Cell Membranes Flashcards
What are roles of membranes ?
Compartmentalises the cell.
Exchange of molecules, controls what goes in and out of the cell. Site of chemical reactions.
Cell signalling and Vesicle formation.
Describe the formation of the Bilayer Membrane
The bilayer membrane is made out of phospholipids.
The phosphate heads are facing outwards as they are polar and so they face towards the aqueous solution, the fatty acid tails are hydrophobic and so it faces inwards away from the aqueous solution.
Contain cholesterol in the bilayer to maintain fluidity.
Describe the Fluid Mosaic Model
It is described as this as the molecules are constantly moving relative to each other [fluid].
And all the proteins are embedded in the bilayer in a pattern [mosaic].
What are intrinsic proteins
Carrier and Channel proteins.
They span the width of the bilayer.
Allow the passage of charged and large molecules.
Extrinsic Proteins
Do not span the width of the bilayer.
Involved in chemical reactions.
What are glycoproteins and glycolipids used for in the membrane
Used for cell signalling.
Act as receptors.
Act as surface antigens.
Produced in Golgi.
Simple Diffusion
A passive movement of small molecules down a concentration gradient.
No ATP required.
Facilitated diffusion
Used with ions and large molecules.
High to low concentration.
Uses mostly channel proteins.
It is passive.
Active Transport
Needs ATP, low to high concentration. Carrier protein. E.g. sodium/potassium pump.
What happens in an animal cell when too much water enters?
In animals the membrane bursts and cytolysis happen
What happens in a plant cell when too much water enters?
The plant cell just becomes turgid
What happens when water leaves an animal cell?
The cell shrivels up.
Crenation
What happens when water leaves a plant cell?
The membrane detaches from cellulose cell wall.
The cell becomes flaccid.
