Membrane Structure & Transport Flashcards
What does the cell membrane consist of?
Proteins, glycoproteins, phospholipids, cholesterol and carbohydrates
What does the cell surface membrane do?
-controls the entry and exit of molecules in cells
-surrounds by cytoplasm of a cell
-it is selectively permeable
Why is the fluid mosaic model described as ‘fluid’?
-phospholipid molecules form a bilayer that are constantly moving around, giving the membrane a fluid structure
Why is the fluid mosaic model described as ‘mosaic’?
-the different protein molecules are unevenly distributed throughout the membrane forming a mosaic
What are all membranes made from?
Phospholipid bilayers
What decides the selective permeability of the cell surface membrane?
-the type and distribution of specific proteins and phospholipids molecules present in the membrane
Draw/describe the fluid mosaic model
What components does the fluid-mosaic model consist of?
-carrier protein
-channel protein
-phospholipid bilayer
-cholesterol
-glycolipid
-glycoprotein
-hormones
-receptor
-enzyme
Describe the function of phospholipids
-form a bilayer
-found in all membranes
-allows lipid soluble molecules to pass through by simple diffusion and prevents larger molecules (glucose) from passing through
describe the function of cholesterol
-decreases permeability and increases stability of the membrane
-more cholesterol = less fluid membrane
-different cells have different proportions of cholesterol
Describe the function of channel proteins
-only allow specific charged ions/ small molecules to move across the membrane through facilitated diffusion
-complimentary to specific charged molecules & ions
Describe the function of carrier proteins
-aid transport of ions/polar molecules by facilitated diffusion and active transport
Describe the function of receptor proteins
-other protein molecules act as specific receptors for complimentary molecules
-specific cels have specific receptors
What is the function of an enzyme?
-embedded in cell membrane (Maltese & Dipeptidase)
-specific shaped active site which is complimentary to substrate and forms ESCs
What is the function of a glycoprotein?
-composed of carbs and proteins on outer surface of membrane and are important in cell recognition (often act as antigens)
-immune cells detect specific shapes of glycoproteins to identify cells as self or non self/ foreign
-produced in Golgi body within cell that displays them
-all cells have glycoproteins on their cell surface membrane
What do all cells have on their cell surface membrane?
Glycoproteins
What is the function of an aquaporin?
-Special type of channel protein specific to water.
-cells with lots of aquaporins are very permeable to water and will carry out osmosis easily
name the 6 processes in which substances can move in or out of cells
-simple diffusion
-facilitated diffusion
-osmosis
-active transport
-co transport
-bulk transport
Describe simple diffusion
-passive process
-doesn’t require energy /ATP
-n loves small, non polar, lipid soluble molecules
-(net) diffusion stops when there are equal numbers f a specific molecule on either side of the membrane (reached equilibrium)
define simple diffusion
The net movement of molecules from an area of higher concentration to a lower concentration across a partially permeable membrane
Which factors affect the rate of diffusion?
-temperature
-surface area
-concentration gradient
-diffusion distance/ pathway
Describe facilitated diffusion
-passive process/doesnt require ATP
-large, charged, water soluble can’t pass through hydrophobic tails of phospholipid bilayer so to enter or exit the cell must move through the membrane via carrier or channel proteins
-carrier/channel proteins help specific molecules pass through
-levels off when all carrier proteins are saturated/ binding site is full
-number of carrier proteins is the limiting factor
Define osmosis
The net movement of water molecules from higher water potential to a solution with lower water potential through a partially permeable membrane
Describe water potential
-free water molecules can move and collide with the membrane (water potential)
-more free moving water molecules= more pressure = higher water potential
-pure water -= highest water potential
-adding a solute makes the solution negative
describe an isotonic solution in osmosis
-no net movement of water in or out of cells
-water potential inside the cell is the same as outside the cell
-no water potential gradient = no change in mass
Describe a solution with a higher water potential than tissue in osmosis
-animal cells swell & lysis occurs
-plant cells swell, increasing mass
-higher water potential outside cell
-lower water potential inside cell
-waters moves IN by osmosis
Describe a solution with
describe a solution with lower water potential than tissue in osmosis
-animal cells shrivel
-plant cell membrane pulls away from cell wall (plasmolysed)
-higher water potential inside cell
-lower water potential outside cell
-waters moves moves out by osmosis, mass is lost
Describe active transport
-transports molecules across a membrane against their concentration gradient (lower to higher conc)
-active transport ONLY uses carrier proteins
-it requires a specific shaped carrier protein with a complimentary binding site
-requires a source of energy/ ATP
-molecule binds to binding site of specific carrier proteins
-hydrolysis of ATP into ADP and Pi provides very little energy/ phosphorylates the carrier proteins so it changes shape
What does bulk transport include?
Endocytosis and exocytosis
Describe exocytosis in bulk transport
-exo = out
-uses Golgi to move large quantities of molecules from inside the cell to outside
-used to move enzymes and glycoproteins from Golgi to cell surface membrane to secrete proteins
-ATP is required to move the vesicles to the cell surface membrane and the vesicle FUSE with the membrane
describe endocytosis in bulk transport
-endo = inside
-cell surface membrane is ‘pulled’ inwards to create a vesicle, any molecules near that part of the membrane are enclosed within the vesicle
-requires the breakdown of ATP into ADP and Pi
-movement of vesicle in the cell also requires breakdown of ATP into ADP and Pi
Create a summary table for simple diffusion, facilitated diffusion, osmosis & active transport
What happens if aerobic respiration is inhibited (stopped/ slowed)
-active transport can’t occur as there is less/ no ATP
-all other types of transport will continue until equilibrium is reached
What happens if the tertiary structure of the carrier protein changes?
Facilitated diffusion/active transport can’t occur as the binding site has changed shape and is no longer complimentary to the molecule therefore wont fit/bind
Many different substances enter and leave a cel by crossing its cell surface membrane. describe how substances can cross a cell surface membrane (5)
-small/ non polar/ lipid soluble molecules pass via phospholipids/ bilayer
-(simple/ facilitated) by diffusion from high to low concentration/ down concentration gradient
OR
Large/polar/water soluble molecules go through proteins
-water moves by osmosis (from higher water potential to lower water potential)
-active transport is movement from low to high concentration/ against concentration gradient
-active transport/ facilitated diffusion involves proteins/ carriers
-active transport requires energy/ ATP
-Na+ Glucose/ co transport
