Membrane Transport - Week 2 Flashcards
Cells and Tissues - Week 2
What substances need to be transported across the Plasma Membrane?
Both nutrients and waste products from the cell, need to be transported across the plasma membrane.
It allows the passage of some substances but prevents the passage of other substances.
What are the two types of transport of substances across the plasma?
Passive transport - does not require any energy expenditure.
Active transport - requires the cell to use ATP (cellular energy) for transport to occur.
What is Passive Transport?
Passive transport is transport across the plasma membrane that doesn’t require any energy expenditure.
What is Active Transport?
Active transport requires the cell to use ATP (energy) for transport to occur.
Happens when moving against the concentration gradient i.e. from an area of low concentration to an area of high concentration.
As energy is used, substances can be moved irrespective of the intracellular and extracellular concentration of the substance.
What is Diffusion?
Diffusion is a form of passive transport involving movement of a substance down a concentration gradient, from an area of HIGHER concentration to LOWER concentration.
What are the 4 mechanisms by which Diffusion can occur?
- Simple diffusion (Passive Transport)
- Carrier mediated facilitated diffusion
- Channel mediated facilitated diffusion
- Osmosis (Passive Transport)
What is simple diffusion?
Non-polar and lipid soluble (plasma membrane compatible substances) diffuse directly across the plasma membrane down a concentration gradient.
Substances include oxygen, carbon dioxide, and soluble vitamins
Explain how Oxygen is a simple diffusion?
Oxygen concentration is high in the blood in the capillaries and low in the cells, therefore oxygen will move into the cells from the blood by simple diffusion, moving from the area of higher concentration, to the area of lower concentration.
What is Carrier Mediated Facilitated Diffusion?
Refers to specific ions or molecules being carried across the plasma membrane by integral proteins in the plasma membrane.
Substance to be transported is water-soluble
Integral proteins are carriers and when molecules bind the carrier it changes shape, allowing the molecules to be encased by the carrier, then released on the other side of the membrane.
This type of transport is still passive, as substances are still moving down a concentration gradient.
Explain how Glucose is a Carrier Mediated Facilitated Diffusion
Glucose transporters - the movement does not require energy as the glucose is moving down a concentration gradient.
What is Channel Mediated Facilitated Diffusion?
Channels are transmembrane proteins, able to transport substances through a water-soluble environment across a membrane.
These channels are selective for size and charge.
Leakage channels are always open and allow molecules to move across concentration gradients.
Gated channels are controlled by signals
What are 3 Gated Channels and what signals are they controlled by?
- Ligand Gated Channels – Chemical Signals
Chemical to bind to the receptor to open the channel. - Mechanically Gated Channels - Mechanical signals
Require pressure or other mechanical force to open the channel - Voltage-gated Channels - Electrical signals
Require a change in membrane potential to open the channel.
What is Osmosis?
Osmosis is the diffusion of a solvent
Solvents such as water, move from areas of low molecule concentration, or high amount of solvent, to areas of high molecule concentration, or low amount of solvent.
What is Secondary Active Transport?
It’s a consequent mechanism following primary active transport.
Involves the movement of ions down a concentration gradient that has actually been created by the primary and active transport mechanism.
This process allows for the cotransport of other charged molecules, either in the same direction ‘Symport’ or the opposite direction ‘Antiport’.
Describe the vesicular transport process?
During vesicular transport, substances move into or out of the cell in vesicles, which are small sacs that form with or at the plasma membrane.
Substances are transported in the form of droplets through vesicles.
Many proteins that are produced and packaged in cells by the Golgi apparatus are transported this way.
What is Endocytosis?
Endocytosis is the process of transporting substances from the extracellular fluid to inside the cell, with vesicles forming at the plasma membrane.
What is Exocytosis?
Exocytosis is the process of transporting substances from inside the cell to the extracellular fluid.
