4.6 immunology and disease Flashcards
(196 cards)
1
Q
endemic definition
A
- a disease that is always present, but at low levels (in an area)
(frequency at a predictable rate in a specific location)
2
Q
toxin definition
A
- a chemical produced by a pathogen/microorganism that causes damage to its host
3
Q
carrier definition
A
an infected individual that is asymptomatic but able to infect other
4
Q
disease reservoir definition
A
- the environment (host) in which an infectious pathogen is normally found
5
Q
infection definition
A
a transmittable disease often aquired by inhalation, ingestion or physical contact
6
Q
antigenic type definition
A
organisms that possess the same or very similar antigens on their surface
- such types are sub-groups or strains of a microbial species which may be used to trace infections
- they are usually identified by using antibodies
7
Q
epidemic definition
A
the rapid spread of infectious disease to a large number of people within a short period of time
- significant increase in the usual number of cases of a disease
8
Q
pandemic definition
A
an epidemic occurring worldwide or in multiple countries, usually affecting a large number of people
9
Q
antigen definition
A
- a chemical present on the surface of a cell that induces an immune response
10
Q
vector definition
A
a living organism that carries and transmits infectious pathogen between organism
11
Q
what is cholera caused by?
A
the Gram-negative bacterium Vibrio cholerae
12
Q
is cholera endemic?
A
- yes
- in some parts of the world
13
Q
what are the symptoms of cholera?
A
- whilst infected with cholera, the bacteria release a toxin, affecting the gut lining, resulting in watery diarrhoea and severe dehydration
14
Q
how is cholera transmitted?
A
- fecal/oral transmission
- ingesting contaminated food or water
- people become infected when they consume contaminated food or water
- they become carriers of the disease, acting as reservoirs
- humans act as reservoirs or carriers and contaminate water supplies in which the organism is transmitted, although it only multiplies in the human host
15
Q
what is the treatment for cholera?
A
- dehydration is treated by giving clean water and electrolytes (rehydration), and the infection can be treated with antibiotics
- prevention = better sewage and water treatment, safe handling of food, by washing hands and good hygiene
- antibiotics
- a vaccine is available which may provide temporary protection
16
Q
what is Tuberculosis (TB) caused by?
A
- the bacillus Mycobacterium tuberculosis (bacteria)
17
Q
what are the symptoms of TB?
A
- lymph nodes in the lungs become damaged, forming tubercles or nodules
- patients present with chest pain, blood in their sputum, and a fever
- weakened immune system
- if left untreated it can be fatal due to extensive lung damage
- areas of dead and damaged cells in the lungs show up clearly on x-rays
18
Q
how is TB spread?
A
- airborne droplet transmission
- infection spreads rapidly by inhalation of water droplets from coughs and sneezes from infected people
- it spreads more rapidly amongst people with depressed immune systems e.g from HIV-AIDS, and in crowded conditions
19
Q
what is the treatment of TB?
A
- treatment: is by a long course (6 months) of antibiotics, but some strains are now showing antibiotic resistance
- prevention: a BCG vaccine (made from a weakened strain of a related bacterium M.bovis) is available
20
Q
what is small pox caused by?
A
- the virus Variola major
21
Q
what are the symptoms of smallpox?
A
- it causes fever and pain with a rash and fluid-filled blisters
- headache, fever and pockmarking of the skin
- it can leave patients with blindness and limb deformities
22
Q
how is smallpox transmitted?
A
- infection enters small blood vessels in the skin and mouth, quickly spreading throughout the body
- droplet transmission
- bodily fluids
23
Q
what is the treatment for smallpox?
A
- pain killers and fluid replacement therapy help relieve the symptoms
- antibiotics can help treat secondary infections but mortality is high at 60%
- a vaccine made from the Vaccinia virus resulted in the eradication of smallpox by 1979
24
Q
what means that the immune system is unable to produce adequate protection from all types of flu, which can result in epidemics?
A
- the influenza virus has three subgroups which contain viruses with different antigenic types (have different antigens on their surface)
- within each sub-group, there are many different antigenic types
- so epidemics can occur
- pandemics can also occur e.g Spanish flu in 1918-20 which killed over 50million people worldwide
25
what are the symptoms of the influenza virus?
- flu virus attacks the mucous membranes in the upper respiratory tract resulting in fever, sore throat and cough
- headache, coughing and sneezing, muscular and joint pain
- may cause secondary bacterial infections can result in vulnerable people e.g children and the elderly
26
how is the influenza virus transmitted?
- droplets from coughs and sneezes
- contact with contaminated surfaces
27
what is the treatment of the influenza virus?
- quarantine
- antibiotics treat secondary bacterial infections (ineffective against the actual virus)
- management of symptoms e.g painkillers
- infection spread can be reduced by regular washing of hands, using tissues to catch sneezes and coughs and isolating patients
- vaccines have some effect depending upon the degree of mutation in the viral antigens
- antiviral drugs, e.g Tamiflu, have some success in reducing length of symptoms and may prevent flu from developing if taken as a preventative measure
28
what is malaria caused by?
- a protoctistan parasite Plasmodium spp
29
what are the two species that cause the largest number of cases of malaria?
- P.falciparum
- P.vivax
- which are transmitted by over 100 different species of Anopheles mosquitoes
- they have many different antigenic types
- dont need to learnn
30
what acts as the vector in transmitting malaria?
- it’s the female mosquito that acts as the vector when it feeds on blood
31
is malaria endemic?
- yes
- in some sub-tropical regions and can become epidemic during wet seasons
32
what are the symptoms of malaria?
- the cycle of red blood cells bursting repeats every few days and gives rise to recurring fevers
- can be fatal
33
how is malaria transmitted?
- when a female mosquito feeds on blood
- it ingests the Plasmodium parasite which migrates to the liver where they develop
- before being released to infect red blood cells causing them to burst
34
how is malaria treated?
- treatment targets the parasite whilst it is in the blood rather than in the cells
- using a variety of anti-malarial drugs, the first of which was quinine
- Plasmodium now shows resistance to many of these drugs, so drug combinations are commonly used
- prevention by using mosquito repellants and insecticide bed nets
- use of insecticides
- drainage of stagnant water where mosquitos lay their eggs
- releasing sterile male mosquitoes
- biological control using fish that eat mosquito larvae (mosquito larvae are aquatic and can be eaten by introducing fish)
35
what are viruses?
- non-living infectious agents that invade host cells and take over cell metabolism, replicating within them
36
viruses cause pathogenic effects to the host in several ways. what are some of these ways:
- during cell lysis, the cell bursts allowing virus particles to emerge and infect other cells, which causes many of these symptoms seen
- viruses produce many different toxic substances, e.g viral proteins can inhibit DNA and protein synthesis, and glycoproteins produced by the Herpes virus can cause cell fusion
- cell transformations can occur, which means that viral DNA integrates into the host chromosome. if this occurs into a proto-oncogene or tumour suppressor gene, uncontrollable cell division can result (cancer)
- immune suppression results from some viruses e.g HIV virus, which destroys T helper cells
37
antibiotic definition
substances produced by microorganisms that inhibits the growth or destroys bacteria
38
what are some ways of controlling bacteria infection?
- sterilisation
- disinfection
- antibiotics
39
what does sterilisation do to bacteria?
- results in all microorganisms and spores being killed
40
how is sterilisation of bacteria usually achieved?
- by autoclaving in excess of 121°C for at least 15 minutes
- or by use of gamma radiation
41
what does disinfection do to bacteria?
- will remove the majority of microorganisms but not all
42
by using what is something disinfected?
- using antiseptics
- or disinfectants
43
what are the two types of antibiotics?
- bactericidal
- bacteriostatic
44
what does it mean if antibiotics are bactericidal?
- kill bacteria
- e.g penicillin
45
what does it mean if antibiotics are bacteriostatic?
- they prevent the growth of bacteria within the body
- e.g tetracycline which inhibits protein synthesis
- tetracycline only prevents growth whilst the antibiotic is present
46
________ greatly influences the type of antibiotic that will be effective?
the structure of the bacterial cell wall
47
gram-positive bacteria’s cell wall structure:
- thicker cell walls
- containing peptidoglycan with polysaccharide molecules cross-linked to amino acid side chains
- the cross-linking confers strength and protects against osmotic lysis
48
gram-negative bacteria’s cell wall structure:
- thinner but more complex cell walls
- still have a little peptidoglycan, but this is covered by a layer of lipoprotein and lipopolysaccharide, which protects the bacteria from some antibacterial agents such as lysozyme and penicillin
49
what does penicillin prevent? why?
- the synthesis of the cross-links in peptidoglycan
- because transpeptidase enzymes that cross-link the polysaccharide molecules to the amino acid side chains are inhibited by penicillin
50
what does preventing the synthesis of the cross-links in peptidoglycan lead to?
- it weakens the cell wall
- and as water enters by osmosis, the cell bursts (osmotic lysis)
51
why is penicillin referred to as narrow spectrum antibiotics?
- because penicillin only causes lysis in Gram-positive bacteria
52
how do Tetracycline and chloramphenicol work as antibiotics?
- differently to penicillin
- they stop protein synthesis within the bacterial cell
- but dont affect normal cell metabolism
- tetracycline works by binding to the 30S subunit of the bacterial ribosome in the second position blocking further tRNA attachment
53
is tetracycline bacteriostatic or bactericidal? why?
- bacteriostatic
- as tetracycline binds to the ribosomes reversibly
54
is tetracycline referred to as a narrow spectrum antibiotic or a broad spectrum antibiotic?
- broad spectrum antibiotic
- because tetracycline affects both Gram-positive and negative bacteria
55
what is antibiotic resistance?
- the ability of a microorganism to withstand the effect of an antibiotic
56
how does antibiotic resistance evolve?
- naturally as bacteria have a high mutation rate and divide rapidly
57
steps of antibiotic resistance:
- if a mutation arises which changes one allele within the bacterium’s plasmid
- resulting in the bacterium being able to produce an enzyme which can break down the antibiotic
- the bacterium has a selective advantage in the presence of antibiotics
- so passes the advantageous allele on, by plasmid transfer or in asexual reproduction
58
what is an example of a bacterium that is antibiotic resistant to many antibiotics?
- MRSA
- (methicillin resistant Staphylococcus aureus)
- is resistance to beta-lactam antibiotics, including methicillin, oxacillin, penicillin and amoxicillin
59
what has antibiotic resistance arisen due to?
- largely through the over use of antibiotics for viral infections
- and prevention of infection in farmed animals
60
why are antibiotics ineffective against viruses?
- because viruses don’t have metabolic pathways present or possess any peptidoglycan
61
what does the primary defences (natural defences) against entry of pathogens in animals include?
- skin
- natural skin flora
- lysozymes
- stomach acid/hydrochloric acid
- cilia and mucus
- blood clotting
- inflammatory response
- phagocytosis
62
how does skin help against the entry of pathogens in animals?
- its a physical barrier
- and has a slightly acidic pH preventing the growth of pathogens
(vitamin C is needed to maintain strong connective tissue)
63
how does natural skin flora help against the entry of pathogens in animals?
- it offers protection by competing with pathogenic bacteria, and unlike these bacteria, the flora is not easily removed by washing
64
how do lysozymes help against the entry of pathogens in animals?
- produced in tears (and saliva) which can hydrolyse peptidoglycan in bacterial cell walls
- the weakened cell wall breaks as water from the tears and saliva enters the microbe by osmosis, causing the cells to lyse, killing the bacteria
65
how does stomach acid help against the entry of pathogens in animals?
- it kills ingested bactera
66
how do cillia and mucus help against the entry of pathogens in animals?
- in the trachea and other mucous membranes these trap and remove particles and microbes from the air
67
how does blood clotting help against the entry of pathogens in animals?
- it seals open wounds and prevent entry of microbes
68
how does an inflammatory response help against the entry of pathogens in animals?
- it increases the blood flow to the site of the injury
- bringing large numbers of phagocytic cells
- and increased temperature is unfavourable to microbes and decreases their growth
69
what are lymphocytes?
- a type of cell found in the body
- that originate from stem cells in bone marrow
- every individual possess many types of lymphocytes and each lymphocyte is capable of recognising one specific antigen
70
where do lymphocytes originate from?
- stem cells in bone marrow
71
what are the two types of lymphocytes involved in the immune response?
- B-lymphocytes
- T-lymphocytes
72
where do B-lymphocytes mature?
- in the spleen and lymph nodes
73
where are T-lymphocytes activated?
- in the thymus gland
(T-lymphocytes = T = thymus)
74
what are the three types of T-lymphocytes?
- killer (cytotoxic) T cells
- helper T cells
- T memory cells
75
what do killer (cytotoxic) t cells do?
- bind to foreign cells (target cells) with complementary antigens and destroy/engulf/lyse them
- cause lysis of damaged or infected cells
76
what do helper t cells do?
- regulate the immune response through the release of cytokines
- cytokines stimulate the proliferation of B lymphocytes
- cooperate with B-lymphocytes to initiate antibody response
- release chemicals including cytokines which stimulate pathogens to engulf pathogens and digest them
77
what do t memory cells do?
- remain in the blood and can respond quickly in case the same infection is encountered again / provide immunological memory
78
what is the immune response?
the body’s reaction to a substance which is recognised as non-self e.g a foreign antigen
79
what are the two components to the adaptive immune response?
- the humoral response
- the cell-mediated response
80
what does the humoral response result in?
the production of antibodies by the B-lymphocytes
81
what happens when a B lymphocyte recognises its specific antigen?
- it divides rapidly to produce clones which then change into two cell types
82
what are the two types of cells a b-lymphocyte divides into when it recognises its specific antigen?
- plasma cells
- memory cells
83
what are plasma cells? what do they do?
- short lived
- immediately secrete antibodies
84
what are memory cells? what do they do?
- live for considerably longer than plasma cells
- give rise to the secondary immune response if the same infection is encountered again
85
the variable region on the antibody is specific to each antigen and acts as the ______, allowing each antibody to bind to two antigen molecules
antigen binding site
86
antibody definition
- an immunoglobulin (protein) produced by the body’s immune system in response to an antigen
- are specific to the antigen with which they bind to form an antigen-antibody complex
87
microbes with antigens on their surface clump together (agglutinate). what does this result in?
- making it more difficult for them to infect other cells
- and more easy for macrophages to engulf them
88
what does the cell-mediated response involve?
- attacking foreign material inside cells, e.g a virus
- and phagocytes, B-lymphocytes and T-lymphocytes are all activated
89
what do T-lymphocytes respond to? what do they then do?
- specific antigens on the surface of cells
- and divide rapidly by mitosis to form clones
90
what are the three types cells involved in the cell-mediated response?
- T helper cells
- T killer cells
- T memory cells
91
what are the two types of immune responses?
- primary response
- secondary response
92
what is the primary response? (brief)
- during the latent period, the body reacts to a foreign antigen by producing antibodies
93
are antigens proteins?
yes
94
what does the primary response involve?
- antigen presenting cells (including macrophages) carry out phagocytosis and incorporate foreign antigen into their cell membrane
- t helper cells detect these antigens and secrete cytokines, which stimulate B cells and macrophages
- B cells are activated and undergo clonal expansion to produce plasma cells and memory cells
- plasma cells secrete antibodies
- memory cells remain in the blood to protect against reinfection
95
memory cells confer long-term protection
96
what happens in a secondary response?
- if the body receives a second exposure to the same antigen, memory cells are stimulated to clone themselves and produce plasma cells, which produce antibodies
- this response is much more rapid than the primary response and produces up to 100 times the concentration of antibodies, which remain in the blood for longer than with the primary response
97
what are the two types of immunity?
- passive immunity
- active immunity
98
when does passive immunity occur?
- this occurs when the body receives antibodies
- either naturally - (e.g from mother’s milk or via the placenta)
- artificially - from an injection where rapid protection is needed e.g when exposed to Rabies virus, antibodies can be given out
99
what is the advantage of passive immunity?
- the body receives immediate protection
100
what is the disadvantage of passive immunity?
- the protection is short-lived
- because the body has not produced memory cells, and the injection of artifical antibodies may be perceived by the body as foreign (non-self) and so it may make antibodies against them
101
when does active immunity occur?
- when the body produces its own antibodies in response to antigens being present
- this protects against reinfection where the antigens on the invading microorganism are the same
- antigen-specific memory cells are produced and some antibodies remain in the blood to protect against reinforcement - providing long-lasting immunity
102
how can active immunity be made?
- natural - production of antibodies by the immune system following infection
- artificial - when antigens are supplied artificially in the form of a vaccine, which triggers antibody production without the symptoms of the disease
103
immunisation programmes:
- vaccination programmes are designed to protect populations from harmful diseases
- any antigens used in vaccines must be highly immunogenic to stimulate a protective immune response
- programmes need to be cost effective and take into consideration any possible side effects
- some vaccination programmes are not 100% effective, e.g influenza, due to antigenic variation within the virus
104
are all vaccine programmes 100% effective?
- no - some are not
- e.g influenza, due to antigenic variability within the virus
105
what is a ‘pathogenic’ organism?
an organism that has the ability to cause damage to a host
106
what is an ‘infection’ disease?
describes a disease that can be transmitted between individuals
107
vaccination definition
- the deliberate exposure of an individual to non-pathogenic forms, antigens or products of pathogens to provide artificial active immunity
108
what are antibiotic resistant bacteria?
- bacteria that mutate to become resistant to an antibiotic, survive and reproduce very rapidly, passing on their antibiotic resistance
109
how are antigenic types usually identified?
using antibodies from serum
110
what is a host?
- the organism from which a pathogen or parasite obtains nutrients and/or shelter
111
give some examples of bacterial infections
- cholera
- tuberculosis
112
give some examples of viral infections
- influenza
- smallpox
113
what tissue is affected by influenza?
upper respiratory tract
114
describe how smallpox has been eradicated
- due to a successful vaccination programme
115
what properties of the smallpox virus made its eradicated possible?
- little variation in antigens
- low rate of antigenic mutation
- immunogenic nature of antigens
- no animal reservoir
116
give an example of a protoctistan infection
malaria
117
name the malarial parasite
Plasmodium spp.
118
outline the mode of transmission and infection of the Plasmodium spp. parasite
- female mosquito acts as vectors when it transfers saliva to another organism during feeding
- parasite reproduces asexually in red blood cells in liver, causing lysis
119
how is endemic malaria controlled?
- preventing mosquito bites - mosquito nets, insect repellent
- controlling mosquito numbers - pesticides, chemical treatment of standing water and sewage, introduction of predators for mosquitoes
- drug treatment
120
outline the forms that the pathogenicity of viruses can take
- cell lysis
- cell transformation
- production of toxins
- immune system suppression
121
what is cell lysis?
- the disruption of cell membranes, destroying the cell
- virions released
122
describe cell transformation
- viruses can stimulate healthy cells to become cancerous
123
give an example of a virus that suppresses the immune system of the host
HIV
124
how do bacteriostatic antibiotics work?
- prevent bacteria from growing by interfering with processes required for their growth such as metabolism or DNA replication
125
what is a narrow-spectrum antibiotic?
- an antibiotics that is only effective against a narrow range of bacteria
126
what is a broad-spectrum antibiotic?
an antibiotic that targets a wide range of bacteria
127
define gram-positive bacteria
- bacteria that have a thick peptidoglycan wall and a purple appearance following gram staining
128
what type of antibiotic is penicillin?
narrow-spectrum antibiotic
129
describe how penicillin affects bacteria
- kills gram-positive bacteria and damages gram-negative bacteria
- prevents the formation of cross-links between molecules in the peptidoglycan wall, so when osmotic changes occur, the cell undergoes lysis
129
define gram-negative bacteria
- bacteria that have a thin peptidoglycan wall with an outer lipopolysaccharide membrane and a red appearance following gram staining
130
how does penicillin prevent the formation of cross-links in the peptidoglycan wall?
- transpeptidase catalyses the formation of cross-links in the peptidoglycan wall
- penicillin is a competitive inhibitor of transpeptidase
131
why doesn’t penicillin kill Gram-negative bacteria?
- gram-negative bacteria do not completely lose their cell walls due to the presence of an outer lipopolysaccharide membrane
132
what type of antibiotic is tetracycline?
broad-spectrum antibiotic
133
describe the effect of tetracycline on bacteria
- inhibits translation during protein synthesis
- competitive inhibitor of an anticodon-binding site on the 30S ribosomal subunits, preventing the formation of new proteins
134
why are some bacteria resistant to treatment by antibiotics?
- random genetic mutation, often on plasmid, confers resistance e.g antigen shape changes
- these bacteria have selective advantage in the presence of antibiotics, reproduce and pass allele for resistance to offspring
- directional selection results in resistant strain
135
what are natural barriers?
defences that are always present and are the same for all organisms
136
describe the specific immune response
- second line of defence against pathogens triggered by foreign antigens
- two types: humoral immune response and cell-mediated immune response
137
where are B-lymphocytes produced?
in the bone marrow
138
outline the process of the cell-mediated response
- complementary t helper lymphocytes bind to foreign antigens on antigen-presenting cell
- t cells undergo clonal expansion
- three main types of t lymphocytes produced:
• t effector cells (killer)
• t helper cells
• t memory cells
139
explain the role of antigen-presenting cells
- macrophages displays antigen from pathogen on its surface (after hydrolysis in phagocytosis)
- enhances recognition by T helper cells, which cannot directly interface with pathogens/antigens in body fluid
- secrete cytokines that are involved in stimulating specific immune response
140
outline the process of the humoral response
1. complementary t helper lymphocytes bind to foreign antigens on antigen-presenting t cells
2. cytokines released that stimulate the clonal expansion of complementary B lymphocytes
3. B lymphocytes differentiate into plasma cells
4. plasma cells secrete antibodies with complementary variable region to antigen. antibodies destroy the pathogen
141
describe the structure of an antibody
- Y-shaped
- two ‘light chains’ bonded to two longer ‘heavy chains’
- two binding sites
- specific to a particular antigen
142
compare the primary and secondary immune responses:
- primary immune response - initial response when a pathogen is first encountered. a small number of antibodies are produced slowly
- secondary immune response - patient encountered for a second (third, fourth … etc) time. immunological memory gives a rapid production of a large number of antibiotics
143
what is happening during the latent period of the immune response?
- antigen-presenting cells carrying out phagocytosis and incorporate foreign antigen into their cell membranes
- t helper cells detect antigens and secrete cytokines
- proliferation and differentiation of specific B and T cells
144
give an example of artificial active immunity
- vaccination against rubella
145
give an example of artificial passive immunity
treatment of rabies
146
describe the different levels of effectiveness of vaccination programmes against different diseases
- single round of vaccinations - protects against pathogens that have low levels of antigenic variation/mutation e.g rubella
- repeated vaccinations - used against pathogens that have various antigenic types and mutate frequently e.g influenza
147
outline the ethical considerations that must be considered when designing vaccination programmes:
- cost of developing the vaccine
- effectiveness of the vaccine
- rights of the individual vs rights of the entire population to be protected
- rights of individuals to refuse vaccinations - (may apply to parents choosing for their kids)
- possible side effects
- religious concerns
- testing on animals and unaffected individuals
148
pathogenic definition
- an organism that causes a disease, damaging its host
149
vaccine definition:
- uses non-pathogenic forms, products or antigens of microorganisms to stimulate an immune response which confers protection against subsequent infection
150
- the human body is a host for a wide variety of microorganisms
- what is this called?
- this is termed the microflora of the body
151
flora of the body:
- many of the species of bacteria and fungi are in a symbiotic relationship with the human body
- in return for a habitat and food, they provide a number of different services
- some gut bacteria aid digestion and absorption
- some provide vitamin K, a vitamin needed for blood clotting
- on the outer surface of the skin, they outcompete pathogenic organisms
- some species are pathogenic or parasitic; they have the potential to cause disease if they secrete toxins or if their numbers increase too much
152
symbiotic microbes help prevent infectious disease in humans by doing what?
outcompeting pathogens
153
- outbreaks of cholera are not uncommon where earthquakes have disrupted sewage pipes and water treatment
- refugee camps with little sanitation and clean water can also suffer from outbreaks
154
what is a big concern in the treatment of TB?
antibiotic resistance
155
what made the smallpox vaccine so successful?
- due to the virus’s low rate of antigenic variation/mutation
- the highly immunogenic nature of its component antigens
- there was no animal reservoir
- and people were keen to be immunised because of the devastating effects of the disease
156
what are examples of the animal reservoirs of the influenza virus?
- chickens
- pigs
(bird flu, swine flu)
157
malaria stages:
- the organism initially invades liver cells (hepatocytes)
- it then multiplies in red blood cells that burst, releasing more parasites into the blood and causing severe bouts of fever
- female Anopheles mosquitoes, through feeding on blood, act as vectors to transmit the parasite to new victims
158
what does the prevention of malaria rely on?
- knowledge of the life cycle of both the vector and the parasite in order to exploit their weak points
159
what is the structure of viruses?
- a core of nucleic acid (DNA or RNA)
- surrounded by a protein coat of capsid
160
what is the capsid of viruses made of?
- repeating subunits of protein called capsomeres
161
- some viruses are surrounded by a lipid coating, often derived from the cell membrane of the host
- this can contain antigens, e.g the flu virus has haemagglutinin (H) antigens and neuraminidase (N) antigens
- the different types of antigen in combination give a number of different _____
strains
162
are viruses capable of reproducing without a host cell? why?
no
- because they have no ‘cellular machinery’ organelles or cytoplasm
163
life cycle of viruses:
1. gain entry to a host cell
2. the viral DNA inserts itself into the host DNA and instructs the cell to make new virus particles
3. when the host cell fills up with virus particles it ruptures (lysis)
4. the cell dies and the new virus can infect new cells
164
how does a virus usually gain entry to a host cell?
- the virus attaches to receptors on the host cell membrane and enters the cell often by phagocytosis
165
if the virus nucleic acid is RNA, what takes place to make a DNA copy of the virus genome?
reverse transcription
- RNA viruses are often called retroviruses as a result of
166
when the host cell fills up with virus particles it ruptures. the cell bursting is called ____, and this life cycle is a _____ cycle
- lysis
- lytic cycle
167
what does it mean if some viruses are lysogenic?
- the same thing happens in terms of entry and modification of DNA of the host
- the virus genome remains dormant until an environmental or cellular trigger results in a lytic phase, which causes the symptoms
168
what are other ways in which viruses can be pathogenic?
- by releasing toxins, some viral components are toxic
- viral DNA can activate oncogenes which can subsequently lead to cancer formation
- if the virus is specific to an immune cell, like HIV infects t-helper cells, then the immune response to other diseases is compromised
- viral diseases are difficult to treat because the virus is inside the host cells. any treatment would damage host cells as well as the virus
169
how are antibiotics safe to use to treat bacterial infections in humans?
- because they don’t affect eukaryotic cells
170
what can the effectiveness of different strengths/types of antibiotic against a species of bacteria be assessed by?
- making a lawn plate of bacteria
- placing discs of different strengths of one antibiotic or different antibiotics on surface
- measuring the clear zone where the bacteria have not grown or have been killed
- the larger the area of the clear zone, the more bacteria have been killed, so the more effective the antibiotic is
171
what effect do bacteriostatic antibiotics have on bacteria?
they inhibit replication
172
is penicillin more effective against Gram positive or Gram negative bacteria?
gram positive
173
how is phagocytosis a natural barrier in the body to reduce the risk of infection?
- destroys and engulf invading microbes, macrophages and neutrophils
174
the adaptive immune response is (specific/non-specific) to the pathogen
specific
- and it involves recognising antigens being ‘foreign’ to the body
175
what does each B-lymphocyte have to enable it to do its job?
- receptors for the detection of its specific antigen
(once it binds to the specific antigen it is activated) - called clonal selection
176
what is clonal selection?
- there are many different B lymphocytes and each B lymphocyte has receptors for the detection of a specific antigen
- when a B lymphocyte with a specific receptor binds to the specific antigen it is activated
- this is called colonial selection
177
what is clonal expansion?
- activation stimulates the proliferation of B lymphocytes by repeated mitotic divisions
- this is known as clonal expansion
(there B lymphocytes differentiate to form antibody-secreting cells called plasma cells and memory cells )
178
antibody structures:
- Y shaped
- made from four polypeptide chains
- have two binding sites
- there are two heavy and two light polypeptide chains in antibodies - these chains are held together by disulphide bonds
- the binding sites are variable regions that have specific complementary shapes to the antigen
- as there are two binding sites, two different antigens can be joined by one antibody molecule - called agglutination
179
how many binding sites do antibodies have?
two
180
what are the polypeptide chains in antibodies held together by?
disulphide bonds
181
what is importance about the fact that antibodies have two binding sites?
- two different antigens can be joined by one antibody molecule
- this is called agglutination
182
what is importance about the fact that the hinge region of antibodies is flexible?
- the antibody can flex and bind to two antigens on the same organsim when they are different distances apart
183
an antigen-antibody complex renders the antigen inactive in some way e.g though agglutination. what does agglutination do?
- increases the rate of engulfment by phagocytosis
- and if viruses or toxins are joined together by agglutination it means that they are too large to enter a cell
184
where do t-lymphocytes originate from?
stem cells in the bone marrow (like b lymphocytes)
185
helper T cells release cytokines. what do the cytokines do?
- stimulate B lymphocytes to initiate an antibody response
- they also stimulate phagocytosis by macrophages
- stimulate clonal expansion of b and t lymphocytes - mitosis results in a large population of cells specific to that particular antigen
186
- only a very small amount of antigen is required to stimulate rapid production of plasma cells from activated memory cells
187
which of these is true about the secondary immune response:
- more antibodies are made faster
- there is a short latent period
- the latent period is longer
- antibodies remain in circulation for a shorter time
- more antibodies are made faster
- there is a shorter latent period
188
- NATURAL ACTIVE IMMUNITY = catching the disease so developing antibodies (has secondary response)
- ARTIFICIAL ACTIVE IMMUNITY = vaccine (has secondary response)
- NATURAL PASSIVE IMMUNITY = antibodies passed from mother to child across placenta or in breast milk (no secondary response)
- ARTIFICIAL PASSIVE IMMUNITY = antibodies transfused into patient - rabies treatment (no secondary response)
189
what do vaccines promote?
- a primary immune response without causing the disease
- memory cells are produced so that when the individual is exposed to the disease, a secondary response occurs so symptoms dont develop
190
what are the three main differences between a primary and secondary immune response?
- no latent period in the secondary immune response - antibodies are produced immediately
- the secondary immune response is faster than the primary
- a higher level of antibodies is produced which remain at a higher level for longer than in the primary immune response
191
vaccines must not cause the disease but should provide a strong immune response.
what are the main types of vaccines?
- contain microorganisms that have been killed with chemicals or heat
- contain live, attenuated microorganisms that have been cultivated under conditions that make them non-pathogenic
- contain inactivated toxic compounds (where these compounds cause the illness)
- contain specific antigens or sub-units of a microorganism
192
successful vaccines have the following features:
- they provoke a strong immune response, are highly immunogenic and protect the individual from developing the disease
- have no or few side-effects which are mild in nature
- lead to long-lasting immunity from the disease
193
if the pathogen has little antigenic change a single round of immunisation is needed to provide long-term immunity
- e.g rubella
- children are immunised as babies, and a booster vaccine given in their teens providing life-long protection
194
- organisms with many antigenic types like influenza require annual vaccination programmes against the most common antigen types for that year
- even so, it is not 100% effective
195
to be successful, a vaccination programme should be taken up by enough of the population to provide ________
‘herd immunity’
- this is the idea that if enough people are immune to the disease trough vaccination, there is a reduced reservoir of the pathogen in the population
- this provides protection to people who are unable to be vaccinated because of compromised immune systems or illness
