Biological Membranes- cell membrane/movement of molecules across membranes Flashcards
what is the role of membranes within cells at the surface of a cell?
Plasma memebrane
-separate cells components from its external envirnoment
-regulates movements in and out of the cell
-have enzymes thta are involved in chemical reactions
-contains antigens for cell recognition
-contain receptors for cell signalling
Organelles have membranes that separate their environment with cytoplasm:
-compartmentalisation
-separate inside and outside of organelles
-enzymes in membranes that carry out chemical reactions
what is cell signalling? and whats parts of the membrane is involved in cell signalling?
involved: glycolipids, glycoproteins, extrinsic protein
-A gland cell produces a hormone signalling molecules which then binds to a receptor (specific to that hormone/complementary to messenger molecule) that is connected to a target cell. Then this sends a signal inside the cell
What is the fluid mosaic model of membrane structure and the roles of its components?
2 layers of phospholipids (the hydrophilic heads facing outwards of the membrane and the hydrophobic tails facing inwards of the membrane.
A glycolipid (lipid with carbohydrate chain attached) connected to a phospholipid
-involved in antigens and receptors but not enzymes as theres no protein
Instrinsic protein going all the way through the membrane
-involved in transporting molecules/ions in or out of the cell
Cholesterol (lipid) is inside of the membrane between the phospholipids
-it is non polar
-involved in regulating fluidity of membrane - how far apart the phospholipids are from each other.
Extrinsic protein on the side of the membrane with the cytoplasm
-involved with enzymes/antigens/receptors
Glycoprotein (protein with a carbohydrate chain attached)
-involved with enzymes/antigens/receptors
what are the factors affecting permeability?
Polar molecule - molecules which has a slightly positive and negative end (electrons not distributed evenly)
Small polar molecule - can pass through phospholipid bilayer very slowly (e.g. water)
Small non polar molecule - pass through phospholipid bilayer quickly (e.g. oxygen, carbon dioxide)
Large polar/non polar molecule - can’t cross phospholipid bilayer as they are too big -need a transport protein to across (e.g. glucose)
Ions - need a transport protein to cross phospholipid bilayer (e.g. sodium)
what is a channel protein?
channel protein move ions down concentration gradient through the aqueous centre of the protein
-not specific for certain molecules
-moves from a high concentration to the low concentration
Has a ‘gate’ that opens and closes
-If open permantly anything likke ions can move through constantly
-If closed permantly nothing will get through
Both bad for the cell
what is a carrier protein?
when a glucose molecule binds to complementary carrier protein, the proetin changes shape and releases the glucose into the cytoplasm
-opens at 1 end and then closes and opens at the other side
define concentration
define concentration gradient
concentration - amount of particle in a certain volume
concentration gradient - a difference in concentration between 2 areas gradient
what is simple diffusion?
+ examples
the movement of molecules from a high concentration to a low concentration
e.g oxygen
carbon dioxide
-both small and non polar
what is facilitated diffusion?
+ examples
the movement of molecules or ions using transport proteins
this is needed for molecules that are too big or polar
e.g. channel protein
carrier protein
how does thickness of diffusion pathway affect rate of diffusion?
the thicker the membrane across which molecules have to diffuse, the slower the rate of diffusion
-it will take particle longer to get through
how does surface area affect the rate of diffusion?
more diffusion can take place across a larger surface area
cell specialised for absorption have extensions to their cell surface membranes, called microvilli. these increase the surface area
how does concentration gradient affect rate of diffusion?
the steeper this gradient (more molecules there are on one side of the membrane compared with the other side), the faster the diffusion to the side where there are fewer molecules, down are gradient
-which will increase rate of diffusion
how does temperature affect the rate of diffusion?
-as temperature increase, molecules have more kinetic energy, so their rate of diffusion will increase
-conversely, as they lose heat their rate of diffusion will slow down
