transport across cell membranes Flashcards
The structure of the cell membrane
bilayer of phospholipids with a phosphate head pointing out where there is water
and tails that face inwards, away from anything polar
the functions of the phospholipid bilayer
1) act as a barrier form internal contents of cell + external environment / organelle from cytoplasm
2) separates parts of the organelle
3) location of chemical reactions
4) cell signalling
what type of molecules cannot enter the membrane freely - why
cell surface has a hydrophobic centre that prevents hydrophilic molecules from entering
water is exception because it is small, enters through very slow rate
what types of molecules does the cell surface contain
- proteins
- cholesterol - increasing strength of cell by rigidity,
restricts movement of phospholipid tails so controls fluidity in hot + cold temps
reduces movement of water soluble chemicals leaving the cell surface
why is it called the fluid mosaic model
fluid - phospholipids move like a fluid - they are flexible
mosaic - includes proteins of different shapes, sizes scattered over the membrane like tiles
what are intrinsic proteins + examples
proteins fully embedded in bilayer of phospholipid - helping with transport
carrier proteins - change shape in order to transfer molecules
protein channel - act as walls and inside they are hydrophilic
what are extrinsic proteins
protein that span on only one phospholipid layer - structural role / enzyme/ receptor
cholesterol and the phospholipid bilayer
- cholesterol - increasing strength of cell by rigidity,
restricts movement of phospholipid tails so controls fluidity in hot + cold temps
reduces movement of water soluble chemicals leaving the cell surface
glycolipids and the phospholipid bilayer
carbohydrate + covalent bond + lipid
extends from the phospholipid bilayer into the water environment, where it acts as a RECEPTOR
- maintains stability
- helps cells to attach to one anther
glycoproteins + the phospholipid bilayer
attached to extrinsic proteins
- receptor
- allows cells to attach together
- present as antigens
process of diffusion
1) we have a concentration gradient
2) movement happens across concentration gradient
3) continues until equilibrium is reached
definition of diffusion
net movement of particles from a region of high concentration to low concentration gradient
factors affecting diffusion
1) concentration (greater concentration = grater ROD
2) particle charge / size (charged ions do not enter + smaller molecules enter easily
3) temperature (movement is from kinetic energy, mammals have constant body temp
4) surface area (greater surface area = more area for site of diffusion
5) distance (thin membranes) more energy to move
6 the Prescence of channel/ carrier proteins
why do we need facilitated diffusion
for particles that are too big or polar that are repelled by the hydrophobic tails
so those particles can get in WITHOUT INTERACTING WITH THE HYDRTOPHOBIC CENTRE
what type of proteins are involved in facilitated diffusion
intrinsic proteins
the role of carrier proteins in facilitated diffusion
carrier proteins have a binding site for specific chemicals.
when chemical binds, the tertiary structure changes (change carrier chemical across membrane)
the role of protein channels in facilitated diffusion
this acts as a barrier between the hydrophobic tails
they have hydrophilic central pore, lined with hydrophilic amino acids
the process of active transport
move chemicals from one side against concentration gradient (requires metabolic energy - ATP)
1) molecule attaches to receptor site of carrier protein (LOW concentration side)
2) ATP binds to carrier proteins
3) ATP undergoes hydrolysis to become ADP and pi. phosphate attaches to carrier protein causes shape change - transports the molecule needed
4) phosphate leaves causing it to change shape to normal
ADP + pi will react again to make ATP
why is there many mitochondria in cells of active transport
mitochondria need to be able to form ATP which is needed in active transport because its active, so energy is quickly transported
carrier proteins - being unique
they have a unique active site for each chemical. so its only able to transport one type of molecule at a time
why do we need cotransport in the ileum
diffusion relies on a steep concentration gradient in order for particles to travel
after digestion, glucose is high but then decreases, not all molecules can be transported so we need cotransport
glucose in ileum to bloodstream
glucose ————> lumen of ileum
-----------> epithelial cell
-------------> bloodstream
co - transport
after digestion there’s high concentration of glucose, diffusion is rapid
gradually glucose is carried away concentration reaches equilibrium
there is a sodium potassium pump that remove sodium actively and create low concentration of sodium within epithelium
in lumen, there is a high concentration of sodium. Sodium is transported down concentration gradient by sodium glucose cotransporter that brings glucoses along with it. glucose transported AGAINST gradient
energy comes indirectly from concentration gradient of sodium
mitochondria in epithelial cells
many mitochondria for ATP synthesis for sodium potassium pump which is active transport
