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A-Level Biology > 2.1.5 Biological membranes > Flashcards

2.1.5 Biological membranes Flashcards

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1
Q

permeability definition

A

ability to let substances pass through

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2
Q

roles of membranes

A

partially permeable barrier between cell and environment or organelle and cytoplasm (to maintain conditions within membrane)
site of chemical reactions
site of cell communication

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3
Q

fluid mosaic model

A

fabric of membrane made up of phospholipid bilayer with protein randomly arranged (mosaic pattern)
lipid and protein molecules can change places with each other, giving fluidity

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4
Q

plasma membrane structure

A 
phospholipid bilayer (7 nm)
cholesterol spanning bilayer between phospholipids (regulates fluidity and gives stability, makes membrane less permeable to water molecules and ions - “plugs gaps”)
integral proteins:
channel proteins (allows ions to pass through membrane)
carrier proteins (changes shape to carry specific molecules across membrane)

peripheral proteins:
only on one side of lipid bilayer

lipid-bound protein (found enclosed within lipid bilayer)

glycocalyx (carbohydrate group attached to lipid/protein):
glycoproteins
glycolipids

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5
Q

how temperature affects fluidity of membrane

A

higher temperature = more fluidity
more heat energy in environment = more kinetic energy and movement of phospholipids = greater distance between between phospholipids = less IM forces
lower temperature = lower fluidity
less heat energy in environment = less kinetic energy and movement of phospholipids = closer together = more IM forces

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5
Q

factors affecting fluidity of membrane

A

temperature
cholesterol
ratio of saturated and unsaturated phospholipids

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6
Q

how cholesterol affects fluidity of membrane

A

higher temperatures = lowers fluidity
shape pulls phospholipids closer together = more IM forces
lower temperatures = higher fluidity
shape distances phospholipids from each other = less IM forces
also prevents water-soluble molecules diffusing through membrane

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7
Q

how ratio of saturated and unsaturated phospholipids affects fluidity

A 
saturated = no double = straight chains = can get closer together = more IM forces = less fluidity
unsaturated = double bonds = more awkward shape (not straight) = can’t get closer together = less IM forces = more fluidity
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8
Q

diffusion definition

A

passive net movement of molecules from an area of high concentration to an area of low concentration, down the concentration gradient
only gases and liquids
doesn’t need ATP (only kinetic energy)

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9
Q

facilitated diffusion definition

A

movement of molecules from an area of high concentration to an area of low concentration across a partially permeable membrane via protein channels or carriers
doesn’t involve metabolic energy (ATP)

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10
Q

how diffusion works

A

all molecules have kinetic energy and move freely
higher concentrations = molecules more likely to bump into each other
eventually spread further from each other (towards area of lower concentration) and become evenly dispersed (reach equilibrium)
still move randomly but remain evenly dispersed (no net diffusion)

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11
Q

factors affecting diffusion rate

A 
stirring/moving/temperature 
diffusion distance
surface area 
concentration gradient 
size of diffusing molecule
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12
Q

how stirring/moving/temperature affects diffusion rate

A

higher stirring/moving/temperature = higher KE in molecules = higher rate of random movement = higher rate of diffusion

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13
Q

how diffusion distance affects diffusion rate

A

thicker membrane = higher diffusion distance = lower rate of diffusion

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14
Q

how surface area affects diffusion rate

A

higher surface area = more area for more diffusion at one time = higher rate of diffusion

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15
Q

how conc. gradient affects diffusion rate

A

steeper gradient = higher rate of diffusion

16
Q

how size of diffusing molecule affects diffusion rate

A

smaller molecules/ions diffuse faster than larger molecules

17
Q

why water can still diffuse through plasma membrane

A

polar and insoluble (shouldn’t pass through phospholipid bilayer)
water can still pass through at high concentrations (less negative water potential) via direct diffusion (osmosis)
aquaporins via facilitated diffusion

18
Q

active transport definition

A

movement of particles against concentration, using ATP and involves specific protein carriers

19
Q

how active transport works

A

molecule/ion to be transported binds to receptors in channel of carrier protein outside of cell
ATP binds to carrier protein (inside of cell)
hydrolysed into ADP and phosphate ion
binding of phosphate molecule to carrier protein causes it to change shape (conformational change)
molecule/ion is released into insides of cell
phosphate molecule released from carrier protein and recombines with ADP to form ATP
carrier protein returns to its original shape

20
Q

bulk transport definition

A

active transport of large molecules/cells

21
Q

prefixes for bulk transport

A

exo-: out of a cell
endo-: into a cell
phago-: solids
pino-: liquids

22
Q

where energy is required into endocytosis

A

to move the membrane (pseudopodium) around to form a vesicle in endocytosis

23
Q

where energy is required into exocytosis

A

move vesicles to cell surface membrane to fuse in exocytosis

24
Q

endocytosis method

A

molecule binds to receptor on cell surface membrane
causes cell surface membrane to fold in (invaginates)
cell surface membrane fuses with itself (forms vesicle, requires ATP)
vesicle moves through cytoplasm to where it is needed in cell

25
Q

exocytosis method

A

vesicle moves towards cell surface membrane on microtubules (requires ATP)
vesicle fuses with cell surface membrane (requires ATP)
molecules ejected from cell

26
Q

osmosis definition

A

passive net movement from region of high water potential to a region of water potential, down water potential gradient across a partially permeable membrane (continues until equilibrium reached, water potential on each side of membrane is equal)
measured in kPa
pure water = 0 kPa

27
Q

water potential definition

A

measure of tendency of water molecules to diffuse from one region to another
water moves towards region with more negative water potential

28
Q

animal cell / protoplast in hypertonic solution

A

more water moves out of cell than in

shrivels (crenation)

29
Q

animal cell / protoplast in isotonic solution

A

no net movement of water

structure stays the same

30
Q

animal cell / protoplast in hypotonic solution

A

more water moves in than out

bursts (cytolysis)

31
Q

plant cell in hypertonic solution

A

more water moves out than in

plasma membrane pulls away from cell wall (plasmolysed)

32
Q

plant cell in isotonic solution

A

no net movement of water

overall tissue becomes flaccid

33
Q

plant cell in hypotonic solution

A

more water moves in than out
plasma membrane pushes against cell wall (turgid)
cell wall prevents cell from bursting

34
Q

permeability and structure of plasma membrane as temperature increases

A

fluidity increases
permeability increases
membrane-embedded proteins reaction rates change (increases / may denature)
more fluidity may affect invagination of plasma membrane during endocytosis
may change cell signalling by releasing chemicals via exocytosis
cholesterol helps reduce increase in fluidity

35
Q

structure of plasma membrane as temperature decreases

A

unsaturated fatty acids maintain membrane fluidity (kinks in tail push adjacent phospholipid molecules away)
cholesterol maintains fluidity (prevents phospholipid molecules from packing together too closely)

36
Q

cell signalling definition

A

communication between cells in order to:
coordinate their actions
to trigger actions/responses in the cell
cell recognition

37
Q

glycoproteins

A

interact with water molecules to stabilise membrane/cell
antigen for cellular recognition
binding site for cell aggregation
receptor in cell signalling
binding site for chemicals e.g. hormones/drugs

38
Q

glycolipids

A

recognition site for cellular recognition
interact with water molecules to stabilise cell surface membrane
helps cell attach to other cells to form tissue (aggregation)

A-Level Biology (24 decks)

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