2.1.5-Biological Membranes Flashcards
what are the 3 roles of cell membranes?
1-as a bilayer (partially permeable membrane), so that small molecules can pass whereas large cannot.
2-Site of chemical reactions
3-Site of cell communication/signalling
what is the main role of membranes?
to control the movement of substances in and out of the cell.
what are some example of substances that can pass through membranes?
lipids
small water solubles
what are some examples of substances that cannot pass through membranes?
large water solubles
ions
what is the fluid mosaic model?
it describes the structure of the plasma membrane as mosaic of components
it is a sea of membrane-composed phospholipids with protein molecules between.
what are the 3 things that the fluid mosaic model can help to explain?
- Passive and active movement between cells and their surroundings
- Cell-to-cell interactions
- Cell signalling
what are the four main components within the fluid mosaic model?
- phospholipids
- cholesterol
- glycoproteins/glycolipids
- transport proteins
what is the role of phospholipids?
- form the basic structure of the membrane
- the phospholipid bilayers act as a barrier to most water-soluble substances, so they cannot leak out of the cell/unwanted cannot enter the cell
what is the role of cholesterol?
- it increases the fluidity of the membrane, preventing it from becoming too rigid at low temps.
- it stops phospholipid tails from packing too closely together
- it increases the mechanical strength and stability of the membrane.
what is the role of transport proteins?
- create a hydrophillic channel to allow ions and polar molecules to travel through the membrane, controls what enters/leaves the cell
- each specific to a molecule
what are carrier proteins?
transport proteins that change shape to transport substances
as well as carrier proteins, what is the other type of transport protein?
channel(pore) proteins
what do glycolipids/glycoproteins acts as?
- receptor molecules, that bind with certain substances at cell’s surfaces
- some act as cell markers/antigens for cell-to-cell recognition.
what are the 3 main receptor molecules?
- Signalling receptors for hormones and neurotransmitters
- Receptors involved in endocytosis
- Receptors involved in cell adhesion and stabilisation
what is the plasma membrane?
=the cell surface membrane that separates the cell from it’s external environment
why do membranes exist as bilayers?
- inside/outside of cell are aqueous so a single layer would repel on one side (tails)
- bilayer=heads face the aqueous tissue/cytoplasm, while the tails face away/in the middle
what are the two main factors that affect membrane permeability and structure?
- temperature
- solvents/alcohol
how does temperature affect membrane structure/permeability?
- increased temp, phospholipids gain more kinetic energy, so move more
- therefore, the membrane becomes more fluid so loses it’s structure and can break
- loss of structure means that the membrane has an increased permeability, so molecules can cross over it more easily
- carrier/channel proteins become denatured
how does solvents/alcohol have an affect on membrane structure/permeability?
- less polar solvents/non-polar dissolve membrane
- dissolvement disrupts cells between phospholipids
- membrane becomes more fluid/permeable
- this can affect the transmission of messages
what are the two passive methods of the movement of molecules across membranes?
- diffusion
- fascilitated diffusion
what is diffusion?
the net movement of particles from a region of higher concentration to an area of lower concentration
what is fascilitated diffusion?
the same as diffusion, but a channel protein is required to transport polar, charged and water soluble molecules across the partially permeable membrane
what are the key differences/similarities between simple and fascilitated diffusion?
- S=fat soluble through lipid bilayer, F=lipid soluble through protein channel
- S=direction of down conc gradient, same with F
- both are passive movements
- S=solubles include oxygen, CO2, water and fats, F=insolubles include amino acids, sugars and ions
what factors affect diffusion and how?
- temp=increased temp, increased rate due to more ke
- conc difference=increased difference, increased rate as movement becomes larger
