1.3 Membrane Structure Flashcards
amphipathic
has hydrophobic and hydrophilic parts (ex. phospholipid)
what is the hydrophilic part of a phospholipid?
the head / phosphate group
what is the hydrophobic part of a phospholipid?
the hydrocarbon tails
what is the phospholipid bilayer
phospholipids arranged into double layers; hydrophobic tails facing each other inwards, hydrophilic heads facing water on either side
what did gorter & grendel do?
- 1920s
- figured out membrane contains a BILAYER
- their model didn’t explain where proteins were located
what did davson & danielli propose?
- 1930s
- proposed layers of protein adjacent to both sides of bilayer
- aka sandwich model
falsification of d&d
- freeze-etched electron microscopes
- rapid freezing then fracturing of cells along membrane
- globular structures scattered around centre of membrane
- transmembrane proteins
falsification of d&d
- structure of membrane proteins
- proteins extracted from membrane
- varied in size, globular shapes
- not like structural proteins that would be in continuous layers around bilayer
- some parts of proteins= hydrophobic, therefore attracted to hydrocarbon tails
falsification of d&d
- fluorescent antibody tagging
- fluorescent marks on antibodies that bind to membrane proteins used on 2 diff cells
- when 2 cells fused, markers mixed throughout membrane
- showed that proteins moved, not a static layer
3 evidences for falsifying d&d
- freeze etched electron microscopes
- structure of membrane proteins
- fluorescent antibody tagging
what did singer & nicolson
- 1966
- made fluid mosaic model
- proposed that proteins occupied many positions throughout membrane
- peripheral proteins on inner/outer surface
- integral proteins embedded in bilayer, some protrude
how do phospholipids / proteins appear on electron microscopes?
- phospholipids appear light
- proteins appear dark
what’s the cell membrane’s primary function?
to serve as a barrier that ions & hydrophilic molecules can’t pass through
4 types of membrane proteins
- transporters
- anchors
- receptors
- enzymes
transporters
- pumps for active transport (use ATP to move particles across membrane)
- channels for passive transport (allow hydrophilic particles across by facilitated diffusion)
anchos
- cell adhesion: form tight junctions b/ween cells
- cell-to-cell communication (glycoproteins serve as identification tags)
receptros
- hormone binding proteins
- bind to specific receptors on membrane to be released to interior of cell
enzymes
- proteins attached to membrane interior/exterior
- catalyse chemical reactions
- immobilised enzymes w/ active site on outside
relation between membrane activity and protein content
the more active the membrane, the higher the protein content
which membranes have the highest protein content?
chloroplasts and mitochondria membranes
membranes outside the cell have _ protein content
50%
integral proteins
- partly hydrophobic (embedded in hydrocarbon chains)
- many are transmembrane
- hydrophilic parts project through phosphate head regions
peripheral proteins
- hydrophilic surface, not embedded
- most are attached to surface of an integral protein
- some have single hydrocarbon chain attached to them that’s inserted into membrane, anchoring protein into membrane surface
protein channels
control entry and removal of specific molecules from cell
carbohydrates
- glycoproteins (cell recognition/immune responses) attached to proteins
- glycolipids attached to lipids
cholesterol
- is found where?
- what is it?
- only in animal cell membranes, not plant cells
- type of lipid specifically steroid
- amphipathic (mostly hydrophobic, attracted to hydrocarbon chains
- positioned b/ween phospholipids
role of cholesterol in membrane
- regulates fluidity of membrane by immobilising outer surface of membrane
- separates phospholipid tails to prevent crystallisation & behaving as solid
- reduces permeability to small water soluble molecules
- secures peripheral proteins, forms high density lipid rafts to anchor the protein
- due its shape, helps membrane curve into concave shape, helpful in formation of vesicles during endocytosis
