5.4. ACTIVE TRANSPORT Flashcards
Why is diffusion no good for cellular life?
it leads to equilibrium however biological processes rely on concentration gradients -eg.compartmentalisation
How is a concentration gradient maintained?
molecules or ions must move up the concentration gradient faster than they diffuse down
What is active transport?
Movement of molecules or ions across a cell membrane from a region of lower concentration to a region of higher concentration
-UP or AGAINST the gradient
-selective (specific to the ion)
What do molecules/ions move through in the membrane in active transport?
Carrier proteins
How do carrier proteins work in active transport?
Have a receptor site that bind to specific molecules and transport them across the cell membrane
Where does active transport often take place?
Internal lining of the small intestine (eg. glucose into the blood)
What type of energy is required for active transport?
Immediate source - ATP
What are some examples of active transport?
-transportation of sodium out of the cell
-transportation of potassium into the cell
(sodium-potassium pump)
How do plants absorb mineral ions from the soil?
active transport enables these cells to take up salts (from the dilute solution in the soil water) against the direction of the concentration gradient
What are the three types of carrier protein used in active transport?
-Uniporter
-Synporter
-Antiporter
What does the uniporter carrier protein transport ?
one molecule/ion in one direction
What does the Synporter carrier protein transport ?
2 molecules/ions in one direction
What does the Antiporter carrier protein transport ?
Two molecules/ions in two different directions
What are the steps in the Possible Mechanism for Active Transport?
1) molecule bonds to receptor site on inner wall of the carrier protein pore
2) ATP binds to the carrier protein on the cytoplasm side -it is then hydrolysed into ADP + Pi
3) energy is transferred to the carrier protein and Pi is bound to it
4) carrier protein changes shape to open the pore on the other side of the membrane and the molecule is released
5) Pi is released from the carrier protein and it changes shape again to adopt the original conformation
What are the two types of bulk transport?
Endocytosis (into the cell)
Exocytosis (out of the cell)
What are the three types of endocytosis?
Phagocytosis
Pinocytosis
Receptor Mediated
What is Phagocytosis (in terms of endocytosis)?
Where the membrane engulfs solid particles (ie. bacteria) with ATP via pseudopodium into a phagosome (food vacuole)
What is pinocytosis (in terms of endocytosis)?
Molecules/ions are absorbed by the membrane into a vescicle in the cytoplasm (i.e. drinks a molecule/ion)
What is receptor-mediated endocytosis?
A membrane with a coated pit and receptors collect molecules/ions into a coated vesicle inside the cytoplasm
What does a coated pit do?
acts as a cage on the inside of a membrane - pinched off the membrane to form a coated vesicle
What is exocytosis?
a mechanism by which cells are able to insert membrane proteins, lipids and other components into the cell membrane
-vesicles containing these membrane components fully fuse with and become part of the cell surface membrane
What are the main stages of exocytosis?
-membrane bound secretory vesicles are carried to the plasma membrane
-vesicle contents are secreted into the extracellular environment
Why is the secretion in the vesicles possible in exocytosis?
because the vesicles transiently fuse with the plasma membrane
