Chapter 5 Flashcards
Compartmentalisation
The formation of membrane bound areas. These membrane bound areas can contain important materials and they also have the correct conditions which are important to reactions taking place in the cell
Fluid Mosaic Model
Phospholipids are able to move within the membrane because it is not solid. Flexible membrane (Fluid)
The mosaic part is made through the proteins both intrinsic and extrinsic
Components of the Phospholipid Bilayer
- Glycoproteins
- Glycolipid
- Cholesterol
- Phospholipid
Intrinsic Proteins
Transmembrane proteins which are embedded within the phospholipid layer. Hydrophobic R-groups interact with the hydrophobic centre of the phospholipid bilayer, the fatty acid tails and this keeps the intrinsic proteins embedded
Channel Proteins
Hydrophilic channel, allows polar molecules to pass.
Held in position by hydrophobic R groups and hydrophobic core
Carrier Proteins
Important role in passive transport. Occurs down the concentration gradient. Changes shape when allowing molecules through
Glycoproteins
Intrinsic proteins meaning they are embedded within the phospholipid bilayer.
Role in:
- Cell adhesion
- Cell signalling as they are receptors
Glycolipid
Lipids attached to a carbohydrate chain. Cell markers and Antigens
Extrinsic proteins
Outside and in only one layer. Hydrophilic meaning they are attracted to the phosphate heads
Factors that affect membrane structures
-Temperature. The higher the temperature, the more fluid the phospholipid bilayer becomes and begins to break down
-Solvents. Polar solvents like water can pass through slowly, but less polar substances cannot pass through and can damage or kill cells like alcohols. Used for antiseptic techniques. Alcohols are less polar because they have one less hydrogen than water
Cell Communication
This occurs using glycoproteins embedded within the phospholipid bilayer. Glycoproteins are receptors. When a chemical binds to it, it elicits a response. These chemicals could be glucagon or insulin, in charge of controlling the blood sugar levels
Investigating membrane permeability
Beetroot experiment. Dry beetroot cores and place them in test tubes into water baths varying in temperature.
We then check light absorbance to see how much betalain left the beetroot cores.
Use a colorimeter to measure light absorbency
Diffusion and limiting factors
Net movement of particles from an area of high concentration to an area of low concentration, Diffusion occurs because particles gain kinetic energy, allowing them to move. Movement of particles is random.
Limiting factors of diffusion:
- Temperature, higher the temperature the more kinetic energy particles have to increase the rate of diffusion
- Diffusion distance, a large diffusion distance means particles are likely to collide with each other causing a low rate of diffusion
- Concentration difference, the larger the concentration difference, the quicker the rate of diffusion because there is a larger net movement of particles
- Surface area, larger surface area = more diffusion
Investigating rate of diffusion dependent on surface area
- Agar jelly blocks cut into different sizes that have phenolphthalein indicator that turns pink when in the presence of an alkali
- Place the blocks into sodium hydroxide for 10 minutes
- Blocks with a larger surface area would be more pink
Diffusion across a membrane and limitations
Diffusion across a membrane occurs through the phospholipid bilayer. Non polar and partially polar molecules can pass through. Water passes through at a slow rate because of hydrophobic centre
Limited by the thickness of the membrane and the surface area of the membrane
Facilitated diffusion
Diffusion across a membrane through a protein channel. Membranes that have channel proteins are specific, allowing only certain molecules to pass through. Needed to allow for polar molecules to enter the cell. ATP not needed. Facillitated diffusion is limited by the number of channel proteins present, temperature and the thickness of the membrane
Active transport
Active transport is the movement of molecules in or out of a cell from an area of low concentration to an area of high concentration. ATP is required because this process works against the concentration gradient.
Process of Active transport
- ATP hydrolyses to form ADP and Phosphate.
- Phosphate binds to carrier protein, allowing it to change shape and allow molecules to enter cell.
- Phosphate molecule released and goes back to ADP to form ATP
Bulk Transport
Large molecules cannot fit into channel and carrier proteins so are transported within cells.
Endocytosis - Movement of material into cells
1) Cell membrane invaginates (bends inwards)
2) Membrane enfolds the material
3) Vesicle formed
4) Vesicle pinched off and then further processed in cell
Exocytosis is where vesicles meet the cell surface membrane and then the contents within the vesicle are released
