5. Plasma Membrane Flashcards
1
Q
Functions of membrane (role of membrane in cells = 18ii)
A
Compartmentalisation
• Site for attachment of enzymes
• Provide selective permeability
• Create concentration gradients
Site of chemical reactions
2
Q
Why can glucose not pass through a cell membrane through simple diffusion
A
Glucose molecules too large
Phospholipids act as a barrier
3
Q
Function of cholesterol in plasma membrane
A
Regulates fluidity = sits between tails
Increases strength and stability
4
Q
Role of membrane in RER (19)
A
- compartmentalisation
- separating proteins from cell cytoplasm
- hold ribosomes in place
5
Q
Compartmentalisation
A
creating organelles within a cell e.g. Mitochondria
6
Q
What organelles have membranes
A
Lysosomes
Golgi body
ER
Mitochondria
Chloroplast
Vacuole
Nucleus
7
Q
Organelles without membrane
A
Centrioles
Ribosome
8
Q
Model of membrane name
A
Fluid mosaic model
9
Q
Why is the model called fluid
A
o The phospholipids and proteins can move around via diffusion
o The phospholipids mainly move sideways, within their own layers
10
Q
Main components in the fluid mosaic model
A
o Phospholipids o Cholesterol
o Glycoproteins and glycolipids
o Transport proteins - carrier + Channel proteins
11
Q
What’s the cell surface membrane also known as
A
Phospholipid bilayer
12
Q
How are phospholipids arranged in the cell surface membrane
A
tails form a hydrophobic core comprising the innermost part of both the outer and inner layer of the membrane
Heads face outwards - hydrophilic sides
13
Q
What does the cell surface membrane act as a barrier to
A
most water-soluble substances (due to hydrophobic tails)
14
Q
What does having a membrane that acts as a barrier most water-soluble substances ensure
A
ensures water-soluble molecules such as sugars, amino acids and proteins cannot leak out of the cell and unwanted water-soluble molecules cannot get in
15
Q
Can water go through the membrane
A
Yes kind of
16
Q
Why can water go through the membrane
A
Water - very small molecule - can still slowly squeeze its way through, despite being hydrophobic core
17
Q
What is a micelle
A
Phospholipids arranged in a spherical form
18
Q
Why do micelles form
A
not enough phospholipids to form a full bilayer
19
Q
Two types of phospholipids
A
Saturated and unsaturated
20
Q
What is the difference between saturated and unsaturated phospholipids
A
saturated fatty acids - straight tails
• unsaturated fatty acids = double bond = - tails with kinks/bends in them
21
Q
What increases the fluidity of the membrane
A
Increasing the number of unsaturated fatty acids / phospholipids
22
Q
Why does increasing the number of unsaturated fatty acids increase the fluidity of the membrane
A
more unsaturated fatty acids = more distance between the tails and thus
fewer intermolecular interactions = more fluidity
23
Q
How does cholesterol stop the membrane from becoming to fluid at high temps
A
Cholesterol molecules bind to the hydrophobic tails of phospholipids, stabilising them and causing phospholipids to pack more closely together= decreasing fluidity
24
Q
Extrinsic proteins
A
proteins which are found on the surface of the plasma membrane.
25
General function of extrinsic proteins
usually function as enzymes and catalyse chemical reactions inside the cell.
26
what are Intrinsic proteins
proteins which span both bilayers of the plasma membrane.
27
General function of intrinsic proteins
act as channels or carrier proteins to transport water-soluble molecules.
28
What are glycoproteins
Proteins Embedded in the cell-surface membrane with attached carbohydrate (sugar) chains of varying lengths and shapes.
29
Function of glycoproteins
Cell Signalling
Recognition sites
30
Example of cell signalling
Receptors for peptide hormones, inc. insulin and glucagon, which affect the uptake/storage of glucose by cells.
31
What type of proteins are glycoproteins
Intrinsic proteins
32
What are glycolipids
lipids with attached carbohydrate (sugar) chains
33
Function of glycolipids
Recognition sites / antigens
can be recognised by cells of immune system as self (of the organism) or non-self (belongs to another organism).
34
What are extrinsic proteins also known as
Peripheral protein
35
Function of transport proteins
create hydrophilic channels to allow ions and polar molecules to travel through the membrane.
36
Types of transport proteins
Channel protein
Carrier protein
37
Function of channel proteins
Transport polar substances down a concentration gradient
allow the cell to control which substances enter or leave
38
Function of carrier proteins
Transport molecules against the concentration gradient
allow the cell to control which substances enter or leave
39
Adaption of carrier proteins
change shape to transport a substance across the membrane
40
Can any molecule go down any channel / carrier protein
No = • Each transport protein is specific to a particular ion or molecule
41
What two factors effect membrane permeability
Temp + solvent concentration
42
Initial effect of increase temp on membrane permeability
• Phospholipids in a cell membrane are constantly moving.
• When temp. increased, the phospholipids have more kinetic energy = move more.
• This makes a membrane more fluid, and it will start to lose structure =
REVERSIBLE
43
Later effect of increased temp on membrane permeability
Temp. continues to increase = cell will break down completely.
• Loss of structure increases permeability of membrane, making it easier for particles to cross it.
• Carrier and channel proteins in membrane will be denatured at high temps.
These proteins -> involved in transport across membrane = so as they denature
= membrane permeability is affected. = IRREVERSIBILE
44
What also takes place at increased temps across a membrane
• Any diffusion taking place through the cell membrane will also occur at a higher speed (due to increased kinetic energy)
45
How does solvent concentration effect membrane permeability
Organic solvents can increase cell membrane permeability as they dissolve the lipids in the membrane, causing the membrane to lose its structure
46
Define diffusion
the net passive movement of molecules from an area of high concentration to an area of low concentration
47
What happens after a long period of diffusion
Reaches equilibrium
48
How does temp effect rate of diffusion
Molecules and ions have more kinetic energy at higher temperatures
• They move faster, resulting in a higher rate of diffusion
49
How's does the concentration gradient effect rate of diffusion
o This is the difference in the concentration of the
substance on the two sides of the surface o If there are more molecules on one side of a membrane than on the other, at any one moment more molecules will randomly move across the membrane from that side than from the other
• A greater difference in concentration means a greater difference in the number of molecules passing in the two directions and therefore a faster rate of diffusion
50
How does SA effect the rate of diffusion
The greater the surface area across which diffusion is taking place, the greater the number of molecules or ions that can cross it at any one moment and therefore the faster diffusion occurs
51
How can you increase the SA of an organelle / organism
Or decreasing it's size
• The surface area of cell membranes can be increased by folding (eg. microvilli in the intestine or cristae in mitochondria)
52
How does the properties of the molecules or ions dissolving effect the rate of diffusion
• Large molecules diffuse more slowly than smaller ones as they require more energy to move
• Uncharged and non-polar molecules diffuse directly across the phospholipid bilayer
• Non-polar molecules diffuse more quickly than polar ones as they are soluble in the non -polar phospholipid bilayer
53
how do decrease the fluidity of a membrane
An increased proportion of saturated fatty acid chains as the chains pack together tightly and therefore there is a high number of intermolecular forces between the chains
• A lower temperature as the molecules have less energy and therefore are not moving as freely which causes the structure to be more closely packed
54
how to increase the fluidity of a membrane
• An increased proportion of unsaturated fatty acid chains as these chains are bent, which means the chains are less tightly packed together and there are less intermolecular forces
• At higher temperatures, the molecules have more energy and therefore move more freely, which increasing membrane fluidity
55
What can no diffuse through phospholipid bilayer
o Large polar molecules such as glucose and amino acids o lons such as sodium ions (Nat) and chloride ions (CI-)
56
What is facilitated diffusion
When certain molecules require transport proteins to diffuse across a membrane
57
What two types of molecules enable facilitated diffusion
Channel proteins
Carrier proteins
58
Properties of transport proteins
Highly specific
59
What are channel proteins
Water filled pores
60
What do channel proteins allow
charged substances (eg. ions) to diffuse through the cell membrane = down conc
Gradient
61
Most channel proteins are…
Gated
62
What does gated mean
that part of the channel protein on the inside surface of the membrane can move in order to close or open the pore
• This allows the channel protein to control the exchange of ions
63
How do carrier proteins function in facilitated diffusion
the binding site of the carrier protein to be open to one side of the membrane first, and then open to the other side of the membrane when the carrier protein switches shape
64
Define active transport
net movement of molecules against the concentration gradient, across a cell membrane, using ATP
65
What does active transport require
ATP + carrier proteins
66
Carrier proteins can change shape. Can it change shape in facilitated diffusion + why
No - requires energy for it to change shape = ONLY CHANGES SHAPE IN ACTIVE
TRANSPORT
67
In facilitated diffusion molecules move
Down a conc gradient
68
How does atp release energy
It is hydrolysed
69
Importance of active transport
The reabsorption of useful molecules and ions into the blood after filtration into the kidney tubules
• The absorption of some products of digestion from the digestive tract
• The loading of sugar from the photosynthesising cells of leaves into the phloem tissue for transport around the plant
• The loading of inorganic ions from the soil into root hairs
70
What is diffusion / osmosis / active transport responsible for
the transport of individual molecules or ions across cell membranes
71
Exocytosis
bulk transport in which the vesicle containing the product fuses with the plasma membrane, allowing the content to be released out.
72
Endocytosis
bulk transport in which a vesicle fuses with the plasma membrane, allowing substances to be released inside.
73
For Endocytosis and Exocytosis need…
ATP = vesicles need it to move around
74
Example of bulk transport materials that need to cross the membrane
o Large molecules such as proteins or polysaccharides o Parts of cells o Whole cells e.g. Bacteria
75
If both exocytosis and endocytosis require energy, what does that make them
Forms of active transport
76
Two forms of endocytosis
Phagocytosis
Pinocytosis
77
What is phagocytosis
bulk intake of solid material by a cell
78
Cells that specialise in phagocytosis are called.
Phagocytes
79
The vacuoles formed in phagocytosis are called
phagocytic vacuoles
80
Example of phagocytosis
engulfing of bacteria by phagocytic white blood cells
81
What is pinocytosis
bulk intake of liquids
82
How’ does Exocytosis work
• The substances to be released (such as enzymes, hormones or cell wall building materials) are packaged into secretory vesicles formed from the Golgi body
• These vesicles then travel to the cell surface membrane
• Here they fuse with the cell membrane and release their contents outside of the cell
83
Example of Exocytosis
secretion of digestive enzymes from pancreatic cells
84
Which processes require energy
ALL EXOCTYOSIS + ENDOCYTOSIS + ACTIVE
TRANSPORT REQUIRE ENERGY
85
Define osmosis
Net movement of water molecules from an area of high water potential, to an area of lower water potential, across a partially permeable membrane
86
Water potential of pure water
O kPa (at standard temp. and at pressure, -25 degrees C and 100kPa)
87
Symbol of water potential
88
All solutions have … water potentials
Negative
89
If the concentration of a solution increases, what happens to the numerical value of the water potential
more concentrated the solution, the more negative the water potential
90
What happens if an animal cell is placed in a hypertonic solution
cell water will leave the cell through its partially permeable cell surface membrane by osmosis and the cell will shrink and shrivel up
• Crenation = fatal
91
What happens if an animal cell is places in a hypotonic solution
water will enter the cell through its partially permeable cell surface membrane by osmosis
• Cell will gain water until cell membrane is stretched too far
• Lysis = bursts = hypotonic
92
What happens if a plant cell is placed in a hypertonic solution
water will leave the plant cell through its partially permeable cell surface membrane by osmosis
• As water leaves the vacuole of the plant cell, the volume of the plant cell decreases
• The protoplast gradually shrinks and no longer exerts pressure on the cell wall and begins to pull away from the cell wall
• the plant cell is plasmolysed
93
What happens if a plant cell is placed into a hypotonic solution
water will enter the plant cell through its partially permeable cell surface membrane by osmosis
• As water enters the vacuole of the plant cell, the volume of the plant cell increases
• The expanding protoplast pushes against the cell wall and pressure builds up inside the cell - the inelastic cell wall prevents the cell from bursting
• The pressure created by the cell wall also stops too much water from entering and this also helps to prevent the cell from bursting
• When a plant cell is fully inflated with water and has become rigid and firm, it is described as fully turgid
94
What is the protoplast
(living part of the cell inside the cell wall = everything except the cell wall
95
Why is turgidity important in plant cells
Provides support and strength to plants
96
Co transport
When there is no concentration gradient of an ion, we create one ourself. If you pump the sodium ions out there’s more outside than inside = sodium ion concentration gradient. Sodium will want to move back in. It comes back through facilitated diffusion because it’s an ion. In doing so, it’ll bring glucose with it. Pumping of the ions against the concentration gradient = active transport = used to push the ions out to create a gradient.
97
Hypertonic
any external solution that has a high solute concentration and low water concentration compared to body fluids
98
Hypotonic
when the solute concentration is lower than the concentration inside the cell.
99
Isotonic
any external solution that has the same solute concentration and water concentration compared to body fluids.
100
Effect of low temperature on phospholipid bilayer
he phospholipid molecules in the membrane are packed closely together and are less mobile, making the membrane more rigid and less permeable.
101
Effect of incredibly low temperatures on permeability
When temperatures fall low enough for ice crystals to form, these can puncture the membrane which increases its permeability when the cell membrane rethaws, damaging the cell.
102
Effect of incredibly high temperature on membrane permeability
permeability increases rapidly because proteins in the membrane become denatured and start to unravel
103
Effect of ethanol on permeability
Ethanol is non polar solvent so it dissolves non polar substances such as lipids
- if you place a cell in ethanol, its membrane will become permeable and allow substances to leak into and out of the cell.
As the ethanol concentration increases, membrane permeability will increase.
104
Testing effect of temperature change in membrane permeability practical
Prepare eight cylinders of beetroot of equal size. Make these samples as similar as possible, e.g. by cutting from the same part of each plant. Rinse each piece to remove any pigment released during cutting.
If you are investigating the effect of temperature, prepare eight water baths of varying temperatures ranging from 0-70oC.
Prepare a series of test tubes containing the same volume of water (e.g. 10 cm3). Place the tubes in different water for five minutes.
Place a single sample of beetroot into each of the eight test tubes. Leave for 15 minutes.
Use forceps to remove the pieces of beetroot from each tube. Keep the coloured liquid and transfer into a cuvette.
Use a colorimeter to measure how much light is absorbed by each liquid. The darker the solution (i.e. the more permeable the membrane), the more light is absorbed.
Draw a graph plotting absorbance against temperature.
105
General pattern of effect of temperature change in membrane permeability practical
as temperature increases, membrane permeability also increases
106
Limitations of beetroot practical
- beetroot pieces may not be identical size and shape
- some part of beetroot tissue have more pigment than others
- excess pigment may not have been washed off the beetroot properly
107
How are plants strong and supported
- water enters vacuole
- pressure against cell wall
- turgor pressure
- turgid cells support plant
108
What is cell signalling
communication between cells;
- molecule released by one cell causes change in another cell;
109
B = larger SA:V = faster diffusion
110
111
What two substances are required to break the glycosidic bond in lactose?
Water and enzyme
112
113
Suggest and explain why a low pH might cause the red pigment to leak out of the beetroot cells.
114
Outline how the students could modify their investigation to get a more accurate value for the pH at which the red pigment begins to leak out of the beetroot cells.
115
116
How does the fluid mosaic model describe the structure of plasma membranes?
117
Describe the structure of the rough endoplasmic reticulum.
118
119
For which macromolecule does a plant need both nitrogen and phosphorus?
DNA
120
Explain how the Casparian strip prevents these ions from reaching the xylem of the plant by the apoplast pathway.
121
122
123
124
ii
125
Before the students began their investigation they made a hypothesis.
State the hypothesis the students would have made and state the scientific process that supports your choice.
126
Justify whether the results from the investigation support your hypothesis given in part (b)(i).
127
detect the
presence of acid /
H*
128
Use the data in Table 22.1, on the insert, to calculate the rate of diffusion of acid in
Cube C from the outer surface to the centre of the cube.
129
130
Identify one limitation in the practical procedure that may have caused the results to be inaccurate and explain which cube's results are most likely to have been affected by this limitation.
131
idea of involvement of cytoskeleton / vesicles (1)
132
Describe how the student should represent the data from Table 20 as a graph and explain why this is the correct way to represent these data.
line graph v
(because) both variables are continuous v
concentration on x / horizontal axis, because it is independent variable
AND
(%) change in mass on y/ vertical axis, because it is dependent
133
Considering the data in Table 20, suggest three improvements to the design of this experiment. For each improvement explain how it will increase the validity of the data collected.
134
Explain how the treatment results in the difference in the final lengths of rod A and rod E.
135
Explain how the treatment results in the difference in the final lengths of rod D and rod F.
136
State how the student could reduce the uncertainty of their data.
Use more precise apparatus
137
The students identified replicate 3 of the potato in 0.7 mol dm 3 sucrose as anomalous.
Suggest a practical error by the students that might have caused this result to be anomalous and explain the likely effect of this error.
inadequate drying
more mass / heavier (than other pieces) v
138
Use Table 16 to identify which plant cells contained the highest concentration of sucrose.
Justify your conclusion.
139
