2.5- how substances cross membranes using active transport Flashcards
What is active transport?
The movement of substances against their concentration gradient across a cell membrane, using ATP and proton carriers.
What is endocytosis?
The bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins, into a cell.
What is exocytosis?
The bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins, out of a cell.
What is active transport like moving against the concentration gradient?
Sometimes cells need to move certain substances in or out, across their plasma membrane against each substance’s concentration gradient.
- This is like swimming against the tide and needs more energy than the kinetic energy of the molecule.
- This energy is provided by the hydrolysis of ATP, ATP is often described as the universal energy currency, as all cells make use of it to supply their energy needs
- Cells or organelles may need to accumulate more of a particular ion than they could do by simple or facilitated diffusion alone.
Which transport do root hair cells use?
Root hair cells use active transport to absorb ions from soil
How does the sodium-potassium pump work?
- 3 sodium ions bind to the specific site.
- On the sodium-potassium pump protein, ATP binds to its site.
- The ATP is hydrolysed to ADP+Pi, releasing energy.
- 2 potassium ions bind to their specific site.
- The energy released from the hydrolysis of ATP enables the sodium-potassium pump protein to change its shape so that the 3 sodium ions are now on the outside of the cell and the 2 potassium ions are on the inside.
What do carrier proteins have?
These membrane proteins have specific regions or site that combine reversibly with only certain solute molecules or ions.
They also have a region that binds to and allows the hydrolysis of a molecule of ATP, to release energy and in this way they act as enzymes.
What does the enryg help the carroier protein with?
The energy helps the protein change its conformation (SHAPE) and in doing so it carries the ion from one side of the cell membrane to the other.
What happens in guard cells?
In guard cells ATP made by chloroplast provide energy to actively transport potassium ions form the surrounding cells into the guard cells. This influx of ions lowered the water potential, in the guard cells, so that water enters from the surrounding cells by osmosis. As the guard cells swells their tips bulge and this opens the stoma between them.
How are large molecules transported?
Some cells need to transport large molecules and particles that are too large to pass through the plasma membrane in or out. They do this by bulk transport, a process that requires energy from ATP.
What is endocytosis?
This is how large particles may be brought into a cell. They do not pass through the plasma membrane. -A segment of the plasma membrane surrounds and encloses the particle and brings it into the cell, enclosed in a vesicle.
- This type of endocytosis is also called phagocytosis. This means ‘eating cells’ and refers to this type of intake of solid matter.
- If cells ingest liquids by endocytosis this is called pino (endo) cystosis.
ATP is needed to provide energy to form the vesicles and move them using molecular motor proteins, along cytoskeleton threads into the cell interior.
What is exocytosis?
This is how large molecules may be exported out of cells. They do not pass through the plasma membrane . Instead a vesicle containing them is moved towards and then fuses with the plasma membrane.
What is an example of exocytosis?
Seen at the synapse, where chemicals in vesicles are moved by motor proteins moving along cytoskeleton threads, to the presynaptic membrane. Here, the vesicle membrane and plasma membrane fuse and the neurotransmitter chemicals are released into the synaptic cleft.
In all cases, ATP is needed to fuse the membranes together as well as for moving the vesicles.A molecule of ATP is hydrolysed for every step that a motor protein takes along the cytoskeleton thread, as it drags the vesicles.
Give example of exocytosis:
1) A membrane bound vesicle containing the substance to be secreted is moved towards the cell surface membrane
2) The cell surface membrane and the membrane of vesicle fuse
3) The fused sites opens, releasing the content of the secretory vesicles
Give example of endocytosis:
1) Phagocytic cell, amoeba approaches a bacterioum2)Cell extends to surround the bacterium
3) Bacterium is now enclosed within a phagocytic vesicle a phagosome
