Flashcards in Biological Membranes Deck (25):
What is the plasma membrane for, on the surface of the cell?
separates cell's components from external env.
regulates transport of materials in/out
contain enzymes involved in metabolism
has antigens so immune system recognises it
signals to other cells by chemicals/ has receptors
site of chemical reactions
What is the plasma membrane for, within the cell?
epithelial cell membrane..
separates organelle contents from cytoplasm
in mitochondria, folded membrane increases SA for reactions
in chloroplasts, thylakoid (inner membrane) contains chlorophyll for photosynthesis
in epithelial cells, digestive enzymes on membrane to catalyse breakdown of sugar
Fluid mosaic model
proteins embedded in sea of phospholipids, bilayer more dynamic, interact with env.
Proteins in the membrane can do 3 things
have pores to act as channels for charged ions
be carriers, change shape to carry specific molecules across
be attached to carriers, act as enzymes, antigens, receptor site
What regulates fluidity? and what else does it do?
regulates mechanical stability, resists temperature change
thickness of membrane
carbohydrate chains attached to lipids/proteins?
What is a passive process?
uses only kinetic energy, not ATP of the cell
What happens when molecules are evenly dispersed (in terms of diffusion)?
no net diffusion, in equilibrium
What molecules can diffuse?
What can't pass through the bilayer?
small molecules (oxygen, CO₂)
fat-soluble molecules because dissolve in lipid bilayer (steroid hormones)
water because it is polar so insoluble in bilayer, but passes through aquaporins which are channel proteins
What is facilitated diffusion?
What happens with glucose?
when polar molecules are insoluble so diffuse through water-filled protein channels in the membrane
Glucose is too large for the water-filled channels so bind to transmembrane carrier proteins which open to allow it through.
How do carrier proteins work?
they combine reversibly with certain solute molecules or ions and have region that allows hydrolysis of ATP to release energy so carrier proteins act as an enzyme.
The energy changes the carrier protein's conformation and so carries ions to the other side.
What if molecules are too large to pass through membrane?
bulk transport (uses energy)
eating by sells, solid matter, is...
ingesting liquids is
What happens when solute molecules turn into charged ions?
they exert more effect on the relative number of water molecules because dissociating creates more solute particles. Large non-polar molecules like glucose have less effect because there are less particles.
Water potential is...
the measure of tendency of water molecules to diffuse from one region to another
What is cytolysis?
in animal cells, if lots of water enters, the cell will swell up and burst because the plasma membrane breaks.
What is turgid?
in plants, the cell becomes swollen but the cell wall prevents it from bursting.
What is crenated?
when water leaves an animal cell and shrivels
What is plasmolysed?
when water leaves a plant cell, the cytoplasm shrinks and the membrane pulls from the cell wall. The metabolism can't proceed because the cell is dehydrated.
What is flaccid?
a plant tissue with plasmolysed cells.
What do organic solvents do to cell membranes?
damage them because they dissolve lipids.
What happens to membranes when temperature drops?
fish and microorganisms..
- saturated fatty acids compress.
- proportions of saturated and unsaturated fatty acids in the cell membrane determine its fluidity. Unsaturated fatty acids compress so kinks in tails push adjacent phospholipid molecules away and maintains fluidity.
- cholesterol buffers the effect of low temperature by preventing the reduction in fluidity. It prevents phospholipid molecules packing close
- fish and microorganisms change the composition of fatty acids in membranes in response to low temp.