemical) gradient (uphill)
- Requires metabolic energy (other than kinetic) and carrier proteins
- Example: Epithelial cells absorb water through osmosis in the lumen, and sodium through diffusion. They can then use active transport to “push” the salt water out into connective tissue on the basal side of the cell.
Explain the difference between primary active transport and secondary active transport
Primary active transport:
- Energy is derived directly from breakdown of ATP
- Utilizes ATPase transporters
Secondary transport:
- Energy is derived secondarily from concentration differences of molecular or ionic substances created originally by primary active transport.
- Utilizes multiporters
Describe what sort of multiporters are used in secondary active transport
- Multiporters include symporters and antiporters.
- In secondary active transport, at least one of the solutes moves down its electrochemical gradient while one or more of the other solutes moves up its electrochemical gradient.
- Sodium is often one of the solutes involved in secondary active transport.
- Sodium is more concentrated outside the cell.
- Movement of sodium into cell (down its electrochemical gradient) generates the energy needed to transport another substance against its electrochemical gradient.
- What’s one of the easiest ways to tell that something being transported across a membrane is active?
- Question: Sodium/calcium antiporters move three sodium ions per calcium ion. Why does it take three sodium ions to move one calcium ion?
- If it involves a substance moving “against” it’s concentration gradient, it’s active or it uses energy facilitated elsewhere. This applies to sodium/calcium transporters too, since sodium moving with it’s concentration gradient is facilitated by energy generated elsewhere.
- Calcium is divalent, and much larger than sodium, which is why more sodium ions are needed.
Describe how potassium usually gets into a cell?
- Via the sodium/potassium pump
- When 2 potassium ions bind to the outside of the large subunit of the carrier protein and 3 sodium ions bind to the inside of the large subunit, the ATPase function of the protein becomes activated. ATP is dephosphorylated as the 5 ions are pushed to the other side of the pump.
- ATP is still required, making this primary active transport. The Sodium Potassium Transfer Pump.
Mitochondria are able to do something else with the Na/K pump. What is it?
- Mitochondria, if the need arises, can perform the reaction in reverse, phosphorylating ADP into ATP by switching the direction of the mechanism, however this is dependent on the respective concentrations of everything involved.
