Cells Flashcards
• Cell structure • Transport across cell membranes • Cell recognition and the immune system
1
Q
What is the maximum resolution of a light microscope?
A
2x10^-7 m
2
Q
What is the limitation with light microscopes?
A
The relatively long wavelength of light
3
Q
What is the resolution of an electron microscope?
A
1x10^-10 m
4
Q
What is the material put under the microscope called?
A
The object
5
Q
What is the appearance of the object when viewed under a microscope called?
A
The image
6
Q
What is the magnification?
A
How many times bigger the image is when compared to the object
7
Q
How do you work out magnification?
A
Magnification = Size of image / Size of real object
8
Q
What is the resolution of a microscope?
A
The minimum distance apart that two objects can be in order for them to appear as separate items
9
Q
What is the resolving power of a microscope?
A
The minimum distance apart that two objects can be in order for them to appear as separate items
10
Q
What does greater resolution do to an image?
A
Greater image clarity
11
Q
What does greater magnification do to an image?
A
Increases the size of the image
12
Q
What happens to the image if you increase magnification beyond the limit of resolution?
A
The image will be larger, but more blurred
13
Q
What is cell fractionation?
A
The process where cells are broken up and the different organelles they contain are separated out
14
Q
What three things must the solution in which the tissue is placed be for cell fractionation?
A
Cold
Isotonic
Buffered
15
Q
Why must you use a cold solution to place the tissue in for cell fractionation?
A
To reduce enzyme activity that might break down organelles
16
Q
Why must you use an isotonic solution to place the tissue in for cell fractionation?
A
To prevent organelles bursting or shrinking as a result of osmotic gain or loss of water
17
Q
Why must you use a buffered solution to place the tissue in for cell fractionation?
A
So that pH doesn’t fluctuate
18
Q
Why must the pH remain constant for cell fractionation?
A
Any change in pH could alter the structure of organelles or affect the functioning of enzymes
19
Q
What are the two stages in cell fractionation?
A
Homogenation
Ultracentrifugation
20
Q
What happens in homogenation?
A
Cells broken up by homogeniser Resultant fluid (homogenate) is filtered
21
Q
Why are cells broken up by a homogeniser in homogenation?
A
To release the organelles from the cells
22
Q
Why is the homogenate filtered in homogenation?
A
To remove any complete cells and large pieces of debris
23
Q
What is ultracentrifugation?
A
The process by which fragments in the filtered homogenate are separated in a centrifuge
24
Q
What does a centrifuge do?
A
Spins tubes of homogenate at very high speed in order to create a centrifugal force
25
In ultracentrifugation what speed do you start to spin at?
The lowest, working up to highest after removing the sediment/pellet
26
After a sample has been spun in a centrifuge, what is the fluid at the top of the tube called?
Supernatant
27
After a sample has been spun in a centrifuge, what is the layer at the bottom of the tube called?
The sediment or pellet
28
In ultracentrifugation, which part of the sample is spun again at a higher speed?
Supernatant
29
In animal cells, what are the first three organelles to form sediment (in order)?
Nuclei
Mitochondria
Lysosomes
30
In plant cells what are the first three organelles to form sediment (in order)?
Nuclei
Chloroplasts
Mitochondria
31
What is the speed of centrifugation that will cause nuclei to form the sediment?
1000 revolutions/minute
32
What is the speed of centrifugation that will cause mitochondria to form the sediment?
3500 revolutions/minute
33
What is the speed of centrifugation that will cause lysosomes to form the sediment?
16500 revolutions/minute
34
Why is cell fractionation important?
Allows scientists to study isolated components of cells
35
What are the two main advantages of an electron microscope?
High resolution
| Beam can be focused using electromagnets
36
Why does an electron microscope have a high resolution?
The electron beam has a very short wavelength
37
Why can the electron beam in an electron microscope be focused using electromagnets?
Electrons are negatively charged
38
What has to be created within the chamber of an electron microscope in order for it to work properly?
A vacuum
39
Why does a vacuum have to be created in order for an electron microscope to work properly?
Electrons can be absorbed or deflected by molecules in air
40
What are the two types of electron microscope?
Transmission electron microscope (TEM)
| Scanning electron microscope (SEM)
41
What is the resolution of a TEM?
0.1nm
42
What is the resolution of an SEM?
20nm
43
Why can a resolution of 0.1nm always be achieved with a TEM?
Difficulties preparing the specimen limit the resolution
| A higher energy electron beam is required which could destroy the specimen
44
What are the main limitations of a TEM?
Whole system must be in a vacuum so living specimens cannot be observed
Complex staining process required (even then image isn't in colour)
Specimen must be extremely thin
Image may contain artefacts
45
What are artefacts?
Things that result from the way that the specimen is prepared
46
What is a photomicrograph?
A picture taken of the image produced by a TEM on a screen
47
Why does a TEM produce a 2D image?
Specimens must be extremely thin
48
Why must specimens be extremely thin in order for them to be observed under a TEM?
So electrons can penetrate the specimen
49
How does a TEM form an image of a specimen?
Parts of the specimen absorb electrons and appear dark
| Other parts allow electrons to pass through and so appear bright
50
What does a TEM consist of?
An electron gun that produces a beam of electrons
| A condenser electromagnet that focuses the electron beam onto the specimen
51
What limitation of the TEM doesn't apply to the SEM?
Specimens need to be extremely thin (not for SEM)
52
Why don't specimens need to be thin for the SEM?
Electrons do not need to penetrate
53
How does the SEM direct an electron beam on the specimen?
From above onto the surface of the specimen, it is then passes back and forth across a portion of the specimen in a regular pattern
54
What happens to the electrons in an SEM?
The electrons are scattered by the specimen
55
What does the pattern of electron scattering in an SEM depend on?
The contours of the specimen's surface
56
How can an SEM be used to produce a 3D image of a specimen?
Computer analysis of the pattern of scattered electrons and secondary electrons produced
57
What is used to measure the size of an object being observed under a light microscope?
Eyepiece graticule
58
What is needed to calibrate the eyepiece graticule?
Stage micrometer
59
How do you calculate the scale for different objective lenses?
By dividing the differences in magnifications
60
Cells have a specific internal structure to suit their functions. What is this known as?
Ultrastructure
61
What is the nucleus made up of?
```
Nuclear envelope
Nuclear pores
Nucleoplasm
Chromosomes
Nucleolus
```
62
What is the function of the nucleus?
Production of mRNA and tRNA (and hence protein synthesis)
Retain genetic information
Manufacture ribosomal RNA and ribosomes
63
What is the nuclear envelope?
A double membrane that surrounds the nucleus
64
What is the outer membrane of the nuclear envelope continuous with?
The endoplasmic reticulum
65
What is often found on the surface of the nuclear envelope?
Ribosomes
66
What is the purpose of the nuclear envelope?
Controlling entry and exit of materials in and out of the nucleus
Containing reactions taking place within the nucleus
67
On average how many nuclear pores are there in each nucleus?
Around 3000
68
Roughly how big are nuclear pores in diameter?
40-100nm in diameter
69
What is the purpose of nuclear pores?
Allowing the passage of large molecules (e.g. RNA) out of the nucleus
70
What is the nucleoplasm?
The granular, jelly-like material that makes up the bulk of the nucleus
71
What do chromosomes consist of?
Protein bound, linear DNA
72
What is the nucleolus?
A small spherical region within the nucleoplasm
73
What does the nucleolus do?
Manufactures ribosomal RNA and assembles to ribosomes
74
How many nucleoli are found in a nucleus?
There may be more than one
75
Roughly how big is a 'normal' nucleus?
10-20 micrometers in diameter
76
How long is a mitochondrion in length normally?
1-10 micrometers
77
What is a mitochondrion made up of?
Double membrane
Cristae
Matrix
78
What is the purpose of the double membrane around a mitochondrion?
To control the entry and exit of material to and from the mitochondrion
79
What is the inner membrane around a mitochondrion folded to form?
Extensions known as cristae
80
What are cristae?
Extensions of the inner membrane
81
What purpose do cristae serve?
Increasing surface area for the attachment of enzymes and other proteins required for respiration
82
What does the matrix do?
Makes up the rest of the mitochondrion
83
What is found in the matrix?
```
Proteins
Lipids
Ribosomes
DNA
Enzymes
```
84
What are the enzymes found in the matrix involved in?
Respiration
85
What does the DNA found in the matrix allow the mitochondrion to do?
Control the production of some of the mitochondrion's own proteins
86
How many mitochondria are typically found in a cell?
It varies depending on the function of the cell
87
What cells will contain a large amount of mitochondria?
Cells that have a high level of metabolic activity
88
What are chloroplasts made up of?
Chloroplast envelope
Grana
Thylakoids
Stroma
89
What is the function of chloroplasts?
To carry out photosynthesis
90
What is the chloroplast envelope?
A double plasma membrane that surrounds the chloroplast
91
What is the function of the chloroplast envelope?
To be highly selective in what it allows to enter and leave the chloroplast
92
What are grana?
Stacks of up to 100 thylakoids
93
What takes place in the grana?
The first stages of photosynthesis (light absorption)
94
What is found in thylakoids?
Chlorophyll
95
What is chlorophyll?
The photosynthetic pigment
96
What do some thylakoids have?
Tubular extensions
97
If a thylakoid has a tubular extension, what does the extension do?
Join up with thylakoids in adjacent grana
98
What is the stroma?
A fluid filled matrix
99
What takes place in the stroma?
The second stage of photosynthesis (synthesis of sugars)
100
What can be found in the stroma?
A number of other structures (e.g. starch grains)
101
What does the fluid of the stroma possess?
All the enzymes required to make sugars in the second stage of photosynthesis
102
What do the granal membranes do?
Provide a large surface area
103
What attaches to the granal membrane?
Chlorophyll
Electron carriers
Enzymes required for the first stage of photosynthesis
104
How are chemicals attached to the granal membrane?
In a highly ordered fashion
105
Do all plant cells contain chloroplasts?
No
106
What do chloroplasts contain?
DNA and ribosomes
107
Why do chloroplasts contain DNA and ribosomes?
So chloroplasts can quickly and easily manufacture some of the proteins required for photosynthesis
108
What are the two type of endoplasmic reticulum?
Smooth endoplasmic reticulum (SER)
| Rough endoplasmic reticulum (RER)
109
What is the endoplasmic reticulum?
An elaborate, 3D system of sheet-like membranes
110
Where is the endoplasmic reticulum found?
Spread through the cytoplasm of cells
111
What is the endoplasmic reticulum continuous with?
The outer nuclear membrane
112
What do the membranes in the endoplasmic reticulum enclose?
A network of tubules and flattened sacks called cisternae
113
What is the general structure of the rough endoplasmic reticulum?
Ribosomes present on outer surfaces of the membranes
114
What is the general structure of the smooth endoplasmic reticulum?
More tubular in appearance than the RER
| No ribosomes on outer surfaces of membranes
115
What are the functions of the rough endoplasmic reticulum?
Provide a large surface area for the synthesis of proteins and glycoproteins
Provide a pathway for the transport of material (especially proteins) throughout the cell
116
What are the functions of the smooth endoplasmic reticulum?
```
Synthesise lipids
Synthesise carbohydrates
Store lipids
Store carbohydrates
Transport lipids
Transport carbohydrates
```
117
What cells have a very extensive endoplasmic reticulum?
Cells that manufacture and store large quantities of lipids, proteins, and carbohydrates
118
What are cisternae?
Flattened membrane discs/sacks
119
What is the Golgi apparatus similar in structure to?
Smooth endoplasmic reticulum (but more compact)
120
What passes through the Golgi apparatus?
Proteins and lipids produced by the endoplasmic reticulum
121
What does the Golgi apparatus do to the proteins that pass through it?
Modifies the proteins (often by adding a non-protein group)
| 'Labels' the proteins
122
Why does the Golgi apparatus 'label' proteins?
To allow the proteins to be accurately sorted and sent to the correct destinations
123
What are regularly pinched off from the ends of the Golgi cisternae?
Golgi vesicles
124
What happens if Golgi vesicles move to the cell surface?
They fuse with the membrane and release their contents to the outside of the cell
125
Where are glycoproteins formed?
Golgi apparatus
126
What does the Golgi apparatus add to proteins to make glycoproteins?
Carbohydrates
127
What are the functions of the Golgi apparatus?
```
Form glycoproteins
Produce secretory enzymes
Secrete carbohydrates
Transport, modify and store lipids
Form lysosomes
```
128
Where is the Golgi apparatus especially well developed?
In secretory cells
129
When are lysosomes formed?
When Golgi vesicles contain enzymes (such as proteases and lipases)
130
What enzymes do lysosomes isolate from the rest of the cell?
Lysozymes
131
How many lysozymes can a lysosome contain?
As many as 50
132
Where do lysosomes release lysozymes?
Either to the outside of the cell or into a phagocytic vesicle within the cell
133
What are the functions of lysosomes?
```
Hydrolyse material ingested by phagocytic cells
Exocytosis
Autolysis
Digest warn out organelles
Apoptosis
```
134
What is exocytosis?
A process by which a cell transports secretory products through the cytoplasm to the plasma membrane
135
Why do lysosomes carry out exocytosis?
To destroy material around the cell
136
What is autolysis?
The process by which lysosomes cause a cell to self-digest itself from the inside out (often as a response to illness or injury)
137
What cells are most susceptible to autolysis?
Unhealthy cells
138
What is apoptosis?
Programmed cell death that occurs in specific biochemical steps leading to characteristic morphological changes
139
What are phagocytic cells?
Specialized cells that engulf and ingest other cells or particles
140
What is an example of a phagocytic cell found in vertebrates?
Phagocytes (specific type of white blood cells)
141
What is the function of a ribosome?
Protein synthesis
142
What are the two types of ribosome?
80S and 70S
143
Where are 80S ribosomes found?
Eukaryotic cells
144
Where are 70S ribosomes found?
Prokaryotic cells
Mitochondria
Chloroplasts
145
How big are 80S ribosomes?
About 25nm in diamater
146
How many subunits do ribosomes have?
2
147
What sub-units are ribosomes made up of?
One large sub-unit
| One small sub-unit
148
What do the ribosomal sub-units contain?
Ribosomal RNA
| Protein
149
How many types of ribosome are there?
2
150
What do cell walls consist of?
Cellulose microfibrils embedded in a matrix
151
What is the purpose of the cellulose microfibrils found in cell walls?
To contribute to the overall strength of the cell wall
152
What marks the boundary between adjacent cell walls?
The middle lamella
153
What cements adjacent cells together?
The middle lamella
154
What is the middle lamella?
A thin layer found in the cell wall
155
What are the functions of the cell wall?
Provide mechanical strength in order to prevent osmotic rupture
Give mechanical strength to the plant as a whole
Contribute to the movement of water along plants
156
How do cell walls contribute to the movement of water along plants?
By allowing water to pass along
157
What are the cell walls of algae made up of?
```
Cellulose
or
Glycoproteins
or
Cellulose & Glycoproteins
```
158
Do the cell walls of fungi contain cellulose?
No
159
What is chitin?
A nitrogen-containing polysaccharide
160
What are the cell walls of fungi made up of?
Chitin
Glycan
Glycoproteins
161
What is glycan?
A polysaccharide
162
What is a vacuole?
A fluid-filled sac bounded by a single membrane
163
What is the membrane around plant vacuole's called?
The tonoplast
164
What does a plant vacuole contain?
A solution of: mineral salts, sugars, amino acids, wastes and pigments
165
What pigments can be found in a plant vacuole?
Anthocyanins
166
What functions do plant vacuoles serve?
Support for herbaceous plants and herbaceous parts of woody plants
Temporary food store
Attracting pollinating insects
167
How do plants vacuoles provide support?
By making cells turgid
168
How do plant vacuoles act as a temporary food source?
The sugars and amino acids they contain can be used as such
169
How do plant vacuoles attract pollinating insects?
The pigments they contain may colour petals to attract pollinating insects
170
What are similar cells grouped together to form?
Tissues
171
What are similar tissues grouped together to form?
Organs
172
What are similar organs grouped together to form?
Organ Systems
173
How do cells become specialised?
Controlled gene expression
174
Why are similar cells grouped together?
For working efficiency
175
What is an example of a tissue found in animals?
Epithelial tissue
176
What is an example of a tissue found in plants?
Xylem tissue
177
What is an organ?
A combination of tissues that are coordinated to perform various functions, often with a predominant major function
178
What tissues make up the stomach organ?
Muscle
Epithelium
Connective tissue
179
What tissues make up the leaf organ?
```
Palisade mesophyll
Spongy mesophyll
Epidermis
Phloem
Xylem
```
180
Are blood capillaries organs?
No, they are tissues
181
Are arteries organs?
Yes
182
Are veins organs?
Yes
183
Why are blood capillaries considered a tissue?
They are only made up of one tissue (epithelium)
184
Why are veins considered to be organs?
They are made up of many tissues (muscle, epithelial, etc)
185
Why are arteries considered to be organs?
They are made up of many tissues (muscle, epithelial, etc)
186
What are three examples of organ systems?
Circulatory system
Digestive system
Respiratory system
187
What organs make up the digestive system?
```
Salivary Glands
Oesophagus
Stomach
Duodenum
Ileum
Pancreas
Liver
Etc
```
188
What organs make up the respiratory system?
Trachea
Bronchi
Lungs
Etc
189
What organs make up the circulatory system?
Heart
Arteries
Veins
Etc
190
What are the two main types of cell?
Prokaryotic
| Eukaryotic
191
Compare prokaryotic and eukaryotic cells in relation to nuclei
Prokaryotic cells have no true nucleus, only an area where DNA is found
Eukaryotic cells have a distinct nucleus with nuclear envelope
192
Compare prokaryotic and eukaryotic cells in relation to DNA protein association
The DNA found in prokaryotic cells is not associated with proteins
Eukaryotic cells have DNA that is associated with proteins known as histones
193
Compare prokaryotic and eukaryotic cells in relation to DNA plasmids
Prokaryotic cells may have DNA in the form of circular strands known as plasmids
Eukaryotic cells have linear DNA and no plasmids
194
Compare prokaryotic and eukaryotic cells in relation to membrane-bound organelles
Prokaryotic cells have no membrane-bound organelles
| Eukaryotic cells have membrane-bound organelles (e.g. mitochondria)
195
Compare prokaryotic and eukaryotic cells in relation to chloroplasts
Prokaryotic cells have no chloroplasts, but some bacteria may have chlorophyll associated with the cell surface membrane
Eukaryotic cells from plants and algae contain chloroplasts
196
Compare prokaryotic and eukaryotic cells in relation to ribosomes
Prokaryotic cells have smaller ribosomes (70S)
| Eukaryotic cells have larger ribosomes (80S)
197
Compare prokaryotic and eukaryotic cells in relation to cell walls
Prokaryotic cells have a cell wall made of murein (peptidoglycan)
If present, eukaryotic cells have a cell wall made of cellulose (of chitin in fungi)
198
Compare prokaryotic and eukaryotic cells in relation to capsules
Prokaryotic cells may have an outer mucilaginous layer known as a capsule
Eukaryotic cells have no capsule
199
What is a capsule?
An outer mucilaginous layer found around some prokaryotic cells
200
What is the function of a capsule?
Protects bacterium from other cells and helps groups of bacteria to stick together for further protection
201
What are viruses?
Acellular, non-living organisms
202
What is bigger, a virus or a bacterium?
A bacterium is bigger than a virus
203
How big is the average bacterium?
0.1-10 micrometers
204
How big is the average virus?
20-300 nanometers
205
Where is the nucleic acid found in a virus?
In the capsid
206
What parts make up the human immunodeficiency virus (HIV)?
```
Genetic material (RNA)
Reverse transcriptase (enzyme)
Capsid
Matrix
Lipid envelope
Attachment proteins
```
207
What are attachment proteins attached to on a virus?
The lipid envelope, or (if this isn't present) the capsid
208
What are the purpose of attachment proteins on a virus?
To allow the virus to identify and attach to a host cell
209
How is genetic material contained in a virus?
As nucleic acids
210
What nucleic acids might a virus contain?
RNA
| DNA
211
What two processes can cell division occur by?
Mitosis
| Meiosis
212
What is the structure of a chromosome?
Two sister chromatids joined by a centromere
213
What four stages make up mitosis?
Prophase
Metaphase
Anaphase
Telophase
214
What happens in prophase? (animal and plant)
Chromosomes become visible
Nuclear envelope breaks down
Nucleolus disappears
Chromosomes free in cytoplasm start to be drawn to cell equator
215
What happens in prophase (but only in animal cells)?
Spindle fibres develop from each centriole
| Spindle fibres attach to centromere and draw chromosomes to equator
216
What do spindle fibres form?
Spindle apparatus
217
What happens in metaphase?
Chromosomes seen to be made of two chromatids
Microtubules from poles attach to centromere
Chromosomes pulled along spindle apparatus to arrange across equator
218
What happens in anaphase?
Centromeres divide into 2
Spindle fibres pull individual chromatids apart
Chromatids move rapidly to opposite poles (now called chromosomes)
219
What provides the energy for anaphase?
Mitochondria
220
What happens in telophase?
Chromosomes reach respective poles
Chromosomes become longer and thinner then disappear (leaving chromatin)
Spindle fibres disintegrate
Nuclear envelope and nucleolus reform
221
What are the three parts of the cell cycle?
Interphase
Mitosis or Meiosis
Cytokinesis
222
What happens in cytokinesis?
The cell membrane (and cell wall if present) divides
223
How do prokaryotic cells divide?
Binary fission
224
Describe the process of binary fission
```
Circular DNA molecule replicates
Both DNA copies attach to cell membrane
Plasmids replicate
Cell membrane grows between two DNA molecules
Cytoplasms begins dividing in two
Cell wall forms between DNA molecules
Cell divides into two daughter cells
```
225
Do daughter cells produced by binary fission have equal quantities of plasmids?
No
226
Do daughter cells produced by binary fission have equal quantities of the circular DNA?
Yes, each cell has one copy
227
Can viruses undergo cell division?
No
228
What is mitosis important for?
Growth
Repair
Reproduction of single celled organisms
229
What stage occupies most of the cell cycle?
Interphase
230
Roughly how long is a mammalian cell cycle?
24 hours
231
Roughly what percent of the cell cycle is spent in interphase in a mammalian cell?
90%
232
What three stages make up interphase?
G1
S
G2
233
What happens in G1?
Organelles replicated (excluding nucleus)
234
What happens in S?
Each of the 46 chromosomes replicate
235
What happens in G2?
Replicated DNA is checked for errors
236
What do drugs used to treat cancer normally do?
Disrupt the cell cycle
237
How to cancer drugs disrupt the cell cycle?
Preventing replication of DNA
| Interfering with spindle formation and so inhibiting metaphase
238
Why are cancer cells damaged more than normal cells by cancer treatment drugs?
Cancer cells divide more rapidly
239
What body cells are more susceptible to damage from cancer drugs?
Rapidly dividing body cells
240
Why do cancer drugs often cause hair loss?
Hair cells divide rapidly
241
What name is given to the membranes around cells?
Plasma membranes
242
What makes up a plasma membrane?
```
Phospholipids
Proteins
Cholesterol
Glycolipids
Glycoproteins
```
243
What do phospholipids form in a plasma membrane?
A hydrophobic bilayer
244
How are phospholipids arranged in a plasma membrane?
2 layers of phospholipids
Hydrophobic tails point inwards
Hydrophilic heads point outwards
245
What are the functions of the phospholipids in a plasma membrane?
Allow lipid-soluble substances to enter and leave the cell
Prevent water-soluble substances from entering or leaving the cell
Make the membrane flexible and self-sealing
246
What are the two main types of protein found in a plasma membrane?
Carrier protein
| Channel protein
247
What do channel proteins do?
Allow the diffusion of water-soluble substances across the membrane
Provide structural support
248
What do carrier proteins do?
Allow active transport across the membrane
| Provide structural support
249
What is the function of cholesterol in a plasma membrane?
Reduce lateral movement of the membrane
Make membrane less fluid at high temperatures
Prevent water leakage
250
What are the functions of glycolipids in a plasma membrane?
Act as recognition sites
Maintain stability of membrane
Helps cells adhere together and so form tissues
251
What are the functions of glycoproteins in a plasma membrane?
Act as recognition sites
Help cells adhere together and so form tissues
Allow cells to recognise one another
252
Why properties of molecules mean that they can't freely diffuse across a plasma membrane?
Not soluble in lipids so can't pass through phospholipid bilayer
Too large to pass through channel proteins
Same charge as charge on protein channel
Polar
253
What is the arrangement model of a plasma membrane known as?
Fluid-mosaic model
254
Explain the name 'fluid-mosaic model'
Fluid: individual phospholipid molecules can move relative to one another
Mosaic: proteins embedded in bilayer vary in shape, size and pattern
255
What is the benefit of individual phospholipid molecules having the ability to move relative to one another?
Membrane has a flexible structure that is constantly changing in shape
256
What are the functions of membranes within cells?
Control entry and exit of materials in discrete organelles
Separate organelles from cytoplasm
Provide an internal transport system
Isolate enzymes that might damage the cell
Provide surfaces on which reactions can occur
257
What is 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 they are evenly distributed
258
What is diffusion an example of?
Passive transport
259
What does passive mean in passive diffusion?
That the energy required for diffusion comes from the natural motion of particles rather than from an external source (such as ATP)
260
What sort of process is facilitated diffusion?
Passive
261
Can diffusion occur between different concentrations of different molecules?
No, diffusion only occurs between different concentrations of the same substance
262
What factors impact the rate of diffusion?
Concentration gradient
Area over which diffusion takes place
Thickness of exchange surface
Temperature
263
What is osmosis?
The passage of water through a semi-permeable membrane from a region where it has a higher water potential to a region where it has a lower water potential
264
What is the water potential of pure water under standard conditions?
0
265
What will adding a solute to pure water do to the water potential?
Lower it
266
What must the water potential of a solution be?
Less than zero (a negative number)
267
What is the relationship between water potential and the amount of solute added?
The more solute added, the lower the water potential of the solution
268
What is one method of finding the water potential of cells or tissues?
Place samples of the cells or tissues in a series of solutions of different water potentials. Where there is no net gain of water from the cells or tissues, the water potential inside the samples must be equal to that of the external solution.
269
What is water potential normally measured in?
kPa (kiloPascals)
270
What is established when the water potentials on either side of a semi-permeable membrane are equal?
Dynamic equilibrium
271
What is haemolysis?
The bursting of red blood cells due to osmotic intake
272
Explain what will happen when an animal cell is placed in a solution of higher water potential
Water will enter the cell, causing it to swell and burst open which will then release the contents of the cell
273
Explain what will happen to an animal cell when it is placed in a solution of equal water potential?
No change will occur to the cell as there will be no net movement of water in or out of the cell because dynamic equilibrium will be established
274
Explain what will happen to an animal cell when it is placed in a solution of lower water potential
Water will leave the cell and enter the solution which will cause the cell to become shrunken and shrivelled. (If the cell is a red blood cell it will appear darker as haemoglobin is more concentrated)
275
Explain what will happen when a plant cell is placed in a solution of higher water potential
Water will enter the cell and cause the protoplast to swell. The swollen protoplast will push up against the cell wall and make the cell turgid.
276
Explain what will happen to a plant cell if it is placed in a solution of equal water potential
There will be no net movement or water and so the protoplast will not change however may begin to pull away from the cell wall depending on the original water potential of the cell. The cell will be at incipient plasmolysis.
277
What is incipient plasmolysis?
The stage at which the protoplast no longer presses on the cellulose cell wall in a plant cell
278
Explain what will happen to a plant cell when it is placed in a solution of lower water potential
Water will leave the cell which will cause the protoplast to shrink and completely pull away from the cell wall. When the protoplast has pulled away from the cell wall, the cell is plasmolysed.
279
Explain why an animal cell placed in pure water will burst but a plant cell place in pure water will not
Both cell have a lower water potential than pure water so water will enter them by osmosis.
The animal cell is only surrounded by a thin cell-surface membrane so it will swell until it bursts.
The plant cell is surrounded by a rigid cellulose cell wall and once the cell is turgid the cell wall will prevent the cell expanding so water cannot enter and the cell will not burst.
280
What sort of processes are osmosis and diffusion?
Passive processes
281
What is 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
282
In active transport, what is ATP used to do?
Directly move molecules
| Co-transport
283
How does active transport differ from passive forms of transport?
Metabolic energy is required (in the form of ATP)
Substances are moved against the concentration gradient
Carrier protein molecules are involved
The process is very selective
284
Describe the direct active transport of a single molecule or ion
The carrier proteins span the plasma membrane and bind to the molecule or ion due to be transported on one side of the membrane
The molecule or ion binds to receptor sites on the carrier protein
On the inside of the cell or organelle, ATP binds to the protein causing it to split into ADP and a phosphate molecule
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 and so the protein reverts back to its original shape
During respiration the phosphate molecule will recombine with the ADP molecule to form ATP
285
Compare the similarities and differences of facilitated diffusion and active transport
Both use carrier proteins
Facilitated confusion occurs down a concentration gradient, active transport occurs up a concentration gradient
Facilitated diffusion does not require metabolic energy and so is a passive process, active transport requires metabolic energy
286
What is the purpose of mircovilli?
To increase the surface area for the insertion of carrier proteins through which diffusion, facilitated diffusion and active transport can take place
287
What is one mechanism to increase transport across membranes?
Increase the number of protein channels and carrier proteins in any given area of a membrane
288
Explain the role of diffusion in the absorption of molecules in the ileum
Carbohydrates and proteins are digested continuously so there is normally a greater concentration of glucose and amino acids in the ileum than in the blood
This creates a concentration gradient for glucose to move into the blood via facilitated diffusion
Blood is constantly circulated by the heart so the glucose absorbed into the blood is constantly moved away from the ileum and used up by respiring cells
This maintains the low concentration of glucose in the bloodoutside the ileum and helps to maintain the favourable concentration gradient between the inside of the ileum and the blood
This means the rate of movement by facilitated diffusion across the epithelial cell surface membrane is increased
289
What mechanism is used to absorb glucose and amino acids from the small intestine?
Co-transport
290
Why is the movement of glucose or amino acids out of the small intestine an example of indirect active transport?
The glucose or amino acids are drawn into the cell along with sodium ions
The sodium ion concentration gradient powers the movement of glucose or amino acids into the cell
The glucose or amino acids move against the concentration whilst the sodium ions move along the concentration gradient
The concentration of sodium ions is maintained by active transport
291
Why is the movement of glucose or amino acids into epithelial cells in the ileum an example of co-transport?
Sodium ions move down a concentration gradient into the cell, carrying the glucose or amino acids with them
292
Describe and explain the absorption of glucose or amino acids into the blood via co-transport
Sodium ions are actively transported out of epithelial cells, by the sodium-potassium pump, into the blood
This maintains a much higher concentration gradient of sodium ions in the lumen if the intestine than inside the epithelial cells
Sodium ions diffuse into the epithelial cells down the concentration through a co-transport protein in the cell surface membrane
As the sodium ion diffuse in through the carrier protein, they carry either amino acid molecules or glucose molecules into the cell with them
The glucose or amino acids pass into the blood plasma by facilitated diffusion through a carrier protein
293
What are the two types of defence mechanisms against pathogens?
Specific
| Non-specific
294
What are the differences between specific and non-specific defence mechanisms?
Non-specific responses are immediate and the same for all pathogens
Specific responses are slower and specific to each pathogen
295
What are non-specific defence mechanisms?
Physical barriers
| Phagocytosis
296
What is an example of a physical barrier?
Skin
297
What are the two types of specific defence mechanisms?
Humoral response
| Cell-mediated response
298
What do specific defence mechanisms involve?
Lymphocytes
299
What are lymphocytes?
A type of white blood cell
300
What are the two types of lymphocyte?
T lymphocytes
| B lymphocytes
301
What do cell-mediated responses involve?
T lymphocytes
302
What do humoral responses involve?
B lymphocytes
303
In order to act as a defence mechanism, what do lymphocytes need to be able to do?
Distinguish the body's own cells and material (self), from those that are foreign (non-self)
304
What would happen if lymphocytes were unable to distinguish self and non-self material?
The lymphocytes would destroy the organism's own tissues
305
What is the immune system able to identify?
Pathogens
Non-self material
Toxins
Abnormal cells
306
What is an example of non-self material?
Cells from other organisms of the same species
307
What is an example of abnormal cells?
Cancer cells
308
How do lymphocytes recognise cells belonging to the body?
In the fetus, lymphocytes are constantly colliding with other cells
Infection in the fetus is rare as it is protected by the placenta
Lymphocytes will therefore almost exclusively collide with the body's own material (self)
Some of the lymphocytes will have receptors which exactly fit those of the body's own cells
These lymphocytes will either die or be suppressed
The only remaining lymphocytes are those that might fit foreign material (non-self), and therefore only respond to foreign material
In adults lymphocytes produced in the bone marrow initially only encounter self-antigens
Any lymphocytes that show an immune response to these self-antigens undergo apoptosis before they can differentiate into mature lymphocytes
No copies of any anti-self lymphocytes will appear in the blood, leaving only lymphocytes that might respond to non-self antigens
309
What are the two types of white blood cell?
Lymphocytes and phagocytes
310
What type of white blood cell is involved in immune response?
Lymphocytes
311
What is the process by which phagocytes ingest and destroy pathogens called?
Phagocytosis
312
Where are phagocytes found?
Some phagocytes travel in the blood but can move out of blood vessels and into other tissues
313
Describe the process of phagocytosis
Chemical products of pathogens or dead, damaged and abnormal cells act as attractants, causing phagocytes to move towards the pathogen
Phagocytes have several receptors on their cell-surface membrane that recognise and attach to chemical on the surface of the pathogen
The phagocytes then engulf the pathogen to form a vesicles known as a phagosome
Lysosomes move towards the vesicles and fuse with it
Enzymes called lysozyme are present within the lysosome. These enzymes destroy ingested bacteria via hydrolysis of the bacterium cell wall.
The soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte
314
When a phagocyte is attracted to a pathogen, what does it move along?
A concentration gradient
315
What is the vesicles formed in phagocytosis known as?
A phagosome
316
What fuses with the phagosome?
Lysosomes
317
What is found in a lysosome?
Lysozymes
318
What are lysozymes?
An enzyme
319
What is an antigen?
Any part of an organism or substance that is recognised as non-self by the immune system and stimulates an immune response
320
What does the presence of an antigen do?
Triggers an immune response
321
Is phagocytosis a specific or non-specific immune response?
Non-specific
322
Where are lymphocytes produced?
Stem cells in adult bone marrow
| Fetus
323
Where do B lymphocytes mature?
In the bone marrow
324
What immunity are B lymphocytes associated with?
Humoral immunity
325
Where do T lymphocytes mature?
Thymus gland
326
What immunity are T lymphocytes associated with?
Cell-mediated immunity
327
Why can T lymphocytes distinguish invader cells from normal cells?
Phagocytes that have engulfed and hydrolysed a pathogen present some of a pathogen’s antigens on their own cell-surface membrane
Body cells invaded by a virus present some of the viral antigens on their own cell-surface membrane
Transplanted cells from individuals of the same species have different antigens on their cell-surface membranes
Cancer cells are different from normal body cells and present antigens on their cell-surface membranes
328
What is the name given to cells that display foreign antigens on their cell-surface membrane?
Antigen-presenting cells
329
Will T lymphocytes respond to any antigens?
No, T lymphocytes will only respond to antigens that are presented on a body cell and so will not respond to antigens within the body fluids
330
What do the receptors on T lymphocytes do?
The receptors on each T cell respond to a single antigen
331
What are the stages in the response of T lymphocytes to infection by a pathogen?
Pathogens invade body cells or are absorbed by phagocytes
The body cells or phagocytes present antigens from the pathogen on their cell-surface membrane
Receptors on a specific helper T cell fit exactly onto these antigens
This attachment activated the T cell to divide rapidly by mitosis and form a clone of genetically identical cells
The cloned T cells will:
-develop into memory cells
-stimulate phagocytes
-stimulate B cells
-activate cytotoxic T cells
332
What four things can cloned T cells do?
Develop into memory cells that enable a rapid response to future infections by the same pathogen
Stimulate phagocytes to engulf pathogens by phagocytosis
Stimulate B cells to divide and secrete their antibody
Activate cytotoxic T cells
333
What do cytotoxic T cells do?
Kill abnormal cells and body cells that are infected by pathogens
334
How do cytotoxic T cells kills abnormal cells and body cells that are infected by pathogens?
By producing a protein called performing that makes holes in the cell-surface membrane
335
What pathogen are cytotoxic T cells most effective against?
Viruses
336
Why are cytotoxic T cells to effective against viruses?
Viruses use living cells in which to replicate and so by sacrificing body cells it prevents viruses replicating and infecting more cells
337
What can cloned B cells develop into?
Plasma cells
| Memory cells
338
How long do plasma cells survive?
A few days
339
What is the production of antibodies and memory cells known as?
Primary immune response
340
What do plasma cells do?
Secrete antibodies into the blood plasma
341
What are memory cells responsible for?
The secondary immune response
342
Do memory cells live longer than plasma cells?
Yes, memory cells live a lot longer than plasma cells
343
How long do memory cells often live for?
Several decades
344
What do memory cells provide?
Long term immunity
345
Where do memory cells circulate?
In the blood and tissue fluid
346
What happens when memory cells encounter the same antigen at a later date?
They divide rapidly and develop into plasma cells and more memory cells
347
How many antibodies can a plasma cell produce?
Around 2000 every second
348
What is the role of B cells in humoral immunity?
The surface antigens of an invading pathogen are taken up by a B cell
The B cell processes the antigens and presents them on its surface
Helper T cells attach to the processed antigens in the B cell and thereby activate the B cell
The B cell is now activated to divide by mitosis to form clones of identical B cells in a process known as clonal selection
Some of the cloned B cells develop into plasma cells which produce and excrete the specific antibody that exactly fits the antigen on the pathogen’s surface
The antibody attaches to antigens on the pathogen and destroys them
Some B cells develop into memory cells which can respond to future infections by the same pathogen in the secondary immune response
349
How does the antigen enter the B cell?
By endocytosis
350
What does clonal selection account for?
The body’s ability to respond rapidly to any of a vast number of antigens
351
Which is faster, the secondary or primary immune response?
The secondary immune response is faster
352
Why is the secondary immune response faster than the primary immune response?
In the primary response, the antigens of the pathogen have to be ingested, processed and presented by the B cells.
Helper T cells then need to link with the B cells that then clone, some of the cells then developing into the plasma cells that produce antibodies.
These processes occur consecutively and therefore take time.
In the secondary response memory cells are already present and so the only processes are cloning and development into plasma cells that produce antibodies.
Fewer processes means a quicker response
353
What are the differences between cell-mediated and humoral immunity?
Cell-mediated immunity involves T cells whilst humoral immunity involves mostly B cells
Humoral immunity produces antibodies but cell-mediated immunity doesn’t
Cell-mediated immunity is the first stage of immune response but humoral immunity is the second stage of immune response and comes after the cell-mediated stage
Cell-mediated immunity is effective through cells whilst humoral immunity is effective through body fluids
354
How many polypeptide chains are antibodies made up of?
4
355
Why is agglutination possible?
Each antibody has 2 antigen binding sites
356
What is the binding site of an antibody known as?
The variable region
357
What are the shorter chains on an antibody known as?
Light chains
358
What are the longer chains on an antibody known as?
Heavy chains
359
When an antigen bonds to he variable region on an antibody, what is formed?
Antigen-antibody complex
360
Apart from the variable region, what is the rest of the antibody called?
Constant region
361
How are antibodies different to each other?
The variable region is different in different antibodies
362
What do antibodies do?
Prepare the antigen for destruction
363
What is the purpose of agglutination instigated by antibodies?
The non-self material is clumped together, making it easier for phagocytes to locate it as it is less spread out in the body
364
How do antibodies assist in the destruction of non-self material?
Causing agglutination
| Serving as markers that stimulate phagocytes to engulf the non-self material to which they are attached
365
What are some uses for monoclonal antibodies?
Cancer treatment
Medical diagnosis
Pregnancy testing
366
What are the two types of monoclonal antibody therapy used to treat cancer?
Direct monoclonal antibody therapy
| Indirect monoclonal antibody therapy
367
What is an advantage of direct monoclonal antibody therapy?
The antibodies are non-toxic and highly specific so they have fewer side effects than other forms of therapy
368
How does direct monoclonal antibody therapy work?
Monoclonal antibodies are produced that are specific to the antigens on the cancer cells
These antibodies are given to a patient and attach themselves to the receptors on their cancer cells
They attach to the surface of their cancer cells and block the chemical signals that stimulate their uncontrolled growth
369
How does indirect monoclonal antibody therapy work?
A radioactive or cytotoxic drug is attached to the monoclonal antibody
When the antibody attaches to the cancer cells, it kills them.
370
Why are indirect monoclonal antibodies used in smaller dosages?
Cheaper
| Reduces side effects
371
What can monoclonal antibodies be used to diagnose?
Influenza
Hepatitis
Chlamydia
Certain cancers
372
How can monoclonal antibodies be used to diagnose prostate cancer?
Men with prostate cancer often produce more PSA (prostate specific antigen) and so have unusually high levels of it in their blood
By using a monoclonal antibody that interacts with PSA it is possible to obtain a level of PSA from a blood sample
Whilst a higher than normal PSA level is not a full diagnosis it gives an early warning of the possibility of prostate cancer and the need for further tests
373
What sort of molecules are antibodies?
Proteins
374
What do home pregnancy testing kits rely on?
During pregnancy the mother produces a hormone called human chorionic gonadatrophin (hCG) which can be found in the urine
375
What produces the hormone hCG (human chorionic gonadotropin)?
The placenta
376
What does hCG stand for?
Human chorionic gonadotropin
377
What are the monoclonal antibodies found on pregnancy test strips linked to?
Coloured particles
378
What are the common ethical issues with monoclonal antibodies?
The production of monoclonal antibodies involves mice
There are risks and benefits to using monoclonal antibodies
Drug trials present certain dangers
379
Are monoclonal antibodies a risk free treatment?
No, there have been some deaths associated with the use of monoclonal antibodies to treat sclerosis
380
What monoclonal antibody drug trial went badly wrong in 2006?
TGN1412
381
How are monoclonal antibodies produced?
A mouse is exposed to the non-self material against which an antibody is required.
The B cells in the mouse then produce a mixture of antibodies, which are extracted from the spleen of the mouse.
The B cells are mixed with cancer cells to enable them to divide outside the body.
Detergent is added to the mixture to break down the cell-surface membranes of both types of cell and allow them to fuse together. The fused cells are called hybridoma cells.
The hybridoma cells are separated under a microscope and each single cell is cultured to form a clone.
Each clone is tested to see whether it is producing the required antibody.
Any clone producing the required antibody is grown on a large scale and the antibodies are extracted from the growth medium.
382
Before the monoclonal antibodies produced by mice can be used in human treatment, what has to be done?
The antibodies have to be modified to make them like human cells in a process called humanisation
383
What are some of the ethical issues of using mice to produce monoclonal antibodies?
Injecting mice with foreign substances
In order to harvest the B cells from the spleen, the mice must be killed
The mice may be used to produce tumour cells, so will be deliberately induced with cancer
Animal testing is very controversial
384
What are the two forms of immunity?
Passive immunity
| Active immunity
385
How is passive immunity produced?
By the introduction of antibodies into individuals from an outside source
386
For passive immunity is direct contact with the pathogen or its antigen required?
No
387
How long does passive immunity take to form once antibodies are introduced into an individual?
Immunity is acquired immediately
388
How long does passive immunity last?
Not long
389
Why is passive immunity short-lived?
As the antibodies are not being produced by the individuals themselves, the antibodies are not replaced when they are broken down, no memory cells are formed and so there is no lasting immunity.
390
What are two examples of passive immunity?
Anti-venom given to the victims of snake bites
| The immunity acquired by the Fetus when antibodies pass across the placenta from the mother
391
How is active immunity produced?
By stimulating the production of antibodies by the individuals’ own immune system
392
Is direct contact with the pathogen or it’s antigen required for active immunity to form?
Yes
393
How long does active immunity take to develop?
It is not immediate and takes time
394
How long does active immunity last?
It is generally long lasting
395
How many types of active immunity are there?
2
396
What are the two types of active immunity?
Natural active immunity
| Artificial active immunity
397
What does natural active immunity result from?
An individual becoming infected with a disease under normal circumstances so the body produces its own antibodies
398
What does artificial active immunity involve?
Inducing an immune response in an individual, without them suffering the symptoms of the disease
399
What does artificial active immunity form the basis of?
Vaccination (immunisation)
400
What is vaccination?
The introduction of the appropriate disease antigens into the body, either by injection or by mouth
401
What is the intention of vaccination?
To stimulate an immune response against a particular disease
402
How do vaccines work?
Vaccines contain one or more types of antigen from a specific pathogen
These antigens stimulate an immune response
This means that memory cells specific to the antigens are produced
These memory cells remain in the blood and allow a greater, and more immediate, response to a future infection with the pathogen
This means that if the vaccinated individual comes into contact with the pathogen, there will be a rapid production of antibodies and the new infection will be quickly overcome before it can cause any harm
403
What does the success of a vaccination programme depend on?
A suitable vaccine must be economically available in sufficient quantities to immunise most of the vulnerable population
There must be few side effects, if any, from the vaccination
Means of producing, storing and transporting the vaccine must be available
There must be the means of administering the vaccine properly at the appropriate time
It must be possible to vaccinate the vast majority of the population to produce herd immunity
404
Why is it important that a vaccine has very few side effects?
Unpleasant side effects may discourage individuals in the population from being vaccinated
405
What is often involved in producing, storing and transporting a vaccine?
Technologically advanced equipment
Hygienic conditions
Refrigerated transport
406
What is involved in appropriate vaccine administration?
Training staff with appropriate skills at different centres throughout the population
407
When does herd immunity arise?
When a sufficiently large proportion of the population has been vaccinated
408
What is the theory behind herd immunity?
Pathogens are passed from individual to individual when in close contact
When the vast majority of the population is immune, it is very unlikely that an individual without immunity will come in contact with an infected person
In this way individuals who are not immune to the disease are still protected
409
Why is herd immunity important?
It is never possible to vaccinate everyone in a large population
410
Why are babies and very young children not vaccinated?
Their immune system is not yet fully functional
411
What percentage of the population must be vaccinated in order to achieve herd immunity?
It is different for each disease
412
Why are some diseases not eliminated by vaccination?
Vaccination may fail to induce immunity in certain individuals (e.g. people with defective immune systems)
Individuals may develop the disease immediately after vaccination but before their immunity levels are high enough to prevent the infection
Antigenic variability of the pathogen
There may be so many varieties of a particular pathogen that is almost impossible to develop a vaccine that is effective against them all
Certain pathogens hide from the body’s immune system
Individuals may object to vaccination
413
Why can antigenic variability make vaccines ineffective?
If a pathogen mutates frequently, its antigens may change suddenly rather than gradually so the new antigens on the pathogens are not recognised by the immune system and so antibodies are not produced to destroy the pathogen. This means that the vaccine is no longer effective
414
Why is it possible for individuals to sustain multiple infections of the influenza virus?
Antigenic variability happens with the influenza virus and so it changes its antigens frequently. This makes any immunity acquired against the influenza virus relatively short-lived
415
How can pathogens hide from the immune system?
Concealing themselves inside cells
| Existing in places out of reach (such as in the intestines)
416
What pathogen hides from the immune system by existing in the intestines?
Cholera pathogen
417
Why might individuals object to vaccination?
Religious reasons
Medical reasons
Ethical reasons
418
What does HIV stand for?
Human Immunodeficiency Virus
419
What does AIDS stand for?
Acquired Immune Deficiency Syndrome
420
What does HIV cause?
AIDS
421
What causes AIDS?
HIV
422
What group of viruses does HIV belong to?
Retroviruses
423
Why is HIV a retrovirus?
The presence of reverse transcriptase within HIV and consequent ability of HIV to make DNA from RNA
424
Describe the structure of HIV
On the outside is a lipid envelope
Attachment proteins are embedded in the outside of the lipid envelope
Inside the envelope is a protein layer called the capsid
The capsid encloses 2 single strands of RNA and some enzymes
425
What is found in the capsid of HIV?
2 single strands of RNA
| Enzymes (including reverse transcriptase)
426
What does reverse transcriptase do?
Catalyses the production of DNA from RNA
427
Where does HIV circulate in the body?
The bloodstream
428
What protein does an attachment protein on HIV readily bind to?
CD4
429
What type of cell does HIV most readily attach to?
Helper T cells
430
Describe the replication of HIV inside a human body
HIV enters the bloodstream and circulates around the body
A protein on HIV binds to a protein called CD4 (readily found on helper T cells)
The protein capsid fuses with the cell surface membrane
The RNA and enzymes of HIV enter the helper T cell
The HIV reverse transcriptase convert the virus’s RNA to DNA
The new DNA is moved into the helper T cell’s nucleus where it is inserted into the cell’s DNA
The HIV DNA inside the nucleus creates mRNA using the cell’s enzymes. The mRNA contains instructions for making new viral proteins and the RNA to go in the new HIV
The mRNA passes out of the nucleus through a nuclear pore and uses the cell’s protein synthesis mechanisms to make HIV particles
The HIV particles break away from the helper T cell with a piece of its cell surface membrane surrounding them which forms the lipid envelope
431
How does HIV cause AIDS?
By killing or interfering with the normal functioning of helper T cells
432
How many helper T cells does an uninfected person normally have in each mm^3 of their blood?
800-1200 helper T cells
433
What happens if a person doesn’t have sufficient amounts of helper T cells?
The immune system cannot stimulate B cells to produce antibodies
The immune system cannot stimulate cytotoxic T cells
Memory cells may become infected and destroyed
The body is unable to produce an adequate immune response and becomes susceptible to other infections and cancers
434
Does HIV directly kill individuals?
No
435
What kills individuals infected with HIV?
Secondary infections
436
What do many AIDS sufferers develop?
Infections in the lungs, intestines, brain and eyes
Weight loss
Diarrhoea
437
What does ELISA stand for?
Enzyme Linked ImmunoSorbant Assay
438
How does HIV lead to the death of an individual?
By infecting the immune system and preventing it from functioning normally so the individual is unable to effectively respond to other pathogens
It’s the infections from other pathogens that ultimately cause death
439
What two things does the ELISA test detect?
The presence of a protein in a sample
| The quantity of said protein in the sample
440
How sensitive is the ELISA test?
Very sensitive
441
Describe the process of the ELISA test
Apply the sample to the surface of a spotting well to which all the antigens in the sample will attach
Wash the surface several time to remove any unattached antigens
Add the antibody specific to the antigen that is trying to be detected and allow the two to bind
Wash the surface again to remove excess antibody
Add a second antibody to bind with the first antibody (this antibody has an enzyme attached to it)
Wash the surface again so any antibodies not bound are removed
Add the colourless substrate of the enzyme, the enzyme acts on the substrate to change it into a coloured product
The amount of antigen present is relative to the intensity of the colour that develops
442
Why is it important to wash the surface used in the ELISA test after antibodies and antigens are added?
So that any antibodies not bound won’t react and provide a false positive result
443
What can the ELISA test be used to detect?
HIV
Tuberculosis
Hepatitis
444
What is often more important in drug tests; the presence of a drug or the quantity of the drug? Why?
The quantity of the drug as many drugs are found naturally in low concentrations
445
What two tests is ELISA very useful in (besides pathogen detection)?
Drug testing
| Allergen testing
446
Describe and explain one way that antibiotics such as penicillin work
In bacterial cells, water constantly enters by osmosis
The wall surrounding the bacterium is made of murein which isn’t easily stretched and prevents the cell from bursting via osmotic intake
As water enters the cell via osmosis, the cell expands and pushes against the cell wall
The cell wall is relatively inelastic so reiste expansion and prevents further entry of water
Antibiotics like penicillin inhibit certain enzymes required for the synthesis and assembly of the peptide cross linkages in bacterial cell walls
This weakens the walls and makes them unable to withstand pressure
As water enters the cell naturally by osmosis, the cell bursts and the bacterium dies
447
Why are antibiotics ineffective against viral diseases?
Viruses rely on the host cells to carry out their metabolic activities and therefore lack their own metabolic pathways and cell structures
As a result antibiotics are ineffective as there are no metabolic mechanisms or cell structures for the, to disrupt
Viruses have a protein coat rather than a murein cell wall and so do not have sites where antibiotics can work
When viruses are within an organism’s own cells, antibiotics cannot reach them
