cell membranes Flashcards
(28 cards)
what is the cell membrane made of?
a phospholipid bilayer
double layer allows for selective permeability
what does the phospholipid bilayer consist of? (3)
- cholesterol - binds phospholipids
- protein channels
- glolipids & glycoproteins - for cell signalling + recognition
describe the tails of a phospholipid?
- 2 tails
- non-polar
- hydrophobic
- made of fatty acids
- saturated: straight
- unsaturated: kinked
describe the head of a phospholipid?
- polar
- hydrophilic
- made of phosphate
4 functions of cell membrane
- act as a selective barrier to the passage of molecules
- maintain intracellular balance eg. absorb nutrients, expel waste
- has receptors to allow cells to respond to signals
- barrier separates intra/extracellular contents
4 types of transport across the membrane ?
- simple diffusion
- facilitated diffusion
- active transport
- osmosis
define simple diffusion
The passive movement of particles from a region of a higher concentration to a region of low concentration, through a partially permeable membrane
define facilitated diffusion
transport of particles through a partially permeable membrane, down their concentration gradient, by means of a carrier protein .
what are different type of carrier molecules?
- ion channels,
- gated ion Channels (ligand, voltage, receptor)
define active transport
transport of particles against their conc. gradient, requiring ATP eg. Na+/K+ ATPase
what does amphipathic means?
All lipids in cell membranes are amphipathic - both hydrophilic & phobic
which molecules undergo simple diffusion ?
- hydrophobic eg. O2 & CO2
- small, uncharged, polar eg. urea
which molecules undergo facilitated diffusion?
- charged ions
- large, polar eg. glucose
how does primary active transport work ?
uses energy from ATP breakdown
to transport 1 molecule
how does secondary active transport work ?
energy is provided by the conc.gradient of the driving ion.
this energy allows driven ion to go against its conc.gradient.
2 types are transported at once
define osmosis
whenwater moves from an area of LOW solute concentration (low osmolarity, diluted) to an area of HIGH solute concentration (high osmolarity, more concentrated) through a partially permeable membrane.
via aquaporins
what does endocytosis and exocytosis transport?
larger molecules that can’t diffuse
what is endocytosis?
- molecules bought into cell
- via the cell membrane engulfing the molecule, forming a vesicle, releasing it into the cell
what are the 3 types of endocytosis?
- phagocytosis
- pinocytosis
- receptor mediated
what is exocytosis?
- transporting large molecules out of cell via secretory vesicles
- a form of active transport
what are the 4 main types of membrane receptors?
- channel linked
- enzyme linked
- G protein coupled
- intracellular
what are the 3 main types of cell junctions?
- occluding
- communicating
- anchor
explain tight junctions
- type of occluding junction
- seals neighbouring cells together
- prevents diffusion or leakage between them
- formed by a complex of proteins connecting the 2 membranes
explain a gap junction
- type of communicating junction
- allows the passage of small water soluble ions and molecules between the 2 cells
- eg. protein channels
