Topic 2: Cells Flashcards
Pack 2, 3, some of 5; 6
1
Q
What is the cell theory?
A
- That cells are the most basic form of life
- All living organisms are made of 1 or more cells
- Cells arise from pre-existing cells
2
Q
What is a eukaryotic cell?
A
A cell with a true nucleus with DNA in the form of chromosomes with membranes
3
Q
What is the function of the plasma membrane?
A
To exchange substances in/out of the cell. (Regulates)
4
Q
What extra features do plant cells have which animal cells do not?
A
- Permanent vacuole
- Chloroplasts
- Cell wall
5
Q
What is the average size of nuclei?
A
10-20 µm
6
Q
What is the function of the nucleus?
A
- Store DNA (genetic information)
- Control cell by production of mRNA, tRNA and thus protein synthesis
- Makesribosomes
7
Q
Name some sub-structures of the nucleus
A
- Nuclear envelope
- Nuclear pores
- Nucleoplasm
- Nucleolus
- Chromosomes
8
Q
What is the nuclear envelope? What is its function?
A
- A double membrane surrounding the nucleus, outer membrane continuous with ER
- Controls what enters/exits nucleus
- Controls the reactions within the nucleus; DNA, RNA + Ribosomes
9
Q
What is the function of nuclear pores?
A
Allows passage of very large molecules, inc mRNA
10
Q
What is the nucleoplasm
A
A granular, jelly-like substance making up the bulk of the nucleus
11
Q
What are chromosomes?
A
Protein bound, linear DNA
12
Q
What are ribosomes?
A
- Small granules found in rough ER or cytoplasm
- Made from 2 subunits of ribosomal RNA (rRNA) and many proteins
- NOT enclosed by a membrane
13
Q
What is the function of ribosomes?
A
The site of protein synthesis
14
Q
What is the Endoplasmic Reticulum?
A
- 3D sheet-like membrane system spreading throughout the cytoplasm
- Continuous with outer nuclear membrane
- Encloses a network of tubules and flattened sacks called cisternae
- Cells that make and store carbohydrates, proteins and lipids have an extensive ER
15
Q
What are the two types of endoplasmic reticulum?
A
Rough ER Smooth ER
16
Q
What is the rough ER?
A
- Has ribosomes on outer surface of the membrane - Large SA for protein synthesis
- Pathway for transport of materials (eg mRNA), especially proteins through the cell
17
Q
What is the smooth ER?
A
- No ribosomes, more tubular
- Synthesises, transports + stores lipids or carbohydrates
18
Q
What types of cells contain a lot of ER?
A
Any cell that produces a lot of proteins (inc enzymes)
19
Q
How many cisternae will you find in one cell?
A
Just one which has been folded over many times and appears as many depending on angle of cut
20
Q
What is the golgi apparatus (golgi body)?
A
- 3D sheet-like membrane system in cytoplasm
- Similar to smooth ER but compact
- A cisternae with small vesicles - In secretory cells
21
Q
What are the functions of the golgi apparatus?
A
- Adds carbohydrates to proteins to form glycoproteins
- Produces secretory enzymes (pancreas)
- Secretes carbohydrates (plant cell walls)
- Tranports, modifies and stores lipids
- Forms Lysomers
22
Q
Which cell organelle stores lipids and proteins made by the golgi apparatus?
A
Vesicles
23
Q
Which cell organelle processes and packages new lipids and proteins?
A
Golgi body
24
Q
What are lysosomes?
A
Vesicles produced in the golgi body containing enzymes (proteases and lipases)
25
What do lysosomes do?
- Help in consume bacteria during phagosytosis
- Release enzymes to destroy cell material
- Digest worm out organelles to reuse chemicals
- Break down cells once they die
26
In mitochondria, what sub-structure controls the entry and exit of substances?
A double membrane, with an inner membrane folded forming a cristae for enzymes involved in respiration
27
What molecule used for energy in cells is produced in mitochondria?
ATP
28
What is respiration?
The oxidization of glucose releasing (not producing) energy
29
Why do cells that do a lot of active transport require lots of mitochondria?
- Active transport requires energy to go from low to high concentrations
- Mitochondria are site of respiration
- produce ATP
- ATP needed for active transport
30
Name 3 sub-structures of chloroplasts and their function
1. Chloroplast envelope - Double plasma membrane, v. selective
2. Thylakoids - Disc structures containing chlorophyll in stacks called grana
3. Stroma - Matrix containing starch, DNA and ribosomes
31
What are vacuoles?
Fluid-filled sacks bound by a single membrane found in plants containing mineral salts, sugars, amino acids and waste
32
What is the membrane in vacuoles called?
A tonoplast
33
What is the function of vacuoles?
- To support herbaceous plants (no woody stem)
- Sugars and amino acids stored as emergency food
- Pigments colour petals attracting pollenators
34
What is different about Algae to plant cells?
Nothing - same organelles
35
What do fungal cells have which plant cells do not?
1. Chitin cell walls
| 2. No chloroplasts (don't photosynthesize)
36
What is the function of the cell membrane?
Regulates movement of molecules + receptor molecules to detect hormone changes
37
What are plant cell walls made from?
Cellulose
38
What are fungal cell walls made from?
Chitin
39
How can you study single organelles of cells?
With cell fractionation
40
What are the 2 stages of cell fractionation?
Homogenisation and Ultra-centrifugation
41
What is the first step of cell homogenisation? (most important step)
- Chop up tissues
- Place in isotonic buffer solution at 2-4 degrees
- Prevents enzyme action and organelles bursting
- Buffer solution keeps pH neutral
42
What is the second step of cell homogenisation?
- Blend the chopped cells
| - Releases organelles from the cells
43
What is the third step of cell homogenisation?
- Filter the blended homogenate
44
In ultracentrifuation where do heavy organelles fall? What is this layer called?
- Form at bottom
| - A SEDIMENT
45
In ultracentrifuation where do light organelles fall? What is this layer called?
- Forms ontop of sediment
| - Called a SUPERNATANT
46
Summarize ultarcentrifugation.
1. Spin homogenate at low speed for short amout of time
2. Spin the supernatant from part 1 at a higher speed for longer
3. Spin the supernatant from part 2 at a higher speed for longer still
- Pour off supernatant after each step, leaving just the sediment
47
Where do cells come from?
From the division of other cells by mitosis with the same number of genes
48
Why do cells only do a certain function or role?
All cells contain all the genes necessary to develop into any cell but only some genes are switched on or expressed
49
What is a tissue?
A collection of cells that perform a specific function
50
What is an organ?
A combination of tissues that perform one major function
51
What is an organ system?
A number of organs working together. eg digestive system, respiratory system, circulatory system
52
What is a prokaryotic cell?
- Cells without a nucleus and other membrane-bound organelles
- Genetic material in circular double-stranded DNA
53
Name all organelles prokaryotes have that eukaryotes do not
- Flagellum
- Plasmids
- Circular DNA (instead of nucleus)
54
What is the cell wall in prokaryotes made out of?
Murein (polymer of polysaccharides and protein)
55
What is the function of prokaryotic cell walls?
A physical barrier, protecting against mechanical damage and turgor pressure (like eukaryotes)
56
What is the function of prokaryotic cell membranes?
Controls entry/exit of chemicals (like in eukaryotes)
57
What is different about the storage of genetic material in prokaryotes to eukaryotes?
- DNA in circles (plasmids)
- DNA is not protein bound (no histones)
*ALL DNA is double-stranded*
58
What important genes do plasmids in prokaryotes contain?
Genes that aid survival by antibiotic resistance
59
What are plasmids used for in genetic engineering?
Used as vectors which can carry genetic info eg insulin
60
What is the capsule in bacteria?
- A layer of slime found on some bacteria
61
What is the function of bacterial capules?
- Protection fro other cells
| - Helps bacteria stick together for protection
62
What is the flagellum (prokaryotes) and what is its function?
- A tail, can be more than one
| - For locomotion
63
Are viruses cells?
No. They are acellular, non-living particles
64
How is genetic material stored in viruses?
- Contain nucleic acids like DNA/RNA inside a protein coat or capsid
65
How do viruses identify and attach to host cells?
Attachment proteins line the outside of viruses
66
Where do viruses reproduce?
Inside cells of living organisms, using their DNA and destroying them
67
What is magnification?
How many times bigger the image is than the actual object
68
What is the formula relating magnification (M), image size (D) and actual size (A)?
DAM u!
Image = actualxmagnification
D=AxM
69
What is resolution?
- How detailed the image is
| - Specifically how well a microscope distinguishes between 2 points that are close together
70
How thin do specimens need to be for a light microscope? Why?
- 2-5 um (micrometres)
| - So light can pass through them
71
How do light microscopes work?
Light shines through specimen and through a series of lenses, the resulting image viewed by human eye
72
Why do light microscope have a poor resolution?
Relatively long wavelengths of light cannot pass between very small objects
73
What is the maximum resolution of light microscopes?
0.2 micrometres
74
What is the difference between a capSULE and a capSID?
```
Capsule = Bacteria, slime layer
Capsid = Viruses, Protein coat
```
75
What is the maximum magnification of light microscopes?
1500x
76
How can you accurately measure objects with a light microscope?
With an eyepiece graticule and a stage micrometer
77
What are the two types of electron microscopes?
```
SEM = Scanning electron microscope
TEM = Transmission electron microscope
```
78
How is an image made using a Scanning electron microscope (SEM)?
- 'Scans' the surface to and fro
- Electrons are scattered depending on contours of specimen
- Builds a 3D image
79
What are artifacts?
Inaccuracies made during the preparation of specimens for SEMs and TEMs
80
What is the major difference between light and electron microscopes?
One uses a bean of electrons rather than light
81
Why do electron microscope have a higher resolution?
Electrons have a shorter wavelength compared to light
82
How are electron microscopes focused?
Using magnets as electrons are negatively charged
83
Why does preparation take longer with Transmission electron microscopes (TEMs)?
Specimens need to be stained with heavy metals
84
How does a TEM produce an image?
- Electrons are fired as a beam
- Electrons which pass through appear bright
- Absorbed or reflected electrons appear dark
- 2D image
85
Why can't living specimens be observed with a TEM?
A near vacuum is required as air molecules interrupt electrons
86
What is the maximum magnification of scanning electron microscopes (SEMs)?
x500,000
87
What is the resolution of transmission electron microscopes (TEMs)?
Up to 0.1nm
88
What is the resolution of scanning electron microscopes (SEMs)?
Up to 20nm
89
What are the two ways that eukaryotes divide?
Mitosis and Meiosis
90
Can all cells divide?
No. Nerve and brain cells cannot
91
What is the 'outcome' of mitosis?
MITOSIS
| 2 genetically identical daughter cells, same number of chromosomes as parent cell (exact copy of DNA)
92
What is the 'outcome' of meiosis?
MEIOSIS
| 4 genetically non-identical daughter cells, half number of chromosomes as parent cell
93
What do chromosomes do?
Carry the genes that control protein synthesis in living organisms. PROTEINS DETERMINE THE CHARACTERISTICS.
94
Do all organisms have the same numbers of chromosomes?
No. Humans have 23 pairs
95
What are 'homologous chromosomes'?
Pairs of chromosomes (diploid)
96
What type of cell contains half the dipoid number?
Gametes
97
What are chromatids?
Two parts of a chromosome, joined by a centromere
98
What is a centromere?
Joins the two chromatids in a chromosome together
99
What is the protein found in chromosomes?
Histones
100
What are the 3 main stages of the cell cycle?
Interphase, Mitosis, Cytokinesis (can be sub-divided further)
101
What are the 'sub-stages' of interphase?
G1 - Growth 1
S -Synthesis
G2 - Growth 2
102
What occurs in growth 1 (G1) of interphase?
Organelles replicate, forms many proteins
103
What occurs in synthesis (S) of interphase?
DNA replication, chromosomes become 2 chromatids joined by a centromere
104
What occurs in growth 2 (G2) of interphase?
- Organelles continue to replicate
- Energy store produced
- Centrioles replicate
105
What are centrioles?
Animal cell organelles which develop spindle fibres
106
What are the 4 stages of mitosis (in order)?
```
*PMAT*
Prophase
Metaphase
Anaphase
Telophase
```
107
What occurs during cytokinesis in the cell cycle?
Organelles are equally distributed into two daughter cells
108
What happens in prophase (mitosis)?
- Chromosmes become visible, shorten/thicken
- Centrioles move to opposite poles
- Spindle fibres form a spindle apparatus
- Nucleolus disappears + nuclear envelope brakes down
109
What happens in metaphase (mitosis)?
- Chromosomes clearly seen as two sister chromatids
- Some spindle fibres attach to centrioles, others pole-to-pole
- Chromosomes line up along equator
110
What happens in anaphase (mitosis)?
- Centromeres divide, spindle fibres contract, pulling sister chromatids apart
- Chromatids move to opposite poles
111
What happens in telophase (mitosis)?
- Chromosomes reach poles, become long + thin
- Spindle fibre disintegrates
- Nuclear membranes and nucleoli reform
- Followed by cytokinesis
112
In what stage of the cell cycle does DNA replication occur?
Interphase (S - synthesis)
113
What is the role of the 1/2 spindle fibres in mitosis?
Pull chromatids apart from centromeres
114
How would you recognise metaphase (mitosis)?
Chromatid pairs line up along the cell equator
115
What the the 3 key roles of mitosis in organisms?
GRR!
1. Growth
2. Repair
3. Reproduction
116
What is the mitotic index?
The ratio of cells undergoing mitosis to those in interphase. Proportional to time spent in that stage
117
What causes cancer?
Mutations to genes that regulate mitosis and cell cycle
118
What is a malignant tumour?
A tumour that spreads to surrounding tissues via the blood
119
What is a benign tumour?
A tumour that grows slowly and does not spread easily
120
How is cancer controlled?
Chemicals are prescribed to block a part of the cell cycle, affects all cells
121
How do prokaryotes divide?
By binary fission
122
What are the 4 steps of binary fission?
1. cell elongates, DNA replicated + attaches to membrane
2. Cell wall + cytoplasm begin to divide
3. Cross-wall forms
4. Cells separate with single copy of DNA
123
How do viruses replicate?
- Attach to host cell, inject genetic material (DNA or RNA)
| - Host cell produces all components of the virus
124
What is the function of plasma membranes?
To control what enters/exits the cell/organelles, forming a boundary between the cell cytoplasm and the surrounding environment
125
What are the 5 main components of plasma membranes?
```
Phospholipids
Proteins
Cholesterol
Glycoproteins
Gycolipids
```
126
What 4 molecules make up a phospholipid?
Glycerol, 2 fatty acids + phosphate
127
How do phospholipds line up when they form a
| membrane?
They naturally line up with phosphate head (hydrophyllic) outwards and fatty acid tails inwards - A natural bilayer
128
What is the function of the phospholipid bilayer?
- Allows for lipid soluble substances to enter/exit cell
- Prevents water soluble substances entering the cell
- Membrane is flexible and self-sealing
129
Where are proteins found on/in membranes?
Can completely span membrane or sit in/on one of the surfaces of the bilayer
130
What are the functions of proteins with plasma membranes?
- Structural support
- Helps cells attach to each other
- Channel, carrier proteins
- Cell surface receptors for hormones / cell recognition
131
What is the function of cholesterol with plasma membranes?
- Adds strength
- Less fluid at high temperatures
- Prevents leakage of water and dissolved ions out of cell
132
What are glycolipids?
A lipid (In the membrane) convalently bonded to a carbohydrate, extending out the cell
133
What are the functions of glycolipids with plasma membranes?
- Receptors for specific chemicals
- Maintains membrane stability
- Help cells attach to each other forming tissues
134
What are extrinsic proteins?
Proteins which do not go all through membrane, only one side
135
What are glycoproteins?
A extrinsic protein (part of membrane) covalently bonded to a carbohydrate, extending out/away from cell
136
What are the functions of glycoproteins with plasma membranes?
- Recognition sites for chemicals
- Helps cells attach forming tissues
- Allow cells to recognize each other, eg lymphocytes recognizing organisms own cells (and don't eat them...)
137
Why are plasma membranes described as fluid?
Molecules inside the membrane can move relative to each other, constantly changes shape
138
Why can't most substances pass through plasma membranes?
- Not if they are water soluble (only lipid soluble)
- Not charged particles
- Not large molecules
139
What substance can cross plasma membranes?
- Lipid soluble substances eg oestrogen
| - Small non-polar molecules eg Oxygen +CO2
140
Define diffusion.
The net movement of molecules/ions from a region of high concentration to low concentration, until evenly distributed
141
Is diffusion an active process?
NO! A passive process
| - no metabolic energy required from ATP
142
When does the 'net flow of molecules' over a membrane stop?
At dynamic equilibrium
143
What factors does the rate of diffusion depend on?
- Temperature
- Difference in con
- Distance travelled
- Area it takes place
- Nature of structures
- Size of molecule
144
How does temperature affect the rate of diffusion?
Increase in temp = increase in Kinetic energy of molecules, increases rate (collision theory)
145
How does difference in concentration affect the rate of diffusion?
A greater difference in concentration will cause a faster rate
146
How does width of membrane (distance) affect the rate of diffusion?
A wider membrane means further to travel, so slower. The greater the distance, the slower the rate
147
How does surface area of membranes affect the rate of diffusion?
As the area increases, the rate of diffusion increases
148
What is Fick's law?
Diffusion rate = [directly proportional to]
(surface area x conc difference)
/ Diffusion distance
149
What 2 types of protein facilitate diffusion of molecules?
Channel and carrier proteins
150
What are 3 key points for facilitated diffusion?
- High to low concentration
- Carrier or channel proteins
- No ATP / energy required
151
What do channel proteins do?
- Water filled hydrophillic channels across membrane
- Specific water-soluble molecules pass through
- Selective (only open in presence of a specific ion), changes shape of protein
152
How do channel proteins open?
A specific ion changes shape of protein to allow a molecule to pass through
153
How do carrier proteins move molecules/ions across plasma membranes?
A molecule with a specific, complementary shape binds to carrier protein, causing it to change shape and be released on the other side
154
Why does a large surface area increase the rate of diffusion?
The total area is larger, so there are move channel/carrier proteins present
155
Define osmosis.
The passive movement of water molecules from a region of high water potential to a region of low water potential through a semi-permeable membrane
156
What is a solute?
A substance that dissolves in a solvent to create a solution
157
What is the water potential of pure water under standard temperature and pressure?
0 pascals
158
If you add a solute to water how does it affect the water potential?
Lowers the water potential (more negative)
159
True or false. Water potential can be positive or negative.
FALSE. Always negative
160
What is mean by a protoplast?
Everything in plant cells except the cell wall
161
Why do plant cells not burst in a hypERtonic (less negative WP outside cell) solution?
Because the cell wall is strong. Cell is turgid
162
If a plant cell is placed in a hypotonic (more negative WP) solution what happens?
- Plant cell has higher (less negative WP)
- Net movement of water out of cell
- Protplast shrinks away from cell wall
- Cell is PLASMOLISED
163
What is 'incipient plasmolysis'?
A cell in an isotonic solution (same WP) - no net movement
164
Define active transport.
- The movement of molecules or ions usually from a region of low concentration to a region of higher conc
- OR to speed up intake (high-low)
- Requires respiration, energy from ATP)
- Involves carrier proteins
165
What is an example of active transport?
Sodium/potassium (Na+/K+) pump
166
What other molecule besides Na+ and K+ is required for the sodium/potassium pump to work?
ATP, Pi released (by hydrolysis). Pi changes the shape of carrier protein, releasing Na+ out of cell.Pi rejoins ADP (to form ATP) after two K+ ions move into the cell.
167
What do the epithelial cells of the intestine have to maximize absorption (by increasing SA)?
Microvilli
168
What role does the circulatory system do to help absorb foods from small intestine into the blood?
Blood constantly flows, the concentration gradient is maintained as products of digestion are constantly carried away
169
Over time what will happen to the concentrations of products of digestion in the small intestine and blood?
The concentrations will equal out, reach dynamic equilibrium or become higher in the blood
170
What would happen is the products of digestion across the walls of the small intestine moved by diffusion?
The products of digestion would have equal concentrations in blood and small intestine, many would pass out of the body (uses co-transport instead)
171
What is co-transport?
The facilitated diffusion and active transport of substances from the small intestine into the blood
172
What type of protein moves two molecules through it in co-transport?
A co-transport protein or symporter
173
What is used to set up a concentration gradient in co-transport?
A sodium/potassium pump, moving Na+ ions into the blood
174
In co-transport does glucose move through the co-transport protein down its own concentration gradient?
No. It moves in with Na+ down sodium concentration gradient (glucose is always moving in, regardless of concentrations, glucose moves against it's own conc gradient
175
Give one method of observing mitosis.
Use root tip tissues, squash them and look under a microscope
176
How do you calculate the mitotic index?
No. of cells with visible chromosomes / total no. of cells
177
What is the effect of temperature on membrane permeability?
Below 0 degrees = Too rigid, proteins deform, freeze thaw, increases permeability
Over 45 degrees = Phospholipids melt and proteins deform, increases permeability
178
What is simple diffusion?
When molecules/ions diffuse directly through plasma membrane (not channel proteins)
179
How can you test water potential of plant tissues?
Use a serial dilution of different water potentials, add potato cylinders
180
What factors affect the rate of active transport?
1. Speed of individual carrier proteins
2. Number of carrier proteins present
3. Rate of respiration of cell + availability of ATP
181
What is a pathogen?
Any organism that causes a disease
182
What are the 4 types of pathogen?
- Protozoan (parasites)
- Fungus
- Virus
- Bacteria
183
How do pathogens cause disease?
By making you ill in a number of ways. eg. Bacteria secrete toxins, viruses take DNA
184
What is an antigen?
Any part of an organism or substance that is recognised as "non-self" - stimulates immune response
185
Do antigens have a specific shape?
Yes, a specific, unique structure/shape
186
What do antigens stimulate the production of?
Antibodies (complementary to the given antigen)
187
What molecules can antigens be?
Proteins and glycoproteins found on the surface of a cell
188
What is the generic shape of an antibody?
A Y-shaped protein
189
What part of antibodies bind to the antigen?
The binding sites (NOT active), which is specific in shape to a complementary antigen
190
What makes antibodies in an immune response?
B lympocytes
191
Why are proteins used for cell identification?
There is a wide variety of proteins (20 amino acids in many different orders), creating a specific tertiary structure
192
Why do cancerous cells trigger an immune response?
Cancer cells are abnormal, different antigens in surface than normal body cells
193
What is a non-specific immune response?
An immediate response, same for all pathogens. Uses physical barriers and phagocytosis
194
What is a specific immune response?
A response which is specific to each pathogen (cell mediated/humoral response)
- slower than non-specific
195
Give 6 natural barriers to pathogens.
- Skin
- Nasal hairs
- Ear wax
- Cillia
- Eyes (containing lysozyme)
- Stomach acid
196
What causes inflammation?
Histamines cause blood vessels to dilate, blood flow increases. Capillaries become more leaky too. Phagocytes move in
197
What is a phagocyte?
A white blood cell which carries out phagocytosis, engulfing pathogens
198
What is the 1st stage of phagocytosis?
1) Phagocytes move to pathogen in presence of chemicals
199
What is the 2nd stage of phagocytosis?
2) Phagocyte attaches to receptor molecules on the surface of the pathogen
200
What is the 3rd stage of phagocytosis?
3) Cytoplasm of phagocyte moves around the pathogen, engulfing it. Creates a phagosome
201
What is the 4th stage of phagocytosis?
4) Lysosomes in phagocyte fuse with phagosome
202
What is the 5th stage of phagocytosis?
5) Lysosomes release lysozyme, digest/hydrolyse the pathogen
203
What is the 6th stage of phagocytosis?
6) After the pathogen is digested, products of digestion are absorbed into the cytoplasm or released by exocytosis
204
Where do B lymphocytes originate and mature?
In bone marrow
205
Where do T lymphocytes originate?
In bone marrow
206
What is clonal selection?
The process by which lymphocytes are selected to divide so that sufficient numbers are present to combat infection
207
What is the immune response by T cells called?
Cell mediated immunity
208
What is the immune response by B cells called?
Humoral immunity
209
What activates T cells?
Phagocytes (with presented antigens)
210
What do cloned Th cells do?
a) Form Tm cells
b) Stimulate phagocytosis
c) Stimulate B cells to divide and produce antibodies
d) Activate cytotoxic T cells
211
How do ctotoxic T cells kill infected cells?
Produce a protein called perforin - makes holes in cell surface membrane (esp important with viruses)
212
How do B cells respond to an infection?
Produce antibodies
213
What do B cells develop into?
- Plasma cells (cells which secrete antibodies into blood) primary response
- B memory cells (increased and more rapid response to second infections) secondary response
214
What type of phagocyte presents antigens?
Macrophage
215
What is an antigen joined to an antibody called?
Antigen-antibody complex
216
What hierarchy of protein structure are antibodies?
A quaternary structure
217
What is the constant region of antibodies?
The region which is the same for all antibodies (lower part)
218
What is the variable region of antibodies?
Part of antibody with a specific shape to antibody due to amino acid sequence - complementary shape to antigen
219
How do antibodies prevent disease?
- Antibodies bind to antigens at antigen binding site
| - The pathogens can be clumped together with agglutination, so can no longer attach to host cells
220
What is the primary response?
The first time the immune system encounters a pathogen. Slow as few B cells - takes time for antibodies to be produced, symptoms shown
221
What happens following a primary response?
T and B cells produce memory cells to remain in the body in preparation for any future infections (if any)
222
Why is the secondary response quicker than primary?
There are B and T memory cells already in the blood, so they can divide more quickly
223
How does the scondary response differ from the primary response?
- More magnitude and speed
224
What is a monoclonal antibody?
Antibody produced by a single B cell clone
225
Why is vacination used?
It produces immunity to specific diseases by deliberately exposing a person to antigenic material which is harmless.
226
Why do most vaccines not cause symptoms?
There are antigens which do not make you ill whilst triggering a primary reponse in prepartaion for a future infection. Causes immunity without symptoms
227
Why might booster vaccines be given?
To make sure that memory cells are produced
228
Why are few vaccines taken orally?
- Enzyme breakdown
| - Molecules may be too large to be absorbed in gut
229
What is active immunity?
Immune system creates its own antibodies after stimulation by an antigen
230
What are the two types of active immunity?
1. Natural (catch the disease 'normally')
| 2. Artificial (a vaccine)
231
What is passive immunity?
Given antibodies made by a different organism; babies via placenta/artificial (like antivenom)
232
What is antigenic drift/variation?
When antigens on a pathogen change due to genetic mutations
233
What is the issue with antigen variation?
- New pathogens mean secondary response is useless
- A new primary response is required instead
- Difficult to develop vaccines
234
Between active and passive immunity which requires exposure to pathogen?
Active immunity
235
Between active and passive immunity which results in immediate protection?
Passive immunity
236
Are memory cells produced as a result of passive immunity?
No. Antigens are given, no B cells stimulated
237
Does passive immunity give long-term protection?
No. The given antibodies will break down after infection is tackled
238
Does active immunity give long-term protection?
Yes. Stimulates an immune response which causes memory cells to remain in blood for secondary infection
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Why are many different antibodies produced for one pathogen?
Each pathogen has many different antigens on its surface, so antibodies produced for each one in specific immune response
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What is special about monoclonal antibodies?
They have a specific, identical structure which is complementary to only one antigen. Useful fr medical diagnosis
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What causes an immune response?
Antigens (on pathogen)
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What is the benefit if herd immunity?
There are less carriers, so less likely to be passed on
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What is herd immunity
When over 80% of the population are vaccinated/immune to a disease
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Give some examples of how monoclonal antibodies can be used in medicine.
- Cancer-targeting drugs
- Medical diagnosis
- ELISA tests
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How do cancer-targeting drugs work?
- Tumour markers are antigens only found on cancerous cells
- Monoclonal antibodies to these antigens have anti-cancer drugs attached or natural killer cells
- Drugs only affect cancerous cells, so less side effects
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How can monoclonal antibodies be used to directly target cancers? (no drugs used)
Monoclonal antibodies can attach to antigens (with specific, complementary shape) on cancer cell, blocking attachment proteins etc
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Give an example of use of monoclonal antibodies in medical diagnosis.
Pregnancy tests
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How does a pregnancy test work?
- Urine (containing hormone for pregnancy) applied to the application area
- Joins a blue bead with antibodies to hormone on it
- Hormone attached to blue bead moves up strip
- New antibodies are present on test strip, if hormone is present it binds to antibody
- Positive if blue, negative clear (as no hormone present)
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What does an ELISA test show (in layman's terms)?
The presence of an antibody or antigen in a test sample
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Why are unattached antigens washed off in an ELISA test? (vice-versa for antibodies)
To ensure that only the desired antigen is present, and that no unwanted antigens are present
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Assuming antigens are in the bottom of the well, what do the first antibodies bind onto in an ELISA test?
First antibodies bind to the antigens
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Why must the well be washed out between each step in an ELISA test?
So that there are no false positive results
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What do the second antibodies (attached to enzyme) bind onto in an ELISA test?
The first antibody (only complementary to that). Hence why it is needed to wash well of first antibody because second antibody is independent of the original antigen
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What is added to an ELISA test after the second (and final) antibody (with enzyme) is added?
- Well is washed to remove any unbound second antibodies
- A substrate is added, which will cause a colour change if enzymes are present
- ESCs form
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What organism is commonly used to make monoclonal antibodies? Why is this unethical?
- Mice are used
| - They are deliberately given tumour cells, causing suffering
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What can be done to increase the validity of an investigation?
- Repeats
- Conduct other tests which come to same conclusion
- Larger sample sizes
- Timing of investigation(s)
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What is accuracy?
How close to the real value a result is
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What is reliability?
How "correct" a data is. (i.e is it widely agreed upon?)
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What does HIV stand for?
Human Immunodeficiency Virus
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How is HIV caught?
Transmission of body fluids.
| Unprotected sex, blood sharing, pregnancy (but not saliva/sweat/urine)
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What does AIDS stand for?
Acquired Immune Deficiency Syndrome
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What is AIDS?
The final stages of a HIV infection
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What does HIV do?
Infects and kills T helper cells
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What is the problem with HIV infecting T helper cells?
T helper cells send chemical signals that activate phagocytes, Tc cells and B cells. Immune response is greatly reduced - susceptibility to illnesses increases
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What happens to cause AIDS?
T helper cells become critically low so other infections occur
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What is used to test for HIV?
ELISA test
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What is the core of HIV called?
A capsid
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What is the genetic material of HIV?
RNA
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What is found inside a HIV capsid?
- Genetic material (RNA)
| - Enzymes (reverse transpriptase, protease, intergrase)
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What is the matrix of a HIV made from?
Proteins
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How does HIV fuse with T helper cell membranes?
With attachment glycoproteins which stick to receptors on the Th cell membrane
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What part of HIV is released into T helper cells?
The contents of the capsid (RNA and enzymes)
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What does the enzyme reverse transcriptase (HIV) do?
Copies viral RNA into single-stranded DNA, then double-stranded DNA
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How does viral DNA travel into cell nucleus?
Via nuclear pore
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What HIV enzyme, found in capsid, inserts viral DNA into human DNA?
Intergrase
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In HIV replication, what happens to the human/viral DNA?
It is used to make a new copy of HIV RNA which travels to ribosomes to create viral proteins before new HIV particle is made.
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What is the process called whereby viruses leave cells?
Budding
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How do antibiotics kill bacteria?
Antibiotics interfere with metabolic reactions by targeting bacterial enzymes and ribosomes (enzymes and ribosomes in bacterial are different to humans)
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Why can't antibiotics be used to kill viruses?
Viruses use human ribosomes and enzymes to replicate, so inhibiting these would inhibit vital human reactions
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What do antiviral drugs do?
Inhibit reactions associated only with HIV enzymes, not human enzymes (hence the limited effect)
