transport across membrane

Question 1

what are the 4 components of the membrane?

Answer 1

phospholipids, cholesterol, proteins and carbohydrates

Question 2

why are cell membranes fluid/can move about?

Answer 2

phospholipid molecules in the membrane are held together primarily by weak hydrophobic interactions

Question 3

how do phospholipid molecules move about the membrane?

Answer 3

phospholipid molecules can move about laterally across the membrane, rotate and very RARELY flip transversely

Question 4

how does temperature affect membrane fluidity?

Answer 4

as temperature increases, membrane fluidity increases

increased k.e. = increased lateral mvmts = overcome hydrophobic interactions = increased space to move = more fluid

Question 5

how does length of fatty acid chain affect membrane fluidity?

Answer 5

as length of fatty acid chain increases, membrane fluidity decreases

longer hydrocarbon chain = more hydrophobic interactions = more rigid membrane = less fluid

Question 6

how does degree of saturation of fatty acids affect membrane fluidity?

Answer 6

as degree of saturation increases, membrane fluidity decreases

saturated lipids = long, straight hydrocarbon chains = close packing + more hydrophobic interactions = less fluid

Question 7

how does cholesterol affect membrane stability?

Answer 7

the rigid steroid ring of cholesterol interferes with the motions of the hydrocarbon chains, enhancing mechanical stability

Question 8

how does cholesterol affect membrane fluidity?

Answer 8

cholesterol has dual effects on membrane fluidity.
high temp: restrains movements of phospholipids by interfering with the motions of hydrocarbon chains
low temp: prevents hydrocarbon chains from packing closely together

Question 9

how does the presence of cholesterol affect membrane permeability?

Answer 9

cholesterol decreases the permeability by filling in spaces/plugging transient gaps between hydrocarbon chains in phospholipids

Question 10

ATESCI

what are the 6 functions of membrane proteins?

Answer 10

anchorage
transport
enzymatic activity
signal transduction
cell-to-cell recognition
intercellular joining

Question 11

what are the functions of carbohydrates in the membrane?

Answer 11

1. sorting cells
2. binding extracellular signal molecules
3. intercellular adhesion
4. cell-to-cell recognition

Question 12

what are the 2 types of transport proteins?

Answer 12

channel proteins and carrier proteins

Question 13

is ATP needed for facilitated diffusion?

Answer 13

no

Question 14

what substances are transported by facilitated diffusion?

Answer 14

larger, hydrophilic substances

Question 15

ASSTCD

what are the 6 factors affecting the rate of diffusion?

Answer 15

area across which diffusion occurs
structure through which diffusion occurs
size and type of diffusing molecule
temperature
concentration gradient
distance across which diffusion occurs

Question 16

what does ‘less negative’ water potential mean?

Answer 16

higher water potential

Question 17

what is the sign for solute potential (+ve/-ve)

Answer 17

solute potential is ALWAYS NEGATIVE

pressure potential is always positive

Question 18

what happens when a plant cell is placed in solutions of different water potentials?

Answer 18

less negative water potential -> turgid
same water potential -> no change
more negative water potential -> plasmolysed

Question 19

what happens when an animal cell is placed in solutions of different water potentials?

Answer 19

less negative water potential -> swells & lyses
same water potential -> no change
more negative water potential -> shrivelled

Question 20

how is a solute actively transported across a membrane via a carrier protein?

Answer 20

1. solutes on the cytoplasmic side bind to a specific binding site on the transport protein
2. ATP transfers a phosphate group to the transport protein
3. this causes the protein to change its conformation such that the solute is released on the other side of the membrane
4. the phosphate group detaches and the transport protein returns to its original state

Question 21

what is endocytosis?

Answer 21

the cell TAKES IN macromolecules by invagination

Question 22

what is exocytosis?

Answer 22

the cell SECRETES macromolecules by fusion of vesicles

Question 23

what are the 3 types of endocytosis?

Answer 23

phagocytosis
pinocytosis
receptor-mediated endocytosis

Question 24

what are the key functions of the cell membrane?

Answer 24

1. definition of cell’s boundaries
2. organisation & location of function
3. regulation of cell’s contents
4. signal transduction
5. cell-to-cell communication