cell membrane and transport Flashcards
1
Q
two types of cell membrane
A
cell surface membrane and membrane around the organelles
2
Q
cell membrane size
A
7nm thick
3
Q
functions of cell membrane
A
- Controls movement of substances in and out of the cell
4
Q
the function of the phospholipid bilayer
A
Semi-permeable
The barrier to water-soluble substances
Allows passage of lipid-soluble substances
5
Q
proteins and phospholipid form
A
hydrogen bond with water for stability
6
Q
proteins and glycoproteins are used for
A
cell recognition
7
Q
proteins function
A
- transport proteins
- enzymes
- cytoskeleton
- cell to cell adhesion
- cell signalling
- cell recognition
8
Q
What makes up the biomembrane?
A
- Phospholipids
- Cholesterol
- Proteins
- Carbohydrates – in glycoproteins and glycolipids
9
Q
another name for cell membrane
A
biomembrane
10
Q
Fluid
A
phospholipids and protein molecules are able to move about and diffuse sideways within its monolayer
11
Q
Mosaic
A
proteins scattered within the membrane
12
Q
What can cross the phospholipid bilayer?
A
- Oxygen
- Carbon dioxide
- Uncharged / non-polar molecules
- Small molecules
- Traces of water
- Lipid soluble substances
13
Q
hydrophilic head in phospholipid
A
made of glycerol attached to PO4 [hydrophilic due to the presence of phosphate group[polar]
14
Q
hydrophobic tail in phospholipid
A
made of 2 fatty acid chains [nonpolar)
15
Q
how do the hydrophobic tails and hydrophilic heads in phospholipid help in a cell membrane
A
This allows the phospholipids to form a membrane around the cell; 2 rows of phospholipids arranged with their hydrophilic heads in watery solution on either side of the membrane and middle hydrophobic tails forming a layer impervious to water.
16
Q
individual phospholipid molecules can move in
A
the monolayer through diffusion
17
Q
is the hydrophilic exterior head of a phospholipid polar or nonpolar
A
it’s polar
18
Q
is the hydrophobic interior tail of a phospholipid polar or nonpolar
A
its non polar
19
Q
Some phospholipid tails are unsaturated
A
with double bond
20
Q
more unsaturated makes it more
A
fluid [unsaturated FA’s are bent [KINK]so they fit together more loosely]
21
Q
The longer the fatty acid tail,
A
, lesser the fluidity
22
Q
fluidity is affected by
A
1) length of a fatty acid tail
2) the number of unsaturated fatty acids
3) cholesterol
4) temperature
23
Q
how does the length of a fatty acid affect fluidity?
A
shorter the tails, more the fluidity [longer tails will make more intermolecular interactions, thus less fluidity]
24
Q
how does the number of unsaturated fatty acids affect fluidity?
A
more the number of unsaturated fatty acids, more the fluidity
25
how does the cholesterol affect fluidity?
maintains the fluidity of the cell membrane
26
how does the temperature affect fluidity?
as temperature increases, fluidity increases – cholesterol reduces the fluidity by increasing the intermolecular interactions
As temperature decreases, fluidity decreases – cholesterol increases the fluidity by disrupting the intermolecular interactions
27
cholesterol size
Relatively small molecule
28
cholesterol has
Have hydrophilic head and hydrophobic tails – fit in the membrane same like phospholipids [head facing towards the phospholipid head]
29
In animal cells cholesterol number in the cell surface membrane
is too high as phospholipids
30
In plant cells cholesterol number in the cell surface membrane
very less
31
In prokaryotes cholesterol number in the cell surface membrane
absent
32
Functions of cholesterol in cell membrane:
* For maintaining mechanical stability
prevents ions or polar molecules from passing through the membrane
To maintain the fluidity of the cell membrane –
33
how does cholesterol help in maintaining mechanical stability
strengthens the membrane by getting in between the phospholipids and the membrane increasing or reducing fluidity
33
how does cholesterol prevent ions or polar molecules from passing through the membrane?
Hydrophobic regions of the cholesterol prevents ions or polar molecules from
passing through the membrane – very helpful in myelin sheath because
leakage of ions would slow down the nerve impulse
33
how does cholesterol help To maintain the fluidity of the cell membrane?
at low temperatures, kinetic energy is less, phospholipid tails tend to pack together, but cholesterol prevents this from happening thus maintaining the fluidity of the membrane
at high temperature : Kinetic energy is more, molecules move apart but cholesterol bring them closer and avoid more flexibility by interacting with hydrophobic group
34
Proteins also have hydrophobic and hydrophilic regions
[AMPHIPATHIC] due to the presence of hydrophobic and hydrophilic amino acids
35
transport proteins:
hydrophilic channels or pathways for ions and polar molecules; specific; 2 types – carrier proteins and channel proteins
36
Some membrane proteins are enzymes
e.g. cells lining the small intestine have digestive enzymes in the cell surface membrane
37
Cytoskeleton:
some proteins on the inner cell surface membrane are attached to cytoskeleton
38
Cell signalling
glycoprotein
39
Cell recognition
– glycoprotein and glycolipid
40
INTEGRAL / INTRINSIC PROTEINS
- Found in phospholipid bilayer
- Stuck inside not easily removed
- Some extend across the bilayer called transmembrane proteins e.g. channel and carrier proteins that aid in transport
41
PERIPHERAL / EXTRINSIC PROTEINS
Found on the inner side and the outer side the membrane
Easily removed
42
Membrane proteins are called ‘peripheral’ if they are
temporarily attached to the membrane or ‘integral’ if they are permanently attached to the membrane.
43
Integral proteins are described as ‘intrinsic’ if they extend
across the
whole bilayer and ‘extrinsic’ if they are found only on one side of
the bilayer.
44
Channel and carrier proteins are two types of
integral transmembrane proteins,They are both embedded in the cell membrane
and span the entire membrane
45
glycolipids
= lipids + carbohydrate chain
46
glycoproteins
proteins + carbohydrate chain
47
functions of glycoproteins and glycolipids
- receptor molecules
- cell to cell recognition
48
receptor molecules
carbohydrate chains help the GP and GL to act as receptor molecules. Different
cells have different receptor molecules. e.g. signaling receptor in liver cell to detect glucagon
hormone
49
Cell-to-cell recognition:
some GL and GP act as cell markers or antigens. Carbohydrate chains bind
to complementary sites on other cells; useful in growth and development, immune response. Each
cells have different types antigens
50
Cell signaling
is the molecular mechanism by
which cells detect and respond to external?
stimuli, including communication between
cells.
51
Signaling
getting a message from one place to the other
52
Signalling pathways can be
electrical
[nervous system] or chemical [hormone
system in animals
53
Signalling molecules
neurotransmitters,
hormones
54
insulin is
a horomone
55
stimulus for a release of ligand which is an insulin hormone
high glucose level in blood;
56
Signalling molecules are small for
easy transport
57
transport system for hormones
blood
58
Receptors are protein molecules located in the
cell surface membrane
59
cell signalling process outside the cell
* Stimulus causes cells to release a “ligand” / “signalling molecule”
* Signalling molecule is transported to the target cells
* ligand binds to the cell surface receptor on the target cells – complementary
binding
60
INSIDE THE CELL -
* Complementary binding – between receptor protein and ligand [specific]
* Ligand changes the shape of the receptor protein – conformational change
* Receptor spans the membrane and therefore the message is passed to the inside
of the membrane
* Change in shape of the receptor allows it to interact with the next component of
the signalling pathway, G PROTEIN, so the message gets transmitted –
transduction
CELL SIGNALLING PROCESS
* ‘G protein’ - acts as a switch that brings about the release of a ‘second
messenger’
* amplification of the original signal occurs with the help of secondary
molecules by activation of different enzymes – known as the ‘signalling
cascade’
* Finally enzymes are produced which bring about the required change in cell
metabolism [RESPONSE]
61
‘Transduction
occurs during cell signalling and is the process of converting a
signal from one method of transmission to the other
62
‘Second messenger
is a small soluble molecule which diffuses through the cell
relaying and amplifying the message
63
Signaling cascade
: the sequence of events triggered by the G protein
64
G protein named so
because the switch mechanism
involves binding to GTP [guanine
triphosphate] molecules
65
Some signaling molecules are
hydrophobic, e.g. steroid hormone
[oestrogen]. They can diffuse across the cell surface membrane directly
and bind to receptors in the cytoplasm or nucleus
66
4 other basic ways in which a receptor can alter the activity of the cell:
1. Opening an ion channel and thereby changing the membrane
potential
2. Acting directly as a membrane-bound enzyme
3. Acting as an intra cellular receptor when the initial signal passes
straight through the cell surface membrane [e.g. oestrogen receptor
is in the nucleus and directly controls gene expression when
combined with oestrogen]
4. Direct cell to cell contact is another mechanism of signaling e.g.
lymphocyte detecting foreign antigens
67
Phospholipid bilayer is a very effective barrier, particularly against
ions and water soluble substances
68
5 different ways by which exchange of materials is achieved:
Diffusion
Facilitated diffusion
Osmosis
Active transport
Bulk transport
68
DIFFUSION
The net movement of molecules or ions from a region of higher concentration
to a region of lower concentration down a concentration gradient, as a result
of random movements of particles
69
diffusion movement is because of
the natural kinetic energy of the molecules or ions
70
Through diffusion, molecules or ions tend
to reach an equilibrium
71
some molecules/ions are able to pass through living cell membranes by
diffusion
example respiratory gases like oxygen and carbon dioxide
[uncharged, non-polar].
72
Water molecules are highly polar, but can diffuse
across the phospholipid bilayer because of its small size
73
Hydrophobic substances also can cross membranes because the
interior of membranes are also hydrophobic
74
Factors affecting rate of diffusion:
1. Steepness of the concentration gradient:
2. Temperature:
3. The nature of the molecules or ions:
4. The surface area across which diffusion is taking place:
75
how does the steepness of the concentration gradient affect the rate of diffusion
Steeper the concentration gradient, faster the rate of diffusion of that substance
76
how does the Temperature affect the rate of diffusion
Higher the temperature, more the kinetic energy, faster the diffusion
77
how does the the nature of the molecules or ions affect the rate of diffusion
Larger molecules require more energy, so diffusion is slower.
Non - polar molecules like glycerol, alcohol and steroid hormones, diffuse more
easily than polar ions as they are soluble in non-polar phospholipid tails
78
how does the surface area across which diffusion is taking place affect the rate of diffusion
Greater the surface area, more the rate of diffusion. Surface area of cell membranes can be increased by folding – e.g. microvilli, cristae
Larger the cell, smaller its surface area in relation to its volume [SA:V ratio decreases as the size of any 3D object increases]
This is why cells need to be small [molecules need to cross quickly]
79
Surface area to volume ratio decreases as
cells get larger. Single celled organisms have relatively large SA:V ratio compared to large multicellular organisms
80
The larger the surface area to volume ratio,
the quicker the rate of diffusion takes place
81
No. Of cells In humans [multicellular]
100 trillion
82
No. Of cells In amoeba [unicellular]
1
83
SA to V ratio In humans [multicellular]
less
84
SA to V ratio In amoeba [unicellular]
More
85
Diffusion distance In humans [multicellular]
Large
86
Diffusion distance In amoeba [unicellular]
Less
87
Diffusion speed In humans [multicellular]
Slow
88
Diffusion speed In amoeba [unicellular]
Fast
89
Hence, humans need
respiratory,circulatory and excretory systems to speed up the diffusion process.
90
Amoeba does not need systems as
diffusion is facilitated
91
Facilitated diffusion
diffusion [higher conc. To lower conc.] of a substance through a transport protein [channel protein or carrier protein] in a cell membrane; the protein provides hydrophilic areas that allow the molecule or ion to pass through the membrane, which would otherwise be less permeable to it
92
2 TYPES OF TRANSPORT PROTEINS
Channel proteins and carrier proteins
93
in facilitated diffusion
Larger polar molecules [glucose and amino acids] and ions [sodium and
chloride] require proteins molecules to pass through
94
Most channel proteins are ‘gated’
means part of the protein inside the surface of the membrane can move to close or open the pore like a gate, which allows control of ion exchange
95
Rate of facilitated diffusion depends on the
number of channel or carrier proteins and also whether the channel proteins are open or not
96
Some carrier proteins called ‘pump’,
requires energy and are involved in active transport – movement of molecules against the concentration gradient using ATP
97
The carrier pump is specific for a
particular type of molecule or ion, and also requires energy – provided by ATP
98
sodium potassium pump
a membrane protein that moves sodium ions out and potassium ions into the cell using ATP
99
CHANNEL PROTEINS
* Fixed shape
* Water-filled pores [e.g. aquaporins]
* mostly remains open –sometimes ‘gated’
* Mainly for Facilitated Diffusion
* Not specific
*For polar molecules and ions
*integral Transmembrane proteins
*Proteins with hydrophilic and hydrophobic regions
100
CARRIER PROTEINS
* Flips between two conformations
*For both Active Transport and Facilitated Diffusion
*Specific
*For polar molecules and ions
integral Transmembrane proteins
*Proteins with hydrophilic and hydrophobic regions
101
Factors affecting the rate of facilitated diffusion:
* The number of carrier or channel proteins in the membrane
* The concentration of molecules on each side of the membrane
* Whether the channel proteins are open or not – ‘gated’
102
OSMOSIS
The net diffusion of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane is called osmosis
103
osmosis is a type of diffusion only happening in
water molecules
104
Solution
= solute + solvent
105
in a sugar soln
sugar is the solute; solvent is water
106
WATER POTENTIAL
A measure of the tendency of water to move from one place to another; water moves from a solution with higher water potential to one with lower water potential; water potential is decreased by the addition of solute, and increased by the application of pressure; the symbol of water potential is ψ or ψw
107
Water always moves down a
water potential gradient
108
Water moves till the water potential is the
same throughout the system, i.e. until equilibrium is reached
109
Water potential depends on 2 factors:
1. the concentration of the solution
2. how much pressure is applied to it: as pressure increases, water potential of a solution increases
110
water potential can be measured in
pressure units called ‘kilopascals’ / kPa
111
Water potential of pure water is
always higher than that of a solution[assuming there is no extra pressure applied to the solution]
112
Water potential of pure water is always
‘0 kPa’
113
Therefore, for solutions, since water potential is always less than pure water,
the water potential value is less than ‘0’ [- kPa]
114
A solution with a water potential of -10 kPa
has a higher water potential than a solution with a water potential of -20 kPa
115
Osmosis in animal cells
* If the water potential of the surrounding solution is too high, the cells swell and burst
* If the water potential of the surrounding solution is too low, the cell shrinks
* This shows the importance of maintaining water in our body
116
red cell bursts
117
red cell remains normal
118
red cell shrinks
119
Outer covering of cell wall
very strong and rigid
120
When kept in a solution with high water potential,
water molecule enters till they reach equilibrium; plant cell protoplasm expands, building pressure on the cell wall and the cells will become turgid, but don’t burst
121
plant cells in soln with lower water potential
When kept in a solution with lower water potential, water leaves the cells by osmosis,
protoplast shrinks until it is exerting no pressure on the cell wall. It pulls away from the cell wall – gets plasmolysed
122
incipient plasmolysis
A condition when protoplasm do not exert pressure on the cell wall
123
Active transport
is the movement of molecules or ions through transport proteins across
a cell membrane, against their concentration gradient, using energy from ATP
124
Certain ions like potassium and chloride are often
found to be 10 – 20 times more concentrated inside the cells than outside [i.e. a concentration gradient exists, with a lower conc. outside and a higher conc. inside the cell] Therefore for ions to enter, they have to move against the concentration gradient – ACTIVE TRANSPORT, Achieved by carrier proteins called pumps – each of which is specific for an ion or a particular type of molecule. The process requires energy – provided by ATP – through respiration inside the cell
125
ATP helps to
change the shape of carrier proteins and also to transport molecules against a
concentration gradient across the membrane
126
sodium-potassium (Na+ – K+) pump
* Found in the cell surface membrane of all
animal cells
* Uses 30% of a cell’s energy [70% in nerve cell]
* For each ATP molecule used, this protein
pumps 3 sodium out of the cell and 2
potassium into the cell
* Both are positive ions, the net result is that
inside the cell becomes more negative and
than outside the cell – thus creating a
potential difference
127
example of active transport
sodium-potassium (Na+ – K+) pump
128
Significance of active transport:
1. reabsorption in kidney tubules
2. absorption in the gut
3. to load sucrose from photosynthesizing cells of leaves to the phloem tissue
4. for root hairs to absorb inorganic ions from the soil
129
exocytosis and endocytosis is used for
bulk transport
130
Endocytosis – bulk transport
into the cell
131
Exocytosis – bulk transport
out of the cell
132
exo and endocytosis requires
energy – ACTIVE PROCESS
133
ENDOCYTOSIS
* engulf materials to form a vesicle or a vacuole
* Requires energy
* Happens in 2 forms:
1) phagocytosis
2)pinocytosis
134
phagocytosis
e.g. engulfing of bacteria by WBC forming phagocytic vacuoles
135
pinocytosis
bulk uptake of liquid
136
micropinocytosis
small amount of water uptake forming very small vesicles
137
EXOCYTOSIS
* Reverse of endocytosis
* Requires energy
* Materials are removed from cells
– e.g. secretion of digestive
enzymes, secretory vesicles, in
plants for making cell wall
138
exocytosis
139
endocytosis
140
Osmosis can be made faster using
transport proteins, though membrane is enough for the process
141
Cholesterol is in between the
phospholipid layers and not near the outer surface of phospholipids
142
All water soluble molecules can travel only through the
transport proteins, whereas fat-soluble substances can directly cross the lipid bilayer
143
Active processes requires
ATP [active transport, exocytosis and endocytosis
144
Passive processes do not require
ATP [osmosis, diffusion, facilitated diffusion]
145
Down the conc. gradient means from
higher concentration to lower concentration
146
Up / against the conc. gradient means from
lower concentration to higher concentration
147
Diffusion, facilitated diffusion and osmosis occurs by
random movement of molecules
148
Exocytosis and endocytosis also depends on the
fluidity of the membrane
149
Compared to diffusion, facilitated diffusion is faster due to the
presence of proteins
150
Fluidity of the cell membrane is also important in
cytokinesis[cytoplasmic division during cell division]
151
* S.A =
length x height]
152
Volume =
length x height x depth
153
SA:V ratio =
total surface area / volume
154
larger the surface area to volume ratio,
greater the diffusion
155
156
157
158
159
160
161
162
163
164
165
166
167
168
which process is the movement of molecules that are too large to diffuse in
through a csm?
endocytosis / exocytosis
169
properties of glycolipids / glycoproteins
1. act as receptor sites for hormones
2. form hydrogen bonds w water
3. recognise antibodies
170
properties of phospholipids
1. to allow cytokinesis to occur in mitotic cell division
2. to allow entry and exit of water-soluble gases
3. to allow phagocytosis of a bacterium into cells
171
factors inversely prop to rate of diffusion
1. size of diffusing molecule
2. diffusion distance
172
channel protein vs carrier protein
Channel proteins: water-filled pores that allow charged substances,
usually ions, to diffuse through the membrane. They have a fixed shape
and can be gated to control ion exchange. This does not use ATP and is
in facilitated diffusion.
Carrier proteins: can flip between two shapes, and is mainly in active
transport where it uses ATP to change shape and carry ions/molecules
up the concentration gradient. It is also involved in passive transport
(facilitated diffusion) down the concentration gradient without the use of
energy.
fat-soluble substances could pass through the phospholipids and
water-soluble would pass through a water filled pore (protein channel)
idk why but its thru a carrier protein
carrier proteins only transport solutes in an ezyme-substrate way, not
solvents
173
virus invading a cell
binding to a protein receptor, followed by endocytosis
174
what supports the view that a membrance protein is involved in active
transport?
it can only function if mitochondria are supplied with sufficient oxygen
175
what is correct for the csm and membranes within cells?
both have sites for enzyme attachment
176
as fluidity of csm decreases what process would be least changed?
active transport!
the number and position of transmembrane proteins involved in active
transport would be least changed
177
even distribution of proteins w floresecent dyes in csm cool question
protein molecules in the outer layer of the csm and those which span the
bilayer can move freely between phospholipid molecules
178
which part of phospholipid molecule makes up most of the thickness of a
csm
hydrocarbon chains!!
179
why does rate of facilitated diffusion level off whereas rate of simple diffusion
does not
fd is limited by the number of protein channels in the membrane
180
which molecules are involved in cell signalling?
only trans-membrane proteins
not glycos or surface proteins (idk it could be this too)
181
role of g protein in cell signalling
to act as a switch releasing a second messenger
181
vit c is water soluble so it shud go through carrier na cuz its a vitamin
it isnt
a charged molecule, molecules with charge and dissolved pass through
channel
182
for sa: v ratio take the
greatest sa
183
osmosis is only
solvent
184
active transport does not occur withou
o2 (mitochondria are unable to
produce atp)
185
diffusion can occur within an absence of
membranes
186
prokaryotes have
proteins and phospholipids in their csm
187
glycos + proteins help immune system
identify cells [antigen markers]
188
high concentration of ions in the vacuole does not increase
the efficiency of
ion uptake
189
endo/exo cytosis r not a result of
the random movement of molecules
190
glucose can’t pass directly thru csm
it needs protein / carrier proteins
191
oxygen passes freely through the membrane as it is
soluble in lipids
192
glycoproteins form hydrogen bonds w water to stabilise
membrane
193
phospholipd tails and cholestrol maintain
membrane fluidity
194
facilitated diffusion is driven by the
ke of the molecukes which are diffusing +
it depends on number of protein channels also
195
water can cross cell membrances by passing thru
channel proteins
196
going out of cell / secretion =
exocytosis
197
glycoproteins are most important for recognising
self / non-self antigens
[they would enable a hormone to recognise its target cell aw)
198
membrane proteins have both
hydrophobic and hydrophilic regions
199
fleshy leaves and fewer stomata
DO NOT REDUCE the water potential
gradient in xerophytes
200
cholestrol can help increase
fluidity, but not decrease fluidity
201
since ions r thru carrier proteins,
cystic fibrosis means the carrier protein is
faulty
202
thinner side of cell
expands more
203
in cold weather
ur tryna increase fluidity
204
more cholestrol =
more fluidity
205
active transport does not result in an
equilibirum (cuz lower to higher)
206
some of the csm is lost when endocytosis occurs and
there is an increase in
the csm when exocytosis occurs
207
during lysis, more water enters
s the cell than leaves in (NOT more water
enters the cell and none leaves it) - osmosis is the net movement of water
208
channel proteins are not fixed
in position [ both the membrane and proteins
are fluid ]
209
glycoproteins in the outer layer of the membrane
can move
210
visking tubing can be used to represent
csm and tonoplast NOT CELL WALL
bcz cell wall is fully permeable instead of being partially permeable
211
in those potato piece qs only
water moves
212
no movement is not the same as
no net movement
213
Why is it called the fluid mosaic model?
phospholipid (and protein) molecules, move about/ diffuse/AW ;
protein (molecules), scattered/AW ; A different proteins present
214
Role in cell membrane of
Glycoproteins
receptors / receptor molecules;
for hormones / neurotransmitters / named hormone /
neurotransmitter (e.g. insulin, acetylcholine, noradrenaline);
idea of ( ) antigens / (cell surface) markers / cell
recognition / cell adhesion;
help to stabilise membrane structure / forms H bonds with watermolecules
215
carrier proteins
allow named substance (e.g. glucose / amino acids) / polar substance
/ ion(s) / hydrophilic / water soluble substance (to pass through
membrane);
(ref) against concentration gradient / active transport;
energy / ATP (req for transport);
(and) facilitated diffusion / faster than simple diffusion (for ions
/ polar molecules);
216
Cholesterol
maintains / regulates fluidity of membrane / prevents membrane
being too rigid or fluidfRluid / mechanical stability (qualified) /
prevent ions / polar / water soluble / named molecule, passing /
leaking through membrane;
217
General points to write when asked “how is XYZ a cell signalling mechanism”
The “molecule” [given in qs] acts as a cell signalling molecule
It moves through the bloodstream/extracellular space /intracellular space
To reach the target cell which is the [given in qs]
It will bind to complementary, specific, receptors [on the cell membrane - depends on qs]
This will lead to response which is [given in qs]
AVP e.g. detail of change, such as activating G proteins / secondary messenger / enzyme cascade /chain of reactions
218
Phospholipids
1. can form a bilayer ;
2. link between, hydrophobic core / AW, and barrier to water-soluble substances ; A polar/ ionic
3. idea of, hydrophilic / phosphate, head, forming H bonds with water ; A facing, water / watery environment / aqueous environment / cytoplasm / cytosol
4. ref. contribution to fluid nature of membrane ;
5. further detail ; e.g. mainly saturated fatty acids, less fluid e.g. mainly unsaturated fatty acids, more fluid
6. ref. to control over membrane protein orientation ; e.g. hydrophobic – hydrophobic interaction for ‘floating’ proteins
219
Some cells take in bacteria by endocytosis. Explain how endocytosis occurs at the cell surface membrane.
1. attachment (of bacteria) to receptor(s) ; AW
2. ref. ability to attach to antibody (bound to antigen on bacterium)
3. infolding / invagination / AW, of membrane ; A membrane engulfs A pseudopodia
4. form (round bacterium)
5. fusion / AW, of membrane ;
6. formation of, vacuole / vesicle ;
220
Functions of lysosome in endocytosis of bacteria
break down / digest / destroy, bacteria / pathogen(s) ;
break down / digest / destroy, (worn out / defective / AW), organelles / named organelle (in animal cell) ; A autophagy
catalyses / speed up, hydrolysis ;
any two named substrates ; e.g. (any named) polysaccharides / proteins / (phospho)lipids / (named) nucleic acids
idea that recycle / reuse, biological molecules within cell ;
(macrophage / phagocyte) cut up to present antigen
221
The surface area to volume ratio decreases as animals increase in size.
Use this fact to suggest why multicellular animals require transport systems
dea that diffusion (via, body surface / to cells), cannot satisfy needs / too slow ;OR transport system delivers materials to cells more quickly ; (A) efficient supply of, nutrients / oxygen, to all cells
long(er) distances (to reach some, cells / tissues) ;
takes, materials / AW, close to cells ;
222
How does phospholipid molecule make it suitable for its function.
Hydrophilic phosphate head and hydrophobic fatty acid tail
Forms a bilayer with head outside and tail inside
Head faces aqueous environment and tail faces each other to form hydrophobic core
Forms H-bonds with water
Stabilises membrane
Fatty acid may be saturated/unsaturated
Unsaturated makes membrane fluid
Barrier to polar substance
