Biological Membranes Flashcards
what is the plasma membrane
- controls the entry and exit of substances
- partially permeable
- barrier between cell and environment
what is the structure of the phospholipid membrane
- phospholipid bilayer
- hydrophilic phosphate heads
- hydrophobic fatty acid tails
what is the cell membrane theory
- fluid mosaic model
- phospholipids are free to move within the layers giving flexibility
- scattered proteins
what are intrinsic proteins
-transmembrane proteins embedded through both membrane layers
- amino acids + hydrophobic R groups on the external surface interacting with internal hydrophobic core to provide stability
What are examples of intrinsic proteins
- channel proteins
- carrier proteins
- glycoproteins
- glycolipids
what are channel proteins
- hydrophilic channel allowing passive movement of polar molecules and ions
what are carrier proteins
- role in passive and active transport into cells
- shape of the protein changes
what are glycoproteins
- embedded in cell surface membrane with attached carbohydrate chains
- cell signalling - chemical binds and elicits a response
what are glycolipids
- lipid with carbohydrate chains attached
- recognised by cells of the immune system as self or non-self
what are extrinsic proteins
- present in one side of the bilayer
- hydrophilic R groups on the outer surface and interact with polar heads
- cholesterol
what is cholesterol
- lipid with a hydrophilic and hydrophobic end
- regulates membrane fluidity
- hydrophilic end interacts with heads and hydrophobic with tails
- add stability
- prevents membrane from becoming solid by stopping phospholipid molecules from grouping closely
how does temperature effect membrane structure
- increased temperature the phospholipids have more kinetic energy and move more
- membrane becomes more fluid and loses its structure
- if temperature continues to increase the cell breaks down completely
- carrier and channel proteins are denatured
how do solvents effect membrane structure
- organic solvents (non-polar) dissolve membrane and disrupt cells
- pure/strong alcohol solutions are toxic
- disrupted membrane becomes more fluid and more permeable
what is diffusion
- net movement of particles from a region of higher concentration to a region of lower concentration until it reaches equilibrium
how does temperature affect the rate of diffusion
- high temperature = faster diffusion
- particles have more kinetic energy and move faster
what is facilitated diffusion
- larger molecules diffuse through carrier or channel proteins
How do carrier proteins move substances
- large molecule attaches to a carrier protein
- protein changes shape
- releases molecule on opposite side of the membrane
how do channel proteins move substances
- form pores in membrane for charged particles to diffuse through
what is active transport
- movement of molecules in or out of a cell from a region of lower concentration to a region of higher concentration
- requires energy and carrier proteins
how do carrier proteins use ATP to move substances
- molecule binds to receptor in channel of the protein on the outside of the cell
- on the inside ATP binds to the carrier protein and is hydrolysed to ADP and phosphate
- phosphate binds to protein causing it to change shape
- opens inside the cell
- molecule released inside the cell
- phosphate molecule released from the carrier protein and recombines with ADP to form ATP
- carrier protein returns to its original shape
what is bulk transport
- form of active transport
- molecules that are too larger to move through channel or carrier proteins
what is endocytosis
- bulk transport of materials into cells
- cell membrane bends inwards when it comes into contact with the material to be transported
- membrane enfolds to form a vesicle
- vesicle move into the cytoplasm
- transfers material for further processing in the cell
what is exocytosis
- bulk transport of material out of cells
- vesicle moves towards and fuses with the cell membrane
- contents released outside of the cell
what is an isotonic solution
solution with the same water potential as the cell
what is a hypertonic solution
solution with a lower water potential than the cell
what is a hypotonic solution
solution with a higher water potential than the cell
what happens to an animal cell in a isotonic solution
- water molecules pass in and out in equal amounts
- cell stays the same
what happens to an animal cell in a hypertonic solution
- net movement of water molecules is out of the cell
- cell shrinks
what happens to an animal cell in a hypotonic solutionn
- net movement of water molecules is in the cell
- cell bursts - cytolysis
what happens to a plant cell in a hypotonic solution
- vacuole swells
- vacuole + cytoplasm push against the cell wall
- cell becomes turgid
what happens to a plant cell in a isotonic solution
- water molecules move in and out of the cell in equal amounts
- cell stays the same
what happens to a plant cell in a hypertonic solution
- cell becomes flaccid
- cytoplasm and membrane pull away from the cell wall - plasmolysis
