| What is a cell wall and what does it do? (5) | outer layer for structural support and protection to contorl the hydrostatic P
plant: cellulose
bacteria: peptidoglycan
fungi: chitin
plant and algal cells can be connected by small channels called plasmodesmata between cell walls |
| How do phospholipids form bilayers in water? what is a phospholipid consisted of? features of a phospholipid? (2) | bec of the amphipathic properties =
hydrophilic +hydrophobic regions = amphipathic |
| What do membranes do? what are they made up of? (2) | enclose the cell and separate the intracellular components from the outside = homeostasis
phospholipids and proteins |
| 2 features of a cell membrane? | semi-permeability = some materials can't cross without help
selectivity = cells regulate passage of some materials |
| what is a phospholipid consisted of? (6) | made of a polar head (hydrophilic)= glycerol and phosphate molecule
2 non-polar tails (hydrophobic) = fatty acid chains (hydrocarbons) |
| How does the structure of the fatty acid affect fluidity? | saturated = less fluidity
unsaturated = increase fluidity bec of bent tails |
| Draw and label a phospholipid? (4) | hydrophilic head
hydrophobic tails |
| What are the 2 different types of proteins in the membrane? | integral: permanent and are attached across the bilayer
peripheral: temporarily attached to 1 surface by non-covalent bonds |
| Describe the polarity of membrane proteins (2) | non-polar amino acids: outside of the membrane protein to meet directly w the bilayer
polar amino acids: inside to face the aqueous solutions |
| What are the 2 tertiary structures used by membrane proteins? | single helices / helical bundles = enzymes, transporters, receptors, recognition
beta barrels (eg: channel proteins) = transporters |
| What are the functions of membrane proteins? (JETRAT) | Junctions = connect 2 cells
Enzymes - localizes metabolic pathways
Transport = for facilitated diffusion and active transport
Recognition = markers for cellular identification
Anchorage = places for cytoskeleton to attach to
Transduction = receptors for peptide hormones |
| What is cholesterol made up of? (5) | amphipathic bec it has both non polar and polar regions
hydroxyl (HO) = hydrophilic
Rest is hydrophobic |
| Why is cholesterol only in mammals and not plants? (2) | only in mammalian membranes it reduces membrane fluidity and permeability to some solutes
not in plant cells bec they have a firm cell wall |
| What does cholesterol do? (4) | immobilizes the outer surface of the membrane = less fluidity
makes membrane less permeable to small water soluble molecules
separates fatty acid tails to prevent crystallization in low temps
secures peripheral proteins by forming high density lipid rafts |
| What is the fluid in the cell called? | cytosolic fluid |
| What is the fluid outside the cell called? | interstitial fluid |
| How are the phospholipids arranged? | the hydrophobic tails face inwards and are shielded by the surrounding polar fluuids w/ the polar heads = bilayer |
| What are some of the properties of the phospholipid bilayer? (4) | held together by WEAK HYDROPHOBIC INTERACTIONS bw the tails
the bilayer restricts entry of specific substances
individual phospholipids can move within the layer = fluidity
fluidity allows = endocytosis + exocytosis by breaking + reforming |
| draw and label a fluid mosaic model | phospholipid = polar (glycerol and phosphate) head and non polar fatty acid tail
integral protein
cholesterol
peripheral protein
glycoprotein |
| What structures would you look for in an electron microscopy which would support the Davson-Danielli model? (2) | cell membrane shows a trilaminar (3 layer) 2 outer dark layers and a light middle layer
D&D said that it was a phospholipid bilayer bw 2 layers of protein = lipoprotein sandwich |
| How was the Davson - Danielli model falsified? (4) | membranes don't have a constant lipid : protein ratio (cant be a sandwich model)
membrane proteins vary in sizes + solubility in water (cant form outer layer)
proteins move around (cant form static outer layer) shown by fluorescent antibodies
evidence of integral proteins from freeze fracturing = rough, internal surface |
| Who proposed a new model after the D&D got falsified? | Singer-Nicolson model described the proteins as being embedded within the membrane (transmembrane) instead of being separate outer layers |
| What is a cell wall and what does it do? (5) | outer layer for structural support and protection to contorl the hydrostatic P
plant: cellulose
bacteria: peptidoglycan
fungi: chitin
plant and algal cells can be connected by small channels called plasmodesmata between cell walls |
