Topic 2 : Cells, Cell transport and Immuntiy Flashcards
(256 cards)
1
Q
What is a cell ?
A
the basic unit of living organisms
2
Q
What two main groups can organisms be divided into ?
A
prokaryotes and eukaryotes
3
Q
What 5 structures do all prokaryotic cells contain ?
A
- cell wall made of murein
- cell surface membrane
- circular DNA molecule that is free in the cytoplasm
- 70s ribosomes
- cytoplasm
4
Q
What 3 structures may be present in a prokaryotic cell ?
A
- capsule surrounding the cell wall
- one or more plasmids (extra DNA)
- one or more flagella
5
Q
What are prokaryotic cells ?
A
cells that contain no nucleus and no membrane-bound organelles
6
Q
What are eukaryotic cells ?
A
cells that contain a nucleus and cytoplasm with many organelles
7
Q
What are 7 differences between a prokaryotic and a eukaryotic cell ?
A
- eukaryotes have a nucleus, prokaryotes don’t
- eukaryotes have mitochondria, prokaryotes don’t
- Eukaryotes have a Golgi body, prokaryotes don’t
- Eukaryotes have an endoplasmic reticulum, prokaryotes don’t
- Eukaryotes have larger 80s ribosomes, prokaryotes have smaller 70s ribosomes
- Eukaryotes have linear DNA associated with proteins, prokaryotes have circular DNA not associated with proteins
- Prokaryote cell walls contain murein, eukaryote cell walls (if present) don’t
8
Q
What 3 structures does a plant cell have that an animal cell doesn’t ?
A
- a cell wall
- chloroplasts containing chlorophyll
- vacuole with a transport membrane, containing soluble sugars, salts and sometimes pigments
9
Q
What is a plant cell wall made of ?
A
cellulose microfibrils in a matrix of other polysaccharides
10
Q
What is the purpose of a cell wall ?
A
to provide the cell with strength, support and shape
11
Q
What is an algal cell wall made of ?
A
cellulose or glycoproteins or a mixture of both
12
Q
What is a fungal cell wall made of ?
A
a nitrogen-containing polysaccharide called chitin, a polysaccharide called glycon, and glycoproteins (NO CELLULOSE)
13
Q
What is cell differentiation ?
A
the development of cells into specialised types
14
Q
What are tissues ?
A
groups of similar cells that perform a specific function and have a common origin
15
Q
What is an organ ?
A
a structure consisting of different tissues, which has a specific physiological function
16
Q
What is an organ system ?
A
several organs combining to perform multiple functions together
17
Q
What are epithelial cells ?
A
cells in the small intestine that are specifically adapted for the absorption of digested products
18
Q
How is an epithelial cells adapted for its function ?
A
- cell surface membrane is folded into microvilli, providing a large surface area for absorption of digested food
- contain lots of mitochondria with provide lots of ATP for the active transport of digested food molecules into the cell
19
Q
What are palisade mesophyll cells ?
A
plant cells found below the upper epidermis of a leaf that are adapted for photosynthesis
20
Q
How are palisade mesophyll cells adapted for their function ?
A
- they have thin cell walls providing a short diffusion pathway for entry of CO2 into the cell
- they have lots of chloroplasts to absorb more light for photosynthesis
- the cells are vertically arranged so there are fewer cell walls for light to pass through
21
Q
What are viruses ?
A
acellular, non-living organisms
22
Q
Why are viruses different to prokaryotic and eukaryotic cells ?
A
they have no nucleus, no organelles, no cell-surface membrane and no cytoplasm
23
Q
How do viruses replicate ?
A
they invade living host cells and use the cell’s metabolic processes to replicate
24
Q
How do viruses cause disease ?
A
- damage to host cells after entry and replication of viruses
- toxins produced in the process of virus replication
25
What structures does a virus particle always contain ?
- genetic material (DNA or RNA)
- enzymes
- a capsid
- attachment proteins on the outside
26
What are the attachment proteins on a virus used for ?
- attachment or entry into host cell
- act as antigens that antibodies can be produced against
27
What other structure do some viruses contain an what is its purpose ?
- an outer lipid envelope
- it aids the entry of the virus into the cell by fusing with the plasma membrane
28
Describe the process of virus replication.
- the virus particle attaches to a specific host cell using its attachment proteins, which are complementary to receptors on the cell-surface membrane of the host cell
- most viruses inject their nucleic acid into the cell, which is used as a set of instructions to direct the replication of more virus particles using the organelles of the host cell.
- this involves producing copies of the viral nucleic acids and proteins and other structures to form compete viruses that are often released by lysis of the cell
- these viruses van then infect other cells
29
What is the purpose of the nucleus ?
- contains genetic material (DNA)
- determines the development, structure and function of the cell
- controls protein synthesis
30
Describe the structure of the nucleus.
- bound by a double membrane (nuclear envelope) which has nuclear pores, allowing communication with the cytoplasm and allows transport of substances in and out of the nucleus
- contains chromatin and one or more nucleoli
31
What is chromatin ?
protein-bound, linear DNA
32
What is the function of the nucleus ?
to produce RNA and ribosomes
33
What are ribosomes ?
very small organelles, that are made of protein and ribosomal RNA
34
How do ribosomes exist in the cell ?
- freely in the cytoplasm
- attached to rough endoplasmic reticulum
35
What are ribosomes used in ?
protein synthesis, joining amino acids together
36
What does the endoplasmic reticulum consist of ?
flattened membrane sacs that form an internal transport system in the cell
37
What is the difference between the structures of smooth and rough endoplasmic reticulum ?
the smooth endoplasmic reticulum doesn't have ribosomes on its surface
38
What is the function of the rough endoplasmic reticulum ?
to produce secretory proteins that are sent to the Golgi body for modification or packaging
39
What is the function of the smooth endoplasmic reticulum ?
to produce and transport lipids
40
What does the Golgi body consist of ?
flattened membrane sacs
41
What are the functions of the Golgi body ?
- to add carbohydrates to proteins (received from rough endoplasmic reticulum) to form glycoproteins
- to package proteins/glycoproteins in Golgi vesicles for secretion
- to produce lysosomes
42
Describe the structure of a Golgi vesicle.
it contains a lipid bilayer, which separates the contents of the vesicle from the rest of the cell
43
What does a Golgi vesicle do ?
it transports proteins/glycoproteins
44
Where are lysosomes formed ?
in the Golgi body
45
What is a lysosome ?
a simple sac containing lysozymes surrounded by a single membrane
46
What are lysozymes ?
digestive (hydrolytic) enzymes
47
Why are lysosomes needed ?
to keep the cell from being destroyed by the destructive lysozymes
48
What are the functions of lysosomes ?
- digestion of material from phagocytosis
- digestion of non-functioning organelles in the cell
- release of enzymes outside of the cell
49
How are lysosomes involved in phagocytosis ?
lysosomes fuse with the vesicles formed in phagocytosis, release their lysozymes and hydrolyse the material inside
50
What is the function of mitochondria ?
they are involved in aerobic respiration, which synthesises ATP
51
Describe the structure of a mitochondria.
bound by two membranes, forming an envelope around an inner matrix
52
What are cristae ?
folds of the mitochondria's inner matrix
53
What does the matrix of mitochondria contain ?
- enzymes for respiration
- circular DNA
- ribosomes
54
What is the advantage of cristae ?
they provide an increased surface area for more respiration
55
Where are chloroplasts found ?
in photosynthetic plant cells and algae
56
Describe the structure of a chloroplast.
a flattened biconcave disc, surrounded by an envelope made of two membranes
57
What is a thylakoid ?
a flattened sac
58
What is a granum ?
a stack of thylakoids
59
What is the purpose of grana ?
to provide a large surface area for chlorophyll molecules to absorb light for photosynthesis
60
What does the stoma contain ?
enzymes, sugars and starch granules
61
What is a vacuole and where is it found ?
- a membrane-bound organelle
- found in all plant cells
62
What does the vacuole consist of ?
cell sap
63
What is cell sap made of ?
water containing sugars, amino acids and ions
64
What is the function of the vacuole ?
- to maintain turgor pressure
- to provide support to leaves and flowers due to turgor pressure
65
What is differential centrifugation ?
- centrifuging a substance at different speeds
- can be used to separate and isolate the different organelles in a cell
66
What is the first step in cell fractionation and ultracentrifugation ?
homogenising the tissue in an isotonic, ice cold buffer solution in a blender to break the cells open
67
Why is an isotonic solution used during homogenisation ?
to prevent movement of water in or out of the organelles by osmosis, which would cause them to burst or shrivel
68
What is autolysis of a cell ?
self-digestion of the cell by hydrolytic enzymes
69
Why is an ice cold solution used during homogenisation ?
to prevent digestive enzymes in the cell from destroying the organelles
70
Why is a buffer solution used during homogenisation ?
to maintain pH so that proteins (particularly enzymes) are not denatured
71
Why is the solution filtered after homogenisation ?
to remove cell debris such as plant cell walls or cells that haven't burst
72
In what order are the cell organelles isolated during centrifugation ?
1. nuclei
2. chloroplasts (if plant cell)
3. mitochondria
4. lysosomes
5. endoplasmic reticulum
6. ribosomes
73
Describe the full process of cell fractionation and ultracentrifugation.
- cells broken open by being homogenised in an ice-cold, isotonic buffer solution in a blender
- solution is then filtered to remove cell debris
- homogenate centrifuged at low speed and densest organelles form a pellet at the bottom which can be collected
- homogenate can then be centrifuged at a higher speed for a longer time to collect the next densest organelles
- this is repeated at higher speeds for increasing periods of time to collect pellets of all the organelles
74
What is magnification ?
how much bigger the object appears compared to the actual size of the object
75
What is resolution ?
the minimum distance apart that two objects can be for them to appear as separate images
76
What is the object ?
the material under the microscope
77
What is the image ?
the appearance of the object under the microscope
78
How does a light microscope work ?
light passes through a specimen usually mounted on a glass slide
79
What must the specimen be like for a light microscope and why ?
- thin, so light can pass through and single layer of cells are visible
- stained so that structures are visible
80
How does an electron microscope work ?
a beam of electrons focused by electromagnets is passed through a specimen
81
What must the specimen be like for an electron microscope and why ?
dead, as a vacuum is required
82
What are the 7 differences between a light and an electron microscope ?
1. a light microscope uses a beam of light, whereas an electron microscope uses a beam of electrons
2. an electron microscope has greater resolution
3. a light microscope is focused using glass lenses, whereas an electron microscope is focused using magnets
4. an electron microscope has greater detail and can see smaller structures
5. in a light microscope the specimen can be living but in an electron microscope it must be dead
6. in a light microscope the image is in colour
7. in a light microscope the preparation of the specimen is quick and easy
83
What are the advantages of a light microscope ?
- the specimen can be living
- preparation of the specimen is quick and easy
- image is in colour
84
What are the disadvantages of a light microscope ?
- low resolution
- lower detail and smaller structures aren't visible
85
What are the advantages of an electron microscope ?
- greater resolution
- greater detail and smaller structures are visible
86
What are the disadvantages of an electron microscope ?
- specimen must be dead and dehydrated
- preparation of the specimen is complex and time-consuming
- image isn't in colour
87
What are the two main types of electron microscope ?
- transmission electron microscope
- scanning electron microscope
88
How does a transmission electron microscope work ?
- a beam of electrons is transmitted through the specimen
- electrons are deflected by electron-dense substances on the specimen, and the pattern of electrons that pass through is converted to an image
89
What must the specimen be like for a transmission electron microscope ?
- thin
- stained with electron-dense substances e.g heavy-metal salts
90
What is an artefact ?
something on the slide that shouldn't be there
91
How does a scanning electron microscope work ?
- the specimen is coated with a thin film of a heavy metal
- electron beam is scanned to and fro across the specimen
- electrons that are reflected from the surface are collected and produce an image on a viewing scan
92
What are the 4 differences between a transmission and a scanning electron microscope ?
1. a transmission electron microscope has a higher resolution
2. a transmission electron microscope produces an image of internal structures, whereas a scanning microscope produces an image of external/surface structures
3. a transmission electron microscope produces a 2D image, whereas a scanning electron microscope produces a 3D image
4. a scanning electron microscope can have a thicker specimen
93
What is the advantage and disadvantage of a transmission electron microscope ?
advantage - has a higher resolution
disadvantage - specimen must be very thin
94
What is the advantage and disadvantage of a scanning electron microscope ?
advantage - can have a thicker specimen
disadvantage - has a lower resolution
95
What is an eyepiece graticule used for ?
to measure the size of objects viewed through a microscope
96
What is the equation for magnification ?
magnification = image / actual
97
How do you convert from millimetres to micrometres ?
x 1000
98
How do you convert form micrometres to nanometres ?
x 1000
99
How do you convert for nanometres to micrometres ?
x 10^-3
100
How do you convert from micrometres to millimetres ?
x 10^-3
101
What does the cell-surface membrane control ?
the movement of substances in and out of cells
102
Why can the cell-surface membrane be described as fluid ?
the phospholipid molecules are constantly moving in the bilayer
103
Why can the cell-surface membrane be described as a mosaic ?
the protein molecules are unevenly distributed throughout the membrane
104
How are the phospholipids arranged in the cell-surface membrane ?
- hydrophilic heads face outwards to cytoplasm or to extracellular fluid
- hydrophobic tails face inwards and are attracted to each other
105
What types of molecules can pass straight through the phospholipid bilayer ?
- gases
- hydrophobic molecules
- small polar molecules
106
What types of molecules cannot pass straight through the phospholipid bilayer ?
- large polar molecules (water)
- charged molecules
107
What is the purpose of cholesterol in the cell-surface membrane ?
- to provide strength to the membrane
- to restrict movement of phospholipids, so there is a less fluid membrane and there are less ions from the cell
108
How do fatty acids affect the permeability of the cell-surface membrane ?
- unsaturated fatty acids increase permeability
- saturated fatty acids decrease permeability
109
What is the purpose of carrier and channel proteins in the cell-surface membrane ?
to aid the transport of water-soluble ions and polar molecules across the membrane
110
What is the purpose of receptor proteins in the cell surface membrane ?
- cell-signalling
- they have a specific tertiary structure allowing a specific hormone with a complementary shape to attach to a binding site, and then the cell can respond
111
What is the purpose of glycoproteins in the cell surface membrane ?
- they are involved in cell recognition
- they act as antigens, so foreign antigens can be recognised and attacked by the immune system
112
What are the 5 ways substances can be transported across a membrane ?
- simple diffusion
- facilitated diffusion
- osmosis
- active transport
- co-transport
113
What is diffusion ?
the net movement of molecules down a concentration gradient until the molecules are equally distributed
114
What does "down the concentration gradient" mean ?
from a high concentration to a low concentration
115
What type of process is simple diffusion ?
passive (doesn't require energy)
116
What factors affect the rate of diffusion ?
- surface area
- thickness of exchange surface
- concentration gradient
117
How does simple diffusion occur ?
small and non-polar molecules move freely and diffuse directly through a membrane
118
What is facilitated diffusion ?
diffusion of polar molecules through a carrier or channel proteins across a membrane
119
What type of process is facilitated diffusion ?
passive (doesn't require energy)
120
How does a carrier protein transport molecules across a membrane ?
- the molecule attaches
- the protein changes shape
- the molecule is released on the opposite side
121
What type of molecule do carrier proteins transport ?
large molecules
122
How do channel proteins transport a molecule across a membrane ?
molecules with the complementary structure, size and charge pass through the centre of the protein
123
What type of molecule do channel proteins transport ?
charged particles
124
What factors affect the rate of facilitated diffusion ?
- concentration gradient
- number of carrier and channel proteins
125
What is active transport ?
the movement of molecules through a partially permeable membrane by carrier proteins against a concentration gradient
126
What type of process is active transport ?
active (requires energy)
127
Where does the energy needed for active transport come from ?
it is released from the hydrolysis of ATP during respiration
128
How does active transport occur ?
- the molecule attaches to the carrier protein which has a specific tertiary structure which is complementary to the polar molecule
- the binding causes the carrier protein to change shape and transport the molecule across the membrane
129
Why do cells involved in active transport have lots of mitochondria ?
to provide the ATP required via respiration
130
What factors decrease the rate of active transport ?
- decrease in temperature
- lack of oxygen
- metabolic and respiratory inhibitors
131
Why do the factors that affect respiration also affect active transport ?
because active transport requires respiration to occur
132
What is osmosis ?
the net movement of water from a dilute solution to a concentrated solution across a partially permeable membrane
133
What factors affect osmosis ?
- water potential gradient
- surface area
- thickness of exchange surface
134
How does the water potential gradient affect the rate of osmosis ?
as the water potential gradient increases, the rate of osmosis increases
135
How does the thickness of exchange surface affect the rate of osmosis ?
the thicker the exchange surface, the slower the rate of osmosis
136
How does surface area affect the rate of osmosis ?
the larger the surface area, the faster the rate of osmosis
137
What is water potential ?
the potential of the water molecules to leave a solution by osmosis
138
What is meant by a high water potential ?
the solution has a high concentration of water molecules
139
What is osmosis in terms of water potential ?
the net movement of water molecules from a higher water potential to a lower water potential through a partially permeable membrane
140
What is meant by isotonic ?
two solutions have the same water potential so there is no net movement of water
141
What is meant by hypotonic ?
- higher water potential
- net movement of water into the cell
- may cause animal cells to burst
142
What is meant by hypertonic ?
- lower water potential
- net movement of water out of the cell
- can cause animal cells to shrink
143
What happens to a plant cell when it is placed in distilled water ?
- water enters the cell and the vacuoles get bigger
- vacuole, cytoplasm and cell membrane exert an outward turgor pressure on the cell wall
- cell stiffens and generally retains its shape
144
What happens to a plant cell when it is placed in concentrated salt solution ?
- water moves out of the cell via osmosis
- cell body shrinks and pulls away from the cell wall
145
What is DNA like in prokaryotic cells ?
- short and circular
- doesn't form chromosomes
- not associated with proteins
146
What is DNA like in eukaryotic cells ?
- long and linear
- forms chromosomes
- associates with proteins called histones
147
What is a locus ?
the fixed position a gene occupies on a DNA molecule or chromosome
148
What is an allele ?
a version of a gene that codes for a different type of a gene
149
What does a homologous pair of chromosomes consist of ?
a maternal and paternal chromosome
150
What is a homologous pair of chromosomes ?
a pair of genes that are the same length and carry the genes that control the same characteristics but not necessarily the same allele
151
What is mitosis ?
a type of nuclear division that produces genetically identical cells
152
How many daughter cells does mitosis produce ?
two
153
What is the purpose of mitosis ?
growth and repair of tissues
154
What is a diploid cell ?
a cell that contains the total number of chromosomes in a normal body cell
155
What is a haploid cell ?
a cell that contains a single set of chromosomes (one from each homologous pair)
156
What type of cells does mitosis produce ?
cells with the same number of chromosomes as the parent cell
157
What are the 3 stages of the cell cycle ?
- interphase
- nuclear division (mitosis)
- cytokinesis
158
What happens during interphase ?
- there is an increase in protein synthesis
- DNA content doubles via DNA replication
- cell organelles are replicated
159
What are the 4 stages of mitosis ?
- prophase
- metaphase
- anaphase
- telophase
160
What happens during prophase ?
- chromosomes form as two identical sister chromatids joined at the centre by a centromere
- each chromosome shortens and thickens
- centrioles move to opposite poles of the cell
- nuclear membrane breaks down
161
What happens during metaphase ?
- centrioles form spindle fibres between them
- chromosomes line up along the equator of the cell and attach to the spindle fibres by their centromeres
162
What happens during anaphase ?
- centromere splits and sister chromatids separate
- sister chromatids are pulled by the spindle fibres centromere first to opposite poles of the cell
163
What happens during telophase ?
- chromatids are at opposite ends of the cell and begin to uncoil
- nuclear membrane reforms
- the two cells are genetically identical to each other and to the parent cell
164
What happens during cytokinesis ?
- cytoplasm splits in two
- two new cells form as a cell-surface membrane forms
165
What causes cancer ?
uncontrolled growth and rapid cell division
166
What is a tumour ?
a group of abnormal cells formed by uncontrolled cell division and growth
167
What can drugs inhibit to prevent cancerous cells from dividing ?
- DNA helices and DNA polymerase
- formation of spindle fibres
168
How can you calculate the mitotic index ?
cells in mitosis / total number of cells
169
How can you tell if cells are dividing rapidly ?
they are in interphase for a short period of time
170
How do prokaryotes mainly reproduce ?
asexual reproduction, by binary fission
171
How does binary fission occur ?
- cell elongates
- circular DNA and plasmids are replicated
- septum wall dorms right across the cell, dividing the cytoplasm producing two daughter cells, each with a single copy of circular DNA and some plasmids
- two daughter cells separate and cell cycle begins again
172
How many daughter cells does binary fission produce ?
two
173
Why are the daughter cells from binary fission not genetically identical ?
because the distribution of plasmids is uneven
174
What is the generation time ?
the time taken for a bacteria population to double in number
175
What type of increase does a bacterial population show, and why ?
an exponential increase, as each generation is doubled to produce the next one
176
How do you calculate the number of bacteria in a population ?
population in the nth generation = 2^n
177
What is a pathogen ?
a disease-causing microorganism
178
What are 3 examples of pathogens ?
- bacteria
- viruses
- fungi
179
When does disease occur ?
when an infection leads to recognisable symptoms in the host
180
What is transmission ?
when a pathogen is transferred from one individual to another
181
What are the two types of defence mechanisms ?
- specific
- non-specific
182
What are the 2 differences between specific and non-specific defence mechanisms ?
1. specific is slower, non-specific is immediate
2. specific is specific to each pathogen, non-specific is the same for all pathogens
183
What are non-specific defence mechanisms ?
general defence mechanisms that respond to all pathogens the same way
184
What are 4 examples of non-specific defence mechanisms ?
- barriers to entry (skin)
- mucus
- cilia
- phagocytosis
185
What is mucus ?
a substance secreted by epithelial cells lining the nasal passage and respiratory tract
186
How does mucus act as a non-specific defence mechanism ?
it is sticky, so traps bacteria and dust particles entering the air passage
187
What are cilia ?
minute hairs on the surface of epithelial cells in the upper part of respiratory tract
188
How do cilia act a nonspecific defence mechanism ?
they beat to move mucus and trapped particles to the throat, which are then swallowed and killed by stomach acid or enzymes
189
What is phagocytosis ?
the engulfment and destruction of microorganisms by phagocytic white blood cells
190
Describe the process of phagocytosis.
- phagocyte extends around the pathogen and engulfs it, forming a phagosome
- lysosome fuses with phagosome, and lysozymes hydrolyse the pathogen
- soluble digested products are absorbed, indigestible material is removed
191
How do phagocytes act as antigen-presenting cells ?
- phagocyte removes antigens from the pathogen they destroy and presents them on its cell-surface membrane to T-cells
192
What are specific defence mechanisms ?
they involve the immune system and a specific response against a pathogen, abnormal cell or toxin
193
What are the two types of specific defence mechanisms ?
- humoral response
- cellular response
194
What type of white blood cell does each specific defence mechanism involve ?
- humoral response involves B lymphocytes
- cellular response involves T lymphocytes
195
Where are T and B lymphocytes produced ?
- T lymphocytes are made in the thymus
- B lymphocytes are made in bone marrow
196
What are antigens ?
proteins or glycoproteins that appear foreign to the individual organisms exposed to them
197
What do antigens stimulate ?
the production of antibodies by B lymphocytes
198
In what 4 ways may antigens be present ?
- on the surface of the pathogen
- on the cell-surface membrane of other organisms of the same species
- on abnormal body cells
- as a toxin
199
What is the humoral response ?
involves B cells and the production of antibodies in response to a specific antigen
200
How does the humoral response occur ?
when exposed to the appropriate antigen, B cells secrete the specific antibody into blood plasma to destroy or neutralise the antigen and pathogen
201
What type of protein is an antibody ?
quaternary
202
Where are antibodies found ?
- in blood plasma
- in tissue fluid
- in breast milk
203
Describe the basic structure of an antibody.
- consists of 4 polypeptide chains, 2 heavy and 2 light, each with a constant and variable region, and are joined together by disulfide bonds
204
What is the constant region in an antibody ?
where the sequence of the amino acids is the same in all molecules of the antibody type
205
What is the variable region in an antibody ?
where the amino acid sequence is different in different molecules of the same type of antibody
206
What do the variable regions of the heavy and light chains form ?
two antigen-binding sites
207
How do antibodies bind to an antigen ?
- antigen-binding site has a specific tertiary structure which is complementary to the antigen structure
- the antigen attaches, forming an antibody-antigen complex
208
What two processes are stimulated by the formation of an antibody-antigen complex to destroy the pathogen ?
- agglutination of antigens
- stimulation of phagocytosis
209
What is agglutination ?
the clumping together of cells possessing the antigen against which specific antibodies react
210
How does agglutination occur ?
- an antibody molecule can use both its antigen-binding sites to attach to the same antigen on two different cells
- this joins the cells together
- more antibody molecules attach, linking more cells together and forming an agglutinated mass of cells which can be more easily destroyed
211
When does agglutination of donor red blood cells occur ?
when an individual receives the wrong blood group
212
How does stimulation of phagocytosis occur ?
- one type of antibody attaches to the antigen on the surface of a pathogen and identifies it for destruction by phagocytic white blood cells
- phagocytes have receptors in their cell-surface membranes that recognise the antibody and enable them to bind to, engulf and destroy the pathogen
213
What is antigenic variation ?
the ability of a virus to mutate and alter the proteins on its surface
214
Why is antigenic variation a problem ?
it means that it is very difficult to create a vaccine against the virus
215
Describe the production of antibodies in the humoral response.
- the body has a large number of lymphocytes (B cells) which each produce a different specific antibody
- the B cells secrete small amounts of their specific antibody onto their cell-surface membrane
- if a specific antigen attaches to the complementary on B cells, the B cells are stimulated to divide by mitosis, resulting in a large number of identical plasma cells
- the B cells are also stimulated by helper T cells, and some B cells are stimulated to divide and develop into memory B cells
- the plasma cells all produce the same specific antibody and release it into the blood plasma
- the antibodies bind specifically to the antigens forming on the antibody-antigen complex, which stimulates processes leading to the antigen/pathogen being destroyed
216
What happens if the same antigen reinfects an individual ?
- memory B cells divide and develop into plasma cells
- the plasma cells secrete antibodies quicker and at a higher rate of concentration than the primary response
217
How does antigenic variation prevent an individual from becoming immune to a virus ?
- an individual may become immune to one strain of a virus, but the new forms of the virus won't be recognised by the memory B cells and so the antibodies previously produced are not complementary
218
How does the secondary response provide immunity ?
the microorganisms are destroyed before disease symptoms develop
219
What do T cells do ?
possess T cell receptors which recognise specific antigens
220
What are T cell receptors ?
proteins on the cell-surface membrane of T cells that recognise specific antigens
221
What does a helper T cell do ?
they release chemical signals that stimulate phagocytes
222
What do cytotoxic T cells do ?
they attach to the specific antigen on the pathogen and secrete chemicals to destroy it
223
What do the cloned helper T cells do ?
- activate cytotoxic T cells
- develop into more helper T cells to stimulate B cells to divide into plasma cells and secrete antibodies
- develop into T memory cells
224
What happens during the cellular response ?
- the antigen is presented to a helper T cell by an antigen-presenting cell
- helper T cells with the complementary protein receptor will bind to the antigen
- this stimulates the helper T cells to divide by mitosis and form a clone of genetically identical T cells all with the same receptor
225
What is the purpose of T memory cells ?
they remain in the blood after the infection has cleared and produce a quicker response if a future infection occurs with the same antigen/pathogen
226
What is perforin ?
a protein that destroys antigens/pathogens
227
What is passive immunity ?
where an individual receives preformed antibodies from an outside source
228
What type of protection does passive immunity provide and why ?
- short-term, immediate protection
- antibodies are not produced by the individual and are not replaced once they're broken down
229
How does natural passive immunity occur ?
- antibodies obtained across the placenta and through breast milk
- provides short term protection as the body isn't stimulated into producing its own antibodies and memory cells
230
How does artificial passive immunity occur ?
- the pre-formed specific antibodies are injected usually after exposure to particularly infectious pathogens or toxins
231
What is active immunity ?
where an individual exposed to the antigen produces antibodies and memory cells
232
What type of protection does active immunity provide and why ?
- long term protection
- the immune system has prodded its own antibodies and memory cells
233
How does natural active immunity occur ?
the individual becomes infected and is exposed to the specific antigen
234
What are the 4 differences between active and passive immunity ?
1. passive is short-term, active is long-term
2. passive provides immediate protection, active takes tine for protection to develop
3. passive doesn't need exposure to the antigen, active needs exposure to the antigen
4. passive doesn't produce memory cells, active does produce memory cells
235
How does artificial active immunity occur ?
the individual is vaccinate against a disease and the immune system produces its own antibodies and memory cells
236
What does a vaccine contain ?
antigens from a specific pathogen
237
What form can antigens be in in a vaccine ?
- dead pathogen
- weakened strain of the pathogen
- antigens from the pathogen
238
What does injection of the vaccine stimulate ?
production of plasma cells, which release specific antibodies, memory B-cells and memory T-cells; which provide long-term immunity
239
How does herd immunity work ?
- the higher the percentage of the population vaccinated against a particular infection, the lower the probability of encountering an unprotected individual
- therefore there is a lower risk of an epidemic
240
What are the two main factors in determining whether to vaccinate a child ?
- possibility of side effects
- effectiveness of the vaccine in providing protection
241
What 5 things does a HIV virus particle contain ?
- two strands of RNA
- two reverse transcriptase enzymes
- a capsid
- viral envelope
- surface glycoproteins
242
What is the purpose of RNA in a HIV particle ?
to contain the genetic information to produce more HIV particles
243
What is the purpose of reverse transcriptase in a HIV particle ?
to transcribe RNA into DNA once inside a host cell
244
What is the purpose of a capsid in a HIV particle ?
to protect the nucleic acids inside
245
What is the purpose of surface glycoproteins in a HIV particle ?
to allow the HIV to attach to the host cell
246
What 4 ways is HIV transmitted ?
- sexual transmission
- blood products
- sharing of needles
- mother to baby
247
Describe the process of HIV replication.
- the virus attaches to the T-helper cell by surface glycoproteins attaching to receptor sites on the membrane of the helper T cells
- viral RNA and reverse transcriptase released into T lymphocyte
- DNA formed in the T helper cell by reverse transcriptase using the RNA as a template
- viral DNA enters nucleus and attaches to host DNA
-viral DNA replicates with host DNA
- when activated the viral DNA controls the synthesis of viral proteins and viral RNA in the T cell
- HIV particles are assembled and the T helper cell is destroyed as viruses are released, which go one to infect other T cells
248
How does HIV cause a breakdown in immune response ?
- as the virus particles reproduce, the number of T cells in the blood decreases
- these T cells are essential in stimulating antibody production by B cells in the immune response
- so as the number of T cells decreases, the effectivity if the immune response also decreases
249
What are the symptoms of HIV in the first stage ?
- the body produces HIV antibodies
- short flu-like illness
250
What are the symptoms of HIV in the second stage ?
- no symptoms
- antibody-positive phase
251
What happens to someone with HIV in the third stage ?
- individual may contract a variety of opportunistic infections, that at this stage are not life-threatening
- loss of weight
- reduction of T helper cells
252
What happens to someone with HIV in the fourth stage ?
- opportunistic infections of body organs
- development of secondary cancers
- HIV wasting syndrome with dramatic weight loss
- immune system collapses
253
How can we prevent a HIV infection ?
- reduced promiscuity and safe sex via condoms
- blood screening to prevent HIV-anitbody-positive blood from being passed on
- tissue screening for transplants, to prevent donations from HIV antibody individuals
- providing clean needles to drug users to prevent sharing used needles
- bottle feed instead of breast feed
- elective cesareans
254
Why are antibiotics completely ineffective against viruses ?
viruses don't have cellular structures as they use those of the host cell, so they can be destroyed by the antibiotics
255
How do antibiotics destroy bacteria ?
- they inhibit their division
- they affect their cellular structures
256
