4.4 - Active transport Flashcards
Define active transport
The movement of molecules/ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins
What is ATP used for, during active transport
- directly move molecules
- co-transport: individually move molecules using a concentration gradient which has already been set up by (direct) active transport
How does active transport differ from passive forms of transport
- Metabolic energy generated (ATP) by the mitochondria as a result of respiration is needed
- substances are moved against a concentration gradient, that’s from a lower to higher concentration
- carrier protein molecules which act as ‘pumps’ are involved
- the process is very selective, with specific substances being transported
Describe how active transport of a single molecule/ion is carried out
- carrier proteins span the plasma membrane
- molecule/ion binds to receptors of carrier protein
- on the inside of the cell/organelle, ATP binds to protein = causes it to split into ADP and phosphate molecule. As a result protein molecule changes shape and opens on the opposite side of the membrane
- molecule/ion is then released on the other side of the membrane
- the phosphate molecule is released from the protein (it reverts to og shape, ready for process to be repeated). Phosphate molecule recombines with ADP during respiration = forms ATP
Can more than 1 molecule be moved by active transport
- Yes
- one can be being removed from a cell/organelle at the same time that one is leaving
—> e.g. sodium-potassium pump
How does a sodium-potassium pump work
- Na+ ions are actively transported into the blood from epithelial cell by the sodium-potassium pump. This takes place in 1 type of protein-carrier molecule found in the CSM of epithelial cells
- This maintains a higher concentration conc. of sodium ions in the lumen of the intestine than inside the epithelial cells
- Therefore sodium ions diffuse down this conc. gradient into the epithelial cells via a 2nd protein carrier (co-transport protein). When they diffuse, they’re carrying either amino acid/glucose molecules into the cell with them.
- The glucose/amino acid molecules pass into the blood plasma by facilitated diffusion using another type of carrier
Draw a diagram showing the co-transport of a glucose molecule
Describe what’s going on in each of the 4 steps
- Na+ ions are actively transported (pumped) out of the epithelial cell via protein carriers in exchange for K+
- This makes a (low) sodium conc. in the epithelial cell and so a favourable gradient for diffusion of Na+ from gut
- Diffusion of Na+ is coupled to glucose (or amino acids) via a carrier protein called a co-transporter
- Glucose moves into the blood from the epithelial cell by facilitated diffusion
Explain the differences between Channel proteins and carrier proteins
Channel proteins — Carrier proteins
position is fixed — flip between 2 conformations
transport ions — transports molecules
solute molecules diffuse through the pores — Solute molecules are bound to 1 side and released from the other side
High transport rates — low transport rates
Doesn’t bind with solute molecules it transports — consist of alternative solute-bound conformations
Lipoproteins — Glycoproteins
Synthesised in the rough ER — synthesised in the free ribosomes in the cytoplasm
Only transports water-soluble molecules — transport both water and insoluble molecules
Where does Anaerobic respiration happen
In the cytoplasm
Where does aerobic respiration happen
Mitochondria —> generates ATP
How are carrier proteins involved in active transport
- a molecule attaches to a to a carrier protein
- the protein changes shape and moves this molecule across the membrane
- releasing it on the other side
What are the 2 main differences between active transport and facilitated diffusion
1) active transport moves solutes low to high, whereas in facilitated they always move from high to low concentration
2) active transport requires energy (ATP produced by respiration in the mitochondria), facilitate doesn’t’ (just relies on kinetic energy of molecules)
Does active transport use channel or carrier proteins
- doesn’t use channel proteins
- but does use carrier proteins
What are the factors that affect the rate of active transport
- the speed of individual carrier proteins (the faster they work = the faster the rate of active transport)
- the number of carrier proteins present (the more proteins there are, the faster the rate of active transport
- the rate of respiration in the cell and the availability of ATP (if respiration is inhibited, active transport can’t take place)
