Membranes Flashcards
What is the role of membranes?
separating the cytoplasm from the external environment
separating cell components from the cytoplasm
cell recognition and signalling
regulating the transport of materials
How do phospholipids work?
hydrophillic phosphate head
fatty acid tails are hydrophobic
due to the way charges are distributed across the molecule
molecules with charges can interact with water more easily,
without the presence of phospholipids they would just sit on the surface
How is a bilayer formed?
hydrophillic heads stick in the water hydrophobic tails point towards each tother like a mirror image phospholipids can freely move like lipids within the plane of the membrane
What adaptations do different membrane layers have and why do they need them?
regular phospholipid bilayer would be too fragile to function as a barrier within or around cells
muscle cell membranes contain a large number of channels for the rapid intake of glucose
in plants, a growing shoot contains receptors that regulate growth
What are partially permeable membranes and how are they formed?
cell membranes that are permeable to water and sopme solutes although all water can diffuse through the lipid bilayer membranes with aquaporins are 1000x more permeable to water
What is meant by compartmentalisation and why is it important
separating of organelles from the cytoplasm allows chemical gradients to be maintained protects vital cell components
What is the fluid mosaic model?
Singer and Nicholson proposed the idea
fluid - phospholipids are free to move, giving the membrane flexibility
mosaic - proteins embedded in the bilayer, vary in shape, size and position, resembles a mosaic
What is the function of cholesterol in the membrane?
it is a lipid with a hyrdophillic and a hydrophobic end like a phospholipid
it interacts with the phospholipid (hydrophobic/phillic), pulling them together
cholesterol adds stability w/o making them too rigid
stops the phospholipid molecules grouping too closely and crystallising
Why is site of chemical reactions so important? (give examples)
like enzymes and proteins in the membranes, forming organelles, or present within organelles, have to be in a particular position for the chemical reaction to take place
e,g, electron carriers and the enzyme ATP synthase have to be in correct positions within the cristae for the production of ATP in respiration
enzymes in photosynthesis are found on the membrane stacks within the chloroplasts
What determines the rate at which a molecule can diffuse across a membrane?
less polar molecule, the easier it will diffuse across
non polar molecules such as O2 and CO2 will rapidly diffuse
small polar molecules such as H2O and urea, diffuse but more slowly
ions are unlikely to diffuse across a membrane
What is the width of a membrane?
7nm
