2.5* Flashcards
(179 cards)
1
Q
What is a fluid mosaic model?
A
Theory of cell membrane structure with proteins embedded in a sea of phospholipids.
2
Q
What is a glycolipid?
A
Lipid/phospholipid with a chain of carbohydrate molecules attached.
3
Q
What is a plasma membrane?
A
A cell surface membrane.
4
Q
What is a glycoprotien?
A
protein with a chain of carbohydrate molecules attached.
5
Q
Cell membranes form a barrier to separate the cells contents from the cells or organelles exterior environment. How do molecules pass into, out of or through the membrane?
A
Some very small molecules diffuse straight through the cells membrane, in-between its structural molecules.
Some substances dissolve in the lipid layer and pass through.
Other substances pass through special protein channels or are carried by other proteins.
6
Q
How is the permeability of a membrane described and why?
A
Membranes are described as partially permeable, this is because they do not let all type of molecule pass though them.
The properties of the component molecules of the cell membrane determines its permeability, i.e. which molecules it allows pass through.
7
Q
What is the purpose of a plasma membrane?
A
Separates the cells components from its external environment.
Regulates transport of materials in and out of the cell.
May contain enzymes involved in specific metabolic pathways.
Has antigens so that the organism’s immune system can recognise the cell as being ‘self’ and not attack it.
May release chemicals to signal other cells.
Contains chemical receptors for such chemical signal, and so is a site for cell communication or signalling
8
Q
What a the inner membranes of mitochondria called and what is their purpose?
A
Mitochondria have inner folded membranes called cristae. These give a large surface area for some of the reactions of aerobic respiration and localise some of the enzymes needed for respiration to occur.
9
Q
What a the inner membranes of chloroplasts called and what is their purpose?
A
The inner membranes of chloroplasts, called thylakoid membranes, house chlorophyll. On these membranes some of the reactions of photosynthesis occur.
10
Q
Where and why is there some digestive enzymes on the plasma membranes.
A
There are some digestive enzymes on the plasma membrane of epithelial cells that line the small intestine, and these enzymes catalyse some of the final stages in the breakdown of certain types of sugars.
11
Q
Who proposed a model that allowed the passage of molecules through the membrane, and when?
A
In 1972 Singer and Nicolson proposed a model.
12
Q
What did the fluid mosaic model explain?
A
Their structure explained how cell membranes could be more dynamic and interact more with the cells environment. It was called the fluid mosaic model.
13
Q
What did the fluid mosaic model propose?
A
That the fabric of the membrane consisted of a phospholipid bi-layer (double layer) with proteins floating in it, making up a mosaic patten. The lipid molecules can change places with each other, and some proteins may move giving fluidity.
14
Q
In a membrane explain the two layers of phospholipid molecules.
A
The fabric of the membrane is the lipid bilayer made up of two layers of phospholipid molecules. Their hydrophilic heads are in contact with the watery exterior or watery interior (cytoplasm). The hydrophobic tail regions are in the centre of the membrane, away from the water.
15
Q
Name all the proteins in the fluid mosaic model.
A
Channel protein, peripheral protein, carrier protein (intrinsic) and extrinsic proteins.
16
Q
Give some extra detail on channel proteins.
A
Water-filled channel inside the channel protein is lined with hydrophobic heads and hydrophilic tails.
17
Q
How far do channel and carrier proteins span, explain.
A
Channel and carrier proteins span the whole lipid bilayer - they are integral proteins and their membrane-spanning regions interact with the hydrophobic region of the phospholipid bi-layer.
18
Q
Describe a phospholipid.
A
Their spherical phosphate head has a charge and is hydrophilic.
Their fatty acid tails (2) are hydrophobic.
19
Q
What is the purpose of the carbohydrate chain?
A
Carbohydrate molecules (glycocalyx) on the outside of the membrane are very hydrophilic and attract water with dissolved solutes, helping the cell interact with its watery environment and obtain dissolved substances.
20
Q
What is a carbohydrate chain called and what is its structure.
A
Glycoprotiens are carbohydrate chains attached to a protein molecule.
Glycolipids are carbohydrate chains attached to a lipid.
21
Q
What may an extrinsic protein act as?
A
Protein not spanning the lipid bilayer may act as an enzyme.
22
Q
How thick is a phospholipid bilayer.
A
about 7 nm in width.
23
Q
What maintains mechanical stability and flexibility?
A
Eukaryotic cell membranes contain cholesterol, which is important for helping to regulate the fluidity of the membrane, maintain mechanical stability and resist the effects of the temperature changes on the structure of the membrane.
24
Q
What is the top of a channel protein called?
A
A protein receptor site.
25
Spanning the membrane are various proteins, what are the different purpose's they serve?
Some of them have pores and act as channels to allow ions which have an electrical charge and are surrounded by water molecules, to pass through.
Some proteins are carriers and, by changing their shape, carry specific molecules across the membrane.
Other proteins may be attached to the carrier protein and function as enzymes, antigens or receptor sites for complimentary-shaped signalling chemicals such as hormones.
26
What is the total thickness of the cell membrane?
Between 5 and 10 nm
27
What is outside the cell membrane?
Outside the membrane is the glycocalyx - formed from the carbohydrate chains attached to either lipids (glycolipids) or proteins (glycoprotiens) in the membranes.
28
Do all membranes have the same composition?
No their membranes may have particular distributions of proteins in order to enable them to carry out their specific functions.
29
Describe the plasma membrane on a neurone.
In neurones (nerve cells) the protein channels and carriers in the plasma membrane covering the long wxon allow entry and exit of ions to bring about the conduction of electrical impulses along their length.
30
Describe the neurone sheath.
Neurones have a myelin sheath formed by flattened cells wrapped around them several times, giving several layers of cell membrane. The membrane forming the myelin sheath is about 20% protein and 76% lipid.
31
Describe the plasma membrane on a white blood cell.
The plasma membranes of white blood cells contain special protein receptors that enable them to recognise the antigens on foreign cells, usually from invading pathogens but also from tissue or organ transplants.
32
Describe the plasma membrane on a root hair cell.
Root hair cells in plants have many carrier proteins to actively transport nitrate iron
33
Describe the inner membranes of mitochondria.
The inner membranes of mitochondria are 76% protein and 24% lipid. This is because their inner membranes contain many electron carriers that are made of protein, and hydrogen ion channels associated with ATP synthase enzymes.
34
Why does eating glucose produce a quicker release of insulin than injecting it straight into the blood stream?
As well as cells in your pancreas having receptors to detect sugars, cells lining your intestines also have taste receptors for sugar.
35
Describe the process of discovering taste cells in the intestines.
For 50 years, scientists were mystified as to why eating glucose produces a quicker release of insulin than if glucose was injected straight into the blood stream, In 2007, they discovered that cells lining the intestines contain taste receptors for sugars, and when stimulated these cause a cascade of hormones that ultimately ends in release of extra insulin from the pancreas.
36
Are taste cells in the pancreas just a receptor for glucose?
In fact, these receptors also respond to artificial sweeteners, just as the receptors on your tongue so, so these sweeteners also cause a insulin surge.
37
Describe the permeability of cell membranes.
Cell membranes are partially permeable. This means that they allow some, but not all, substances to pass through. Substances may pass from inside the cell to the outside, or from the cell into its interior.
38
What is diffusion?
Movement of molecules from an area of high concentration or that molecule to an area of low concentration; it may or may not be across a membrane; it does not involve metabolic energy (ATP).
39
What is facilitated diffusion?
Movement of molecules from an area of high concentration of that molecule to an area of low concentration, across a partially permeable membrane via protein channels or carriers; it does not involve metabolic energy (ATP).
40
What do cells need to remove from their interior?
They need to remove the toxic metabolic waste products, such as carbon dioxide.
41
What raw materials do cells need to receive?
Biochemical processes that sustain life go on in cells. Cells therefore need to receive raw material or reactants for these reactions. They respire to make ATP, which provides cellular energy, to drive these biochemical reactions. Therefore they need oxygen and glucose.
42
What molecules do cells need to export?
They need to export some of the molecules that they make, such as enzymes, hormones or other signalling molecules.
43
Describe passive processes.
Some substances can pass across cell membranes without using any of the cells metabolic energy. These are described as passive processes because they use only the kinetic energy of the molecules and do not use ATP.
44
What happens when you have been active a long time concerning adenosine.
When you have been active a long time, a lot of ATP molecules are eventually broken down to adenosine. The build-up in concentration of adenosine eventually acts as a signal to part of your brain triggers you to feel sleepy.
45
What causes diffusion to work?
All molecules have kinetic energy and can move freely and randomly within a gas or liquid media. If there is a high concentration of a certain type of molecule in an area, then the molecules will bump into each other as they randomly move, and eventually they will spread further from each other. More will move to an area where they are in lower concentration, until eventually they become evenly dispersed.
46
All molecules have kinetic energy and can move freely and randomly within a gas or liquid media. Does the water need to be moving or disturbed for this to happen?
This will happen even if the medium is not mixed by stirring or shaking.
47
In diffusion what happens when molecules have moved down their concentration gradient?
When molecules have moved down their concentration gradient, they are still moving randomly but remain evenly dispersed so there is no net diffusion. They have reached equilibrium.
48
When there is a solute for example glucose in a higher concentration outside a cell than inside the cell what would the concentration gradient look like on a graph with concentration on the Y axis and outside to inside the cell on the X axis.
There is a high concentration of the molecules on one side of the membrane and a low concentration on the other side. The difference between them forms a gradient (slope). The steeper the slope, the faster the molecules will diffuse down that gradient.
49
What molecules can pass through the membrane by simple diffusion?
Some molecules such as oxygen and carbon dioxide, which are small, pass through cell membranes by simple diffusion.
50
How do fat-soluble molecules pass through the cell membrane?
Fat-soluble molecules such as steroid hormones, even if they are larger, can diffuse through the cell membranes as they dissolve in the lipid bilayer. They still move down their concentration gradient.
51
How does water pass through the lipid bi-layer?
Water molecules are a special case. Since they are polar and insoluble in lipid the phospholipid bi-layer would seem an impenetrable barrier. However, water is present in such great concentrations that significant direct diffusion does happen.
52
In membranes where a very high rate of water movement what might there be?
In membranes where a very high rate of water movement there may indeed be specific water channel proteins known aquaporins to allow water molecules to cross the membrane without the challenge of moving through a lipid environment.
53
How is the concentration gradient maintained within cells?
Many molecules entering cells then pass into organelles and are used for metabolic reactions; this maintains the concentration gradient and keeps more of the molecules entering the cell.
54
How is the concentration gradient of oxygen diffusing into the cytoplasm maintained?
Oxygen diffusing into the cytoplasm of respiring cells the diffuses into mitochondria and are used for aerobic respiration.
55
How is the concentration gradient of carbon dioxide diffusing into the palisade mesophyll maintained?
Carbon dioxide diffusing into the palisade mesophyll cells of a plant leaf will then diffuse into chloroplasts and be used for photosynthesis.
56
Factors that affect the rate of simple diffusion;
| What does diffusion rely on?
Simple diffusion relies on the molecules own kinetic energy, and so factors that alter this kinetic energy will affect the rate of diffusion.
57
Why is temperature a factor that affects simple diffusion?
As temperature increases, molecules have more kinetic energy, so their rate of diffusion will increase. Conversely, as they lose heat their rate of diffusion will slow down.
58
Why is diffusion distance a factors that affects the rate of simple diffusion?
The thicker the membrane across which molecules have to diffuse, the slower the rate of diffusion.
59
Why is surface are a factors that affects the rate of simple diffusion?
More diffusion can take place across a larger surface area. Cells specialised for absorption have extensions to their cell surface membranes, called microvilli. These increase the surface area.
60
Why is the size the of the diffusing molecule a factors that affects the rate of simple diffusion?
Smaller ions or molecules diffuse more rapidly than larger molecules.
61
Why is concentration gradient a factors that affects the rate of simple diffusion?
The steeper this gradient (the more molecules there are on one side of the membrane compared with the other side), the faster the diffusion to the side where there are fewer molecules, down the gradient.
62
How do you investigate factors that affect the rate of diffusion using universal indicator.
Using model cells to which you have added universal indicator solution.
63
What type of molecules pass through the cell membrane using facilitated diffusion? and why?
Small molecules that have polarity (opposite charges at either end of the molecule), such as ions that have electrical charge, are insoluble in lipid because they cannot interact with the hydrophobic tails of the lipid bi-layer This means that they diffuse through water filled protein channels (pores) embedded in the membrane.
64
How big are the water filled channel proteins (pores)?
0.8 nm in diameter.
65
Why facilitated diffusion is needed;
| What reduces the permeability of the membranes to small water soluble molecules?
Cholesterol molecules within the membrane.
66
How does glucose diffuse across the membrane?
Glucose molecules are too large to diffuse through the water filled protein channel in the membrane, but they can bind to a transmembrane carrier protein, which then opens to allow the glucose to pass out on the other side of the membrane. There are specific carrier proteins for different types of molecules.
67
How do cells us transmembrane proteins control the types of molecule that pass in or out?
Different cell types have membranes with differing proportions of transmembrane protein channels and transmembrane protien carriers. This allows cells to control he types of molecule that pass in or out.
68
What membranes have many channel proteins specific to either sodium or potassium ions an why?
Neurone plasma membranes have many channels specific to either sodium or potassium ions. The diffusion of these ions into and out of the neurone axon is crucial for the conduction of nerve impulses.
69
At synapses in the neurone what other ion channels may there exist in the plasma membrane?
At synapses (gaps between the neurones), there are also calcium ion channels and there may be chloride ion channels.
70
What ions channels would the plasma membrane on epithelial cells have and what purpose would this serve?
The plasma membrane of epithelial cells that line your airways have chloride ion channels, and these play a crucial role in regulating the composition of mucus to trap particles and pathogens.
71
What is osmosis?
The passage of water molecules down their water potential gradient, across a partially permeable membrane.
72
What is water potential?
A measure of the tenancy of water molecules to diffuse from one region to another.
73
In a solution, what is the liquid in which solute molecules are dissolved in called?
A solvent.
74
What is the solvent in an aqueous solution?
Water.
75
Can water pass directly through the phospholipid bilayer?
Yes.
76
What are channel proteins known as and what do they allow?
Some membranes also have protein channel known as aquaporins which allow water molecules to cross the membrane more rapidly.
77
Describe the substance both sides of the plasma membrane.
The inside of cells, the cytoplasm, contains water, and the external medium of cells is also watery - as cells are surrounded by extracellular tissue fluid. Water molecules also have kinetic energy and move randomly, but will spread out.
78
Where dos the net diffusion of water go from and to, and what makes it osmosis?
The net diffusion of water from a region where there are relatively more water molecules to a region where there are fewer water molecules, across a partially permeable membrane, is called osmosis.
79
Osmosis;
| What happens to water when solute molecules are added?
When solute molecules are added to water, the relative number of water molecules, in the resulting solution, is changed.
80
Osmosis;
| What happens to water when solute molecules dissociate into charged ions?
If the solute molecules dissociate into charged ions, such as sodium chloride dissociating into sodium ions and chloride ions, they exert more effect on the relative number of water molecules than do larger but non-polar molecules such as glucose.
81
Why do chloride ions and sodium ions exert more effect on the relative number of water molecules than do larger but non-polar molecules such as glucose?
This is because , as sodium chloride molecules dissociate into sodium ions and chloride ions, the number of particles in the solution doubles.
82
Describe the liquid that the net movement of diffusion would move away from by osmosis.
It would have a lower concentration of solute molecules.
| A higher concentration of free water molecules.
83
Describe the liquid that the net movement of diffusion would move to by osmosis.
Higher concentrations of solute molecules.
| Lower concentrations of free water molecules.
84
Why can osmosis be harmful to prokaryotic cells?
Prokaryotic cells are also subject to osmosis. Water molecules can enter or leave them across the partially permeable plasma membrane. If they loose enough water, then their metabolism cannot proceed and they cannot reproduce.
85
How can osmosis be used in food preservation?
Adding sugar or salt to preserve food prevents spoilage as any bacteria respire, grow or multiply as water is lost from the bacteria cells by osmosis.
86
What does antibiotic penicillin prevent?
The antibiotic penicillin prevents some types of growing bacteria from synthesising their peptidoglycan wall. This makes them vulnerable to the effect of osmosis. If they swell up as water enters, they will burst.
87
What is water potential a measure of?
the tenancy of water molecules to diffuse from on region to another.
88
What has the highest possible water potential?
Pure water.
89
What lowers water potential?
When solute molecules are added, they lower the water potential of the solution. The more solute molecules in the solution, the lower the water potential.
90
If two aqueous solutions are separated by a partially permeable membrane, such as a plasma membrane or a cell organelle membrane what water potential will water move from and to?
Water molecules will move from the solution with the higher water potential to the solution with the lower water potential.
91
What will happen to osmosis if and when the water potential on both sides of the membrane becomes equal?
There will be no net osmosis, although water molecules will continue to move randomly.
92
How should you describe the passage of water by osmosis?
In the context of differing water potential. Water moves via osmosis from a region of higher to lower water potential, down the water potential gradient.
93
What is water potential measured in?
Water potential is measured in kilo-pascals (KPa). Pure water has the highest water potential possible, and is given the value of 0 KPa.
94
As a solute is added what happens to the water potential of a solution?
As solute molecules are added, the water potential of the solution is lowered so, in numerical value, it becomes more negative. The more negative the value, the lower the water potential.
95
What happens to a water potential of 0 KPa as the water potential decreases?
Highest water potential 0 KPa -> lower water potential -10 KPa -> very low water potential -500 KPa.
96
What happens to pure water as the water potential decreases?
Pure water -> dilute solution -> concentrated solution
97
How does the amount of solute dissolved change as the water potential decrease?
No solute dissolved -> Small amount of solute dissolved -> large amount of solute dissolved.
98
What is the water potential inside cells?
The water potential within cells is lower than that of pure water, as there are solutes in solution. in the cytoplasm and inside the large vacuole of plant cells.
99
What happens when a cells are placed in a solution of higher water potential?
Water molecules move by osmosis, down the the water potential gradient, across the plasma membrane, into the cell.
100
How do you determine the water potential of potato-tuber cells?
If cells are immersed in a solution that has the same water potential as they do, then there is no net osmosis and the cells will neither swell nor shrink. They will not gin or loose any mass.
101
Describe and name what the bursting of an animal cell is?
In animal cells, if a lot of water molecules enter, the cell will swell and burst as the plasma membrane breaks. This is called cytolysis.
102
State the background of the term cytolysis.
The term cytolysis literally means splitting (lysis) of cells. This phenomenon was first observed in erythrocytes, and so it is often also called haemolysis, but scientists have since found that it occurs for all animal cells placed in a solution of higher water potential.
103
What will prevent bursting in a plant cell?
The rigid ad string cellulose wall.
104
How is a plant cell swelling up described?
The cell will swell up to a certain size when its contents push against the cell wall, which will resist any further swelling. The swollen cell is described as turgid.
105
What does the turgidity of a plant cell do?
It helps support plants, especially those that aren't woody.
106
What happens when cells are placed in a solution of lower water potential?
Water leaves the cells by osmosis, across the partially permeable plasma membrane.
107
What happens when a animal cells is placed in a solution of lower water potential?
Animal cells shrivel and are described as crenated.
108
How can you observe crenation in animal cells?
Using your own cheek cells, and applying a solution of low water potential.
109
How is it described when the cytoplasm of a plant cell shrinks?
The cytoplasm of plant cell shrinks and the membrane pulls away from the cellulose cell wall. The cells are described as plasmolysed. Plant tissue with plasmolysed cells is described as flaccid.
110
What do cells that are plasmolysed suffer?
A degree of dehydration and their metabolism cannot proceed, as enzyme-catalysed reactions need to be in solution.
111
When a plant and animal cell is put in pure water describe where water moves and what happens to the cell?
Water moved in by osmosis down a water potential gradient. An animal cell would burst open and become cytolysed however a plant cell prevents bursting. Membrane pushes against the wall - the cell is turgid.
112
When a plant and animal cell is put in a concentrated sugar solution describe where water moves and what happens to the cell?
Concentrated sugar solution has a very low water potential. Water moves out of cells by osmosis down a water potential gradient.
An animal cell shrinks and appears wrinkled - it is crenated.
A plant cell membrane pulls away from the cell wall as water leaves - the cell is plasmolysed.
113
How would you observe plasmolysis in plant cells?
Use epidermis cells from red onions, as the cytoplasm will be more easily observed, without any staining, under the optical microscope.
114
Define active transport?
the movement of substances against their concentration gradient (from low to high concentration of that substance) across a partially permeable membrane, using ATP and protein carriers.
115
What is endocytosis?
Bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins, into a cell.
116
What is exostosis?
Bulk transport of molecules, too large to pass through a cell membrane even via channel or carrier proteins, out of a ell.
117
When is active transport used?
Sometimes cells need to move certain substances in or out, across their plasma membranes, against each substances concentration gradient.
118
Describe the energy needed in active transport.
Active transport is like swimming agianst the tide and needs more energy than the genetic energy of the molecules.
This energy is provided by hydrolysis of ATP. ATP is often described as the universal energy currency, as all cells make use of it to supply their energy needs.
119
Give some examples of where active transport may be used.
Cells or organelles may ned to accumulate more of a particular ion than they could do by simple or facilitated diffusion alone. For example, root hair cells use active transport to absorb ions from the soil.
120
Describe how an transport protein called an antiport carriers two different types of ions in opposite directions.
Using ions sodium and potasium.
Three sodium ions bind to a specific site outside the cell on a sodium potassium pump protein.
ATP binds to its site, and is hydrolysed to ADP + P releasing energy.
Two potassium ions bind to their specific site.
The energy released from the hydrolysis of ATP enables the sodium-potassium pump protein to change its shape so that the three sodium ions are now on the outside of the cell and the two potassium ions are inside the cell.
121
State the physical properties of a carrier protien.
These membrane proteins have specific regions, or sites, that combine reversibly with inly certain solute molecules or ions.
They also have a region that binds to and allows the hydrolysis of a molecule of ATP, to release energy, and in this way they act as enzymes.
122
Why is energy needed by carrier proteins?
The energy helps the carrier protein change its conformation (shape), and in doing so it carries the ion from one side of the cell membrane to the other.
123
Give an example of where carrier proteins are needed?
For example, in guard cells ATP made by chloroplasts provides energy to actively transport potassium ions from surrounding cells into the guard cells. This influx of ions lowers the water potential in the guard cells, so that water enters from surrounding cells, by osmosis. As the guard cells swell, their tips bulge and this opens the stoma between them.
124
What is bulk transport of molecules in cells?
Some cells need to transport large molecules and particles that are too large to pass through the plasma membrane, in or out. They do this by bulk transport, a process that requires energy from ATP.
125
What kind of particles pass into the cell in endocytosis?
This is how large particles may be brought into a cell.
126
How do particles pass into the cell in endocytosis?
They do not pass through the plasma membrane. Instead, a segment of the plasma membrane surrounds and encloses the particle and brings it into the cell, enclosed in a vesicle.
127
What is the type of endocytosis that means 'eating by cells' and refers to this type of intake of solid.
Phagocytosis
128
What is it called when cells ingest liquids by endocytosis.
This is called pino(endo)cytosis.
129
Glycoproteins are hydrophilic, how does this help them achieve their purpose?
Glycoproteins are hydrophilic and thus attracts water with dissolved solutes. This helps bring dissolved substances into the cell which it requires.
130
How do glycoproteins allow cell-cell adhesion?
They may hook together with the glycoproteins of another cell.
131
Describe endocytosis in three stages.
A phagocytic cell e.g. amoeba or a neutrophil, approaches a bacterium.
The cell extends to surround the bacterium.
The bacterium is now enclosed within a phagocytic vesicle, a phagosome.
132
Is ATP needed in endocytosis and why?
ATP is needed to provide energy to form vesicles and move them, using molecular motor proteins, along cytoskeleton threads into the cell interior.
133
How does exocytosis work?
This is how large molecules may be exported out of cells. They do not pass through the plasma membrane. Instead , a vesicle containing them is moved towards and then fuses with the plasma membrane.
134
Explain exocytosis at the synapses.
Another example is seen at synapses (gaps between neurones), where chemicals in vesicles are moved, by motor proteins moving along cytoskeleton threads, to the presynaptic membrane. Here, the vesicles membranes and plasma membranes fuse and the neurotransmitter chemicals are released into the synaptic cleft.
135
Is ATP needed in exocytosis and why?
In all cases, ATP is needed to fuse the membranes together as well as for moving the vesicles. A molecule of ATP is hydrolysed for every step that a motor protein takes along the cytoskeleton thread, as it drags its cargo - the vesicle.
136
If you were describing exocytosis in three steps what would the first step be?
A membrane-bound vesicle, containing the substance to be secreted, is moved towards the cell surface membrane.
137
If you were describing exocytosis in three steps what would the second step be?
The cell surface membrane and the membrane of a vesicle fuse together.
138
If you were describing exocytosis in three steps what would the third step be?
The fused site opens, releasing the contents of the secretory vesicle.
139
In your blood how are fatty plaques formed?
Macrophages ingest certain fats that are in your blood. They 'eat themselves to death' and become foam cells, sinking into the lining of the blood vessels and firming fatty plaques.
140
What is pus?
At a wound site, you may have noticed white pus. This consists mainly of dead phagocytic white blood cells have ingested invading bacteria and also eaten themselves to death.
141
How does increasing temperature change kinetic energy?
Increasing temperature gives all molecules more kinetic energy, and as a result these molecules move faster.
142
How does decreasing temperature change kinetic energy?
Decreasing temperature lowers the kinetic energy of the molecules, causing them to move more slowly.
143
Do all organisms create heat?
Many organisms do not generate heat to maintain their body temperature and so their temperature varies with their environment.
144
What happens to saturated fatty acids when the temperature drops.
Saturated fatty acids become compressed.
145
How does the cell membrane maintain its fluidity when the temperature drops?
There are many unsaturated fatty acids making up the cell membrane phospholipid bilayer, and as they become compressed the kinks in their tails push adjacent phospholipids molecules away. The maintains the membrane fluidity.
146
What determines the membranes fluidly at cold temperatures?
The proportions of unsaturated and saturated fatty acids within a cell membrane.
147
What does cholesterol in the cell membrane do to the effect of a lowered temperature.
Cholesterol buffers the effect of lowers temperature, to prevent a reduction in the membranes fluidity.
148
How does cholesterol buffer the effect of lowered temperature?
By preventing the phospholipid molecules from packing together too closely, because cholesterol molecules are in between groups of phospholipids molecules.
149
What organisms can change the composition of what in their cell membranes in response to lower temperatures.
Organisms such as some fish, some microorganisms and some plants can change the composition of the fatty acids in their cell membranes in response to lower temperatures.
150
What happens to phospholipids when the temperature increases?
The phospholipids acquire more kinetic energy and move around more, in a random way. This increases the membrane fluidity.
151
What happens to the permeability of cell membranes as the temperature increases?
The permeability increases.
152
Why would the rate of the reactions enzymes in the cell membrane catalyse be affected by temperature?
Increasing temperature also affects the way membrane-embedded proteins are positioned and may function. If some of the proteins that act as enzymes in a membrane drift sideways, this could alter the rate of the reactions they catalyse.
153
When temperature increases how may phagocytosis be affected?
An increase in membrane fluidity may affect the infolding of the plasma membrane during phagocytosis.
154
When temperature increases how may cells signalling change?
An increase in membrane fluidity may also change the ability of cells to signal to other cells by releasing chemicals often by exocytosis.
155
What buffers increasing heat in cell membranes?
The presence of cholesterol molecule buffers, to some extent the effect of increasing heat as it reduces the increase in membrane fluidity.
156
What does changing temperature do to the movement of phospholipids and their integral structure.
Whereas changing temperature can alter the movement of phospholipids, it does not drastically alter their integral molecular structure.
157
What happens to proteins at higher temperatures?
High temperatures cause the atoms within their large molecules to vibrate, and this breaks the hydrogen bonds and ionic bonds that hold their structure together - they unfold.
158
What is denaturing?
Their tertiary structure (shape) changes and cannot change back again when they are cool - they are denatured.
159
What is just underneath the plasma membrane?
The cytoskeleton threads.
160
What will cause the membrane to become more permeable and holes to appear?
If both the membrane-embedded proteins and the cytoskeleton threads become denatured, then the plasma membrane will begin to fall apart. It will become more permeable as holes will appear in it.
161
What will cause the the rate of the reactions that they catalyse to be slowed?
Membrane-embedded enzymes will cease to function if they become denatured. If the shape of their active sight changes slightly or the enzymes moe within the membrane, the rate of the reactions that they carat jaw will be slowed.
162
The effect of temperature on beet root cell membranes;
| What is inside beetroot cells?
Inside beetroot cells, within the large vacuole that is bound by a tonoplast membrane are nitrogenous, water-soluble pigments called betacyanins, a type of betalain.
163
What experiment could you conduct about the effect of temperature on beet root cell membranes.
If you heat pieces of beetroot tissue, the plasma membrane and tonoplast membrane will be disrupted and the pigment will leak out.
The amount of leakage of the red pigment is proportional to the degree of damage to the beetroot plasma and tonoplast membranes, and can be measured using a colorimeter, by measuring the absorbance of green light (wavelength range 530 - 550 nm)
164
What solvents will damage cell membranes and dissolve lipids.
Organic solvents such as acetone and ethane will damage cells cell membrane as dissolve lipids.
165
Using an investigation the effect of chemicals on beetroot cells membrane what is the first step of designing the experiment.
Betalain pigments do not change as pH changes.
1. Design your investigation - you may wish to use the solvents at different concentrations. This may involve doing a serial dilution of a stock solution. Write a list of the equipment that you will need.
166
Using an investigation the effect of chemicals on beetroot cells membrane what is the second step of designing the experiment.
Make a prediction that you can test.
167
Using an investigation the effect of chemicals on beetroot cells membrane what is the third step of designing the experiment.
State the independent variable, dependant variable and control variables.
168
Using an investigation the effect of chemicals on beetroot cells membrane what is the fourth step of designing the experiment.
Carry out the investigation. Record your data and suggest an explanation for your results.
169
Using an investigation the effect of chemicals on beetroot cells membrane what is the fifth step of designing the experiment.
You may also investigate the effect of detergents, dilute acids, such as hydrochloric acid, and alkalis, such as sodium hydroxide, on the structure and permeability of beetroot cell membranes.
170
What can heat cause to a protein molecule?
Heat breaks some if the bonds that hold a proteins tertiary structure in place. The molecules vibrate as they acquire energy, breaking the hydrogen bonds.
171
What bonds in a protein is not broken by heat?
Disulphide bonds.
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What are disulphide bonds in protein broken by?
By strong reducing agents.
173
What does not break the peptide bonds between amino acids?
Vibrations of the protein molecules.
174
The heat shock pathway;
| What triggers the expression of genes to make heat shock pathways?
In some plants, the plasma membrane acts as a heat sensor. When proteins in the membrane begin to denature, this triggers the expression of genes to make heat shock proteins.
175
The heat shock pathway;
| What are heat shock proteins?
These are chaperone proteins that bind to misshapen proteins, preventing further misfolding.
176
The heat shock pathway;
| How is the heat signalling pathway triggered in plant cells?
By an influx of calcium ions, caused by the opening of calcium ion channels in plasma membranes when plant cells are subject to mild heat.
177
The heat shock pathway;
| What can a calcium ion influx do in bacteria.
In bacteria a calcium ion influx can increase membrane fluidity.
178
The heat shock pathway;
| In bacteria a calcium ion influx can increase membrane fluidity. How can scientists make use if this?
When genetically modifying fluidity, they give the bacteria more calcium ions and subject them to heat shock (exposure to 0•C followed by exposure to 40•C). This increases the influx of calcium ions and the chance of bacteria taking up DNA.
179
What can betacyanin pigments do, and why. (Arteries)
The betacyanin pigments, e.g. betanin, in beetroot help to lower your blood pressure. This is because they are nitrogenous compounds and stimulate the linings of your arteries to produce nitric oxide, which dilates arteries and reduces blood pressure.
