forces acting across cell membranes

Question 1

describe basic structure of membranes

Answer 1

sufficient flexibility
fluid mosaic model - phospholipids, cholesterol, proteins and carbhohydrates - in which components are able to flow and change position, while maintaining integrity of membrane
range from 5-10nm thickness

composed primarily of a phospholipid bilayer with embedded proteins, CHOs, glycoproteins and glycolipids, and in animal cells cholesterol

Question 2

functions of cell membrane

Answer 2

protection
sufficient flexibility - to allow entry and exit of substances 
cell recognition 
carries receptors 
regulate cell growth

Question 3

define diffusion across membranes

Answer 3

the movement of particles across the cell membrane from a high concentration to a low concentration, down the conc gradient
passive process

Question 4

factors affecting rate of diffusion

Answer 4

conc gradient
permeability of membrane
temperature
pressure

Question 5

describe general types of membrane proteins and their functions

Answer 5

integral - span hydrophobic core of lipid bilayer
peripheral - one leaf of lipid bilayer and do not penetrate hydrophobic core
transport -
channels - create pore through membrane through which molecules pass ie water and ions - carrier mediated transport
receptors - integral to structure , allow communication of an extracellular signal
enzymes - catalyse chemical reactions on the cell membrane , enzymatic part may be on external part of membrane

Question 6

define electrochemical gradients

Answer 6

gradient of electrochemical potential, usually for an ion that can move across a membrane

ions = charged particles
chemical gradient = diff in solute conc across membrane
electrical gradient = diff in charge across membrane

Question 7

carrier mediated transport systems

Answer 7

energy-dependent pathway generally used by small hydrophilic molecules - specific receptors on membrane of carriers that recognise target molecules and transport across
three types
uniport, symport, antiport
transported substances = nutrients, ions, glucose etc
eg GLUT1 = uniport mediated transport protein

Question 8

osmolarity v tonicity

Answer 8

total conc of solutes in solution

tonicity takes into account both the relative solute concs and the permeability of membrane to those solutes

Question 9

isotonic v isosmotic

Answer 9

same solute conc in solution as in cell v same osmotic pressure

isosmotic solutions cause cells to absorb water from surrounding or to lose from cells

Question 10

endocytosis v exocytosis

Answer 10

invagination of cell membrane to form vesicle which eventually disintegrates on the cytoplasmic surface of membrane, releasing contents which may migrate within cell to destination

exocytosis = reverse process , many proteins manufactured within cell are released from those cells by exocytosis

Question 11

role of cholesterol in plasma membrane

Answer 11

regulates fluidity of membrane and changes based on temp of cell’s environment
more abundant in animals that live in colder temps

Question 12

phospholipid bilayer

Answer 12

polar ends - heads - of these molecules are in contact with aqueous fluid both inside and outside cell
both surfaces of membrane are hydrophilic
interior of membrane is hydrophobic , non-polar - fatty acid tails, no attraction for water

Question 13

hydrophilic

Answer 13

water-loving

Question 14

hydrophobic

Answer 14

water-hating

Question 15

two types of diffusion

Answer 15

passive and facilitated

Question 16

mechanisms of movement across cell membrane

Answer 16

diffusion
active transport
osmosis 
- between ICF and ECF 
filtration - between plasma and ISF