transport across membranes Flashcards
explain why a cell surface membrane is often called as a fluid mosaic model?
- bilayer membrane
- position of molecules within membrane is fluid = are able to move around in the membrane
- membrane made up of many different molecules arranged in a mosaic
explain the arrangement of the phospholipids in the cell surface membrane
bilayer
- hydrophobic fatty acid tails face away from water and hydrophilic heads attract water
what is the function of the phospholipids in the cell surface membrane
- hydrophobic tails repel water and hydrophilic head attracts water, forming a bilayer
- allows LIPID SOLUBLE (NON-POLAR) molecules to pass
- via SIMPLE DIFFUSION
- prevents small POLAR molecules like ions to pass
what is the function of cholesterol in the cell surface membrane?
- decreases permeability AND
- increases stability of the membrane
(more cholesterol = less fluidity of the membrane)
what is the function of the channel proteins in the cell surface membrane?
- have specific 3 structure only transporting specifically complementary molecules
- only allow SPECIFIC IONS/POLAR or SMALL molecules to move across membrane
- via FACILIATED DIFFUSION
- can be open or closed or intrinsic (allow ions to move straight through)
what is the function of the carrier proteins in the cell surface membrane?
- transport ions and LARGE molecules (eg: glucose, amino acids)
- via faciliated diffusion AND active transport
what is the function of the receptor proteins in the cell surface membrane?
- specific cells have specific receptors, only specific molecules can bind to specific receptors
- protein molecules act as specific receptiors for complementary molecules (ie: hormones like insulin, which cell responds by increasing the cell permeability to glucose).
what is the function of the glycoproteins in the cell surface membrane?
glycoprotein = carb + protein
- used in cell recognition, act as antigens
- on outer surface membrane
- produced in golgi body
- immune cells detect shape of glycoproteins to detect if SELF or NON SELF
what is the function of aquaporins in the cell surface membrane?
- specific type of channel proteins specific to water
more aquaporins = more permeable to water = easier osmosis
diffusion
- passive process = no ATP from respiration
- net movement of non-polar, small molecules (eg: 02, CO2 and oestrogen) from an area of highER concentration to an area of lowER concentration
- across a partially permeable membrane
ficks law
rate of diffusion = (SA x CG) divided by diffusion distance
factors affecting rate of diffusion
- temperature = increased kinetic energy, faster rate of diffusion of molecules
- Surface Area = larger surface area allows more space for molecules to move through, alows more proteins to be present (eg: microvilli)
- concentration gradient = as concentration difference increases, rate of diffusion increases
- diffusion distance = shorter distance/ fewer membranes to cross means faster diffusion
faciliated diffusion
- channel and carrier proteins have a specific shape that are compkementry to a specific ions
- passive, no ATP
- proteins have binding sites
faciliated diffusion graph
- levels off when carrier proteins are saturated/ binding sites are full
- B plateaues at a lower rate because less specific carrier proteins
- number of proteins is a limiting factor
many different substances enter and leave the cell by crossing its cell surface membrane. describe how substances can cross via a CSM
- diffusion from a higher concentration to a lower concentration
- small, non-polar molecules pass via phospholipid bilayer
- water moves by osmosis from a high water potential to a lower water potential
- active transport is movement of substances from low concentration to a higher concentration, against a concentration gradient
- active transport requires energy
- glucose cotransported
- active transport and faciliated diffusion involves proteins
osmosis
- net movement of water molecule from a higher water potential to a lower water potential
- via a selectively permeable membrane
the movement of substances across cell membranes is affected by membrane structure. describe how.
- phospholipid bilayer allows movement of non polar substances
- phospholipid bilayer prevents diffusion of polar substances across bilayer
- carrier proteins allow active transport
- channel and carrier proteins allow faciliated diffusion
- shape determines which substances move
- number of channels determines how much movement
- membrane surface area determines how much diffusion
- cholesterol affects permeability
water potential
pressure water exerts on membrane in kPa
- highest water potential = 0kPa
- adding solute makes it negative
FOR AO2 Questions
- identify and state where water potential is highest
- state where water potential is more negative
- water moves down the water potential gradient via osmosis
- consequence, eg: lysis, shrivelling, stops metabolic reactions
when water potential higher outside than inside organelle
swelling/lysis
cell bursts
water moves in by osmosis
higher water potential inside cell
shrivelling
plant membrane shrivels from cell wall
water moves out by osmosis, mass lost
isotonic
no net movement of water in or out of cells
- no water potential gradient
active transport
used to transport molecules across membrane against the concentration gradient
- only uses carrier proteins; speciifc shape with a complementary binding site
- requires ATP energy; hydrolysis phosphorylates the carrier protein and changes its shape so it can transport the molecule
bulk transport
endocytosis
exocytosis
exocytosis
- uses vesicles to transport large quanitiies of molecules (eg: enzymes, insulin) from inside a cel to outside cell
- also moves enzymes and glycoproteins from golgi body to csm to secrete proteins, atp required to transport vesicles
- vesicles fuse with csm
endocytosis
membrane pulled inwards to create a vesicle
- requires breakdown of atp
- movement of vesicle also requires breakdown of ATP
AO2: ACTIVE TRANSPORT
what happens if aerobic respiration is inhibited
- no ATP
- active transport cant occur
- all other types of transport can still continue
what happens if the tertiary structure of the carrier protein changes
- FD ans active transport cant occur
- binding sites have changed shapes so no longer specifically complementary to molecule, therefore will not bind
