Chap 6 Transport Mechanisms Flashcards
List all the passive transport processes.
- Simple Diffusion
- Facilitated Diffusion
- Osmosis
List all the active processes.
- Active Transport
- Vesicle Mediated Transport
- Endocytosis
- Exocytosis
Define Spontaneous
No energy is required
Define Concentration Gradient
A difference in the concentration of a solute between 2 regions.
Define Diffusion and its characteristics.
Movement of solutes along a concentration from region of high concentration to a region of low concentration. Its is natural phenomenon and molecules diffuse faster in air then in water.
What is the difference between passive and active processes?
In passive processes molecules move along a concentration gradient spontaneously.
In active processes molecules move against a concentration gradient and requires energy usually in the form of hydrolysis of ATP.
Give an example of simple diffusion.
Gas exchange in the lungs. CO2 diffuses from the blood stream to the alveolus through the aveolar and capillary wall. O2 also diffuses from the alveolus to the bloodstream im the same manner.
Explain the permeability of the phospholipid bi-layer.
Small uncharged molecules are hydrophobic and can diffuse through the plasma membrane. Large polar or charged molecules are hydrophillic and cannot freely diffuse through the membrane thus must be transported by other means. This is because hydrophobic fatty acid tails make up the majority of the cell membrane making it hard for hydrophilic molecules to pass through.
Explain facilitated diffusion.
Facilitated diffusion is used for molecules that cant freely diffuse through the plasma membrane. They do this by allowing molecules to pass through the membrane without interacting with the fatty acid tails. This is done with carrier or channel proteins and it is still down a concentration gradient.
Explain how carrier and channel proteins work.
Channel proteins allow passage of molecules that are of appropriate size to cross.They are not permanently opened and selectively open/close in response to extracellular signals.
Carrier proteins selectively bind to small molecules to be transported and then undergoes conformational change to release the molecule on the other side of the membrane. They work like enzymes.
Explain osmosis and give an example.
Osmosis is the diffusion of water across a semi permeable membrane from a region of high concentration to a region of low concentration. (e.g. secretion and absorption of water in the small intestine)
Explain the 3 solute environments.
Isotonic - the concentration of solutes outside is the same as inside
Hypertonic - the concentration of solutes outside the cell is more than inside
Hypotonic - the concentration of solutes outside the cell is less than inside
What happens to RBC if it is placed in a isotonic,hypotonic and hypertonic solution?
Isotonic - no change
Hypertonic - water rushes out of cell and cell shrinks
Hypotonic - water rushes into the cell causing it to swell and eventually burst.
What happens to a plant cell in an hypertonic and hypotonic solution?
Hypertonic - water rushes out of plant cell causing it to be plasmolyzed (due to plasmolysis)
Hypotonic - water rushes into the plant cell causing it to become turgid.
Give an example of active transport.
The sodium potassium pump. It transport sodium ions out of the cell and potassium ions into the cell both against steep concentration gradients. This usually occurs in nerve cells that have internal potassium concentrations 30x greater than the ECM due to these pumps.The ionic gradient is used for the transmission of nerve impulses.
Describe the nature and function of the 3 types of transporters used in active transport. (give examples)
Uniporter - transports one substance at a time
Symporter - membrane protein that co transports 2 separate substances in the same direction. (e.g. symporter can transport protons and a substance across the membrane, it uses the movement of proton called proton motive force to provide the energy to transport the other substance across the membrane)
Antiporter - transports two substances in opposite directions across the membrane (e.g. sodium potassium pump)
List the 3 methods/forms of endocytosis.
Receptor Mediated Endocytosis
Phagocytosis
Pinocytosis
Explain receptor mediated endocytosis with examples.
Substances bind to receptors in a pit coated with clathrin proteins. When enough target molecules bind to receptors, the pit deepens, seals and is invaginated and enters the cell as a coated vesicle known as an endosome. Receptor mediated endocytosis either takes in a molecule or a virus.(e.g. LDL Cholesterol binding to LDL Receptors)
Explain the endocytosis.
large molecular weight materials are enclosed within invagination of the cell membrane to form a pocket which then pinches off into the cell to form a vesicle filled with extracellular fluid called an endosome.
Explain the need for endocytosis.
Substances that are too big or polar thus cannot freely diffuse through the hydrophobic plasma membrane.
What are types of ligands that enter a cell via receptor mediated endocytosis?
- Toxins (Diptheria Toxin, Pseudomonas toxin, Cholera toxin, Ricin)
- Hormones (Insulin,Thyroid Hormone,Glucagon,Inteferon)
- LDL Cholesterol
Explain phagocytosis and give an example.
Phagocytosis is where a cell engulfs whole food particles or other substances which are brought in and later broken down by enzymes and absorbed by the cell. Phagocytosis begins as cell membrane forms finger like projections known as pseudopods to surround the food particle.The cell membrane internalizes the particle to form a vesicle after surrounding it completely. (e.g. WBCs ingesting large particles like bacteria)
Explain pinocytosis.
Pinocytosis is the cell engulfing already dissolved/broken down food.It takes up dissolved solutes and single molecules like proteins.
Explain the process of exocytosis and give an example.
Exocytosis is a process by which cell directs secretory vesicles to the cell membrane. Secretory vesicles fuse with the plasma membrane and its components are ejected into the extracellular matrix. (e.g. secretion of mucus of cells lining stomach wall)
