2.5 PLASMA MEMBRANES Flashcards
What are the roles of membranes?
The roles of membranes are:
-prokaryotes = one cell surface membranes
-eukaryotes = cell surface membranes, membrane bound organelles
-compartmentalisation = contains reactions, separates organelles, separates cell content from environment, keeps harmful substances separate, maintains chemical gradients for transport
-increasing surface area = greater area for exchange
-site of chemical reactions = photosynthesis, membrane proteins
-cell signalling
-cell recognition
Fluid mosaic model.
Fluid mosaic model:
-fluid = phospholipids free to move within bilayer relative to each other (flexibility)
-mosaic = proteins embedded which give varying shape, size and position
What are intrinsic and extrinsic proteins?
Intrinsic- transmembrane (both sides)
Extrinsic- one side of bilayer
Membranes and signalling.
Membranes and signalling:
-specific protein binds to complimentary receptor
-cell surface protein reconfigures its 3D shape, activating another protein
-activated protein begins a reaction inside the cell
Components of a membrane.
Components of membrane:
-channel proteins (intrinsic) = allows passive movement of polar molecules and mineral ions (doesn’t require ATP), held in place by phospholipids
-carrier proteins (intrinsic) = active transport and passive, reconfigures to let ion through
-glycoproteins (intrinsic) = cell adhesion, receptors, cell recognition
-glycolipids (extrinsic) = antigen, cell marker for identification
-extrinsic proteins (extrinsic) = enzymes, embedded to phospholipids
-cholesterol (extrinsic) = regulate fluidity, add stability (more cholesterol prevents phospholipids moving)
What is the affect of solvents on membrane permeability?
Affect of solvents on membrane permeability:
-many organic solvents are less polar than water (e.g alcohol)
-organic solvents will dissolve membranes
-pure or very strong alcohol solutions are toxic as they destroy cells
-non-polar solvents can enter the membrane and disrupt it
-when membrane is disrupted it becomes more fluid and permeable
What is the affect of temperature on membrane permeability?
Affect of temperature of membrane permeability:
-phospholipids are constantly moving
-higher temperatures increase the kinetic energy
-makes the membrane more fluid and lose its structure
-increases permeability and denatures carrier and channel proteins
What is diffusion?
Diffusion is the net movement of particles from an area of high concentration to an area of low concentration along the concentration gradient until an equilibrium is reached
-is a passive process (no ATP)
-particles diffuse through bilayer
-membrane partially permeable
-hydrophobic core of membrane repels ions which makes it difficult for them to diffuse through
-non-polar and smaller polar molecules can be transported by diffusion
What are the types of diffusion?
Types of diffusion:
simple diffusion- diffusion in the absence of a barrier or membrane (rate effected by temperature, concentration gradient, size of particles, diffusion medium)
facilitated diffusion- movement of molecules from an area of high concentration to an area of low concentration via proteins (large or polar molecules pass through membrane in aid of proteins specific to molecule they carry, passive, rate effected by temperature, surface area, concentration gradient, number of proteins, thickness of membrane (diffusion distance))
What are biological diffusion examples?
Biological diffusion examples:
-alveoli (lungs), villi (small intestine)
-thin wall = short diffusion distance
-large surface are = more space for diffusion
-rich blood supply = maintain concentration gradient
What is active transport?
Active transport is the movement of molecules or ions from an area of low concentration to an area of high concentration against the concentration gradient using a carrier or channel protein and ATP
-uses energy gained from hydrolysis of ATP
-uses carrier proteins/pumps
-selectively permeable
-allows large/charged particles to cross the membrane
What is the process of active transport?
Process of active transport:
1. molecule or ion to be transported binds to receptors in the channel or carrier protein on or outside cell
2. on inside of cell ATP binds to the carrier protein and is hydrolysed into ADP+Pi
3. binding of the phosphate molecule to the carrier protein causes the protein to change shape- opening up the inside of the cell
4. molecule is released to inside of cell
5. phosphate molecule is released from the carrier protein and recombines with ADP to form ATP
6. carrier protein returns to its original shape
What is bulk transport?
Bulk transport is the movement of large molecules into and out of the cell e.g enzymes and hormones
-for molecules too big for active transport
-required energy to move vesicles along cytoskeleton alter the shape of cell and fuse membranes
endocytosis- outer membrane of cell folds in on self, transport of material into cell
exocytosis- transport of material out of the cell, e.g phagocytosis, pinocytosis, vesicle formation
What is osmosis?
Osmosis is the net movement of water molecules from a region of high water potential to a region of low water potential through a partially permeable membrane
-water potential = the ability of water molecules to move freely in solution, measured in kPa
What is hypotonic solution?
Hypotonic solution is when the cell has a lower water potential than the solution
- animals = water moves into cell, causes cell to burst (cytolysis)
- plants = cell goes turgid as cell wall prevents it from bursting
