Week 7 - Plasma Membrane and Transport across membranes Flashcards
What are 5 examples of membrane function?
- a physical and chemical barrier
- communication
- recognition
- energy conversion
- a plateform for cellular processes
What is the structure of a membrane?
- a very thin film of lipids and proteins held together by non-covalent interaction
- double lipid layer = lipid bilayer
- forms an impermeable barrier to water soluble (polar molecules)
What are membrane lipids?
- phospholipids
- amphipatic
- two hydrophobid fatty acid chains
- a phosphate containing hydrophilic head group
What is the formation of a fatty acid?
long hydrocarbon chain with a carboxyl end and a methyl end
What does the head of a membrane lipid contain?
polar, hydrophilic head containing choline (example head group) and phosphate and prefer to be in aqueous environment
What does the tail of a membrane lipid contain?
non polar, hydrophobic tail made of fatty acid (hydrocarbon chain) and a glycerol
How do major lipids work in cell membranes?
- phosphate groups replaces a fatty acid attched to central glycerol
- group always binds to 3rd apart from with sponge where its the 2nd
How does the bilayer work?
Unsaturated fatty acids pack loosely which allows the bilayer to remain fluid. if no double bonds, bilayers would solidify
What can form between phospholipids?
cholesterol, has a hydroxyl group, tiny polar head attached to a rigid tail, this fills gaps in the bilayer to stabilise it
What does the layer look like?
Heads face outwards both sides, tails sandwiched in the middle. this means only the hydrophilic heads are exposed to regions of water
forms a continuous spheroid
Are membrane dynamic? If so why?
they are dynamic structures due to the ability of phospholipids to move
What are the ways phospholipids can move?
- lateral
- flexion
- rotation
- flip flop (rarely occurs)
What does the cis bond in unsaturated chain mean?
it makes the phosplipids more difficult to pack together, making membrane thinner
the insertion of cholesterol regulates membrane fluidity
What does the orientation of cholesterol mean for the eukaryotic membranes?
cholesterol is highly abundant in eukaryotic membranes
orientation means that the steroid ring region of the cholesterol stiffens the upper region of the fatty acid chain
= immobilise the phospholipid
= less able to move laterally
= less fluid
What are lipid rafts? Where can they be found?
A lipid raft is a specialised, dynamic microdomain within the plasma membrane that is enriched in certain types of lipids, such as cholesterol, sphingolipids, and specific proteins. These rafts are thought to play key roles in membrane organisation, cell signalling, and protein sorting.
what ae sphingolipids?
an amino alcohol sphintosine is their back bone rather then glycerol
they have long, saturated fatty acid chains and the attractive forces are strong enough to hold adjacent molecules together in lipid rafts
Why do proteins congregate towards lipid raft regions?
In preparation for vesticular budding and trasnport
What are glycoproteins?
proteins glycosylated in RER and golgi (bonded to carbohydrates)
What are glycolipids?
lipids from SER glycosylated in golgi
What is Glycocalyx?
the CHO coating to the termed, it is protective, name for the carbohydrates
What are the 2 main membrane proteins?
1 - Integral/Transmembrane proteins (span membrane from outer to inner)
2 - Peripheral membrane proteins (embedded within one layer or just attached to membrane)
What are the 2 types of phospholipids?
1 - glycerophospholipids (most abundant)
2 - sphingolipids (abundant in lipid rafts)
What are the types of integral/transmembrane proteins?
- multi pass
- single pass
What are the types of Peripheral proteins?
- embedded
- covalently bonded to lipids
- non covalently bonded to other proteins
What is the lipid bilayer an impermeable barrier to?
polar, hydrophilic molecules
this enable a cell or intracellular compartment to maintain a different environment to the outside
to transport molecules across membranes, specialised proteins are required
What can be easily transported across the membrane?
- hydrophobic, non polar molecules such as oxygen, co2, nitrogen, steroid hormones
- small uncharged polar molecules such as water, urea, glycerol, NH3
What will need a transport mechanism to go across the membrane?
- large uncharged polar molecules such as glucose, sucrose
- ions - charged so need a specialised mechanism
What are the transport proteins for the specialised mechanisms?
the transmembrane, multipass proteins
- no contact with the hydrophobic core
What are carrier proteins?
binds to a solute and undergo conformational change to trasnfer across membrane
What are channel proteins?
interact only weakly with solute; form aqueous pore that solutes (normally ions) can pass through quickly - it is a continuous pore
What do channel and carrier proteins do?
They enable facilitated diffusion (passive transport)
the concentration gradient determines the direction of flow
What is an electrochemical gradient?
If it is an ion, then concentration and charge determine the direction of flow
What is active transport?
Where solutes are ‘pumped’ across a membrane against the concentration gradient
mediated by carriers
requires ENERGY
What are the 3 ways you can get energy for active transport?
1 - Light energy (bacteria)
2 - Energy release from electron transfer
3 - ATP hydrolysis
What are the two two main mechanisms eukaryotes use for active transport?
1 - coupled carriers (secondary active transport
2 - ATP driven pumps (primary active transport)
What are the two types of coupled carriers?
1 - symport
2 - antiport
What does the symport channel do?
Transports more then one molecule in the same direction
electrochemical gradient = stored energy
Transport = release of energy
What does the antiport channel do?
Molecules in different directions
What are channel proteins?
form pores across the membrane
some are large and if they were on the plasma membrane then it would allow lots of thing in and out - poor regulation
channels on the membrane are very narrow, highly selective pores that open and close as they are gated.
specifically concerned with transport of ions
only participate in facilited diffusion
What are the 4 types of gated ion channels?
1 - voltage gated
2 - ligand gated (extracellular ligand)
3 - ligand gland (intracellular ligand)
4 - mechanically gated
