Active transport Flashcards
What is active transport?
- transport of a molecule that requires energy because it moves a solute against its concentration gradient (up)
What are four examples of active transport?
- pumps
- cotransport
- exocytosis
- endocytosis
Active transport requires energy in the form of ATP. What is ATP (2)
- adenosine triphosphate is an energy source used by cells
- it is a modified RNA nucleotide
What does ATP do? (2)
- it can transfer the terminal phosphate group to the transport protein which changes the shape of the transport proteins to better move a substance
- also known as conformational change
What do pumps (such as sodium-potassium pumps in neurons) do?
Maintain membrane potential
What is membrane potential?
Unequal concentration of ions across the membrane that result in an electrical charge (electrochemical gradient)
What are 3 examples of pumps?
Electrogenic, sodium potassium, proton pump
What is an electrogenic pump?
- proteins that generate voltages across membranes, which can be used later as an energy source for cellular processes
Why is the sodium potassium pump important, and what happens?
- animal cells will regulate their relative concentrations of Na+ and K+
- 3 Na+ pumped out of cell, 2 k+ into cell
- results in a +1 net charge to the extracellular fluid (outside the neuron)
What is a proton pump? (3)
- integral membrane proteins that builds up a proton gradient (hydrogen ions) across the membrane
- used by plants, fungi, and bacteria
- pumps H+ out of cell
What is cotransport and who benefits from it? (2)
- The coupling of a favourable movement of one substance with an unfavourable movement of another substance
- plants use it for sugars and amino acids
What does cotransport use in order to do what it has to do?
- uses the energy stored in electrochemical gradients (generated by pumps) to move substances against their concentration gradient
What is favourable movement, and what is unfavourable movement?
- favourable movement is downhill diffusion from high to low
- unfavourable movement is uphill transport from low to high
An example of cotransport in plants is the sucrose-H + cotransporter. What happens here?
- sucrose can travel into a plant cell against its concentration gradient only if it is COUPLED with H+ that is diffusing down it’s electrochemical gradient
The transport of large molecules is done through what two types of active transport specifically?
Exocytosis and endocytosis
What is exocytosis?
The secretion of molecules via vesicles that fuse to the plasma membrane
How can vesicles fuse to the plasma membrane in exocytosis? (3)
- vesicles can fuse to the membrane by forming a bilayer
- once fused, the contents of the vesicle are released to the extracellular fluid
- an example would be nerve cells releasing neurotransmitters during an action potential
What is endocytosis?
- The uptake of molecules from vesicles fused from the plasma membrane (opposite of exocytosis)
Three examples of endocytosis?
Phagocytosis, pinocytosis, receptor-mediated endocytosis
What is phagocytosis?
When a cell engulfs particles to be later digested by lysosomes
How does phagocytosis work? (3)
- cell surrounds particle with pseudopodia (meaning false foot)
- packages particles into a food vacuole
- food vacuole fuses with a lysosome to be digested
What is pinocytosis?
Nonspecific uptake of extracellular fluid containing dissolved molecules
What happens in pinocytosis?
- The cell takes in dissolved molecules in a protein coated vesicle
In pinocytosis, cells essentially take in vesicles coated in proteins. Why?
The protein coating helps to mediate the transport of molecules
What is receptor mediated endocytosis?
- specific uptake of molecules via the solute binding to receptor proteins on the plasma membrane
Why is receptor mediated endocytosis important?
- it allows the cell to take up large quantities of a specific substance
What happens in receptor mediated endocytosis?
- when the solute binds to the receptors, they cluster in a coated vesicle to be taken into the cell
