Topic 6 - Infection, Immunity And Forensics Flashcards
1
Q
What are the uses of DNA profiling?
A
- Identifying people from remains
- Determining family relationships - father, mother
- Solving crimes - placing people at crime scenes
2
Q
How many points must be identified for identical fingerprints to match?
A
16
3
Q
What is another way to identify individuals other than fingerprints?
A
Dental records
4
Q
What are introns?
A
(Intragenic regions) non-coding blocks
5
Q
What are exons?
A
(Expressed regions) Coding regions
6
Q
What are short tandem repeats (STRs)?
A
A sequence of repeated bases. A short tandem repeat can contain from 2 to 50 base pairs which can be repeated from 5 to several hundred times.
7
Q
Where are short tandem repeats found?
A
Within introns of the DNA.
8
Q
What is a maternal chromosome?
A
Chromosome inherited from the mother
9
Q
What is the paternal chromosome?
A
Chromosome inherited from the father.
10
Q
Why are two individuals unlikely to have the same combination of STRs?
A
Each person has a large number of introns with lots of STR loci. There is a large variation in the number of repeats of each loci.
11
Q
An STR occurs at the same place on a chromosome of a homologous pair. What’s the difference between them?
A
The number of times they are repeated on each homologous chromosome can be different.
12
Q
Describe the process of how DNA is obtained?
A
1) DNA sample must be obtained from almost all biological tissue (animal or plant) -> check swab/ white blood cells/ bone marrow/ sperm.
2) Tissue sample is physically broken down into a buffer solution that includes salt and a detergent solution to disrupt the the cell membranes.
3) The small suspended particles, including the DNA, are separated from the rest of the cell debris by filtering or centrifuging.
4) Protease enzymes are incubated with the suspension to remove proteins and then cold ethanol is added to precipitate out the DNA.
5) Several stages of washing the DNA in a buffer solution follow.
13
Q
What are the two ways in which fragments are made?
A
- Restriction enzymes
- Polymerase chain reaction
14
Q
Describe how restriction enzymes are used to create fragments?
A
Restriction enzymes (endonucleases) cut DNA at specific base sequences (usually 4 to 6 base pairs). Restriction sites are either side of STR sequence and fragment of DNA is cut away from the rest of the genome. Restriction enzymes cut a DNA into fragments only where their specific restriction sequence occurs.
15
Q
What happens if the same restriction enzyme is used to cut two identical DNA samples?
A
Identical STR fragments are reproduced.
16
Q
Describe how the polymerase chain reaction (PCR) creates a DNA fragment?
A
The forensic sample is placed in a reaction tube with DNA polymerase, DNA primers (with fluorescent tags) and nucleotides. The PCR machine goes under a cycle of temperature changes. Firstly, it is 90 degrees Celsius during which the DNA strands separate into two. It then becomes 55 degrees celsius during which the primers attach at the start of the STR sequence. Lastly, it becomes 70 degrees celsius during which the DNA polymerase attaches. The nucleotides are added, extending the DNA from the primer. The STR repeated sequence and DNA adjacent is replicated. As the cycle continues, huge numbers of the target DNA fragments are produced.
17
Q
What are the DNA samples generally analysed for?
A
The presence of ten short tandem repeats (STRs/ micro-satellites)
18
Q
How can you determine the gender from a DNA sample?
A
A specific primer can be used to determine the gender as it targets the sex chromosome.
19
Q
Describe the process of gel electrophoresis.
A
1) DNA is cut into fragments.
2) Fragments of double stranded DNA are loaded into wells of an agarose gel in a tank (provides a stable medium through which fragments can move).
3) Electrodes are connected which produce a potential difference over the gel. The negatively charged DNA moves towards the positive electrode. The fragments separate into invisible bands. They move depending on their size and charge. Smaller fragments end up closer to the positive electrode.
4) DNA is transferred to a nylon or nitrocellulose membrane by solution drawn up through the gel. DNA double strands split and stick to the membrane.
5) Membrane placed in a bag with a DNA probe. Single stranded DNA probe binds to fragments with a complementary sequence.
6) If the DNA probe is radioactive, x-ray film is used to detect the fragments. If the DNA probe is fluorescent it is viewed using UV light as shown above.
20
Q
What is the benefit of DNA primers with fluorescent tags?
A
As the DNA fragments move through the gel they pass a laser and the dye in the fluorescent tag is detected, effectively giving a time that it has taken for the fragments to pass through the gel.
21
Q
What is the size of the fragment determined by?
A
Number of base pairs it contains.
22
Q
How does the enzyme used in the polymerase chain reaction not denature?
A
DNA tacpolymerase is stable because it is from extreme environments (hot springs) and therefore can withstand high temperatures.
23
Q
What controls the temperature and changes when it is necessary in the Polymerase chain reaction?
A
A thermocycler
24
Q
What do DNA primers attach to?
A
They bind to the complementary base pairs
25
What are the methods used to determine the time of death?
- Body temperature
- Rigor mortis
- Decomposition
- Forensic entomology
26
What is the human bodies usual temperature?
36.2 to 37.6 degrees celsius
27
Why does the body temperature begin to decrease as soon as the person dies?
Absence of heat producing chemical reactions
28
For how long is temperature measured after the death of a person?
24hrs
29
How is the core body temperature recorded?
Via the rectum or an abdominal stab with a long thermometer (sometimes electrical)
30
When measuring the body temperature what must be noted?
The environmental conditions
31
Why is it important to note the environmental conditions of where the body was found?
Because the environmental conditions affect the rate at which body temperature changes. In colder environments the faster the core body temperature decreases.
32
On a graph what does the shape of the temperature follow?
A sigmoid curve (s-shaped)
33
Why is the original core temperate before death not always 37 degrees celsius?
Their body temperature at the time of death could have been elevated or depressed if they were suffering from fevers or hypothermia.
34
What are the factors that affect post-mortem cooling?
- Body size
- Body position
- Clothing
- Air movement
- Humidity
- Temperature of surroundings
- If in water will cool more rapidly
35
What is rigor mortis?
The stiffening of the body after death because of a loss of Adenosine Triphosphate (ATP) from the body's muscles.
36
What does the position where the joints become fixed depend on?
Depends on the body position.
37
Describe the process of rigor mortis.
1) After death, muscle cells become starved of oxygen and oxygen-dependent reactions stop.
2) Respiration in the cells becomes anaerobic and produces lactic acid.
3) The pH of the cells falls, inhibiting enzymes and thus inhibiting anaerobic reactions.
4) The ATP needed for muscle contractions is no longer produced. As a result bonds between the muscle proteins become fixed.
5) The proteins can no longer move over one another to shorten the muscles, fixing the muscles and joints.
38
Regarding rigor mortis, which muscles stiffen first?
Smaller muscles stiffen before larger ones.
39
When does rigor mortis occur?
6 to 9 hrs after death
40
When does rigor mortis set in more early?
Sets in more quickly and lasts for a shorter period of time if the environmental temperature is high or if the person has been physically active before death.
41
What is decomposition of the body?
Occurs after death when the tissues start to break down.
42
What is autolysis?
Body's own enzymes, from the digestive tract and from lysosomes, break down cells.
43
As well as autolysis, how does decomposition also occur?
Bacteria from the gut and gaseous exchange systems rapidly invade the tissue after death releasing enzymes that result in decomposition.
44
What are the signs of decomposition?
- Greenish discolouration of the skin and lower abdomen due to the formation of sulfhaemoglobin in the blood. This then spreads across the rest of the body going from a darken to reddish-green and then to a purple-black colour.
- Gas or liquid blisters on the skin.
- Bacteria and gases (hydrogen sulphide, methane, carbon dioxide, ammonia and hydrogen) cause the body to smell and become bloated.
- As the tissue further decomposes, the gas is released and the body deflates. Fluid associated with putrefaction drain away, the soft tissues shrink and the decay rate of the dry body is reduced.
45
How long does it take until the decolourisation of the body occur?
36 to 72 hrs after death discolouration of the abdominal wall occurs.
46
How do environmental conditions affect the rate of decomposition?
- Lower temperatures slow decomposition
- Warm temperatures speed it up
- Rate of decomposition is highest between 21 and 38 degrees celsius
- Intense heat denatures enzymes involved in autolysis
47
What happens if a dead body remains in conditions above 26 degrees?
Gas formation may occur within about 3 days.
48
What is forensic entomology?
It looks at the presence of insects to make an estimate of how much time has elapsed since death. The forensic entomologists use a predictable sequence of organisms that feed on a decomposing body to determine the time of death.
49
What do forensic entomologists record?
The information about the location and conditions of the body. They take samples of any insects found on, near or under the body. They record the temperature of the air, ground, body and 'maggot mass' are measured.
50
What do forensic entomologists do with the maggots they find on the body?
Some maggots are killed at the time of collection so that their age can be determined. Some maggots are kept alive where they are taken back to the lab and are fed on meat allowing them to completely develop.
51
Why do forensic entomologists keep some maggots to let them develop?
It is useful for species identification and to establish when they pupate.
52
What are the methods in which the ages of maggots are calculated?
- Referring to particular graphs which are made for each species in order to determine the age - you look at the temperature of where the maggot was found as well as its length.
- Identifying the maggot's stage of development with references to the life cycle of the fly.
- If the maggot is not a C.Vicina and its stage of development is unclear the maggot is allowed to mature which gives the date of pupation. This is calculated by subtracting the date of pupation from the time for the egg to develop.
53
When using graphs to calculate the age of maggots when does it not work?
When the temperature conditions have changed/fluctuated and has not remained stable.
54
From the methods used to identify the age of the maggot which is the least accurate? Why?
The method used on maggots which are not C.vicina and works by subtracting the date of pupation from the time for the egg to develop. It is the least accurate because the time of egg laying may give an underestimate of time of death because there is no knowing how long it took the flies to find the body.
55
How long does it usually take for flies to enter the body?
Normally 1 day
56
Describe the succession on corpses.
One group of organisms feed on a decomposing body. This causes the conditions on the corpse to change and it becomes attractive to other groups of organisms. As the corpse continues to change, different organisms are attracted to the conditions and this continues until there is only the skeleton left.
57
Are all of the insects found on the corpse attracted to it?
No some are attracted to the insects on the corpse rather than the decaying corpse itself.
58
What influences the species present found on a decomposing body?
- Season
- Weather
- Size
- Location of the body
59
What is the difference between plant and corpse succession?
Unlike plant succession, where many of the early species are replaced as conditions change, most of the early insects remain on the body until the advanced stages of decay.
60
What can insects also help to determine regarding forensic entomology? How?
Insects can help to determine whether a body has been moved. Species of insects found on a body that are not from that location shows the body has been moved.
61
What are the other decomposers that decompose a body?
Bacteria and fungi
62
Where is the bacteria from that helps decompose the body?
- Bacteria from the gut quickly invades the tissue after death.
- Bacteria and fungi from the surroundings colonise the corpse.
63
What is the sequence in which the bacteria and fungi colonise?
There is no particular sequence in which they colonise.
64
What do corpses provide to decomposers?
- Organic carbohydrates
- Proteins
- Fats
- Nucleic acids
- Energy to grow and multiply
65
What is released into the atmosphere by decomposers?
Carbon dioxide is released into the atmosphere. This can be recycled back into a form which can be used for photosynthesis by plants to synthesise more organic molecules.
66
What are viruses?
Small organic particles with a structure that is quite different from that of bacteria and very much simpler. They consist of a strand of nucleic acid (RNA or DNA) enclosed within a protein coat.
67
Viral DNA can be both ... and ... ...
Single and double stranded.
68
What do you some viruses have on their outer surface?
Some viruses have an outer envelope taken from the hosts cell-surface membrane. This contains lipids, proteins and glycoproteins.
69
What is the importance of the envelope surrounding the virus?
The envelope is important as it helps the virus attach to the cell and penetrate the cell membrane.
70
Describe the replication of viruses.
1) The virus attaches to the host cell.
2) The virus inserts it's nucleic acid.
3) The viral nucleic acid replicates.
4) The viral protein coat synthesised.
5) New virus particles are formed.
6) The virus particles are released due to cell lysis.
71
What type of cell is bacteria?
It is a prokaryotic cell.
72
Which are smaller bacteria or viruses?
Bacteria are larger than viruses normally between 0.5 to 5 micrometers whereas viruses are usually only 20 to 400 nm.
73
What is the structure of bacterial cells?
- Capsule
- Cell wall
- Cell membrane
- Main circular DNA
- Plasmids
- Mesosomes
- Flagellum
- Pilus
- Ribosomes
74
What is the structure of viruses?
- Protein coat
| - Nucleic acid (DNA or RNA depending on virus)
75
How do bacteria reproduce?
They reproduce by form of asexual reproduction known as binary fission which divides the bacterial cell into two identical daughter cells.
76
How can bacteria exchange genetic material?
Pili can attach to other bacteria and exchange genetic material.
77
Can viruses exist outside a living body?
Viruses cannot exist outside of living body this is because they must get inside the cell in order to make more virus particles as they do not have the necessary organelles needed for reproduction.
78
Are all viruses and bacteria pathogens?
All viruses of pathogens however not all bacteria are pathogens.
79
When is a post-mortem examination performed?
The post-mortem examination is performed if there is a sudden or an unexpected death, or if the cause of death is unknown.
80
What is the first part of the post-mortem examination?
The external examination is the first part made by a pathologist.
81
What follows the external examination part of the post-mortem?
The internal examination.
82
What does the internal examination include?
It involves an incision being made down the front of the body so that the organs can be taken out for a detailed examination. The state of the organs may allow conclusions to be made about the health of the person and the illnesses suffered.
83
Blood and tissue samples may also be taken during a post-mortem examination. What are these tested for?
They are tested for toxins, infections or tumours.
84
What is the Capsule?
A protective mucus layer which prevents dehydration and also allows bacteria to form colonies.
85
Describe the cell wall properties of bacteria.
It does not contain cellulose it is made up of a peptidoglycan: a polysaccharide cross-linked by peptide chains.
86
What is the function of the ribosomes within the bacteria?
They are the site of protein synthesis and they occur free in the cytoplasm.
87
What are pili?
Protein tubes that allow bacteria to attach to surfaces and are involved in cell to cell attachment.
88
What are plasmids?
Small circles of DNA.
89
What is the flagellum?
It is used for cell movement.
90
What are the two types of bacterial cell walls?
The gram-positive bacteria cell walls which are thickened with additional polysaccharides and proteins. The gram negative bacteria walls have thinner walls but have a surface layer of lipids for protection.
91
How is TB carried?
It is carried in droplets of mucus and saliva.
92
How does TB spread?
When it is released into the air for example when an infected person talks, coughs or sneezes.
93
How to others develop TB?
When others inhale the droplets through droplet infections.
94
What are increased chances of developing TB?
- Close contact with an infected person
- poor health
- poor diet
- over crowded living conditions
95
TB is a tough bacteria. What does this mean it can do?
It can survive outside the body for long periods of time. Droplets can remain in suspension (in the air) for several hours in poorly ventilated areas. It can survive as dust form from dry droplets for several weeks.
96
What is it known as if you develop TB through droplets?
Droplet infection.
97
HIV is described as being not a very tough virus. What does this suggest?
It cannot survive outside the body for any significant time.
98
How is HIV transmitted?
It can only be passed on by bodily fluids such as; the blood, vaginal secretions or semen.
99
Which bodily fluids can HIV not be transmitted by?
Saliva or urine.
100
For HIV to be transmitted what must happen?
For infection to occur, the body fluids have to be transferred directly into the blood of the next host.
101
List the following ways that HIV can be transmitted.
- Infection can result from sharing needles.
- Unprotected sex (most frequent rate of infection). The virus can enter the bloodstream of a partner through breaks in the skin or lesions caused by other infections (STIs). The use of condoms can prevent transmission. Infection can also occur by oral sex but is rare.
- Direct blood to blood transfer can occur through cuts and graces. Police, paramedics and medical staff are particularly at risk and take precautions to minimise the risk.
- Maternal transmission from mother to unborn child or in breastmilk. The risk of the virus being passed to the baby occurs in the last three weeks of pregnancy, mostly around the birth when mingling of infant and maternal blood is likely to happen. A 5 to 20% chance of the child being born with HIV is reduced when the mother takes anti-HIV drugs during the last three months of pregnancy and gives birth by a Caesarian section.
102
What are lysozymes?
Enzymes which catalyse the destruction of cell walls of certain bacteria.
103
Where are the enzymes lysozymes found?
In tears, saliva and nasal secretions.
104
How does the lysozyme break down the bacterial cell wall?
They break down the polysaccharide within the cell wall by breaking the glycosidic bonds by targeting the layer of peptidoglycan.
105
Why are gram-positive bacteria cell walls more readily affected by the lysozymes compared to gram negative bacteria cell walls?
On a gram positive bacteria, this peptidoglycan layer is on the outermost surface of the cell. However on a gram negative bacteria the peptidoglycan layer of the cell wall is located further inwards. The gran negative has a lipid later around the peptidoglycan layer which acts as a form of protection and for this reason the lysozymes can more readily destroy gram-positive bacteria than gram negative bacteria.
106
What is the inflammatory response?
The inflammatory response occurs when tissues are injured by bacteria, trauma, toxins or heat causing the damaged cells to release chemicals including histamine. This causes blood vessels to leak fluid into the tissues causing swelling.
107
What is the inflammatory response a response to?
Inflammatory response is the response to microbes entering the body by passing the external barrier.
108
Following a cut or graze what happens before the inflammatory response? What is the importance of this?
Blood clotting to stop blood loss and to prevent more microbes from entering.
109
What is the main function of the inflammatory response?
To destroy invading microbes.
110
Describe in detail what happens during the inflammatory response.
Damaged white blood cells and mast cells found in the connective-tissue below the skin and around the blood vessels release special chemicals such as histamine. These histamines increase the permeability of the capillaries by causing cells in the capillary walls to separate slightly so the vessels can leak. The histamines also cause the arteries to dilate which allows increased blood flow to the damaged area, allowing white blood cells to get to the damaged area faster and in higher numbers. Due to the capillary walls separating slightly plasma fluids, white blood cells and antibodies leak from the blood into the tissue causing oedema. The infecting microbes can be attacked by the intact white blood cells.
111
What are phagocyte?
Phagocytes are white blood cells which engulf and digest bacteria and other foreign matter in the blood and tissues.
112
What are the two types of phagocytes?
- Neutrophils
| - Monocytes
113
What are neutrophils?
Neutrophils are white blood cells which leave blood capillaries by squeezing between the cells of capillary walls. They ingest and destroy bacteria.
114
What are monocytes?
Monocytes circulate in the blood for a day or two before they move into the tissue by squeezing between the cells of capillary walls. Here they become macrophages and engulf bacteria, foreign matter and cell debris. There are numerous in the lungs, liver, kidneys, spleen and lymph notes.
115
What are the two types of lymphocytes?
B cells and T cells.
116
What does the non-specific response to infection involve?
- Lysozymes
- Inflammation
- Phagocytosis
117
Define antigen.
Any molecule the body recognises as not being of its own self, which therefore induces an immune response.
118
What is the external barrier?
Skin and mucous membranes which normally prevent the entry of microbes.
119
What is the first line of defence regarding the immune response?
The physical and chemical barriers. Physical barriers include the skin or a membrane and the chemical barriers which involve acid in the stomach, ear wax and nose hair.
120
Regarding the immune response which occurs faster the non-specific on the specific response?
The non-specific response this is the second line of defence and occurs quickly following an antigen entering the body whereas the specific response is the third line of defence which is slower.
121
What is the function of the non-specific responses?
The function of the non-specific response is to help destroy any invading pathogens.
122
What is the function of the specific immune response?
The function of the specific immune response is always directed at specific pathogen.
123
Do red blood cells have a nucleus?
No they have no nucleus.
124
What do your red blood cells contain and what is there function?
They contain haemoglobin and the function of the red blood cells is to transport oxygen some carbon dioxide.
125
Describe the phagocytosis that occurs at the infected site.
1) Phagocytic white cells attracted by chemicals released from bacteria and damage cells at the site of the infection.
2) Neutrophils are the first to arrive; they engulf 5 to 20 bacteria before becoming inactive and dying.
3) The neutrophils are followed by macrophages. These are larger and longer lived cells which have the potential to each destroy as many as 100 bacteria by phagocytosis. They also ingest debris from damaged cells and foreign matter (e.g. particles of carbon and dust in the lungs).
4) Ingested material is enclosed within a vacuole.
5) Lysosomes containing digestive enzymes fuse with the vacuole, the enzymes are released, and they destroy the bacteria or other foreign material.
126
A few days later what is the area like at the action of the infected site where phagocytosis had occurred?
After a few days the area is full of dead cells, mainly neutrophils, which from a thick layer called pus.
127
What happens to the pus that forms following the death of neutrophils?
Normally it is broken down and absorbed into the surrounding tissue but sometimes breaks through the surface of the skin.
128
How do you neutrophils or macrophages destroy bacteria or foreign material?
Bacteria with antigens on the surface are detected by Neutrophils and macrophages. These bacteria with the antigens are engulfed by neutrophils or macrophages. They are enclosed into a vacuole. Lysosomes fuse with the vacuole, releasing enzymes that destroy foreign material.
129
How is the spread of live bacteria which usually gets carried away by the blood or lymph prevented?
The spread of these live bacteria is hindered by the action of macrophages in the lymph nodes, spleen and liver.
130
Define lymphatic system
Network of vessels through which the lymph drains from the tissue into the blood.
131
Define lymph
A colourless fluid containing white blood cells, which surrounds the tissue and drains through the lymphatic system into the bloodstream.
132
Describe the role of the lymphatic system in the immune system and how it aids in destroying microbes.
1) Tissue fluid drains into the lymphatic vessels. Substances (water and protein) are continuously leaking out of tiny blood capillaries into the surrounding body tissue. Lymphatic system drains the excess fluid otherwise the lymph fluid would build up in the tissue and would cause it to swell.
2) The lymph flows along the lymph vessels. It passes through the lymph nodes and eventually returns to the blood via the lymphatic and thoracic ducts.
3) As lymph passes through the lymph nodes any pathogens present activate lymphocytes and macrophages, which can destroy the microbes.
133
Why is plasma forced out of the blood capillaries?
Plasma is forced out of the blood capillaries because of the high pressure.
134
Define interferon
A protein released by animal cells, in response to the entry of a virus, which can inhibit virus replication.
135
How does interferon provide a non-specific defence against viruses?
Microbe infected cells produce interferon which diffuses into the surrounding cells which prevents microbes from multiplying. It inhibits microbial protein synthesis limiting the formation of new microbe particles.
136
Where are B lymphocyte cells produced?
In the bone marrow.
137
Define lymphocytes
White blood cells that help to defend the body against specific diseases which includes antibody production and immunity.
138
Explain how B cells aid in the killing of pathogens?
Each cell has one specific type of antigen receptor on its surface. The B cell is activated when its receptor binds to an antigen with the complimentary shape. Once activated the B cells secrete antibodies in response to the antigen. Antibodies bind to the antigens on the microbe cell-surface membrane and they act as labels, allowing phagocytes to recognise and destroy the cell.
139
Explain how T helper cells aid in the killing of pathogens?
When activated these stimulate B cells to divide and become capable of producing antibodies and enhance the activity of phagocytes.
140
Explain how T killer cells kill pathogens?
These destroy any cells with antigens on their surface membrane that are recognised as foreign or on non-self. This includes body cells infected with pathogens.
141
Define immunoglobulins
Any of a class of proteins present in the serum and cells of the immune system, which function as antibodies.
142
Explain the activation of T-helper cells
1) When macrophages engulf a pathogen, protein fragments from the material become attached to the macrophage's cell-surface membrane and is displayed as 'non self'. The macrophage becomes an antigen-presenting cell (APC).
2) These antigens presented on the surface of the macrophage act as signals to alert the immune system to the presence of foreign antigens in the body.
3) A T helper cell with the complimentary shape receptors called CD4 on its surface binds to the antigen on the surface of the APC.
4) Once activated by this binding, each T-helper cell divides to produce a clone of active T-helper cells and a clone of T memory cells.
143
What are T memory cells?
Cells that remain in the body for months or years and if an individual is exposed to the same antigen in the future their immune system can respond quickly.
144
Explain how B cells are cloned
1) Complimentary receptors of B cells bind to 'non self' antigens and become antigen-presenting cells (APC).
2) APC's bind with active, cloned T helper cells presenting the same antigen. Once attached T helper cells release chemicals called cytokines, which stimulate the division and differentiation of B cells.
3) Influence of cytokine causes two types of B cells to form; B effector cells and B memory cells.
145
Explain the role of T killer cells
If a bacterium or virus in infects a body cell, a fragment of the antigen is presented on the cell-surface membrane. T killer cells with the complimentary receptors bind to the antigen present on the body cell. T killer cells divide to form two clones: active and memory T killer cells. Cytokines from T-helper cells stimulate the differentiation. The active T killer cells bind to infected cells presenting antigens. The T killer cells release enzymes that create pores in the membrane of the infected cells. This enables ions and water to flow into the infected cells, which swells and bursts (undergoes lysis). The pathogen within the cell is released and can be labelled by antibodies from B cells.
146
Explain how the secondary immune response responds to bacterium or viruses.
If the body is infected by the same bacteria or virus, the immune system responds much faster. The secondary immune response involves memory cells and only takes about 2 to 7 days. B memory cells produced in the primary response can differentiate immediately to produce cells and release antibodies. There is a greater production of antibodies and the response lasts long. Invading virus or bacteria is often destroyed so rapidly the person in unaware of any symptoms.
147
How does the immune system not attack bodies own cells?
There are membrane proteins on the surface of cells that mark the body as self. They allow us to distinguish between our own cells and those of foreign invaders.
148
Define apoptosis and explain when this happens in relation to lymphocytes
Apoptosis is programmed cell death. As lymphocyte cells mature in the bone marrow and thymus, any lymphocytes for 'self' membrane proteins are destroyed by apoptosis. Only lymphocytes with receptors for foreign, non-self-antigens remain.
149
What is tuberculosis?
Tuberculosis is a contagious disease caused by the bacterium Mycobacterium tuberculosis.
150
How are TB rates reduced and how has that been reduced to cases of TB?
By controlling the risk factors. Improved housing and living conditions and the development of antibiotics reduce the number of TB cases.
151
Describe the primary infection of TB.
The immune system of a person infected with TB responds to deal with the infection. The first phase can last several months and may have no symptoms. M.Tuberculosis causes an immune response from the host's immune system. Macrophages engulf the bacteria. A mass of tissue granuola forms, which is produced in response to the infection. In tuberculosis these tissue masses are anaerobic and have dead bacteria and macrophages in the middle of the called tubercules. Normally after 3 to 8 weeks, the infection is controlled and the infected region of the lung heels. Most primary infection happens during childhood and the majority of infections heal without ever be noticed.
152
How do TB bacteria evade the immune system?
M.Tuberculosis is not always killed by macrophages and can survive inside them. Bacteria are taken up by the phagocytosis but once inside they resist the killing mechanism of some cells. This is because bacteria have thick, waxy cell walls making them difficult to break down. Therefore the bacteria are able to lie dormant for years as latent TB in tubercules, alive but inactive.
153
What is it latent TB?
Means a patient is infected with Mycobacterium tuberculosis, but the patient does not have active tuberculosis. The M.Tuberculosis remain alive in tubercules.
154
When you have latent TB, do you suffer symptoms?
No
155
What is the issue with latent tuberculosis?
When your immune system is weakened, the infection can become active again.
156
How can TB cells affect T cells?
TB bacteria can suppress T cells. This reduces antibody production and attack by T killer cells.
157
What is the second phase of tuberculosis known as?
Active tuberculosis
158
When does active tuberculosis occur?
It occurs if the patient immune system cannot contain the disease when it first arrived in the lungs. This may be because the number of bacteria is too great or alternatively an old infection may break out if the immune system is not working properly.
159
What damage does active TB do to the lungs?
With active tuberculosis in the lungs the bacteria multiply and destroy the lung tissue, creating holes or cavities. The lung damage will kill sufferers if not treated.
160
List the symptoms of active TB.
- Coughing
- Shortness of breath
- Loss of appetite and water loss
- Fever
- Extreme fatigue
161
Explain the role of a fever in active TB and how it occurs.
A person infected with TB experiences fever and night sweats. These occur as a result of the inflammatory response. Fever causing substances are released from neutrophils and macrophages. These chemicals affect the hypothalamus and alter the set point for the core body temperature to a higher body temperature. Raised temperatures enhance the immune function and phagocytosis. Bacteria and viruses reproduce more slowly at higher temperatures as well.
162
At what temperature do fevers become life-threatening?
42-43 degrees celsius
163
What type of infection occurs first regarding TB?
A pulmonary infection
164
Following a pulmonary infection of TB where can the bacteria spread?
- Bones
- Lymph nodes
- CNS
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What are the symptoms of glandular TB?
Enlarged lymph glands in the neck or armpits.
166
What are the general symptoms that help with the diagnosis of TB?
- Persistent cough
- Weight loss
- Fever and night sweats
167
List the methods in which TB is diagnosed?
Following the general symptoms, skin and blood tests, identification of bacteria and chest x-rays are carried out in order to determine whether the person has tuberculosis.
168
Explain how a skin or blood test can be used to determine whether a person has tuberculosis.
A small amount of Tuberculin is injected under the skin of the forearm. A positive result shows an inflamed area of skin around the site infection. This is because antibodies in the blood cause this inflammation indicating TB antigens are already present. However tests can give negative results if the person has latent TB. To overcome this blood samples are taken that analyse it for specific T cells to antigens only occurring on mycobacterium tuberculosis.
169
What technique other than skin and blood can be used to identify whether the bacteria of TB is present?
To confirm a positive skin test, a sample of sputum (phlegm) is coughed by a patient. This is then cultured to see you what bacteria are present. Staining techniques are then used because only some types of bacteria takes up particular stains depending on the make up of their cell wall.
170
Explain how chest x-rays are used to determine whether a person has TB.
Chest x-rays were taken to discover the extent of damage of the disease in the lungs. X-rays of other organs may also be taken if the disease is thought to have spread.
171
Define AIDS
Acquired immune deficiency syndrome which is caused by infection with the human immunodeficiency virus (HIV).
172
What are the symptoms of AIDS?
The immune system is weakened.
173
Describe the structure of the HIV virus
HIV is a structurally complex virus. It is an envelope virus. It consists of 2 mRNA copies and viral proteins surrounded by a 20 sided protein capsid enclosed in a layer of viral proteins. Glycoproteins stick through the envelope.
174
Explain how the lipid envelope around the virus is formed
The lipid envelope is formed from the host's cell membrane as the new virus particles emerge from the cell cytoplasm of the cell it infected.
175
Which cells do HIV invade?
T helper cells
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How do HIV viruses invade T-helper cells?
HIV invade T helper cells by glycoproteins called GP 120 located on the viruses surface. These bind to the CD4 receptors on the surface of the T helper cells. The envelope surrounding the virus fuses with the T helper cell membrane enabling the virus RNA to enter the cell.
177
Explain how HIV hijack the cells protein synthesis
Once inside the host T helper cell, the virus needs to make the host cell replicate new virus components.
1) Reverse transcriptase (from the virus) is used to reverse normal transcription and manufacture DNA from RNA.
2) HIV DNA strand is produced, it is integrated into the hosts DNA by another HIV enzyme, called integrase.
3) Once the HIV genome is integrated into the host cell's genome, it can be transcribed and translated to produce new virus proteins.
178
Why is HIV known as a retrovirus?
It is because it is a virus that contains RNA and uses reverse transcriptase to manufacture DNA.
179
In protein synthesis what happens between transcription and translation?
Between transcription and translation, mRNA a is edited with some sections being removed and other sections being put together. The non-coding introns are removed whereas the exons remain which are expressed.
180
How do HIV viruses kill T cells?
New viruses bud out of the T cell, taking some of the host's cell membrane to form the envelope. This kills the host cell as the viruses leave. Infected T-helper cells will also be destroyed by T killer cells.
181
What happens to the number T helper cells as the number of viruses increases?
The number of host T helper cells decreases.
182
HIV result in a loss of T helper cells, why is this a problem?
The loss of T helper cells results the macrophages, B cells and T cells not being successfully activated and therefore not functioning properly. This means that the infected person's immune system becomes deficient.
183
What are the three phases of the development of AIDS?
- Acute
- Chronic
- Disease
184
List factors that affect the development of AIDS
- Health of the host before infection
- Genetic resistance to infection
- Quality of the immune response to initial infection
- Lifestyle and nutrition
- Availability of drug treatment
185
Describe what happens and the symptoms that occur during the acute phase of AIDS
- Development of HIV antibodies 3 to 12 weeks after infection.
- Symptoms include; fever, sweats, headaches, sore throat and swollen lymph nodes.
- Rapid replication of the virus and loss of T helper cells.
- After a few weeks, infected cells are recognised by T killer cells which start to destroy them which causes the rate of virus replication to decrease.
186
What is the chronic phase of AIDS also known as?
The latent phase
187
Describe what happens and the symptoms that occur during the chronic phase of AIDS
- Virus continues to reproduce rapidly but numbers are kept in check by the immune system.
- No symptoms during this phase, but increasing tendency to suffer colds or other infections.
- Dormant diseases like TB and shingles can reactivate.
- Phase can last many years for example in fit young people with drug treatment it can last over 20 years.
188
Describe what happens and the symptoms that occur during the disease phase of AIDS
- Eventually, the increased number of viruses in circulation (viral load) and a declining number of T helper cells indicates the onset of AIDS.
- Decrease in T helper cells leaves the immune system vulnerable to other diseases. Opportunistic infections occur which take advantage of the weakened immune system.
- People suffer weight loss
- Development of dementia
189
List the barriers that prevent infection
- Skin
- Mucus membranes - cilia and lysozymes
- Stomach acid
- Gut flora
190
Explain how the skin prevents the entry of pathogens
- Keratin is a hard protein outer layer that is effective in stopping the entry of microorganisms.
- Blood clots seal wounds you and reduce the number of microorganisms getting into the blood.
- Skin flora on large number of microbes living on the skin surface. These are harmless and prevent the colonisation of the pathogens. They compete with pathogens for nutrients and space which limits the number of pathogens living on the skin. These bacteria are well suited to the environment whereas foreign bacteria are not so well suited to the salty sweat and excreted chemicals.
191
Explain how the mucous membranes of the cilia and lysozymes prevents the entry of pathogens
- Entry of microbes to the lungs this limited by the action of mucus and cilia. Mucus, secreted by goblet cells in the trachea and bronchi, trap microbes and other particles; then the beating cilia carry mucus up to the throat where it is swallowed.
- Secretions in the mouth, eyes and nose contain lysozymes, an enzyme that breaks down bacterial cell walls, causing cells to burst by lysis.
192
Explain how stomach prevents infection
Gastric juices secreted by gastric glands in the stomach walls contain hydrochloric acid which kills most bacteria that enter with food.
193
Explain how Gut flora prevents infection
Large numbers of bacteria which live in the small and large intestines. It is a mutualistic relationship as both the host and bacteria benefit. The bacteria may aid the digestive process and competitively exclude pathogenic bacteria, competing with pathogens for food and space. The bacteria also secrete chemicals that are useful in defence against pathogens
194
What are the different types of immunity?
- Active natural
- Active artificial
- Passive natural
- Passive artificial
195
What is active natural immunity?
An individual has developed immunity to live pathogen by having been exposed to it and by developing the primary immune response which led to immunological memory.
196
What is active artificial immunity?
This is when you become immune after you have been given a vaccine containing a harmless dose of antigen.
197
What is passive natural immunity?
This is when a baby becomes immune due to the antibodies that receives from its mother, through the placenta and in breast milk.
198
What is passive artificial immunity?
This is when you become immune after being injected with antibodies.
199
Which type of immunity either active or passive provides long-term protection?
Active immunity give to long-term protection where is passive immunity gives you short-term protection.
200
Which type of immunity either active or passive gives you immediate protection?
Passive protection is immediate whereas active immunity takes a while to develop.
201
How does a vaccine work?
When you are vaccinated for a particular disease, your immune system responds. Antibodies are produced and memory cells ensure lasting protection. The vaccination does not stop you from contracting the pathogen but if you come into contact with the pathogen in the future, you can rapidly destroy it before the onset of any symptoms.
202
What can vaccines contain?
- Attenuated viruses
- Killed bacteria
- Toxin
- Antigen-bearing fragment of pathogen
203
What are attenuated viruses?
Viruses which have been weakened so they are harmless.
204
Regarding vaccines what needs to occur to ensure long lasting immunity?
After an initial vaccine boosters are needed to ensure long-lasting immunity.
205
Why do vaccines not only protect the individual but also the community?
If a larger population of the community has been vaccinated against a disease, the disease is less likely to be transferred from one person to another and therefore it is described as herd immunity.
206
What issues can occur by having a vaccine?
- Some vaccines cause mild soreness at the sight of infection.
- Some vaccines cause fever or general feeling of being unwell.
207
What are the drugs called that are used to prevent viruses?
Antiviral
208
Why is there no treatment to get rid of HIV?
There is no treatment to get rid of HIV because HIV viruses live in T helper cells which means by killing the HIV virus you kill the T-helper cells which are necessary for the immune system.
209
What are the drugs called that reduce the production of more viruses?
Antiretroviral
210
What are the two main types of antiretroviral drugs?
- Reverse transcriptase inhibitors
| - Protease inhibitors
211
How to reverse transcriptase inhibitors work as an antiretroviral drug?
They prevent the viral RNA from making DNA for integration into the hosts genome.
212
How to protease inhibitors work as an antiretroviral drug?
They inhibit the proteases that catalyse the cutting of larger proteins into small polypeptides for use in the construction of new viruses.
213
Other than reverse transcriptase inhibitors and protease inhibitors, what are the two other antiretroviral drugs that have been approved for use?
- Integrase inhibitors
| - Fusion inhibitors
214
What are the drugs used to kill bacteria infections?
Antibiotics
215
What is the treatment of tuberculosis?
Active TB can be killed by antibiotics. Normally a treatment plan of antibiotics ensures that both active and dormant TB are destroyed.
216
What are antibiotics?
Chemicals that kill or inhibit the growth of microorganisms.
217
Why do some microorganism make antibiotics?
It is unknown however it is thought that antibiotics help microorganisms to compete in the environment. They tend to be produced in large amounts when cells are ageing.
218
Name the two types of antibiotics?
- Bactericidal
| - Bacteriostatic
219
What is the function of bactericidal antibiotics?
They kill bacteria
220
What is the function of bacteriostatic antibiotics?
They prevent the multiplication of bacteria.
221
Explain the ways in which antibiotics disrupt bacterial cell growth and division
- Inhibition of bacterial cell wall synthesis. If a week so all forms it can lead to cell lysis.
- Disruption of the cell membrane, causing changes in permeability that lead to cell lysis.
- Inhibition of nucleic acid synthesis, replication and transcription. This prevents cell division and synthesis of enzymes.
- Inhibition of protein synthesis, meaning enzymes and other essential proteins are not produced.
- Inhibition of specific enzymes found in the bacterial cell but not in the host.
222
Why do bacterial populations evolve very quickly?
- Bacteria reproduce very fast
- Bacterial population sizes are usually in billions, so the number of cells containing mutations is vast
- Some of these mutations will be advantageous to the bacterial cell. Bacteria with useful mutations are more likely to survive, reproduce and spread.
223
How do antibiotics provide a selection pressure?
Mutations arise in pathogenic bacteria which make them resistant to antibiotics. This causes a selection pressure as bacteria without the gene for resistance are more likely to be destroyed whereas those that have the gene; survive, grow and reproduce.
224
Name the two types of bacteria evolution
Vertical and horizontal
225
What is vertical evolution?
Advantageous gene is passed vertically from one generation to the next. Bacteria reproduce by binary fission when one bacterial cell divides into two identical bacterial cells.
226
What is horizontal evolution?
In the process of conjugation, one bacterial cell joins to another in which one strand of plasmid DNA is transferred to the conjugating bacterial cell.
227
What is the issue with using antibiotics?
Bacteria become resistant for example there is now widespread resistance to many antibiotics for TB.
228
What are multiple resistant bacteria?
Bacteria which have evolved resistance to several antibiotics.
229
What are healthcare associated infections?
Infections caught while a patient is being treated in hospital.
230
How are healthcare associated infection is transmitted?
Transmitted by poor hygiene, such as:
- Hospital staff and visitors not washing hands before and after visiting a patient.
- Coughs and sneezes not being contained, E.G. in the tissue.
- Equipment and services not to be disinfected after they are used.
231
Why patients more likely to catch infections in hospital?
There are new systems are weak and they are surrounded by ill people.
232
What are the codes of practice developed to prevent HCAI's?
- Hospital staff and visitors should wash their hands before entering a ward to see a patient.
- Equipment and services should be disinfected.
- People with HCAI's should be moved to an isolation ward.
- Rules preventing doctors/nurses from wearing ties, watches or long sleeves.
233
Why are infections caused by antibiotic resistant bacteria more common in hospitals?
Infections caused by antibiotic resistant bacteria are more common in hospitals because more antibiotics are used there, so bacterial in hospitals and more likely to have evolved resistance against them.
234
What are the codes of practice to prevent and control HCAI's caused by antibiotic resistant bacteria?
- Doctors shouldn't prescribed antibiotic for minor bacterial infection or virus infections.
- Doctors shouldn't prescribe antibiotics to prevent infections.
- Doctors should use narrow spectrum antibiotics (which only affect the specific bacteria)
- Doctors should rotate the use of different antibiotics.
- Patients should take all the antibiotics are prescribed.
