membranes Flashcards
which parts of a phospholipid molecule is hydrophilic / hydrophobic ?
head is hydrophilic
tail is hydrophobic
what is the phospholipid bilayer ?
double layer of phospholipid molecules, with heads facing outwards
which type of cell membrane is cholesterol present in ?
all of them except bacterial cell membranes
what does cholesterol do to the membrane and how ?
Fits between phospholipid molecules and binds to the hydrophobic tails, causing them to pack closer.
This makes membrane less fluid, more rigid.
how do proteins allow substances to pass through membrane?
- form channels which allows small / charged particles through
- carrier proteins transport molecules / ions across membranes by active transport / facilitated diffusion
what are the four functions glyco lipids/proteins linked with the membrane :
- stabilize membrane by forming H-bonds with surrounding water molecules
- sites where drugs/hormones/antibodies bind
- act as receptors for cell signalling
- act as antigens
describe how cells communicate
- cell releases a messenger molecule (e.g. hormone)
- molecule travels (e.g. in blood)
- messenger molecule binds to receptor on cell membrane
what are membrane - bound receptors ?
proteins in cell membrane that act as receptors for messenger molecules
what special structure feature do receptor proteins have?
specific shape, which only messenger molecules with complementary shape can bind to
what is a target cell ?
a cell that responds to a particular messenger molecule
Describe membrane permeability at low temp > 0
- pack close, so membrane is rigid
- channel / carrier proteins deform, increasing permeability
- ice crystals may piece membrane (increase permeability)
Describe membrane permeability at mid temp 0 - 45
- phospholipid have more energy, move more, not as tightly packed
- membrane is partially permeable
- increase in temp increases permeability
Describe membrane permeability at high temp < 45
- bilayer breaks down, membrane becomes more permeable
- channel / carrier proteins deform (increase permeability)
Describe the effect of a solvent on membrane permeability
- increases permeability due to the solvent dissolving lipids in membrane, so it loses structure
- increase in concentration will increase permeability
define diffusion
the net movement of particles from an area of high concentration to an area of low concentration
what does it mean that diffusion is a passive process ?
requires no energy
what are the four factors of rate of diffusion ?
temp / conc gradient / thickness of exchange surface / surface area
what color is phenolphthalein in alkaline conditions ?
pink
what color is phenolphthalein in acid conditions ?
colourlless
what is facilitated diffusion ?
diffusion of larger molecules / ions / polar molecules through carrier / channel proteins in the membrane
how do carrier proteins carry out facilitated diffusion ?
- large molecule attaches to carrier protein
- protein changes shape
- molecule released on other side
how do channel proteins carry out facilitated diffusion ?
- form pores in membrane for charged particles to diffuse through
(there are diff channel proteins for diff charged particles)
what is used in active transport ?
carrier proteins
what is endocytosis ?
cell surrounds substance with section of plasma membrane and pinches off to form a vesicle inside cell, this uses ATP for energy
describe exocytosis
- vesicle buds off from Golgi body
- vesicle moves to plasma membrane
- vesicle fuses with membrane
- contents are released outside of cell
(uses ATP)
define osmosis
diffusion of water molecules across a partially permeable membrane down a water potential gradient
what has the highest water potential ?
pure water
define hypotonic solution
higher water potential
define isotonic solution
same water potential
define hypertonic solution
lower water potential
describe plant cell in hypotonic solution
- water moves into cell
- vacuole swells
- vacuole / cytoplasm push against wall
- cell becomes turgid
describe plant cell in hypertonic solution
- water moves out of cell
- cell becomes flaccid
- cytoplasm / membrane pull away from cell wall
- called plasmolysis
why is membrane described as mosaic ?
arranged w/ lots of different components
