M2 CH5: membranes Flashcards
Explain the structure and mechanism of the phospholipid bilayer in plasma membranes.
(4 points)
- hydrophilic phosphate heads
- hydrophobic lipid tails
- forms bilayer which has a hydrophobic centre, water soluble substances can’t pass through.
- however, fat soluble substances can pass through
explain the role of cholesterol in plasma membranes and how they are positioned
(2 points)
- bind to hydrophobic tails and are positioned amongst the hydrophilic heads
- reduces the fluidity of membrane, increases its stability.
state the 3 types of intrinsic proteins, and outline the role of each.
- channel proteins: hydrophilic channel for passive movement of polar molecules
- carrier proteins: transport of molecules and ions by active transport and F diffusion
- glycoprotein: embedded in cell membrane, involved in cell signalling
explain the role of extrinsic proteins.
(3 points)
- present in one side of bilayer (can be either one)
- have hydrophilic R groups that interact with the hydrophilic phosphate heads
- act as receptors for cell signalling
outline the structure of a glycolipid, and its role in plasma membranes.
( 2 points)
- lipid with attached carbohydrate chain
- act as cell surface antigens for cell recognition
outline the roles of membranes in organisms
(3)
providing a partially permeable barrier between cell organelles and environment
cell communication/signalling
site of chemical reactions: ATP synthase from ETC
outline what happens to a membrane when the temperature is too high (45*+)
(3)
the phospholipid bilayer starts to melt
membrane becomes more permeable
channel and carrier proteins deform, no longer controlling transport of substances across membrane
explain what happens to membranes when the temperature falls to low (below 0)
phospholipids don’t have much energy, as they are packed very tightly
cholestrol can no longer regulate fluidity of membranes
crystals can form which pierces the membrane
outline the forms of passive transport across membranes, and how they work
- diffusion
- allows movement of small non-polar molecules - facilitated diffusion
- with carrier proteins: large mol attatches- changing the porteins shape. molecule is released on other side of the membrane
- with channel proteins: form pores in the membrane for charged particles to diffuse through
state and explain the 2 key factors that affect the rate of diffusion.
concentration gradient: greater gradient increases the rate of diffusion
thickness of exchange surface: thinner surfaces e.g. alveoli have shorter diffusion distance
thicker example: gram + bacteria have thicker peptidoglycan cell walls :. stain cant diffuse through the membrane
state and explain the 3 active methods of transporting substances across membranes
- active transport:
- against concentration gradient
- uses carrier protein (same process) - endocytosis
- cell surrounds substance with part of its membrane
- membrane pinches to form vesicle containing the substance
(example: phagocytosis) - exocytosis
- vesicles fuse with plasma membrane and releases contents outside cell
explain what is meant by a hypOtonic solution, and the impact a hypertonic solution has on animal AND on plant cells.
hypOtonic= solution has a higher water potential that inside the cell
animal: cell bursts (too much movement into cell)
plant cell: becomes turgid
explain what is meant by an isotonic solution, and the impact it has on animal cells AND on plant cells.
the solution has a water potential equal to inside the cell
animal= no net movement
plant= no net movement
explain what is meant by a hypERtonic solution, and the impact it has on animal cells AND on plant cells.
the solution has a lower water potential compared to inside the cell
animal cells: shrinks, net movement= water out of cell
plant cells: becomes flaccid, net movement= water out of cell
