Section 2 - Transport across cell membranes Flashcards
(138 cards)
1
Q
What is the name given to membranes around and within all cells?
A
Plasma membranes
2
Q
What does the cell-surface membrane surround?
A
This surrounds the cell and forms a boundary between the cell cytoplasm and the environment
3
Q
What is the function of the cell-surface membrane?
A
It allows different conditions to be established inside and outside a cell. It also controls the movement of substances in and out of the cell.
4
Q
Why is the phospholipid bilayer important in the cell-surface membrane?
A
- The hydrophilic heads of both phospholipid layers point to the outside of the cell-surface membrane attracted by water on both sides - The hydrophobic tails of both phospholipid layers point into the centre of the cell membrane, repelled by the water on both sides
5
Q
What is the function of phospholipids in the membrane?
A
- Allows lipid-soluble substances to enter and leave the cell - Prevent water-soluble substances entering and leaving the cell - Make the membrane flexible and self sealing
6
Q
What are the main ways that proteins are embedded in the phospholipid bilayer?
A
- some proteins occur in the surface of the bilayer and never extend completely across it. They act either to give mechanical support to the membrane or, in conjunction with glycolipids, as cell receptors for molecules such as hormones - Other proteins completely span the phospholipid bilayer from one side to the other. Some are protein channels, which form water-filled tubes to allow water-soluble ions to diffuse across the membrane. Others are carrier proteins that bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane.
7
Q
What are carrier proteins?
A
They bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane.
8
Q
What are the functions of proteins in the membrane?
A
- provide structural support - act as channels transporting water-soluble substances across the membrane - Allow active transport across the membrane through carrier proteins - form cell-surface receptors for identifying cells - help cells adhere together - act as receptors, for example for hormones
9
Q
Where is cholesterol found?
A
Cholesterol molecules occur within the phospholipid bilayer of the cell-surface membrane
10
Q
What is the structure of cholesterol?
A
The molecules are very hydrophobic and so plays an important role in preventing loss of water and dissolved ions from the cell.
11
Q
What is the function of cholesterol in the membrane?
A
- Reduce lateral movement of other molecules including phospholipids - Make the membrane less fluid at high temperature - Prevent leakage of water and dissolved ions from the cell
12
Q
Why does cholesterol Pull together the fatty acid tails of the phospholipid molecules ?
A
limiting their movement and that of other molecule but without making the membrane as a whole too rigid
13
Q
What are glycolipids made of?
A
a carbohydrate covalently bonded with a lipid
14
Q
What does the carbohydrate do in the glycolipids?
A
It extends from the phospholipid bilayer into the watery environment outside the cell where it acts as a cell-structure receptor for specific chemicals eg. the human ABO blood system
15
Q
What are the functions of glycolipids in the membrane?
A
- act as recognition sites - help maintain the stability of the membrane - help cells to attach to one another and so form tissues
16
Q
What are carbohydrate chains attached to?
A
Many extrinsic proteins on the outer surface of the cell membrane. They also act as cell-surface receptors and more specific for hormones and neurotransmitters
17
Q
What is the function of glycoproteins in the membrane?
A
- Act as recognition sites - Help cells to attach to one another and so form tissues - Allows cells to recognise one another, eg. Lymphocytes
18
Q
What do lymphocytes do?
A
Can recognise an organism’s own cells
19
Q
Why can molecules not freely diffuse across the membrane?
A
- Not soluble in lipids and therefore cannot pass through the phospholipid layer - Too large to pass through the channels in the membrane - Of the same charge as the charge on the protein channels and so, even if they are small enough to pass through, they are repelled - Electrically charged (in other words polar) and therefore have difficulty passing through the non-polar hydrophobic tails in the phospholipid bilayer
20
Q
Define - polar
A
An electrically charged molecule
21
Q
Give an example of a non-polar molecule
A
hydrophobic tails in the phospholipid bilayer
22
Q
Why is the arrangement of molecules called the fluid-mosaic model?
A
- Fluid because the individual phospholipid molecules can move relative to one another. This gives the membrane a flexible structure that is constantly changing in shape. - Mosaic because the proteins that are embedded in the phospholipid bilayer vary in shape, size and pattern in the same way as the stones or tiles of a mosaic
23
Q
What are the functions of membranes within cells?
A
- Control the entry and exit of materials in discrete organelles such as mitochondria and chloroplast - Separate organelles from cytoplasm so that specific metabolic reactions can take place within them - Provide an internal transport system - Isolate enzymes that might damage the cell - Provide surfaces on which reactions can occur
24
Q
Give an example of a system that provides an internal transport system
A
Endoplasmic reticulum
25
Give an example of a system that provides isolation for enzymes that might damage the cells.
Lysosomes
26
Give an example of a molecule that provides a surface on which reactions can occur
Protein synthesis using ribosomes on rough endoplasmic reticulum
27
Give an example of a passive transport
- Diffusion - Osmosis
28
Give an example of an exchange between cells and the environment that occurs in ways of requiring metabolic energy
active transport
29
Define - Active Transport
The exchange of substances between cells and the environment occurring in ways that require metabolic energy.
30
What does passive mean in turns of transport?
The energy comes from a natural, inbuilt motion of particles, rather than from some external source such as ATP.
31
Define - Diffusion
The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed
32
Give two examples of non-polar molecules that can diffuse across membranes
- Oxygen - Carbon Dioxide
33
Why don't polar molecules diffuse easily?
The hydrophobic nature of the fatty acid tails of the phospholipids in the membrane.
34
How is movement in diffusion made easier?
Transmembrane channels and carriers that span the membrane. This is called facilitated diffusion.
35
What is facilitated diffusion?
- Transmembrane channels and carriers that span the membrane. - A passive process - Relies only on the in bulit motion (Kinetic energy) of the diffusing molecules. - Occurring down the concentration gradient - Either using protein channels or carrier proteins.
36
State the two types of proteins used in facilitated diffusion
- Protein channels - Carrier Proteins
37
What do protein channels produce?
- Water-filled hydrophilic channel across the membrane
38
What do protein channels allow through?
Specific water soluble ions to pass through
39
Explain the structure of protein channels
- They are selective and each opening in the presence of a specific ion - If this specific ion is not present the channel will remain closed - This gives them control over the entry and exit of ions to the cell - The ions bind with the protein causing it to change shape in a way that closes it to one side of the membrane and opens it to the other side
40
How do protein channels open and close?
The ions bind with the protein causing it to change shape in a way that closes it to one side of the membrane and opens it to the other side
41
What are carrier proteins?
- A form of facilitated diffusion - Spanning the plasma membrane
42
Explain how a carrier protein may react to the presence of glucose
If it is specific to the protein it binds with the protein causing it to change shape in such a way that the molecule is released to the inside of the membrane. No external energy is used for this using only the kinetic energy of the molecules themselves.
43
Define - Osmosis
The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane
44
What is meant by selectively permeable?
They are permeable to water molecules and a few other small molecules but not to larger molecules.
45
What is a solute?
Any substance that i dissolved in a solvent eg. water.
46
What makes up a solution?
A solute and the solvent.
47
How can you represent water potential?
Greek Letter Psi
48
What is water potential measured in?
Units of pressure KiloPascals (kPa)
49
What is water potential?
The pressure created by water molecule.
50
Under what conditions does pure water have a water potential of zero
Under standard conditions of temperature and pressure 25\*C and 100kPa
51
What can lower pure water's water potential?
Adding a solute
52
What does adding a solute do to pure water's water potential?
Lower's the water potential
53
What is the rule of water potential?
The water potential of a solution must always be less than zero. A negative value
54
Explain osmosis in terms of water potential
Water will move by osmosis from a region of higher (less negative) water potential (eg. -20kPa) to one of lower (more negative) water potential (eg. -30kPa)
55
How can you find the water potential of cells or tissue?
To place them in series of solutions of different water potentials. Where there is no net gain or loss of water from the cells or tissues, the water potential inside the cells or tissues must be the same as that of the external solution.
56
Explain the osmosis in a hypothetical of which a selectively permeable plasma membrane separates two solutions.
- A place with lower concentration of solute molecules while the solution on the right has a high concentration of solute molecules. - Both the solute and water molecules are in random motion due to their kinetic energy. - The selectively permeable plasma membrane, however, only allows water molecules across it and not solute molecules. - The water molecules diffuse from the place of higher water potential - lower concentration - to the lower water potential side - higher concentration - that is down a water potential gradient - At the point where the water potentials on either side of the plasma membrane are equal, a dynamic equilibrium is established and there is no net movement of water.
57
Give an example of a cell that contains a variety of solutes dissolved in their watery cytoplasm
Red blood cells - Animal
58
What will happen when red blood cells are placed in pure water?
It will absorb water by osmosis because it has a lower water potential.
59
What is the width of a cell surface membrane?
7 nm They are flexible and cannot stretch to any great extent.
60
What will happen when there are water goes into a cell surface membranes?
Will break, bursting the cell and releasing its content (in red blood cells this is called haemolysis).
61
What is the specific name for when red blood cells rupture?
haemolysis
62
What is haemolysis?
The rupture or destruction of red blood cells.
63
How can you prevent cells from rupturing?
Animal cells normally live in a liquid which has the same water potential as the cells. Eg. the liquid in the blood plasma. As this and the red blood cell has the same water potential.
64
What is the protoplast in a plant cell?
Consisting of the outer cell-surface membrane, nucleus, cytoplasm and inner vacuole membrane. This is what changes when the water potential also changes.
65
What happens when plant cells are placed in pure water?
They absorb water by osmosis due to their lower water potential.
66
What happens if a plant cell is in a solution with a higher water concentration than its own?
The plant cells are unable to control the composition of the fluid around their cells. Indeed, plant cells are normally permanently bathed in almost pure water, which is constantly absorbed from the plants roots. This causes the protoplast to swell and press on the cell wall. The cell wall is capable of very little expansion and the pressure builds which resists the entry of further water, The cell is Turgid
67
What happens if a plant cell is in a solution with a lower water concentration than its own?
Water will leave by osmosis. The volume of the cell decreases. A stage is reached where the protoplast in no longer pressing on the cellulose cell wall. At this point the cell is knowledge to be at incipient plasmolysis. Further loss of water will cause the cell contents to shrink and further pull the protoplast away from the cell wall this is known as plasmolysed.
68
What does incipient plasmolysis mean?
The point at which - where the protoplast in no longer pressing on the cellulose cell wall.
69
What can happen after incipient plasmolysis?
Further loss of water will cause the cell contents to shrink and further pull the protoplast away from the cell wall this is known as plasmolysed.
70
When is a plant cell turgid?
When too much water has been pulled into the cell
71
What is plasmolysed for a plant cell?
Further loss of water will cause the cell contents to shrink and further pull the protoplast away from the cell wall
72
Define - Active transport
The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins.
73
What does active transport use?
ATP and carrier proteins
74
What is ATP used for in active transport?
- The direct movement of molecules - Individually move molecules using a concentration gradient which has already been set up by (direct) active transport. This is known as co-transport
75
What is co-transport?
Individually move molecules using a concentration gradient which has already been set up by (direct) active transport.
76
How does active transport differ from other forms of transport?
- Metabolic energy in the form of ATP is needed. - Substances are moved against a concentration gradient that is from a lower to a higher concentration. - Carrier protein molecules which act as 'pumps' are involved - The process is very selective, with specific substances being transported.
77
What is the metabolic energy used in active transport?
ATP
78
Describe the process of direct active transport of a single molecule or ion
- The carrier protein span the plasma membrane and bind to the molecule or ion to be transported on one side of it. - The molecule or ion binds to receptor sites on the carrier protein. - On the inside of the cell/organelle, ATP binds to the protein, causing it to split into ADP and phosphate molecule. As a result the protein molecule changes shape and opens to the opposite side of the membrane. - The molecule or ion is then released to the other side of the membrane. - The phosphate molecule is released from the protein which causes the protein to revert to its original shape, for the process to be repeated. The phosphate molecule then recombines with the ADO to form ATP during respiration.
79
What is the difference between active transport and facilitated diffusion?
Both use carrier proteins but facilitated diffusion occurs down the concentration gradient while active transport occurs against a concentration gradient. This means the facilitated diffusion does not require metabolic energy while active transport does.
80
Give an example of when molecules move at the same time as a different one is being removed from it in terms of active transport
Sodium-potassium pump
81
What happens in the sodium-potassium pump?
Sodium ions are actively removed from the cell/organelle while potassium ions are actively taken in from the surroundings. This process is essential to a number of important processes in the organism including the creation of a nerve impulse.
82
Why is the sodium-potassium pump so important?
This process is essential to a number of important processes in the organism including the creation of a nerve impulse.
83
What does the epithelial cells lining possess?
Microvilli
84
What are microvilli?
Finger-like projections of the cell-surface membrane about 0.6um in length.
85
What is the collective term of microvilli?
Brush border
86
Why are the collective microvilli called brush borders?
When viewing them under a light microscope they look like the bristles of a brush
87
What do microvilli do?
provide more surface area for the insertion of carrier proteins through which diffusion, facilitated diffusion and active transport can take place.
88
How can you increase transport across membranes?
Increase the number of microvilli Increase the number of carrier proteins and protein channels in the membrane.
89
What molecules are continually digested?
Carbohydrates and proteins
90
What substances are always in the ileum?
Glucose and amino acids
91
How does glucose get into the ileum from the blood?
Facilitated diffusion A concentration gradient down
92
Why is glucose continually being removed by the cells?
Blood is continually being circulated by the heart.
93
What does a high concentration gradient mean?
The rate of movement by facilitated diffusion across epithelial cell-surface membranes is increased.
94
Define - Antigen
A toxin or other foreign substance which induces an immune response in the bod
95
Describe what happens to the pathogen once it is engulfed into a vesicle by a phagocyte.
Vesicle fuses with phagosome, lysosomes release hydrolytic enzymes into phagosome to digest the pathogen
96
State two responses that are part of the specific immune system
- Cell-mediated response - Humoral response
97
Vesicle fuses with phagosome, lysosomes release hydrolytic enzymes into phagosome to digest the pathoge
Passive
98
B cells are associated with what type of immunity
Humoral immunity
99
Are antibodies received in breast milk active or passive immunity
Passive
100
What is the reason why the flu vaccine has to change every year
Antigenic variability
101
What can T cells differentiate into?
Helper cells Cytotoxic cells
102
What do B cells differentiate into?
Plasma cells Memory cells
103
State two processes associated with non-specific immune system
Physical barrier Phagocytosis
104
Are vaccinations active or passive immunity
Active
105
T cells are associated with what type of immunity?
Cell-mediated immunity
106
When do cells use glucose?
respiration
107
What helps to maintain the concentration gradient between the indie of the ileum and the blood?
Given that the blood is constantly being circulated by the heart, the glucose absorbed in it is continually being removed by the cells as they use it up during respiration.
108
What is the process by which glucose and amino acids are absorbed by the small intestine?
co-transport
109
Explain the co-transport of glucose and sodium going into the blood from the ileum
1. Sodium ions are actively transported out of epithelial cells, by the sodium-potassium pumps, into the blood. This takes place in one type of protein-carrier molecule found in the cell-surface membrane of the epithelial cells. 2. This maintains a much higher concentration of sodium ions in the lumen of the intestine than inside the epithelial cells 3. Sodium ions diffuse into the epithelial cells down this concentration gradient through a different type of protein carrier (co-transport protein) in the cell-surface membrane. As the sodium ions diffuse in through this second carrier protein, they carry either amino acid molecules or glucose molecules into the cell with them. 4. The glucose/amino acids pass into the blood plasma by facilitated diffusion using another types of carrier.
110
How does sodium ions get out of the epithelial cells and into the blood?
actively transported out of epithelial cells, by the sodium-potassium pumps, into the blood.
111
What process does glucose use to pass into the blood plasma?
Facilitated diffusion
112
What powers the movement of glucose and amino acids into the cells?
The sodium ion concentration gradient rather than ATP. Making it indirect rather than a direct form of active transport
113
What type of active transport is the movement of glucose and amino acids into the cells?
Indirect active transport
114
State the treatment to prevent death from diarrhoea
Oral rehydration therapy
115
What is diarrhoea?
An intestinal disorder where watery faeces are produced frequently.
116
What is the cause of diarrhoea?
- damage to the epithelial cells lining the intestine - Loss of microvilli due to toxins - Excessive secretion of water due to toxins for example cholera toxin
117
Give an example of a toxin that causes diarrhoea
Cholera toxin
118
what happens as a result of diarrhoea?
Insufficient fluid is taken into, and/or excessive fluid is lost from, the body. Either way, dehydration results and may be fatal
119
How can you treat diarrhoea diseases?
- A drip - requires trained personnel and means the patient is confines to bed for much of the time.
120
Why does drinking water not help treat diarrhoea?
- Water is not being absorbed from the intestine - indeed as in the case of cholera, water is actually being lost from calls - Drinking water does not replace the electrolytes (ions) that are being lost from the intestinal cells
121
Diarrhoea - How does a patient become rehydrated if the intestine is not absorbing water?
There is more than one type of carrier protein in the plasma membranes of epithelial cells that absorb sodium ions. Trick to develop a rehydration solution that uses these alternative pathways. Sodium ions absorbed so water potential of cells falls and water enters the cells by osmosis.
122
What does the diarrhoea rehydration solution need to contain?
Water Sodium ions Glucose Potassium ions Other electrolyse - eg. chloride and citrate ions
123
What is water needed to treat someone from diarrhoea?
To rehydrate the tissues
124
What is sodium ions needed to treat someone from diarrhoea?
To replace the sodium ions lost from the epithelium of the intestine and to optimise use of the alternative sodium-glucose carrier proteins
125
What is glucose needed to treat someone from diarrhoea?
To stimulate the uptake of sodium ions from the intestine and to provide energy
126
What is potassium ions needed to treat someone from diarrhoea?
To replace lost potassium ions and to simulate appetite
127
What are other electrolyes needed to treat someone from diarrhoea?
Such as chloride ions and citrate ions to help prevent electrolyte imbalance and a condition called metabolic acidosis.
128
What do oral rehydration solutions do?
They do not prevent or cure diarrhoea. They simply rehydrate and nourish the patient until the diarrhoea is cured by some other means
129
What is a homemade remedy for diarrhoea?
8 level teaspoons of sugar 1 level teaspoon of table salt Dissolved in 1 litre of boiled water
130
Why was the early treatments of diarrhoea not effective?
Led to side effects especially in children. Caused by excess sodium. So tried more glucose but this reduced water potential in lumen so more water was drawn of the epithelial cells. But glucose was needed as a respiratory substrate and reduced the amount of energy being supplied to the patient.
131
Why is starch better for diarrhoea than water?
Starch is broken down steadily by amylase and maltase in the ileum into its glucose monomers It releases glucose as the optimum rate to be taken up as it is produced.
132
What enzymes break down starch in the ileum?
amylase and maltase
133
Why is rice starch so popular in diarrhoea treatment?
- readily available in many parts of the world, especially those where diarrhoeal diseases are common - Provides other nutrients like amino acids. Keeping the uptake of sodium ions from the ileum.
134
Why did rice flour hard to swallow?
Produces a very viscous solution
135
Explain how testing is normally carried out
- Small number of healthy people - Larger of those with the condition the drug is aimed at - Large scale with placebos - If passed each stage they can be licensed.
136
Why are drugs first tested by .a small number of healthy people?
20-80 people Test for side effects. Dose may be increased gradually during the trials over around 6 months
137
Why are drugs tested by a slightly larger number of people with the condition being tested for?
100-300 See if the drug works and look as any safety issues take up to 2 years
138
Why are drugs tested in a large-scale trial with placebos?
Double blind trials take many years
