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2.1.5 Biological Membranes (Partially Permeable Membranes (need to allow…
2.1.5 Biological Membranes
Roles of Membranes
At Surface of Cell
seperates cells components with external components
regulates transport of materials into and out of cells
may contain enzymes
has anigens to prevent immune system from attacking it
release chemicals to signal to other cells; contains receptors
site of chemical reactions
protect cell from adverse environmental effects
Within Cell
seperates organelle contents from rest of cell
increase surface area of inner membrane
allow chemical reactions to happen
may contain enymes
Partially Permeable Membranes
need to allow some molecules through and others not
some small molecules diffuse through cell membrane in between structural molecules
some subsances dissolve in lipid layer and pass through
other substances pass through special protein channels or are carried by carrier proteins
Fluid Mosaic Model
fabric of membrane consisting of phospholipid bilayer with proteins floating in it making up a mosaic pattern that can move, giving it fluidity
Components
Phospholipids
hydrophylic charged phosphate head
contact with watery exterior or interior (cytoplasm)
two hydrophobic fatty acid tails
in centre of membrane, away from water
make up bilayer, around 7nm wide
amphiphatic
Cholesterol
help regulate fluidity of membrane
maintain mechanical stability
resist effects of temperature change on structure of membrane
more cholesterol means more fluidity
Glycolipids
carbohydrate chain attached to lipid
contribute energy
involved in cell recognition, cell signalling and cell attachement
Proteins
Glycoproteins
carbohydrate chain attached to protein molecule
help stabilise membrane structure
act as antigens
adhesion of cells to form a tissue
receptors for hormones
Cell recognition of self and non-self: recognise foreign pathogens
Cell signalling and communication:
Signal protein produced and released. Binds to complementary receptor on other cell. Bonding triggers response.
Receptors have specific shape complementary to the protein signal shape. When protein signal binds, a response is triggered
signal transduction pathway: one signal causes a response which causes another signal which causes another response
Integral Proteins
Carrier Proteins
change shape and carry specific molecules across membrane
integral proten
Channel Proteins
proteins that have pores and allow charged ions surrounded by water molecules to pass through
channel lined with hydrophobic amino acids
span width of membrane
may be receptors for hormones and neurotransmitters, or catalysts
Peripheral Proteins
don't cross membrane
span on outside or inside
e.g receptors or antigens
Membrane Bound Receptors
sites where hormones and drugs can bind
Plasma Membrane, or Cell Surface Membrane
Sammer Sheikh
