Transport Across Cells Membranes Flashcards
(30 cards)
What are the functions of cell-surface membranes?
- Forms the boundary between the cell and its environment.
- Controls the movement of substances in and out of the cell.
How can substances move across the cell-surface membrane?
- Diffusion
- Osmosis
- Active transport
What are all cell membranes composed of?
Proteins, carbohydrates and lipids?
What are the functions of the membranes surrounding organelles? Check wording
- Divide the cell into different compartments, acting as a barrier between the organelle and the cytoplasm.
- Partially permeable and control what substances enter and leave the organelle.
What is the structure of cell membranes known as?
The fluid mosaic model
What does the fluid mosaic model describe?
The arrangement of molecules in the membrane
Describe the fluid mosaic model of a cell membrane and explain why the model holds this name.
- Phospholipid molecules form a continuous double layer (bilayer).
- The bilayer is fluid as the phospholipids are constantly moving.
- Cholesterol molecules are present within the bilayer.
- Proteins are scattered through the bilayer, like tiles in a mosaic.
What are the names of the proteins present in cell membranes?
- Channel proteins
- Carrier proteins
- Receptor proteins
What is the role of the channel proteins?
Form pores in the membrane for charged particles to diffuse through down their concentration gradient.
What is the role of the carrier proteins?
- They move large molecules across membranes, down their concentration gradient.
- First a large molecule attached to a carrier protein in the membrane.
- Then the protein changes shape.
- This releases the molecule on the opposite side of the membrane.
What is the role of the receptor proteins?
What are glycoproteins?
Proteins that have a polysaccharide (carbohydrate) chain attached
What are glycolipids?
Lipids that have a polysaccharide (carbohydrate) chain attached
What is the role of the cholesterol?
- Gives the membrane stability
- They help to maintain the shape of animals cells (which don’t have cell walls) which is particularly important for cells that aren’t supported by other cells, e.g. red blood cells which float free in the blood.
Where is cholesterol in a cell membrane?
- Cholesterol molecules fit between the phospholipids, binding to the hydrophobic tails which causes them to pack more closely together.
- This restricts the movement of the phospholipids, making the membrane more rigid and less fluid.
What is the role of the phospholipids?
- Form a barrier to dissolved substances.
- Automatically arrange themselves into a bilayer (the head face out towards the water either side of the membrane and the tail face into the bilayer).
What are the two modes of transport across a membrane?
- Passive transport
- Active transport
Define passive transport.
Does not require any external energy, due to the kinetic energy of particles.
Define active transport.
Requires energy in the form of the energy molecule ATP (an immediate energy source for cells).
Define diffusion.
Define simple diffusion.
When molecules diffuse directly through a cell membrane.
What does facilitated diffusion
What factors affects the rate of simple diffusion?
- Concentration gradient
- The thickness of the exchange surface
- The surface area
What factors affects the rate of facilitated diffusion?
- Concentration gradient
- Number of channel or carrier proteins