transport across cell membranes Flashcards
cell membranes
-All cell-surface membranes and organelle membranes have
the same structure.
- the membranes are described as a fluid-mosaic model due to the mixture and movement of the phospholipids, proteins, glycoproteins and glycoproteins it is made of.
- all of these molecules arranged within the phospholipid bilayer r create the partially permeable
membrane, that is the cell-surface and organelle membrane.
phospholipids
The phospholipids align as a bilayer due to the hydrophilic heads being attracted to water and the
hydrophobic tails being repelled by water
-saturated fatty acid
- unsaturated fatty acid
phospholipid bilayer
-hydrophobic tail
and hydrophilic head
top extracellular bottom intracellular
components of the membrane
-cholesterol is present in some membranes and this will restrict the lateral movement of other molecules in the membrane
-useful as it makes the membrane less fluid at high high temperatures
-and prevents water and dissolved ions from leaking out of the cell.
-glycoprotein - protein with carbohydrate attached
-glycolipid - lipid with carbohydrar attached
-channel protein
integral membrane protein
peripheral membrane protein
proteins in the cell membrane
-proteins that are embedded across the cell surfaced membrane are either:
1. peripheral
2. integral
peripheral meaning
does not extend completely across the membrane
integral meaning
span across from one side of the bilayer to the other
peripheral proteins
provide mechanical support
along with carbohydrate chains that are connected to proteins or lipids to make glycoproteins and glycolipids
- the function of these is cell recognition as receptors
integral proteins
-protein carriers or channel proteins involved in the transport of a molecule across the membrane
channel proteins
-form tubes that fill with water to enable water soluble ions to diffuse.
whereas carrier proteins will bind with other ones and larger molecules such as glucose and amino acids,
they change shape to transport them to the inside of the cell or organelle
partially permeable membrane
molecules that pass through the plasma membrane
-lipid soluble substances (some hormones)
-very small molecules
molecules that cannot pass through the membrane
-water soluble (polar) substances (sodium ions) -hydrophobic tails
-large molecules (glucose) not enough room
the Four key types of transport
simple diffusion
facilitated diffusion
active transport
osmosis
adaptions to increase the rate of these four types of transport
increase transport either across the cell surface membrane or organelle membranes
main two adaptions :
increasing the surface area
increasing the number of channel and carrier molecules in the membranes
simple diffusion
-movement of molecules from an area of high concentration to an area of lower concentration until equilibrium is reached.
-this process does not require ATP
-therefore is a passive process.
simple diffusion
movement of molecules
-movement of molecules by simple diffusion is due to the kinetic energy they possess to enable them to constantly move in fluids
simple diffusion
what must molecules require to be able to diffuse across a membrane
they must be lipid soluble and small
facilitated diffusion
-a passive process -doesn’t require ATP
-differs from simple diffusion as membrane proteins are used to transport molecules
ions and polar molecules which cannot simply diffuse can be transported across membranes by facilitated diffusion using protein channels and carrier proteins.
facilitated diffusion
use of protein channels
protein channels form tubes filled with water and this enables water soluble ions to pass through the membrane
this is still selective- as the channel proteins only open in the presence of certain ions when they bind to the protein
facilitated diffusion
use of carrier proteins
carrier proteins will bind with a molecule such as glucose, which causes a change in the shape of the protein
-this change in shape enables the molecule to be released to the other side of the membrane.
osmosis definition
the net movement of water from an area of high water potential to an area of low water potential across a partially permeable membrane.
what is water potential
is the pressure created by water molecules
measured in kPa and represented with the symbol that looks like a candle
what water potential does water have
what does this mean
water potential of 0
so when solutes are dissolved in water the water potential will become negative
-the more negative the water potential the more solute must be dissolved in it.
what is an isotonic solution
a solution where the water potential of the solution is the same as the water potential of the cell
what is a hypotonic solution
when the water potential of a solution is more positive ( closer to zero) than the cell
what is a hypertonic solution
when the water potential of a solution is more negative than the cell
osmosis and types of solutions in animal cells
animal cells bursting
-in animal cells if they are placed in an hypotonic solution such as pure water, alot of water will move into the cells by osmosis.
-animal cells dont have a cell wall, therefore the pressure will cause the cell to burst (lyse)
why dont plant cells burst
because of their strengthened cell wall and instead become turgid.
what will both animal and plant cells do
-both animal and plant cells will shrink and become shriveled if they are placed in hypertonic solutions, due to large volumes of water leaving the cell by osmosis.
Active transport
diagram in notes.
the movement of ions and charged particles from an area of low concentration to an area of high concentration
against the concentration gradient
using ATP and carrier proteins
how are carrier proteins used in active transport
-act as pumps to move substances across the membrane
-this is very selective as only certain molecules can bind to the carrier [proteins to be pumped
this is due to their specific tertiary structure
How are ATP and carrier proteins used in active transport.
-certain molecules can bind to the receptor site on carrier proteins
-due to specific tertiary structure
-ATP will bind to the protein o the inside of the membrane
-and is hydrolyzed into ADP and Pi
-by ATP hydrolase
-This causes the protein to change its tertiary structure. and open towards the inside of the membrane.
-this causes the molecule to be released on the other side of the membrane
-the Pi molecule is then released on the other side of the membrane
-The Pi molecule is then released from the protein , this results in the protein reverting to its original tertiary structure
Co-transport
diagram in notes
-To absorb glucose from the lumen of the intestines into the epithelial cells, there must be a high concentration of glucose in the lumen compared to the epithelial cell ( for facilitated diffusion)
-However there is usually more glucose in the epithelial cells and this is why active transport is needed.
co transport of glucose and amino acid process
-sodium ions are actively transported out of the epithelial cell into the blood in the capillary using the sodium potassium pump.
-this reduces the sodium ion concentration of the epithelial cell
-sodium ions can then diffuse from the lumen down their concentration gradient into the epithelial cell
-the protein and the sodium ions diffuse through a co transporter protein, so either glucose or amino acids also attach and are transported into the epithelial cell against their concentration gradient
-glucose then moves by facilitated diffusion from the epithelial cell into blood.
look at diagram in notes.
what is the sodium potassium pump.
- a carrier protein
-actively transporting 3 sodium ions out of the cell
-2 potassium ions into the cell
-requiring ATP.
what is co transport
-coupled movement of molecules
-one molecule with its concentration gradient another molecule against its concentration gradient.
-using intrinsic proteins
-prevents equilibrium.
what impacts the rate of diffusion
-temp = molecules have more kinetic energy
-SA= greater surface for molecules to pas
-conc gradient= greater difference between the two concentrations more ‘space’ for molecules to move
ficks law
relationship between the rate of diffusion at constant temperature and the
1. concentration gradient
2. length of diffusion pathway
3. surface area over which diffusion is occuring.
rate of diffusion (fish) SA x concentration gradient / length of diffusion pathway.
what is the ileum
-the very end of the small intestine
-the last opportunity for glucose, nutrients and amino acids to be absorbed into the blood.
past exam question
explain how the structure of the ileum maximises the rate of transport into and out of the cell
- large surface area due to foldings in the cell wall ( villi)
-further foldings on the epithelial cells( microvili)
-larger surface area for carrier and channel proteins to prevent saturation
-muscle of cell wall can contract
-hydrolyse food to become more small and soluble
process of the sodium potassium pump.
-initially open on the intracellular part of the cell
- binding room for 3 sodium ions
- protein becomes phosphorilated (phosphate been released that attaches to protein) atp synthase
-this changes the specific tertiary structure of the pump/protein
- protein can now flip- releasing sodium ions to the outside
-now open to extracellular side of cell
-binding space for 2 potassium ions to bind.
-phosphate ion then dissociates.
-reverts back to original specific tertiary structure.
melon?
yes
