1.4 Membrane transport Flashcards
Properties of Membranes
Properties of Membranes
Semi-permeable (only certain things can cross)
* Selective (membranes can regulate material passage)
Membranes Transport
Types of membrane transport
- Passive (along concentration gradient, no ATP expenditure)
- Active (against concentration gradient, ATP is required)
Passive Transport
Diffusion
The net movement of molecules from a region of high concentration to a region of low concentration.
Passive Transport
Types of passive transport
q. Simple diffusion – movement of small or lipophilic molecules (e.g. O2, CO2, etc.)
2. Osmosis – movement of water molecules (dependent on solute concentrations)
3. Facilitated diffusion – movement of large or charged molecules via membrane proteins (e.g. ions, sucrose, etc.)
Passive transport
What is passive transport?
Passive transport involves the movement of material along a concentration gradient (high concentration ⇒ low concentration)
Because materials are moving down a concentration gradient, it does not require the expenditure of energy (ATP hydrolysis)
Active transport
What is active transport?
Active transport involves the movement of materials against a concentration gradient (low concentration ⇒ high concentration)
Because materials are moving against the gradient, it requires the expenditure of energy (e.g. ATP hydrolysis)
Active transport
What are types of active transport?
Primary (direct) active transport – Involves the direct use of metabolic energy (e.g. ATP hydrolysis) to mediate transport
Secondary (indirect) active transport – Involves coupling the molecule with another moving along an electrochemical gradient
Passive transport
Simple Diffusion
The net movement of particles from a region of higher
concentration to a region of lower concentration (i.e. along
the gradient) until equilibrium is reached
* Involves small / lipophilic molecules (e.g. O2, CO2, steroids)
Passive transport
Facilitated Diffusion
The passive movement of molecules across a cell membrane
via the aid of a membrane protein (carrier / channel protein)
* Involves large / charged molecules (e.g. ions, glucose, etc.)
* E.g. Voltage-gated channels control the flow of ions in neurons
Passive transport
Osmosis
The net movement of water molecules across a semi-permeable
membrane from a region of low solute concentration to a region
of higher solute concentration (diffusion of free water molecules)
Osmolarity
What is osmolarity?
Osmolarity is a measure of solute concentration
Solutions can be measured as:
* Hypertonic: High solute concentration (gains water)
* Hypotonic: Low solute concentration (loses water)
* Isotonic: Same solute concentration (no net flow)
Active Transport
Active transport uses energy to move molecules against a concentration gradient
This energy may either be generated by:
The direct hydrolysis of ATP (primary active transport)
Indirectly coupling transport with another molecule that is moving along its gradient (secondary active transport)
Active transport
Active transport involves the use of carrier proteins (called protein pumps due to their use of energy)
A specific solute will bind to the protein pump on one side of the membrane
The hydrolysis of ATP (to ADP + Pi) causes a conformational change in the protein pump
The solute molecule is consequently translocated across the membrane (against the gradient) and released
Vesicular Transport
The fluidity of the plasma membrane allows it to break and
reform around certain materials (this process requires ATP)
- Exocytosis: Materials released from a cell via vesicles
- Endocytosis: Materials internalised within a vesicle
Intracellular vesicles can move materials between cell organelles
