Cell Membranes Flashcards
5 Roles of Membranes
Separate contents of cells from their environment.
Separate the different organelles from each other.
Facilitates the exchange of substances between the cell and its environment (Selective permeability)
Endocytosis and Exocytosis
Cell signalling using glycolipid.
Compartmentalization
Formation of separate membrane-bound areas in a cell.
Separate contents of cells from their environment.
Separate the different organelles from each other.
Pros of Compartmentalisation
Metabolic processes contain many different and mostly incompatible reactions that require unique conditions.
Compartmentalization allows for each unique condition required for cellular reactions.
Partially Permeable
A membrane that allows some (selective) substances to cross but not others.
Cell Signalling
A complex system of intercellular identification and communication.
larger surface area increases or decreases rate of diffusion?
increases
Larger concentration difference increases or decreases rate of diffusion?
increases
larger distance for particles to travel increases or decreases rate of diffusion?
decreases
What is Brownian motion?
The constant random motion of fluids
Define diffusion
The NET movement of particles from where they are at a higher to where they are at a lower concentration
lower temperature increases or decreases rate of diffusion? and why
lowers - at a lower temperature the lower the kinetic energy of particles, and therefore speed so it takes longer for particle to reach equilibrium. At higher temperatures vice versa
A more permeable membrane increases or decreases rate of diffusion?
increases - easier for particles to get through
Give an example in organisms where these factors are optimised for diffusion
The lungs - large surface area from alveolus and good blood supply form the pulmonary vein and artery, as well as many capillaries. Also high core body temperature.
Define osmosis
the net movement of water from a solution of higher to lower water potential through a partially permeable membrane.
What are the differences between osmosis and diffusion ?(2)
Only applies to water
Movement is only through a partially permeable membrane
define water potential
the pressure exerted by water molecules
how do solutes lower water potential?
water is attracted by solutes, therefore is less able to move and doesn’t exert as much pressure.
How is water potential measured?
water potential is a arbitrary scale shown by Ψ. Within pure water it always equals 0, but if you lower the water pressure the water potential turns negative.
Describe what happens to a hypotonic animal cell
A hypotonic ( low solute potential, high water potential) animal will swell and possibly burst this is known as lysed.
Describe what happens to a hypotonic plant cell
A hypotonic ( low solute potential, high water potential) plant cell will swell up but not burst this is know as becoming turgid.
Describe what a isotonic plant cell is like
An isotonic (equal solute and water potential) plant cell is flaccid. hehe.
Describe a hypertonic animal cell
A hypertonic (higher solute potential, lower water potential) animal cell will become shrivelled.
Describe a hypertonic plant cell.
A hypertonic plant cell will become plasmolyzed
Describe simple diffusion, give examples
Passive movement of small, hydrophobic particles through the bilayer. O2, steroids
describe facilitated diffusion. two types
- passive movement of large molecules which bind to specific carrier(proteins), which then a conformational change occurs and the substance is released on the other side. 2 passive movement of charged or polar substances through a channel or pore protein e.g. ion.
what are aquaporins?
channel proteins specifically for water
facilitated diffusion proteins may also be selective or gated - what do these terms mean in relation to channel proteins
selective - only allow particular proteins
Gated - can be opened or closed
lowkey wanna
die, smiley face.
Describe osmosis
Passive Movement of water molecules down the water potential gradient, often through aquaporins.
describe active transport
Specific substances bind to carrier, a conformational change occurs and the substance is released the other side. This is a active process (requires ATP) which goes against the concentration gradient and requires the aid of carrier proteins with complementary fit with associated molecules.
What is cytosis
cytosis is a active process (requires ATP) which is the bulk transport of large materials across the cell surface membrane with the use of VESICLES.
what is the difference between endocytosis and exocytosis
exo - exporting, secretion
endo - importing
both done with aid of vesicles
What is phagocytosis?
The bulk uptake of solids by vesicle formation, e.g. ingestion of bacteria
What is pinocytosis?
bulk uptake if fluids by vesicle formation e.g. lipid absorption by epithelial cells of small intestine
why is the current model of membranes known as the ‘fluid mosaic model’
Fluid - its fluid, the phospholipids can move around.
mosaic - reminiscent of a mosaic with the proteins embedded in it.
How does increased temperature impact membrane structure
Increased kinetic energy of phospholipids, increases average phospholipid separation, increases permeability of bilayer, bilayer may even melt, proteins by even denature affecting permeability.
How does cholesterol effect membrane permeability?
membrane permeability increases with more cholesterol, as it breaks up the membrane. More cholesterol may be an adaption of organisms in low temperature environments.
