12.7 Transport Across Membranes Flashcards
1
Q
Phospholipids cell membrane
A
They have a hydrophilic phosphate head and a hydrophobic fatty acid tail which means they can form a bilayer by the head facing water and tail repelling water.
2
Q
the cell surface membrane controls…
A
the entry and exit of molecules in cells
3
Q
the cell surface membrane surrounds…
A
the cytoplasm of a cell
4
Q
the cell surface membrane is described as…
A
selectively permeable
5
Q
the cell surface membrane consists of…
A
proteins, glycoproteins, phospholipids, cholesterol and carbohydrates
6
Q
phospholipid molecules form… that are… giving the membrane a… structure
A
1 a bilayer (double layer)
2 constantly moving around relative to 1 another
3 fluid
7
Q
the selective permeability of the cell-surface membrane is related to the type and distribution of…
A
specific proteins and phospholipid molecules present in the membrane
8
Q
components in the fluid mosaic model
A
- phospholipids
- cholesterol
- channel proteins
- carrier proteins
- receptor proteins
- enzymes
- glycoproteins
- aquaporins
9
Q
function of the phospholipids in the fluid mosaic model
A
- hydrophobic tails (fatty acid chains) of phospholipid molecules are attracted towards each other
- hydrophilic heads are orientated either inwards towards the cytoplasm or outwards towards the watery extra-cellular fluid
- forms the phospholipid bilayer (PB)
- most abundant molecule found in all membranes
- PB allows lipid-soluble (non-polar) molecules to pass through by simple diffusion
- prevents passage of small polar / charged molecules (like ions) and larger molecules (glucose)
10
Q
function of the cholesterol in the fluid mosaic model
A
- decreases permeability and increases the stability of the membrane
- more cholesterol = less fluidity of the membrane is and vice versa
- different types of cells have different proportions of cholesterol
11
Q
function of the channel proteins (complementary to specific charged molecules & ions) in the fluid mosaic model
A
- like pores within the membrane
- only allows specific charged ions / small molecules to move across the membrane by facilitated diffusion
- can be open or closed + intrinsic (allow ions to pass straight though)
- Na+ only pass through sodium ion channel proteins embedded within and through the membrane
- proteins have specific tertiary structures -> they are specific and can only transport molecules that are complementary to the shape of the channel protein
12
Q
function of the carrier proteins in the fluid mosaic model
A
- aid the transport of ions / polar molecules and large molecules (glucose and amino acids) by facilitated diffusion and active transport
13
Q
function of the receptor proteins in the fluid mosaic model
A
- other protein molecules act as specific receptors for complementary molecules (hormones - insulin - may bind to the insulin receptor protein -> allows a cell to respond by increasing the cells permeability to glucose)
- proteins have specific tertiary structures -> only specific molecules can bind to specific receptor proteins -> specific cells have specific receptors
14
Q
function of the enzymes in the fluid mosaic model
A
- found embedded in the cell membrane (maltase + dipeptidases)
- shape of enzyme’s active site is specific + complementary to its substrate -> allows binding + forms ESC
15
Q
function of the glycoproteins in the fluid mosaic model
A
- GP composed of carbohydrate and protein
- on outer surface of the membrane
- important to cell recognition, often acting as antigens
- the immune cells detect the specific shapes of glycoproteins to identify the cells as SELF or if they are NON-SELF (foreign)
- GP produced in the golgi body / apparatus within the cell that displays them
- all cells have GP on their cell-surface membrane
16
Q
function of the aquaporins in the fluid mosaic model
A
- AP -> special types of ‘channel proteins’ specific to water
- a cell with lots of AP -> very permeable to water + will carry out osmosis easily
17
Q
specific transport proteins will transport…
A
specific molecules (proteins have specific shapes -> only bind to molecules that are complementary to their binding sites)
18
Q
movement of substances into or out of cells can occur by:
A
- diffusion
- facilitated diffusion
- osmosis (water only)
- active transport
- cotransport (see digestion & absorption)
- bulk transport (endo / exocytosis)
19
Q
NEVER say ALONG the gradient say…
A
DOWN / AGAINST the gradient
20
Q
simple diffusion definition
A
the net movement of molecules from an area of higher concentration to a lower concentration across a partially permeable membrane
21
Q
what type of process is simple diffusion
A
a passive process
22
Q
does simple diffusion require energy
A
doesn’t require energy / ATP from respiration
23
Q
when does simple (net) diffusion stop
A
when there are equal numbers of that specific molecule on either side of the membrane -> when molecules have reached equilibrium
24
Q
does simple diffusion require a specific protein
A
doesn’t require a specific protein
25
what molecules are involved in simple diffusion
only involves non-polar, small, lipid soluble molecules (O2, CO2, oestrogen)
26
fick's law
rate of diffusion = (SA x conc gradient) / diffusion distance
27
why is fick's law very important
helps with AO2 Qs / adaptation Qs
28
factors affecting rate of diffusion
- temp
- SA
- conc gradient
- diffusion distance / pathway
29
how does temp affect rate of diffusion
increased KE, therefore faster rate of diffusion of molecules
30
how does SA affect rate of diffusion
larger SA provides more 'space' for molecules to pass through, therefore faster -> allows for more proteins to be present (channel / carrier) - microvilli increase SA of a cell
31
how does conc gradient affect rate of diffusion
as conc difference increases, rate of diffusion increases
32
how does diffusion distance / pathway affect rate of diffusion
- the shorter the diffusion distance (fewer membranes to cross), the faster molecules will travel from 1 area to the next
- phospholipids bilayers are all the same thickness
33
facilitate means...
to help or aid
34
how do molecules pass through the phospholipid bilayer
specific proteins help specific molecules to pass through the phospholipid bilayer
35
what cannot pass between hydrophobic tails of the phospholipid bilayer
hydrophilic (water soluble, charged or larger) substances
36
why can hydrophilic (water soluble, charged or larger) substances not pass between hydrophobic tails of the phospholipid bilayer
the fatty acid tails are non-polar and they repel polar molecules
37
How do hydrophilic (water soluble, charged or larger) substances enter or exit the cell
Water soluble molecules move through the membrane via channel proteins or carrier proteins
38
channel and carrier proteins are a...
specific shape (due to their unique primary and therefore unique tertiary structures)
39
channel and carrier proteins only transport...
specific molecules that are complementary (to the binding site)
40
all proteins have which sites
binding sites
41
only enzymes have which sites
active sites
42
what process is facilitated diffusion
a passive process
43
does facilitated diffusion require ATP
it does not require ATP
44
on a graph when does facilitated diffusion level off
when all the carrier proteins are saturated / binding site full
45
B plateaus at a lower rate because...
there are fewer specific carrier proteins for this molecule in the membrane
46
B plateaus at a lower rate as there are fewer specific carrier proteins for this molecule in the membrane
what becomes the limiting factor?
number of carrier proteins becomes the limiting factor
47
osmosis definition
the net movement of water molecules from higher water potential to a solution with lower water potential through a selectively (partially) permeable membrane
48
water potential symbol
ψ
49
lower water potential
the more solute dissolved in water the lower (more negative) the water potential (-10kPa)
50
higher water potential
pure water has the highest water potential = 0kPa
nothing is dissolved in the water
51
free water molecules are able to...
move and collide with the membrane exerting pressure
52
this pressure is known as...
water potential
53
water potential is measured in...
kPa
54
higher water potential equation
MORE free moving water molecules = MORE pressure = HIGHER water potential
55
pure water meaning
every water molecule is free moving, therefore the highest water potential, given a value of zero (0kPa)
56
adding what makes a solution more negative
a solute (molecules that are water soluble - glucose, ions)
57
why does adding a solute make a solution more negative
water is a dipole and is attracted to the charges on those molecules / ions; therefore, the number of free moving water molecules decreases
58
if water is separated by a partially / selectively permeable membrane, it will diffuse...
down the water potential gradient from where there are more free water molecules to where there are fewer free water molecules
59
what to say when water moves down water potential gradient by osmosis
water diffuses from the region of higher water potential to the region of lower water potential by osmosis
60
different solutions have... water potentials
different
61
exam tip always refer to... NOT...
1 water potential
2 concentration of water
62
exam tip how to structure a water potential Q
- identify & state where water potential is higher (less negative)
- state where water potential is lower (more negative)
- state 'water moves down the water potential gradient by osmosis'
- state the linked consequence of this
63
ways how different solutions with different water potentials affect cells
- higher water potential than tissue / organelle
- lower water potential than tissue / organelle
- isotonic
64
ways how different solutions with different water potentials affect cells -> the IMPACT of higher water potential than tissue / organelle
- animal cells swell & lysis occurs (bursts + destroys cell with all contents lost)
- plant cells swell increasing mass (cellulose cell wall prevents lysis)
- higher water potential outside cell
- lower water potential inside cell
- water moves in by osmosis
65
ways how different solutions with different water potentials affect cells -> the IMPACT of lower water potential than tissue / organelle
- results in animal cells shrivelling (crenatation)
- plant cell membrane pulls away from the cell wall (plasmolysed)
- higher water potential inside cell
- lower water potential outside cell
- water moves out by osmosis, mass is lost
66
ways how different solutions with different water potentials affect cells -> the IMPACT of solution being isotonic
- no net movement of water in or out of cells
- water potential inside cell = water potential outside cell
(no water potential gradient = no gain in mass)
67
what is active transport used for
used to transport molecules across the membrane against their conc gradient from a lower conc to higher conc
68
which proteins does active transport use
only uses carrier proteins
69
what does active transport require (in terms of the protein)
requires a specifically shaped carrier protein, with a complementary binding site, that only complementary molecule binds to
70
what does active transport require (in terms of energy)
requires a source of energy, supplied by ATP
71
what is ATP, when is it produced and what is it produced by
- energy molecule in the cell
- produced during respiration
- via a condensation reaction
72
the molecule for transport does what with the protein
the molecule for transport binds to the binding site of the specific carrier protein
73
how does ATP aid the process of active transport
the hydrolysis of the ATP into ADP and Pi provides a small amount of energy / phosphorylates the carrier protein causing the protein to change shape (conformational change)
74
what does the change in protein shape do in the process of active transport
this change in protein shape transports the molecule across the membrane, into an area where the conc of the molecule is relatively high (compared to where it came from)
75
other forms of active transport
exocytosis and endocytosis
76
what are the processes of exocytosis and endocytosis used for and require
used for bulk transport and requires ATP
77
what does exocytosis use for transport and why
uses (Golgi) vesicles to move very large quantities of molecules (enzymes, other proteins - insulin and neurotransmitters) from inside of the cell to the outside of the cell
78
how is exocytosis used to secrete proteins
used to move enzymes and glycoproteins from the golgi apparatus to the cell surface membrane to secrete the proteins
79
how is ATP used in exocytosis
ATP is required to move the vesicles to cell surface membrane and the vesicle fuse with the membrane
80
process of endocytosis
- the cell surface membrane is 'pulled' inwards, to create a vesicle
- any molecules next to that part of the membrane are enclosed within the vesicle
81
process of endocytosis requires...
the breakdown of ATP into ADP and Pi
82
the movement of the vesicle into the cell also requires...
the breakdown of ATP into ADP and Pi
83
(summary - transport across membranes) -> types of transport
- diffusion (simple)
- facilitated diffusion
- osmosis
- active transport
84
(summary - transport across membranes) -> types of protein required for each type of transport
- diffusion (simple) - NONE
- facilitated diffusion - SPECIFIC CHANNEL OR CARRIER
- osmosis - AQUAPORIN
- active transport - CARRIER ONLY
85
(summary - transport across membranes) -> active or passive process for each type of transport
- diffusion (simple) - PASSIVE
- facilitated diffusion - PASSIVE
- osmosis - PASSIVE
- active transport - ACTIVE
86
(summary - transport across membranes) -> gradients for each type of transport
- diffusion (simple) - HIGH to LOW CONC, DOWN the gradient, net movement stops when equilibrium is reached
- facilitated diffusion - HIGH to LOW CONC, net movement stops when equilibrium is reached
- osmosis - HIGH water potential to LOW water potential, net movement stops when equilibrium is reached
- active transport - LOW to HIGH CONC, AGAINST the gradient using ENERGY from ATP
87
(summary - transport across membranes) -> characteristics and examples of molecules transported for each type of transport
- diffusion (simple) - SMALL, NON-POLAR molecules, O2, CO2, alcohol
- facilitated diffusion - LARGE = carrier (GLUCOSE); CHARGED (ions) = channel
- osmosis - WATER only
- active transport - IONS / GLUCOSE
88
what happens if aerobic respiration is inhibited (stopped / slowed)?
active transport can't occur as there is no / less ATP. all the other types of transport can still continue until equilibrium is reached.
89
what happens if the tertiary structure of the carrier protein changes
facilitated diffusion / active transport can't occur (because the binding site has changed shape and is no longer complementary to the molecule, therefore they will not fit / bind)
