Topic 1.4: Membrane Transport Flashcards
What are the two qualities of cellular membranes?
semi-permeable and selective
Define semi-permeable in terms of the membrane
only certain materials may freely cross – large and charged substances are typically blocked
Define selective in terms of the membrane
membrane proteins may regulate the passage of material that cannot freely cross
Define passive transport
involves the movement of material along a concentration gradient (high concentration ⇒ low concentration)
What involves the movement of material along a concentration gradient (high concentration ⇒ low concentration)?
passive transport
What are the 3 main types of passive transport?
simple diffusion, osmosis, and facilitated diffusion
Define simple diffusion
movement of small or lipophilic molecules (e.g. O2, CO2, etc.)
Define osmosis
the net movement of water molecules across a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration (until equilibrium is reached)
Define facilitated diffusion
the passive movement of molecules across the cell membrane via the aid of a membrane protein
Define active transport
involves the movement of materials against a concentration gradient (low concentration ⇒ high concentration)
What involves the movement of materials against a concentration gradient (low concentration ⇒ high concentration)?
active transport
Define primary (direct) active transport
Involves the direct use of metabolic energy (e.g. ATP hydrolysis) to mediate transport
Define secondary (indirect) active transport
Involves coupling the molecule with another moving along an electrochemical gradient
Define diffusion
the net movement of molecules from a region of high concentration to a region of low concentration
What are the 3 factors that affect the rate of diffusion?
temperature, molecular size, and steepness of gradient
Define osmolarity
a measure of solute concentration, as defined by the number of osmoles of a solute per litre of solution (osmol/L)
Define hypertonic
Solutions with a relatively higher osmolarity are categorised as hypertonic (high solute concentration ⇒ gains water)
Define hypotonic
Solutions with a relatively lower osmolarity are categorised as hypotonic (low solute concentration ⇒ loses water)
Define isotonic
Solutions that have the same osmolarity are categorised as isotonic (same solute concentration ⇒ no net water flow)
Define the sodium-potassium pump
An integral protein that exchanges 3 sodium ions (moves out of cell) with two potassium ions (moves into cell)
What is the first step of the sodium-potassium pump?
Three sodium ions bind to intracellular sites on the sodium-potassium pump
After the Three sodium ions bind to intracellular sites on the sodium-potassium pump What is the next step of the sodium-potassium pump?
A phosphate group is transferred to the pump via the hydrolysis of ATP
After A phosphate group is transferred to the pump via the hydrolysis of ATP What is the next step of the sodium-potassium pump?
The pump undergoes a conformational change, translocating sodium across the membrane
After The pump undergoes a conformational change, translocating sodium across the membrane What is the next step of the sodium-potassium pump?
The conformational change exposes two potassium binding sites on the extracellular surface of the pump
After The conformational change exposes two potassium binding sites on the extracellular surface of the pump What is the next step of the sodium-potassium pump?
The phosphate group is released which causes the pump to return to its original conformation
After The phosphate group is released which causes the pump to return to its original conformation What is the next step of the sodium-potassium pump?
This translocates the potassium across the membrane, completing the ion exchange
What is the first step of vesicular transport?
Materials are transported from the ER when the membrane bulges and then buds to create a vesicle surrounding the material
After Materials are transported from the ER when the membrane bulges and then buds to create a vesicle surrounding the material What is the next step to vesicular transport?
The vesicle is then transported to the Golgi apparatus and fuses to the internal (cis) face of the complex
After The vesicle is then transported to the Golgi apparatus and fuses to the internal (cis) face of the complex What is the next step to vesicular transport?
Materials move via vesicles from the internal cis face of the Golgi to the externally oriented trans face
After Materials move via vesicles from the internal cis face of the Golgi to the externally oriented trans face What is the next step to vesicular transport?
While within the Golgi apparatus, materials may be structurally modified (e.g. truncated, glycosylated, etc.)
After While within the Golgi apparatus, materials may be structurally modified (e.g. truncated, glycosylated, etc.) What is the next step to vesicular transport?
Material sorted within the Golgi apparatus will either be secreted externally or may be transported to the lysosome
After Material sorted within the Golgi apparatus will either be secreted externally or may be transported to the lysosome What is the next step to vesicular transport?
Vesicles containing materials destined for extracellular use will be transported to the plasma membrane
After Vesicles containing materials destined for extracellular use will be transported to the plasma membrane What is the next step to vesicular transport?
The vesicle will fuse with the cell membrane and its materials will be expelled into the extracellular fluid
Define endocytosis
The process by which large substances (or bulk amounts of smaller substances) enter the cell without crossing the membrane
What is The process by which large substances (or bulk amounts of smaller substances) enter the cell without crossing the membrane?
endocytosis
What is the first step of endocytosis?
An invagination of the membrane forms a flask-like depression which envelopes the extracellular material
After An invagination of the membrane forms a flask-like depression which envelopes the extracellular material, what is the next step of endocytosis?
The invagination is then sealed off to form an intracellular vesicle containing the material
What are the two main types of endocytosis?
phagocytosis and pinocytosis
Define phagocytosis
The process by which solid substances are ingested (usually to be transported to the lysosome)
Define pinocytosis
The process by which liquids / dissolved substances are ingested (allows faster entry than via protein channels)
Define exocytosis
The process by which large substances (or bulk amounts of small substances) exit the cell without crossing the membrane
What happens during exocytosis?
Vesicles (typically derived from the Golgi) fuse with the plasma membrane, expelling their contents into the extracellular environment
Define kidney dialysis
involves the external filtering of blood in order to remove metabolic wastes in patients with kidney failure
