2C | Cells and the Immune System Flashcards
(97 cards)
1
Q
What is an antigen?
A
Antigens are molecules, usually proteins, that can generate an immune response when detected by the body.
2
Q
What are antigens used to identify?
A
Pathogens
Abnormal body cells
Toxins
Cells from other individuals of the same species
3
Q
What is a pathogen?
A
An organism that can cause disease.
4
Q
What is an abnormal body cell?
A
Abnormal body cells are body cells produced by the individual that underwent some sort of mutation to become different, for example cancer cells often have different antigens.
5
Q
Are toxins antigens?
A
Yes
6
Q
Do cells from other individuals of the same species have different antigens to other people?
A
Yes, though not always
7
Q
Describe how bacteria are destroyed by phagocytes.
A
A phagocyte recognizes the foreign antigens on a pathogen.
The cytoplasm of the phagocyte moves around the pathogen, engulfing it.
The pathogen is now contained in a phagocytic vacuole in the cytoplasm of the phagocyte.
The lysosome (an organelle that contains enzymes known as lysozymes) fuses with the phagocytic vacuole, meaning the enzymes can now interact with the pathogen. The lysozymes hydrolyse the pathogen.
The phagocyte then presents the pathogen’s antigens - it sticks the antigens on its surface to activate other immune system cells.
8
Q
What is a phagocyte?
A
A phagocyte (e.g. a macrophage) is a type of white blood cell that carries out phagocytosis, which is the engulfment of pathogens.
They’re found in the blood and in tissues and are the first cells to respond to an immune system trigger inside the body.
9
Q
Give 2 structures that a bacterial cell may have that a white blood cell will not have.
A
Flagella
Capsule
Plasmid
70S/smaller ribosomes
10
Q
What is a T-Cell?
A
A T-cell is another type of white blood cell. It has receptor proteins on its surface that bind to complementary antigens presented to it by phagocytes, wherein it is activated.
11
Q
What is a helper T-cell?
A
A helper T-cell is a type of white blood cell that releases chemical signals that activate and stimulate phagocytes and cytotoxic T-cells, as well as B-cells.
12
Q
What are cytotoxic T-cells?
A
Cytotoxic T-cells are a type of white blood cell that release a chemical called perforin, which form holes in the cell membrane of cells it invades, causing it to leak to death.
13
Q
What is a B-cell?
A
B-cells are a type of white blood cell. They’re covered with antibodies - proteins that bind to antigens to form an antigen-antibody complex.
Each B-cell has a different shaped antibody on its membrane, so different ones bind to different shaped antigens.
14
Q
Where are B-cells matured?
A
Bone marrow
15
Q
Where are T-cells matured?
A
Thymus gland
16
Q
Explain the cell-mediated (cellular) immune response.
A
Firstly, an antigen presenting cell must be found, which can be in the form of a phagocyte, abnormal body cell, body cells from different individuals of the same species or toxins.
Helper T cells have receptors on their surface that fit exactly onto the antigens on antigen-presenting cells (their receptors have a complementary shape to the antigen).
The attachment of antigens to the T-cell receptors causes the T-cell to divide rapidly by mitosis to form many genetically identical (cloned) cells.
The T cells then undergo clonal selection, wherein the new cloned T-cells now either differentiate into Cytotoxic T cells, or stay as Helper T-cells to stimulate B cells for the humoral response or phagocytes for more phagocytosis to take place.
17
Q
State 2 similarities between B-cells and T-Cells.
A
Both are a type of white blood cell
Both have a role in immunity and the immune response
18
Q
State 2 differences between B-cells and T-Cells.
A
T-Cells are matured in the thymus gland, B-cells are matured in the bone marrow
T-cells are involved in the cellular response
B-cells are involved in the humoral response
19
Q
Why is the response of T-cells and B-cells specific?
A
The cells only respond to specific antigens due to the specific shape of their receptors, compared to phagocytes which can respond to any antigen presenting cell.
20
Q
List and describe the 3 roles played by helper T-cells.
A
- Are capable of differentiating into Cytotoxic T-cells that produce a chemical called perforin that forms holes into the cell membrane which causes an invading pathogen to leak to death
- Activate other phagocytes to engulf pathogens by phagocytosis
- Stimulate B cells to divide and secrete antibodies
21
Q
List A to F:
https://media.discordapp.net/attachments/352951793187029005/829447144204140644/unknown.png
A
B = Light chain C = heavy chain A = antigen binding sites F = variable region E = constant region D = receptor binding site
22
Q
Describe the structure of an antibody.
A
Antibodies are proteins synthesized by B-cells.
There is a massive variety of antibodies, with one antibody being complementary to one antigen due to the fact they are made from proteins.
They are made from 4 polypeptide chains, thus they are quaternary.
They have one pair of long chains - these are called ‘heavy’ chains. They are attached by disulfide bridges.
There is also a pair or shorter chains, called ‘light’ chains.
They also have variable regions, which varies between different antibodies.
Outside the variable region where the antigen binding site is, we have the constant region which makes up most of the antibody - this is the area of the antibody that is seen identically between all antibodies.
They also have a receptor binding site where they bind to B cells from.
23
Q
Antibodies are specific - describe how.
A
Antibodies are specific, because they have antigen binding sites which are a highly specific shape, meaning they only attach to antigens with a complementary shape to them so they can bind to them by the antigen binding sites, wherein there are 2 of.
24
Q
Describe why the antigen binding site is known as the variable region.
A
The reason why the antigen binding site is known as the variable region is because the antigen binding site varies between all antibodies, as each antibody is specific to a different antigen, their antigen binding sites must be a different shape to be complementary to the antigen to successfully bind onto it.
25
Describe why antibodies made of proteins, rather than carbohydrates or fats, are more likely to be effective against a wide range of diseases.
There must be a massive variety of antibodies as each responds to a different antigen, of which there are millions.
Only proteins have the diversity of molecular structure to produce millions of different types.
26
Explain how antibodies lead to the destruction of pathogens.
An antibody has two binding sites so can bind to two pathogens at the same time. This means that pathogens become clumped together.
This is called agglutination - this prevents pathogens from binding to the receptor on human cells. It also means that pathogens can recognize the foreign cells and phagocytose many pathogens at one time. This process leads to the destruction of pathogens carrying this antigen in the body at a much faster pace.
27
What is agglutination?
Agglutination refers to the fact that antibodies have 2 binding sites, and so they are able to bind to 2 pathogens at the same time which allow for pathogens to be clumped together.
28
Why is agglutination effective at hydrolyzing pathogens at a faster rate?
Agglutination means that many pathogens are clumped up in a small space, meaning that when the phagocyte undergoes phagocytosis, it is able to phagocytose many pathogens at once.
This means that disease is combatted at a much faster rate, as phagocytes would otherwise have to phagocytose one pathogen at a time.
29
Describe and explain the Humoral response.
Refer to the primary and secondary response in your answer.
When an antigen, for instance, a protein on the surface of a pathogen, foreign cell, damaged or abnormal cell, or a toxin, enters the blood, there will be one B-cell that has one antibody on its surface with a complementary shape to the antigen.
The antibody therefore attaches to this complementary antigen. The antigen enters the cell by a process called endocytosis and gets presented on its surface - it is now known as a processed antigen.
Helper T cells bind to these processed antigens and stimulate the B-cell to divide by mitosis to form a clone of identical B-cells (plasma cells), all of which produce the antibody that is specific to the foreign antigen - these are monoclonal antibodies -many copies of one antibody. This is called clonal selection.
The plasma cells secrete antibodies, usually into the blood plasma. These antibodies lead to the destruction of the pathogen and this is known as the primary immune response.
Memory cells are also produced by B-cells which live longer than plasma cells and do not produce antibodies directly, but if the same antigen is encountered again they divide rapidly into plasma cells and destroy the pathogen very quickly (clonal selection is much quicker). This is the secondary immune response.
30
List differences between the cellular and humoral response.
Humoral response involves the production of antibodies, cellular response involves no production of antibodies
Cellular response involves no use of B-cells, while humoral response is mostly B-cells
Cellular response is the 1st stage of the immune response, Humoral is 2nd
Cellular response is effective through individual cells, while Humoral response is effective through bodily fluids (usually blood plasma is needed to transport antibodies to desired areas).
31
Describe how the presentation of a virus antigen leads to the secretion of an antibody against this virus antigen.
The virus antigen must exist in the environment with a B cell that has an antibody attached to it that is complementary to the virus antigen.
The antibody attached to the B cell will attach to the antigen on the virus and makes the antigen enter the cell by endocytosis, making it presented on its surface - this makes it a processed antigen.
A Helper T then cell binds to the antigen presenting cell by their receptor proteins.
This stimulates the B cell with the complementary antibody to divide by mitosis. This produces many clones with the same antibody shape known as plasma cells that release antibodies complementary to the virus antigen.
32
What are monoclonal antibodies?
Monoclonal antibodies are antibodies produced from a single group of genetically identical B-cells (plasma cells).
This means that they are all identical in structure.
33
Why are antibodies specific?
They have an unique tertiary structure shown in their variable region where the antigen binding site is present.
Only one particular antigen will be able to fit into the binding sites from having a complementary shape, and so they can only work on an extremely specific range of, if not one, antigen.
34
Cancer cells are abnormal body cells and thus they have different shapes of antigens.
Drugs have been targeted to a particular cell type. Describe the process.
Cancer cells have antigens called tumour markers - they are not found on normal body cells.
Monoclonal antibodies can be made that will bind to the tumor markers.
You can also attach anti-cancer drugs to the antibodies.
When the antibodies come into contact with the cancer cells they will bind to the tumor markers.
This means the drug will only accumulate in the body where there are cancer cells, so the side effects of an antibody based drug are lower than other drugs because they accumulate near target cells.
35
Cancer drugs are able to be attached to antibodies which target specific antigens - the drugs then kill the cell the antibody is attached onto.
Describe why cancer drugs that also kill cells but aren't attached to antibodies are less effective.
Cancer drugs that also kill cells but aren't attached to antibodies cannot find the difference between a cancer cell, what it's meant to kill, and a normal cell.
As a result of this, the cancer drug may be wasted and kill cells that are normal and this can cause more side effects.
Since the cancer drug is being used in areas that aren't cancer cells, due to the fact it isn't specific, the drug is also less efficient, as it kills less cancer cells.
36
Targeting a particular substance for medical diagnosis can be seen in pregnancy testing.
Describe the technique used.
Pregnancy tests detect the hormone hCG (Human chorionic gonadotropin). It is found in the urine of pregnant women.
Pregnancy tests take part on a test strip with an application area - the application area contains antibodies for hCG bound to a colored bead (blue).
When urine is applied to the application area any hCG will bind to the antibody on the beads, forming an antigen-antibody complex.
The urine moves up the stick to the test strip, carrying any beads with it.
The test strip contains antibodies to hCG that are stuck in place (immobili\ed).
If there is hCG present, the test strip turns blue because the immobilized antibody binds to any hCG- concentrating the hCG antibody complex with blue beads attached. If no hCG is present, the beads will pass through the test area without binding to anything, so it won't go blue.
37
Describe what the ELISA test attempts to find out.
The ELISA test allows you to see if a patient has any antibodies to a certain antigen, or any antigen to a certain antibody.
It can be used for testing pathogenic infections, for allergies and just about anything you can find an antibody for.
38
In the ELISA test, an antibody attached to an enzyme is used.
Outline what the function of this is.
An antibody is used in the ELISA test that has an enzyme attached to it.
The antibody is used to carry the enzyme so it can react with a substrate to produce a colored product which would cause the solution in the reaction vessel to change color.
39
An indirect ELISA test can be used to see if a patient possesses antibodies to the HIV virus.
Describe the process.
HIV antigen is bound to the bottom of a well in a well plate (a plastic tray with loads of little circular pits on it)
A sample of the patient's blood plasma, which might contain several different antibodies, is added to the well. If there are any HIV-specific antibodies (i.e. antibodies against HIV) these will bind to the HIV antigen stuck to the bottom of the well. The well is then washed out to remove any unbound antibodies.
A secondary antibody, that has a specific enzyme attached to it, is added to the well.
The secondary antibody can bind to the HIV-specific antibody (also called primary antibody).
The well is washed out again to remove any unbound secondary antibodies. If there's no primary antibodies in the sample, all the secondary antibodies will be washed away.
A solution is added to the well - this solution contains a substrate which is able to react with the enzyme attached to the secondary antibody and produce a colored product. If the solution changes color, it indicates that the patient has HIV-specific antibodies in their blood and is infected with HIV.
40
What are the 2 types of ELISA test?
Indirect - Two different antibodies are used
| Direct - One antibody is used
41
An investigator carries out the indirect ELISA test for HIV on two different individuals in 2 different well plates. He got his primary antibodies from their blood plasma.
Both produce a colored solution.
The investigator wants to know which individual had more HIV antibodies. How can he investigate this?
The investigator can look at which color is more pigmented - a more pigmented and concentrated color means that more enzyme has reacted with more enzymes on secondary antibodies, which indicate more primary antibodies on the individual.
If they are very similar or not easy to distinguish:
Try to draw out the colored solution of each person into separate cuvettes and plot it on a colorimeter. The higher absorption rate shows a higher concentration thus they have more primary antibodies.
42
What is a well plate?
A well plate is a plastic tray with loads of little circular pits in it.
43
In the ELISA test, what are well plates used for?
Well plates have antigens that are bound to the bottom of a well - these are used as binding sites for complementary primary antibodies to be bonded onto which is required for getting any potentially positive result.
44
What does the ELISA test stand for?
Enzyme-Linked Immunosorbent Assay
45
What are plasma cells? How are they formed?
When a B-cell steals an antigen by endocytosis, it becomes an antigen-presenting cell as it processes the antigen to show it on their cell surface membrane.
A Helper T-cell with a receptor complementary to the antigen binds to the B-cell, stimulating it to divide by mitosis to produce other genetically identical B cells (clones), some of which produce the antibody that is specific to the foreign antigen known as plasma cells.
Plasma cells are a type of white blood cells, derived from B-lymphocytes that are capable of secreting thousands of antibodies each second into the blood and other bodily fluids. They are involved in the humoral response and have identical antibodies to the initial B-lymphocyte.
46
https://media.discordapp.net/attachments/352951793187029005/829862064645865552/unknown.png
Describe the Indirect ELISA test for HIV using these images as an example.
Firstly, The ELISA test (Enzyme-Linked Immunosorbent Assay) is a test conducted to find if an individual has antibodies to a certain antigen.
Firstly, a well plate is received which have a lot of wells (pits) in them which all have the desired antigen at the bottom, this being the HIV antigen.
The patient's antibodies are then drawn, usually from their blood plasma, and put into the well. This is the primary antibody, as this is an indirect ELISA test - time is given for antibodies to bind to the HIV antigen if possible. If antibodies successfully bind to the HIV antigen, it means that there is a presence of HIV antibodies which suggests the individual is HIV positive as it has responded to the HIV virus from presence of the same antigen.
Since other types of antibodies may be in the blood plasma, the well is washed out to remove any unbound antibodies that have not attached to an antigen. After that is done, the investigator is still not aware there are HIV antibodies remaining and to they need to add a secondary antibody - these antibodies added to the well are attached to an enzyme and are capable of attaching to the HIV antibody if it is present. Time is given for them to attach if there is any HIV antibodies present and it is washed out again, washing out any unbound antibodies.
The reason why we wash out a second time is because it guarantees that any antibodies removed from the washing out is not bound to the primary antibody or antigen which means they are irrelevant for the test - the first washing out is done to remove other antibodies that may be present and this could potentially remove every single antibody present, to give a reliable negative test.
At F, a solution is added with a substrate that the enzymes attached to the secondary antibody react to, to produce a visible colour change. If a colour change is seen, the individual is HIV positive. If not, then HIV negative.
47
https://media.discordapp.net/attachments/352951793187029005/830159790021148702/unknown.png
Describe the humoral response with this image to help you.
Firstly, a foreign antigen must be present in the body, in the form of, for example, toxins, pathogens or abnormal body cells. A B-cell must then go to the pathogen and snatch one of the surface antigens by endocytosis. It then processes the antigens and features it on it's cell surface becoming an antigen-presenting cell.
A Helper T-lymphocyte with a complementary receptor will then reach the B-cell with the antigen presented and bind to it by it's complementary receptor to stimulate the B-cell to divide by mitosis, creating genetically identical daughter cells. Some of them become memory cells, which live much longer than plasma cells and are responsible for the secondary response, and some become Plasma cells, which secrete many of the same antibody, known as monoclonal antibodies, to erase the foreign antigen from the body.
48
What is the primary immune response?
When an antigen enters the body for the first time it activates the immune system. This is called the primary response - it's much slower than the secondary response.
49
Why is the primary immune response slower than secondary?
The primary response is relatively slow, as there aren't that many B-cells that can make the antibody needed to bind to it.
50
Describe and explain the whole immune response.
Firstly a foreign antigen, for example, attached onto a pathogen or abnormal body cell, or a toxin, must be present.
A phagocyte must then go to the pathogen which will be used in this example, and engulf it by extending it's cytoplasm and effectively swallowing it; this is known as phagocytosis.
The pathogen is then in a phagocytic vacuole in the cytoplasm of the phagocyte and the lysosome inside the phagocyte fuses with the phagocytic vacuole, exposing enzymes called lysozymes which hydrolyze the pathogen.
The phagocyte then processes the antigens left alone and features it on it's cell surface membrane.
After the phagocyte becomes an antigen presenting cell, a Helper T cell with complementary receptors to the antigen must be found and when the receptors are bonded to the antigen, the specific T cell begins to divide, wherein some will end up as cytotoxic T cells or Helper T cells which can end up stimulating B cells.
The Cellular response is finished. Then, a B cell must be found that has complementary antibodies to the foreign antigen presented and it will have to be presented to the foreign antigen - the B cell is able to attach to the complementary foreign antigen and snatches it into the cell by a process called endocytosis to get presented and processed on the cell surface membrane.
After this, a Helper T cell with a complementary receptor must then bind onto the antigen presented by the B cell, stimulating the B cell to divide by mitosis to produce genetically identical B cells, which can either be memory cells or plasma cells.
Plasma cells then go and produce many of the same antibody, known as monoclonal antibodies to fight off the foreign pathogen.
Memory cells stay dormant and last for much longer than plasma cells. They stay in the body in order to be used to activate the secondary response if the same antigen is ever found in the body again, they divide rapidly into plasma cells and the reaction will be quicker and stronger.
51
What is a memory cell?
Memory cells are B-cells produced during the Humoral response that live very long in the body.
They are responsible for triggering the Secondary response related to an infection by diving rapidly into plasma cells if the same antigen is ever found in the body a second time.
52
Describe why the Primary Immune Response is much slower and weaker than the Secondary Immune Response.
Firstly, in the Secondary Immune Response, memory cells have been present due to the fact the body has fought off the same antigen presented before, and so memory cells make clonal selection much quicker, which means the pathogen is generally fought off much faster and before they divide so the reaction is much quicker and much stronger.
Comparatively, the Primary Immune Response does not use memory cells because the antigen is presented a first time and so clonal selection happens much slower as a B cell complementary to the pathogen's foreign antigens must be found first which can take time. This means that the pathogen has time to divide and so symptoms can then occur in the individual.
53
Describe the function of antibodies.
Antibodies are secreted by plasma cells wherein their function is to increase the efficiency and speed of the immune response against foreign pathogens.
They do this with their 2 binding sites. Antibodies are able to bind onto 2 foreign antigens at once, meaning that many antibodies can cause pathogens attached to the antigens to clump up.
This means that agglutination occurs, where a lot of pathogens are enclosed in a small space. This is essential as it means the efficiency of phagocytosis is much higher as white blood cells are able to hydrolyze many antibodies at once, rather than one at a time.
This means the destruction of pathogens occur faster when antibodies are present.
54
Vaccines protect individuals and populations against disease.
Describe and explain the function of vaccines.
Vaccines refer to when a dead or weakened version of a pathogen with certain antigens are inserted into an individual.
It is done in order to allow people to generate immunity to certain diseases without experiencing symptoms that would be seen in a primary response with the natural pathogen's associated antigens.
This is because the pathogens are weakened and will usually cause no or very mild symptoms in the individual. As a result of this, an individual can become immune to a certain pathogen by their associated antigens by taking a vaccine without experiencing symptoms.
As a result of this, when the real pathogen comes with it's associated antigens, assuming the individual has had a vaccine, it is highly likely that the secondary response will occur instantly as memory cells that are present will be able to divide into plasma cells as to speed up the duration of clonal selection - it becomes much quicker, and much stronger, and the pathogen is often destroyed in the body before it causes any symptoms.
55
Describe why, when vaccines only protect individuals who have them, non-vaccinated individuals may also benefit.
When individuals are vaccinated, the occurrence and transmission of a disease decreases as individuals that are vaccinated do not experience symptoms, and as a result, when a population is mostly vaccinated, there are less people you could potentially get the associated disease from if you aren't vaccinated.
This is called herd immunity.
56
Vaccines always contain antigens.
In what form could they be seen as?
Can be free, meaning not attached to anything
| Attached to a dead/weakened pathogen
57
Describe why Antigenic Variation helps some pathogens evade the immune system.
Antigens on the surface of pathogens activate the primary response, and vaccines use the specific antigen to allow individuals to advance to the secondary response - gain immunity - without experiencing symptoms.
However, if the antigens on the associated pathogen change, for example, from a DNA mutation, the individual will not be able to trigger a secondary response even though a vaccine for the associated pathogen was used. This is because the memory cells produced from the first vaccination with different antigens of the same associated pathogen won't recognize different antigens.
So, the immune system has to start from scratch and carry out a primary response. This means you experience symptoms.
Antigenic Variation refers to when a pathogen changes their surface antigens, which can mean this is possible.
58
Why may antigenic variation in certain pathogens make it hard to develop vaccines against the associated pathogen?
Antigenic variation may occur at a high rate in certain pathogens, for example, influenza often has antigenic variation every year.
Memory cells produced for one strain of the flu with associated antigens will not work for when the flu mutates and changes it's antigens next year, as the memory cells won't recognize the new antigens presented by the associated pathogen.
This means the primary response occurs again which means that the individual will have symptoms.
This means that a new vaccine for the influenza vaccine must change every year - this is costly.
59
What is Active immunity?
Active immunity is a type of immunity you get when your immune system makes its own antibodies after being stimulated by an antigen.
There are 2 different types:
Natural - this is when you become immune after catching a disease.
Artificial - this is when you become immune after you've been given a vaccination containing a harmless dose of antigen.
60
What is Passive immunity?
Passive immunity is a type of immunity you get from being given antibodies made by a different organism - your immune system doesn't produce any antibodies of it's own.
Again, there are 2 types:
Natural - when a baby becomes immune due to antibodies received from it's mother, through the placenta and in breast milk.
Artificial - this is when you become immune after being injected with antibodies from someone else. E.g. if you contract tetanus you can be injected with antibodies against the tetanus toxin.
61
List differences between active immunity and passive immunity.
In Active immunity, exposure to the antigen is required. This is not required in passive immunity.
In active immunity, it takes a while for immunity to develop (as clonal selection takes time to occur for the rapid production of antibodies made by yourself). In Passive immunity, protection is immediate.
Memory cells are produced in Active immunity. Memory cells aren't produced in Passive immunity.
Protection is short term in Passive immunity because the antibodies given eventually break down. In Active immunity, protection is long term due to the creation of memory cells which can react for secondary responses.
62
Not all individuals in a population must receive the vaccine for a vaccination progamme to be successful.
Describe why this is the case.
This is due to Herd Immunity - when a high percentage of individuals are vaccinated against a certain pathogen, it means that then they come in contact with the pathogen, the secondary response is triggered.
This means that the individual is likely to not be contagious, as they often do not experience symptoms.
As a result of this, transmission of the pathogen as a whole decreases and there are less people you can get the disease from. This decreases the chance every single person will even get in contact with the pathogen in the first place.
As a result of this, a vaccination progamme can be successful by decreasing the occurrence of the disease by the associated pathogen without needing everyone to be vaccinated.
63
The influenza virus causes the flu.
Explain why it is possible to suffer from the flu more than once.
In the primary response of the influenza virus, individuals suffer from the flu's symptoms, as clonal selection takes longer and so the reaction to the pathogen is weaker.
If the individual has gained immunity to the flu's associated antigens, it means it shouldn't get sick to it again as the secondary response means an individual generally won't develop symptoms as the reaction is much quicker and stronger.
However, it is possible to suffer from the associated disease, the flu, even though you contracted it before.
This is due to antigenic variability - a DNA mutation in a gene happens yearly in the influenza virus, and this causes the antigens of the virus associated with the flu disease to change shape.
As a result of this, the immune system must start from scratch as the past memory cells can't recognize the new antigens, which means they must begin from the primary response.
During the primary response, a person often experiences symptoms associated with the pathogen, so in this case, the flu.
64
What virus causes AIDS?
HIV
65
What does HIV stand for?
Human Immunodeficiency Virus
66
What does HIV eventually lead to?
AIDS
67
What does AIDS stand for?
Acquired Immune Deficiency Syndrome
68
What is AIDS?
AIDS is a condition where the immune system deteriorates and eventually fails - this makes someone with AIDS more vulnerable to other infections, like pneumonia.
69
What does HIV infect and kill?
Helper T cells.
70
What is HIV's host cell?
Helper T cells
71
HIV's host cells are Helper T cells. They damage and eventually kill them.
Outline the damage this causes to the immune system.
Helper T cells are necessary for the stimulation of phagocytes and B-cells for the humoral and cellular response. Without Helper T cells, certain processes, such as the division of B cells into memory cells or plasma cells, may not occur and this can leave the individual exposed to certain diseases.
With less Helper T-Cells, the immune system is unable to mount an effective response to infections because other immune system cells don't behave how they should.
72
When an individual contracts HIV, when are they considered to have AIDS?
When their Helper T-Cell count reach a critically low level.
73
Describe HIV's structure.
HIV has a spherical structure. It is a virus, thus it is acellular - it is not living.
It has a core that contains the genetic material (RNA) and some proteins, including an enzyme, reverse transcriptase, needed for virus replication.
An outer coating is seen in HIV, called a capsid.
An extra outer layer in HIV is seen beyond the capsid, called an Envelope. This is made of membrane stolen from the cell membrane of a previous host cell.
Sticking out from the envelope are loads of copies of an attachment protein that help HIV attach to the host Helper T-cell.
74
Label A to D:
https://media.discordapp.net/attachments/352951793187029005/830522876414656542/unknown.png
```
A = Attachment protein
B = Capsid
C = RNA
D = Reverse Transcriptase
E = Envelope
```
75
The virus HIV has something called an 'envelope'.
What is it?
The envelope found on HIV is an extra outer layer that is made of membrane stolen from the cell membrane of a previous host cell.
It covers the capsid which features the genetic material and extra proteins, and attachment proteins are found on the envelope which stick out.
76
Where does HIV replicate in?
Helper T-Cells
77
How does HIV replicate?
HIV replicates in Helper T-Cells.
The attachment protein attaches to a receptor molecule on the cell membrane of the host helper T-Cell.
The capsid is released into the cell, where it uncoats and releases the genetic material (RNA) into the cell's cytoplasm.
Inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template - this creates a DNA molecule.
From this, the double-stranded DNA is inserted and integrated into the human DNA.
Host cell enzymes are used to make viral proteins from instructions in the viral DNA - this is possible with the access to resources such as ribosomes in the host cell which are not found in HIV alone.
The viral proteins are assembled into new viruses, which bud from the cell and go on to infect other cells.
78
Describe how HIV replicates with help from the image:
https://media.discordapp.net/attachments/352951793187029005/830524890783154226/unknown.png?width=392&height=563
HIV replicates in Helper T-Cells.
The attachment protein attaches to a receptor molecule on the cell membrane of the host helper T-Cell.
The capsid is released into the cell, where it uncoats and releases the genetic material (RNA) into the cell's cytoplasm.
Inside the cell, reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template - this creates a DNA molecule.
From this, the double-stranded DNA is inserted and integrated into the human DNA.
Host cell enzymes are used to make viral proteins from instructions in the viral DNA - this is possible with the access to resources such as ribosomes in the host cell which are not found in HIV alone.
The viral proteins are assembled into new viruses, which bud from the cell and go on to infect other cells.
79
When an individual gets HIV, what are symptoms like?
During the initial infection period, HIV replicates quickly and the infected person may experience severe flu-like symptoms. After this period, HIV replication drops to a lower level.
This is the latency period. During the latency period (which can last for years) the infected person won't experience any symptoms.
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When HIV replication in an organism drops to a lower level, what is this known as?
Latency period
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When does an individual develop severe flu-like symptoms from the HIV virus itself?
During the initial infection - it then calms down
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People with AIDS generally develop diseases that wouldn't cause serious problems in people with a healthy immune system.
True or false?
True
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The length of time between infection with HIV and the development of AIDS varies, but it usually takes how long?
10 years
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When an individual acquires AIDS, what are symptoms like?
The initial symptoms of AIDS include minor infections of mucous membranes, e.g. the inside of the nose, ears and genitals, and recurring respiratory infections.
As AIDS progresses, the number of immune system cells decreases further and patients become susceptible to more serious infections including chronic diarrhoea, severe bacterial infections and tuberculosis.
During the late stages of AIDS, patients have a very low number of immune system cells and can develop a range of serious infections such as taxoplasmosis of the brain (a parasite infection) and candidiasis of the respiratory system (fungal infection).
It's these serious infections that kill AIDS patients, not HIV itself.
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Do antibiotics work against viruses?
No
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Antibiotics don't work against viruses.
Why?
Antibiotics kill bacteria by interfering with their metabolic reactions, such as targeting bacterial enzymes and ribosomes used in the reactions.
Bacterial enzymes and ribosomes are different than human enzymes and ribosomes, and so antibiotics can be designed to target specifically bacterial ones so they don't damage human cells.
Viruses don't have their own enzymes and ribosomes - they use the ones in the host's cells. So, because viruses in humans use human enzymes and human ribosomes to replicate, antibiotics can't inhibit them because side effects would be very powerful - antibiotics don't target human processes.
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How do antibiotics work against bacteria?
Antibiotics kill bacteria by interfering with their metabolic reactions, such as targeting bacterial enzymes and ribosomes used in the reactions.
Compared to viruses, enzymes and ribosomes specific to bacteria do exist and so antibiotics can be used to target the bacteria only so that side effects are much better.
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Antiviral drugs exist - how do they target viruses?
Most antiviral drugs are designed to target the few virus-specific enzymes (enzymes that only the virus uses).
For example, HIV uses reverse transcriptase to replicate. Human cells don't use the enzyme so drugs can be designed to inhibit it without affecting the human host cell. These drugs are called reverse-transcriptase inhibitors.
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The antiviral drug against HIV targets the enzyme reverse transcriptase.
What are they called?
Reverse-transcriptase inhibitors.
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Does HIV have a cure?
No
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HIV does not have a cure.
Describe what individuals can do to reduce spread of HIV.
Have protected sexual intercourse
Make sure that bodily fluids used in transplants are not HIV positive
Taking antiviral drugs (reverse transcriptase inhibitors in this instance) during pregnancy if you're HIV positive to reduce the chance of the baby being HIV positive.
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Use of vaccines raise ethical issues.
List 3 ethical issues.
All vaccines are tested on animals before being tested on humans - some people disagree with animal testing.
Animal based substances may also be used to produce a vaccine, which some people disagree with as well.
Testing vaccines on humans can be tricky, as volunteers may put themselves at unnecessary and potentially harmful risk of contracting the disease because they think they're fully protected, even though vaccines don't provide 100% protection (e.g. they might have unprotected sex because they have had the new HIV vaccine and think they're fully protected - the vaccine might not work...).
Some people don't want to take the vaccine for the possible risk of side effects, but they are still protected because of herd immunity - other people think this is unfair.
If there was an epidemic of a new disease, there would be a rush to receive a vaccine and difficult decisions would have to be made about who would be the first to receive it, which can be controversial.
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The graph below shows the number of laboratory reports of Haemophilus influenza type b (Hib), in England and Wales, from 1990 to 2004.
Hib affects children and can lead to meningitis and pneumonia:
https://media.discordapp.net/attachments/352951793187029005/830532760149426206/unknown.png
Explain how immunization could have caused the sharp decrease in Hib cases after 1992.
Firstly, immunization refers to when an individual is made immune to a certain pathogen, which in this context, is Hib, and this immunity to Hib also means that individuals do not get symptoms of the disease, meaning it is very likely that they will not be contagious with it and will not develop symptoms. The immunization period here specifically shows that individuals were able to get vaccinated for the disease.
Since much more people were getting immune to the disease, there are now not as many people to get the disease from and this meant that the number of laboratory reports of Hib decreased, as there were less people Hib could successfully spread to - this is called herd immunity.
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The graph below shows the number of laboratory reports of Haemophilus influenza type b (Hib), in England and Wales, from 1990 to 2004.
Hib affects children and can lead to meningitis and pneumonia:
https://media.discordapp.net/attachments/352951793187029005/830532760149426206/unknown.png
Suggest a possible explanation for the increase in Hib cases after 1998.
A mutation might've occurred in Hib that changed it's surface antigens.
As a result of this, memory cells generated in vaccinated immunity in the past would not recognize the new surface antigens, and as a result, Hib would be able to infect the individual, causing symptoms as the immune system must start again from the primary response - this causes opportunity for the spread of the disease.
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What is a lymphocyte?
A lymphocyte is a white blood cell that is involved in the immune response.
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Why is the 'cell-mediated' response called 'cell-mediated'?
It's called the cell-mediated response because T cells only respond to antigens which are presented on antigen presenting cells, such as some phagocytes, and not antigens not associated with cells, or detached from them, such as if they are within bodily fluids such as the blood.
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Why is the 'humoral' response called 'humoral'?
'humour' in the word 'humoral' is an old word for bodily fluids.
The humoral response refers to the immune response involving B cells and antibodies, and antibodies are soluble and transport in bodily fluids, hence the name.
