Forces Driving Movement Across The Cell Membrane Flashcards
What is endocytosis?
There is an invagination of the cell membrane to form a vesicle which eventually disintegrates on the cytoplasmic surface of the membrane, releasing its contents which then migrate within the cell to its destination.
What is exocytosis?
The reverse process of endocytosis.
Many proteins manufactured inside cells are transported out of the cell by this process.
Which mechanisms support movement across the cell membrane?
Diffusion - passive and facilitated
Active transport
Osmosis
What mechanism supports movement between the plasma and interstitial fluid (ISF)?
Filtration
What are the different types of diffusion?
Passive - Directly through the cell membrane e.g. gas
Facilitated - Relies on channels or transporters e.g ions, glucose
Both don’t require energy because they rely on electrochemical gradients. 
What is active transport?
When molecules are moved against the electrochemical gradient, this requires energy.
Define the electrochemical gradient
Occurs due to the concentration gradient and the electrical gradient. It drives passive movement. The electrical gradient and concentration gradient can work together or against each other, the dominating gradient will decide where the ion moves.
Any movement against the electrochemical gradient requires energy (active transport).
What is meant by diffusion?
Passive movement down the concentration gradient, from area of high concentration to area of low concentration.
Substances move in both directions due to randomness but net movement is down the conc gradient.
What is passive diffusion?
Movement directly through the lipid bilayer, quick.
Molecules must be small and charged to move passively.
Molecules are usually lipophillic and pass through the bilayer quickly but they can be lipophobic and pass through slower.
What type of proteins are involved with facilitated diffusion?
Channels
Carrier mediated transport proteins (transporter proteins)
How does water diffuse through the cell membrane?
Through aquaporin
Protein channels that are always open and only transports water.
What do protein channels transport?
Molecules that are too large for passive diffusion. E.g. glucose
Simultaneously diffuses ions and water. 
Describe have protein channels open/close
Ligand gated protein channels - act as both receptors and transporters. Open/close when chemical stimulus (e.g neurotransmitter or hormone) binds to a receptor binding site.
Voltage gated - open/close in response to a change in membrane electrical potential. Found in muscle and nerve cells.
In both cases the stimulus, either chemical or electrical causes a confirmational change in the configuration of the channel causing it open or close.
What is electrochemical equilibrium?
When the concentration gradient and electrical gradient are in balance. This rarely happens because gated channels are usually closed
How do cardio mediated transport proteins (transporters) work?
Move molecules that are too big for ion channels. They are never continuously open pores, always closed at at least one end.
The molecule to be transported binds to the binding site. This causes a conformational in the protein, it closes on one side and open in the other side. Another conformational change happens and the molecule is released as it now has a low infinity for the binding site.
