Topic 4 membranes Flashcards
What is a membrane or plasma membrane
A selectively permeable lipid bilayer that separates the cell from its surroundings.
list some functions of the membrane
Selective uptake of ions/molecules
Energy production (e.g. ATP in mitochondria)
Cell compartmentalization
Cell Signalling
Protein sorting
Cytoskeleton anchoring
Nuclear Division
Adhesion to other cells/extracellular matrix
What 3 components are membranes made up of?
Lipids, proteins and carbohydrates (sometimes)
membrane lipids include…?
Phospholipids, Gylcolpids, Sphingolipids, and steroids
Phospholipids are what type of molecules…?
Amphipathic
what does amphipathic mean?
Containing hydrophobic and hydrophilic regions.
steroids like cholesterol are important for what?
membrane fluidity
importance of membrane proteins
proteins determine most of the membranes specific functions
what is a peripheral protein
are bound to the surface of the membrane
what are integral proteins
penetrates the hydrophobic core
6 major functions of membrane proteins
- Transport of cell; into cell; within cell
- Enzymatic activity
- Signal transduction
- Cell‐cell recognition
- Intercellular joining
- Attachment to the cytoskeleton and extracellular matrix (ECM)
importance of membrane carbohydrates
Carbohydrates of the surface of the membrane act as identity tags, different cell types and different tissues display unique carbohydrates.
how do cells recognize each other?
By binding to surface molecules, often carbohydrates, on the plasma membrane
Type of membrane carbohydrates
glycolipids, Gylcoproteins
Glycolipids are?
carbohydrates convalently bonded to lipids
Glycoproteins are?
carbohydrates covanlently bonded to proteins
Carbohydrates have distinct inside and outside faces which do what…?
The asymmetrical distribution of proteins, lipids, and carbohydrates on the plasma
membrane is determined when the membrane is built by the ER and Golgi apparatus
• This asymmetry is important for the biological functions of many of the proteins and
carbohydrates
Who proposed the fluid mosaic model and give an explanation
J.Singer and G.Nicolson proposed the fluid mosaic model in 1972, that a cell membrane is a mosaic of proteins dispersed withing the bilayer, with only the hydrophilic regions exposed to water
what evidence supports the fluid mosaic model
freeze fracture studies, Hybrid cell experiments, photo bleaching
explain some membrane fluid movements
Phospholipids are able to move within the bilayer, most of the lipids are able to move laterally, rarely does a molecule flip-flop across the membrane
membranes must be….. to work properly
fluid
fluidity depends on what?
temperature and lipid composition of the membrane
Membranes become for solid/fluid when temperatures become cooler?
Solid
membranes rich in unsaturated fatty acids are more or less fluid than those rich in saturated fatty acids?
more fluid
the steroid cholesterol has different effects of membrane fluidity at different temperatures what are they?
at warm temperatures cholesterol restrains membrane fluidity, while cooler temperatures allows more fluidity because the cholesterol prevents tight packing
membrane structure results in selective permeability what does the membrane allow to pass through be specific
O2 and H2O are small molecules and are readily passing through the membrane, Hydophobic (non poplar) molecules such as hydrocarbons can dissolve in lipid bilayer and pass through the membrane readily aswell
what does the membrane not allow to penetrate through
Polar molecules such as sugars do not pass readily as well as large molecules.
What is passive transport?
the diffusion of substances across a membrane with no energy investment
what is osmosis
the diffusion of water across a semi-permeable membrane
isotonic solution
solute concentration is the same as inside the cell; no net water movement across membrane
Hypertonic
solute concentration is higher than inside the cell ; water lost from cell
Hypotonic
cell concentration is less than inside the cell ; water gained in the cell
whatdoes the cell wall help with the plant cell?
helps maintain water balance inside the cell.
a plant cell in hypotonic solution swell until the cell becomes?
Turgid
what is Facilitated transport
transport proteins speed the movement of molecules across a membrane
what do channel proteins do
provide corridors that allow specific molecule or ions to cross the plasma membrane
what do carrier proteins do?
undergo a subtle change in shape that translocates the solute binding site across the membrane
what is active transport what is an example of one
substances are moved against their concentration gradient
example potassium- sodium pump
explain exocytosis give example
transport vesicles migrate to the membrane, fuse wit it, and release their content, secretion of insulin
explain endocytosis
cell takes in macromolecules by forming vesicles from the plasma membrane
types of exocytosis
phagocytosis, pinocytosis, receptor mediated endocytosis
what is phagocytosis
cell engulfs a particle in vacuole. the vacuole fuses with a lysosome to digest the particle.
what is pinocytosis
molecules are taken up when extracellular fluid is “gulped” into tiny vesicles
explain receptor-mediated endocytosis
binding of ligands to receptors triggers vesicles formations
what is a ligand
is any molecule that binds specifically to receptor site of another molecule
