Cell Membranes and Transport Flashcards
Membrane
partially membrane, made of phospholipids arranged in a bilayer and proteins.
Fluid mosaic model
describes the arrangement and movement of the molecules that make up a cell membrane.
Fluid
Mosaic
Phospholipids
Cholesterol
Glycolipids
Intrinsic Proteins
Extrinsic proteins:
- phospholipids and proteins are free to move sideways
-proteins have a scattered arrangement within the bilayer - a molecule that is constituent of the inner bilayer of biological membranes, having a polar, hydrophilic and a non-polar, hydrophobic tail.
: in cell membranes for fluidity and stability.
phospholipids with carbohydrates attached for cell signalling and recognition. - completely span the phospholipids bilayer. Some act as carrier to transport water-soluble molecules across the membrane. Others are enzymes.
- Embedded in the bilayer on one side but don’t extend though. For cell signalling, cell recognition, enzymes and receptors.
Roles of membranes within cells: COMPARTMENTALISATION.
Separate organelles content from cell cytoplasm
Provides large surface area for aerobic respiration.
Contains digestive enzymes
Where some reactions occur
Roles of membranes on the surface of the cells:
Separate cells components from external environment
Transport of materials
Contains enzymes for reactions
Has antigens to recognise cells as their own
Receptors for chemical signals
Cholesterol
Sit in between the fatty acid
They provide mechanical ability to the membrane
They stop certain molecules from being able to squeeze through the fatty acid layer and cross the membrane, reducing its permeability.
Proteins
If incorporated into the membrane they are called intrinsic proteins.
If found on the membrane surface, they are called extrinsic proteins.
Channel proteins span the membrane with a hydrophilic pore running down the middle
This allows charged ions to cross through the hydrophobic membrane layer
Carrier proteins can bind to a molecule on one side of the membrane then undergo a structural change to carry the molecule
Extrinsic proteins
Enzymes to catalyse certain reactions e.g., respiration in the mitochondria.
Glycoproteins
are used for cell recognition where they form antigens that label a cell as being either ‘self’ or ‘non-self’ to the immune system.
Cell signalling process:
One cell releases a messenger molecule (e.g., hormone)
This molecule travels to another target cell (e.g., in the blood)
The messenger molecule is detected by the cell because it binds to a receptor on the target cell’s cell membrane
The cell then responds to the messenger molecule by a change in activity
Diffusion:
The passive net movement of molecules from an area of higher concentration to an area of lower concentration, down a concentration gradient across a partially permeable membrane through the phospholipid bilayer.
Molecules that diffuse through the bilayer: lipid soluble ones, small and non-polar molecules e.g., oxygen, very small polar molecules e.g., water but slowly.
Factors affecting the rate of diffusion: temperature, concentration gradient, thickness of exchange surface and surface area.
Facilitated diffusion:
The passive movement of substances from an area of high concentration to an area of low concentration, down a concentration gradient across the membrane via carrier or channel proteins.
Channel proteins: provide corridors that allow a specific molecule.
Carrier proteins: a protein that transports substances across a cell membrane
Factors affecting the rate of facilitated diffusion: the concentration gradient, temperature, the number of channels or carrier proteins.
Exocytosis
the process by which a substance is released from the cell through a vesicle that transports the substance to membrane to let the substance out.
Osmosis
movement of water from an area of higher water potential to an area of lower water potential, down a water potential gradient across the phospholipid bilayer.
Pure water has a water potential of: 0kPa. Adding solutes to water makes the water potential lower (less than zero)
Water potential is measured in kilopascals (kPa)
Active Transport:
The active movement of ions or polar molecules from a lower concentration to a higher concentration using a carrier protein. This movement against the concentration gradient requires energy from ATP.
Specific protein carriers are required to change shape to move substances from one side of the membrane to the other.
Types of molecules that are actively transported by carrier proteins: large molecule (polar) and Ions.
What could inhibit active transport? - anything which inhibits respiration and therefore ATP production, e.g., cyanide
