plasma membranes

Question 1

role of membranes

Answer 1

• partially perm barriers between the cell + environment , organelles and the cytoplasm + within organelles
• site of chem reactions
• site of cell communication

Question 2

membrane structure

Answer 2

• plasma membrane (seperates cell from external env)
• formed from phospholipid bilayer
• hydrophilic phosphate heads form inner+outer surface
• surrounds the hysrohpohibic FA
• forms hydorphobic core inside the memebrane

Question 3

fluid mosaic model

Answer 3

• phospholipids are free to move
• giving membrane flexibility
• proteins embeeded in the bilayer
• vary in shape sixe + position

Question 4

instrinsic proteins

Answer 4

• transmembrane proteins
• embedded through both layers
• amino acids with hydrophobic R-groups on external surface
• interact with hydrophobic core keeps them in place

Question 5

channel proteins

Answer 5

• intrinsic
• hydrophilic channel
• passive movement of polar mol + ion down a CG
• held in position by hydrophobic core + R group interactions

Question 6

carrier proteins

Answer 6

• intrinsic
• passive + AT into cells
• protein can change shape
• ATP not required

Question 7

glycoproteins

Answer 7

• intrinsic proteins
• embedded
• attached carb chain with diff lengths + shapes
• role in cell adhesion
• ## receptors for chem signals

Question 8

drugs and receptors

Answer 8

• some drugs bind to cell receptors

- beta blockers reduce response of the heart to stress

Question 9

glycolipids

Answer 9

• lipids
• attached carb chain
• cell markers/antigens
• recongised by cells of immuneS as self/non-self

Question 10

extrinsic

Answer 10

• present in one side of bilayer
• hydrophilic R groups
• interact with polar heads of phospholipids / with intrinsic proteins

Question 11

cholesterol

Answer 11

• lipid / sterol
• hyrophilic end
• hydrophobic end
• regulates fluidity
• adds stability
• positioned between phospholipids

Question 12

affect of temp on CM

Answer 12

• temp inc
• phospholipids inc KE
• move more
• membrane more fluid
• loses its structure
• temp inc more : structure breaks down
• nc perm of memB
• easier for particles to cross it
• carrier/channel proteins = denatures

Question 13

solvent affect on CM

Answer 13

• water = polar solvent : essential in CM formation : nonpolar tails away = hydrophobic core and phosphate heads interact = keep bilayer intact
• organic solvent dissolve membranes
• disrupts cells
• more fluid
• more perm

Question 14

diffusion

Answer 14

• net movement of particles
• region of high to low
• passive
• continue until conc equlibrium
• occurs due to particles in g/l have KE = random movement

Question 15

factors affecting rate of diffusion

Answer 15

• temp : inc temp, inc rate : particles have more KE moving at inc speeds
• conc diff : overall movement from high to low conc will be larger
• diffusion pathway : distance the particles have to travel
• SA

in facilitated diffusion :
- number of protein channels present

Question 16

active transport

Answer 16

• movement of mol/ions in/out of cell
• from low to high conc
• requires energy
• requires carrier proteins
• process is selective - specific subs transported by specific carrier proteins.

Question 17

active transport mechanism

Answer 17

• mol/ion being transported binds to receptor on the carrier protein outside of cell
• inside of the cell ATP binds to the carrier protein
• hydrolysed into ADP + phosphate
• causes protein to change shape
• opens up inside of the cell
• mol/ion released inside of cell
• P released from carrier
• recombines with ADP = ATP
• carrier protein returns to normal shape

Question 18

bulk transport

Answer 18

• another form of AT
• large mol (enzymes) move through channel/carrier proteins
• moved in/out of cell
• by bulk transp

Question 19

endocytosis

Answer 19

• BT of material into cells
• phagocytosis = solids
• pinocytosis = liquids
• CSM bends inwards
• when it comes into contact with material to be transp
• membrane enfolds the material
• membrane fuses = vesicle
• vesicle pinches off
• moves into cytoplasm
• transfers material for further processing within cell
• E.g vesicles with bacteria go to lysosomes where bacteria digested by enzymes

Question 20

Exocytosis

Answer 20

• reverse of endocytosis
• vesicles formed in golgi
• moves towards + fuse with CSM
• contents of vesicle released outside of cell

Question 21

movement of vesicles

Answer 21

• requires energy (ATP) bc :
• move along cytoskeleton
• changes shape of cells to engulf materials
• fusion of cell membranes

Question 22

water potential values

Answer 22

• pure water = 0
• high water potential = more dilute = less negative
• low water potential = more concentrated = more negative

Question 23

osmosis in animal cells

Answer 23

• animal cell in water with high water potential (more dilute)
• water osmotes into cell
• inc hydrostatic pressure
• cells have thin CSM + no CW
• CSM can’t withstand the increased pressure
• CSM will breaks and cell will burst
• cytolysis
• animal call in sol with lower water potential (more conc)
• lose water to sol by osmosis
• volume of cell reduces
• CSM puckers
• crenation

Question 24

how to prevent crenation + cytolysis

Answer 24

• control mechanisms
• cells continuously surrounded by aq sol
• with an equal water potential
• isotonic

Question 25

osmosis in plant cells

Answer 25

• high water potential
• water osmotes into cell
• inc hydrostatic pressure
• pushes memB against rigid CW = turgor
• resists entry of more water
• cell = turgid
• sol with low water potential
• water lost from cells by osmosis
• volume in cytoplasm reduces
• pulls CSM away from the CW
• cell = plasmolysis