B - 1 - Cell Membranes Flashcards
What are the main functions of the cell membrane?
- They form a barrier between the cell and its environment
- Control which substances enter and leave the cell
Which processes allow substances to move through the cell membrane and why?
- Diffusion ( also facilitated diffusion)
- Osmosis
- Active transport
Because the cell membrane is partially permeable
What is the fluid mosaic model of the cell membrane?
The model describing the arrangement of molecules in the cell membrane
Why is it known as a ‘fluid mosaic’ model?
- The phospholipids are constantly moving (fluid)
- Proteins are scattered through the bilayer like a mosaic
What is the function of channel and carrier proteins?
They allow large molecules and ions to pass through the membrane
What is the function of receptor proteins?
They allow the cell to detect chemicals released from other cells, which signal the cell to respond in some way.
What are glycoproteins and glycolipids?
Glycoproteins - Proteins that have a carbohydrate attached to them
Glycolipids - Lipids that have a carbohydrate attached to them
Describe the structure of the phospholipid bilayer
- Phospholipids have a head and a tail
- The head is hydrophilic
- The tail is hydrophobic
- The molecules are arranged into a bilayer where the heads face outwards and the tails face inwards
Describe the function of t a phospholipid bilayer
The bilayer allows the membrane to be a barrier to dissolved (water soluble) substances. The centre of the bilayer is hydrophobic so the membrane doesn’t allow water soluble substances to diffuse through it. Only small, non polar substances can diffuse through the membrane
What is the function of cholesterol in the cell membrane?
It gives the membrane stability. It fits between the phospholipids in the cell membrane. They bind to the hydrophobic tails causing them to pack more closely together. This restricts the movement of the phospholipids making the membrane less fluid and more rigid.
Why is cholesterol important for cells that are not supported by other cells?
Because it helps maintain the shape of the cell
How does cholesterol create a barrier to polar substances?
It has hydrophobic regions
How do temperatures below 0 degrees affect cell membranes?
Phospholipids do not have much energy and so they can’t move. They are placed closely together and the membrane is rigid. But channel proteins and carrier proteins in the membrane denature (lost structure and function) increasing the permeability pf the membrane. Ice crystals may form and pierce the membrane, making it. highly permeable when it thaws.
How do temperatures between 0 and 45 degrees affect cell membranes?
The phospholipids cannot move around and aren’t packed as tightly together - the membrane is partially permeable. As the temperature increases the phospholipids move more because they have more energy - increases the permeability of the membrane. As the temperature increases the phospholipids move more because they have more energy - this increases the permeability of the membrane
How do temperatures above 45 degrees have an affect on cell membranes?
The phospholipid bilayer starts to melt and the membrane becomes more permeable. Water inside the cell expands, putting pressure on the membrane. Channel proteins and carrier proteins in the membrane denature so they can’t control what enters of leaves the cell - this increases the permeability of the membrane.
