Biological Membranes Flashcards
What are the functions of cell membranes?
Regulates transport of materials into and out of the cell as the membrane is partially permeable so small, uncharged particles can pass through or charged particles can use channel/carrier proteins
Membranes around organelles divide the cell into compartments and act as a barrier between the organelle and the cytoplasm making reactions more efficient.
Cell signalling-one cell releases a messenger molecule which travels to another cell. The messenger molecule gets detected by the cell as it binds to a receptor molecule on the plasma membrane which then triggers a change in the cell.
attachment site for enzymes- site of chemical reactions
How thick is a cell membrane?
7nm
What are the components of a cell membrane?
Phospholipids
Cholesterol
Channel proteins
carrier proteins
Glycolipids and glycoproteins
What is the function and properties of phospholipids in a membrane?
act as a barrier to most water soluble substances
head is hydrophillic and tail is hydrophobic
The center of the membrane is hydrophobic so water soluble substances such as ions and polar molecules can’t diffuse through it
fat soluble substances dissolve in the bi-layer and pass directly through it
even though water is a polar molecule, it can diffuse through the membrane via osmosis because its so small
What does the cholesterol do in the membrane?
Gives the membrane stability
Present in all cell membranes except bacterial cell membranes
bind to the hydrophobic tails, causing them to pack more closely together
makes membrane less fluid and more rigid
cholesterol also has hydrophobic regions so creates a further barrier to water soluble substances.
What do channel proteins do?
Form pores in the membrane which are hydrophilic channels that allow small, charged particles across the membrane down the concentration gradient
What is the function of carrier proteins?
transport large and charged molecules across the membrane via active transport and facilitated diffusion down the concentration gradient
How do solvents affect membrane permeability?
some solvents dissolve the lipids in a cell membrane
Hence, increasing the concentration of solvents will also increase membrane permeability.
If the temperature is below 0 degrees then what happens to the permeability of a membrane?
The phospholipids don’t have much energy, so they can’t move a lot. They’re packed closely together and the membrane is rigid.
But channel and carrier proteins denature increasing the permeability of the membrane.
If the temperature is between 0 and 45 degrees, then what happens to membrane permeability?
The phospholipds can 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 increasing the permeability of the membrane.
What happens to membrane permeability when the temperature rises above 45 degrees?
The phospholipid bi layer starts to melt (break down) and the membrane becomes more permeable.
Water inside the cell expands putting more pressure on the membrane.
Channel and carrier proteins denature so they can’t control what enters or leaves the cell increasing the permeability of the cell.
What is a membrane bound receptor?
Proteins in the cell membrane that act as receptors for messenger molecules.
What is a target cell?
A cell that responds to a particular messenger molecule is called a target cell
Why can’t messenger molecules bind to the receptors on non-target cells?
This is because receptor proteins have specific shapes so only messenger molecules with a complimentary shape can bind to them.
How do hormones act as messenger molecules?
They bind to receptors in cell membranes and trigger a response in the cell
