Membrane Structure and Function Flashcards
describe the structure of the plasma membrane
-phospholipid bilayer
- has hydrophobic fatty acid chains, hydrophilic phosphate group and glycerol
-also contains sugars which can be joined to proteins or lipids
-also contains cholesterol
-extrinsic and intrinsic proteins
what is the function of the plasma membrane?
-acts as barrier - this is why contents inside and outside the cell are different
-regulates entry and exit from cell
-acts as base of attachment for cytoskeleton so helps maintain shape of cell
what are the four main types of phospholipids in the cell membrane?
-phosphatidylcholine (most numerous)
-phosphatidylserine
-phosphatidylethanolamine
-sphingolipids
-do NOT contain glycerol
describe phosphatidylcholines
-main constituent of membranes
-naturally forms bilayer in right conditions
-kinked fatty acid tails give fluidity
-can have role in signalling
describe phosphatidylethanolamine
-2nd most common membrane lipid
-mainly in inner leaflet
-does not form bilayer alone
-stabilises membrane structure
-forms more H bonds bc more accessible amine groups
-ratio of phosphatidylethanolamine to phosphatidylcholine can change
describe cholesterol
-increases fluidity of membrane
-lipid soluble so can move
-forms lipid rafts
what are lipid rafts?
-clusters of particular molecules which can float around and form/separate
-they bring proteins together e.g. GPI anchored proteins
-can be disrupted which changes way cell behaves
-play role in Alzheimer’s disease
-if amount of cholesterol is changed, amount/content of raft is changed which affects protein activity
what are the four types of membrane proteins?
-transporter
-anchors
-receptors
-enzymes
what do transporter proteins do?
-regulate movement of molecules
-selectively move molecules
describe diffusion
-passive process so no energy required
-gases water and lipids can diffuse
-mols diffuse from area of high conc to low conc
describe facilitated diffusion
-uses protein to speed up diffusion
-molecule binds to protein which causes conformational change
-molecule travels down protein and it changes to og shape
-used when large difference in conc so rapid diffusion required
describe gated channels
- Proteins in membranes form a pore, this is normally either open or closed
-opens or closes in response to stimulus
-AP, ligand binding, phosphorylation
-solutes move down conc . gradient so no energy required
-e.g. wave of propagation for AP
describe active transport
-requires energy(ATP)
-molecules move from low conc to high conc
-can be primary or secondary
what are protein/membrane anchors?
-proteins anchor a cell to surroundings
-most common protein anchor is called integrins
-integrins sit in membrane and bind to cytoskeleton and extracellular matrix on either side
-these are dynamic interactions
-Cells are surrounded by a mixture of proteins – the extracellular matrix (ECM)
what signals do receptors bind in response to?
- autocrine (same cell)
- juxtacrine (neighbouring cell)
- paracrine (cell nearby)
- endocrine (distant source)
what are the three types of membrane-bound receptors?
-ion channel receptors
-heptahelical receptors
-kinase associated receptors
describe ion channel receptors
-closely associated w protein channel
-often bind neuropeptides
-when ligand binds to receptor, causes conformational change in associated ion channel so ion can pass through
describe heptahelical receptors
-binding of signal causes intracellular changes
-involves second non-protein messenger
-this triggers signals to nucleus
describe kinase associated receptors
-when specific signals bind to receptor, they move together so tyrosine (signal molecule) becomes phosphorylated
-this triggers changes in other proteins - signal cascade
membrane-bound receptors example
describe Membrane-bound enzymes
-Cell surface is teeming with enzymes
-Poised to catalyse reactions involving passing substrates
-Or modify other proteins on the cell surface
what is an enzyme
a substance produced by a living organism that acts as a catalyst to bring about a specific biochemical reaction
what do enzymes do?
-can modify proteins on cell surface
-catalyse specific reactions
-if there is an enzyme inside the cell, there will be an associated cell surface receptor
what is ACE and what does it do?
-angiotensin-converting enzyme
-changes AngI to AngII
