Biological Membranes Flashcards
What do membranes allow at the surface of cells
Recognition by other cells, cell signaling, diffusion, osmosis and active transport
What is in the fluid mosaic model
Phospholipid bilayer, cholesterol, proteins (channel, intrinsic, extrinsic, carrier), some have glycoproteins or glycolipids (carbohydrate chain)
What happens at membranes within cells
- Divide the cell into compartments acting as a barrier between the organelle and the cytoplasm
- Can form vesicles
- Control what enters and exits the cell (partially permeable)
- Site of chemical reactions
Phospholipid head is…
Hydrophilic (attracts water)
Fatty acid tail is…
Hydrophobic (repels water)
What does the bilayer not allow in
Water soluble substance such as ions
What does the bilayer allow through
Fat-soluble substances
What is cholesterol
A type of lipid present in all cell membranes except bacteria
Where id cholesterol in cells and how does it act
They fit between the phospholipids and bind to the hydrophobic tails causing them to pack more closely together making the membrane less fluid and more rigid. At low temperatures membrane fluidity is increased
What do proteins do in the membrane
- Form channels in the membrane
- Transport molecules and ions across the membrane
- Act as receptors in cell signaling
What do glycoproteins and glycolipids do
- Act as receptors for messenger molecules by stabilizing the membrane and forming hydrogen bonds with surrounding water molecules.
- Sites where drugs hormones and antibodies bind
- Antigens as involved in immune response
What is cell signaling
Cells communicating with each other to control processes inside the body to respond to changes in the environment
How do cells communicate with each other
1) One cell releases a messenger molecule
2) This molecule travels to another cell
3) This is detected by the cell because it binds to a receptor on its cell membrane
How are receptors used in cell signaling
- Proteins act as receptors for messenger molecules called membrane-bound receptors
- They have specific shapes that can bind to
- Different cells have different types of receptors and respond to different messenger molecules
- A cell that respond to a particular messenger molecule is called a target cell
How to investigate permeability of membranes
1) Cut five equal sized pieces of beetroot and rinse to remove any pigment
2) Place the five pieces in five different test tubes with 5cm of water
3) Place each test tube in a water bath at different temperatures (10,20,30,….)
4) Remove the pieces of beetroot from the tubes, leaving just the colored liquid
5) Use a calirometer to see how much light is absorbed
Best temperature for phospholipids
0-45 degrees celcius
What does changing the solvent do to membrane permeability
Surrounding it in a solvent increases the permeability of cell membranes as they dissolve the lipids in a cell membrane so it loses its structure. Increasing concentration also = increased permeability
Diffusion is …
The net movement of particles from an area of high concentration to low concentration going down the concentration gradient. This is a passive process
What type of molecules diffuse through the cell membrane
Small, non-polar molecules eg oxygen and carbon dioxide
Rate of diffusion factors
Concentration gradient, thickness of exchange surface, surface area, temperature
Facilitated diffusion is…
Diffusion through carrier or channel proteins in the cell membrane down the concentration gradient. It is a passive process
How do carrier proteins work in facilitated diffusion
- They move large molecules down the concentration gradient
1) First a large molecule attaches to a carrier protein in the membrane
2) Then the protein changes shape
3) This releases the molecule on the opposite side of the membrane
How do channel proteins work in facilitated diffusion
They form pores in the membrane for charged particles to diffuse through. Different channel proteins facilitate the diffusion of different charged particles
Active transport…
Uses energy to move molecules and ions across plasma membranes against a concentration gradient involving carrier proteins
The stages of active transport
1) A molecule attaches to the carrier protein
2) The protein changes shape
3) Molecule is moved across the membrane and released on the other side
What is bulk transport
When molecules are too large for carrier proteins such as proteins and lips so a vesicle forms and pinches off the substance
What is endocytosis
When the vesicle of the substance is ingested into the cell
What is exocytosis
Vesicles containing substances pick off from the Golgi apparatus in sacs and fuse with the plasma membrane before being released outside the cell
What is osmosis
The diffusion of water molecules across a partially permeable membrane down a water gradient.
What is water potential
Liklihood of water molecules to diffuse out of or into a solution
What has the highest water potential, and of what
Pure water of 0
What happens when a animal cell is placed in a hypotonic solution (water potential higher than the cell)
Net movement of water molecules is into the cell and so the cell bursts
What happens when a animal cell is placed in a isotonic solution (water potential the same as the cell)
Water molecules pass into and out of the cell in equal amount. The cell stays the same
What happens when a animal cell is placed in a hypertonic solution (water potential lower than the cell)
Net movement of water molecules is out of the cell and so the cell shrinks
What happens when a plant cell is placed in a hypertonic solution (water potential lower than the cell)
Net movement of water is out of the cell. The cell becomes flaccid and the cytoplasm and membrane pull away from the cell wall. Called plasmolysis
What happens when a plant cell is placed in a isotonic solution (water potential the same as the cell)
Water molecules pass into and out of the cell in equal amount. The cell stays the same
What happens when a plant cell is placed in a hypotonic solution (water potential higher than the cell)
Net movement of water is into the cell. The vacuole swells and it with the cytoplasm push against the cell wall and it becomes turgid.
