❌Cells structure- Cell recognition and the Immune System

Question 1

what are the two defence mechanisms?

Answer 1

• Innate - the non specific response which is immediate and the same for all pathogens
• Adaptive - the specific response which is slower and specific to each pathogen

Question 2

give two types of innate defence mechanisms

Answer 2

• physical barriers like skin, ciliated epithelium, tears, mucus, saliva and conc. HCl in the stomach.
• phagocytosis

Question 3

How are phagocytes and lymphocytes able to distinguish between self and non-self cells?

Answer 3

because each type of cell has protein receptor molecules on it’s surface

Question 4

What do the protein receptor molecules on the surface of lymphocytes and phagocytes allow the immune system to identify?

Answer 4

• pathogens
• non-cell material e.g. cells from other organisms of the same species
• toxins including those produced by certain pathogens like the bacterium that causes cholera
• abnormal body cells such as cancer cells

Question 5

How do lymphocytes recognise self cells

Answer 5

1. in the fetus lymphocytes constantly collide with almost only self cells as infection in the fetus is rare as its protected by the placenta
2. some of the lymphocytes will have receptors that exactly fit those of the body’s own cells
3. these lymphocytes either die or are suppressed and remaining lymphocytes are those that fit foreign non-self cells hence only respond to them
4. in adults, lymphocytes produced in the bone marrow initially only encounter self antigens and those that show immune response to self antigens undergo apoptosis hence only lymphocytes that may respond to non-self antigens appear in the blood

Question 6

Explain the phagocytosis of pathogens and subsequent destruction of ingested pathogens by lysozymes

Answer 6

1. chemotaxis by phagocytes
2. protein receptors on the phagocyte recognise the pathogen as a non self cell so the phagocyte engulfs the pathogen in endocytosis
3. the pathogen is contained within the phagocyte through a phagosome
4. a lysosome fuses with the phagosome and releases lysozyme to digest the pathogen via hydrolysis and the pathogen dies
5. the digested material is released from the phagocyte via exocytosis

Question 7

Give three features of an antigen

Answer 7

• they are proteins that recognise as non self
• they often have proteins on the surface (antigens)
• they trigger an immune response

Question 8

What does the shape specific feature of antigens mean for the immune system?

Answer 8

It allows the immune system to identify:

• pathogens e.g. influenza
• toxins e.g. botulism
• abnormal cells
• cells from other organisms

Question 9

What are the three features of antibodies?

Answer 9

• They are quaternary proteins that consist of 2 heavy chains and 2 light chains
• they are highly specific so form an “antigen antibody complex” (KEY WORD)

Question 10

What are the two types of adaptive mechanisms

Answer 10

• the cell mediated response of T lymphocytes

- the humoral response of B lymphocytes

Question 11

What are antigen presenting cells?

Answer 11

Cells that display foreign antigens on their surface

Question 12

What antigens do t lymphocytes respond to?

Answer 12

Antigens that are presented on a body cell rather than those within body fluids

Question 13

What do plasma proteins do and how are they suited for this function?

Answer 13

They manufacture and secrete antibodies and are suited for this as:

• they have a larger number of ribosomes associated with a more extensive rough ER
• they have a larger Golgi
• they have more mitochondria

Question 14

Give the steps of cell mediated immunity

Answer 14

1. Pathogens invade body cells or are taken up by phagocytes
2. The phagocyte places antigens from the pathogen on its cell-surface membrane (antigen presentation)
3. Receptors on a specific helper T cell fit exactly onto these antigens
4. This attachment activates T cells to rapidly divide by mitosis and form a clone of genetically identical cells
5. The cloned T cells then:
   - develop into memory cells that enable a rapid response to future infections by the same pathogen
   - stimulate phagocytes to engulf pathogens by phagocytosis
   - stimulate B cells to divide and secrete their antibody
   - activate cytotoxic T cells

Question 15

How do cytotoxic T cells work?

Answer 15

They kill abnormal cells and body cells infected by pathogens by producing the protein perforin which makes holes in the cell surface membrane causing it to become freely permeable hence the cell dies. It’s most effective against viruses as it prevents them from being able to replicate

Question 16

What do monoclonal antibodies develop into? Give a description of each

Answer 16

• Plasma cells: secrete antibodies which destroy antigens (forms the primary immune response which is the production of antibodies and memory cells)
• Memory cells: circulate in blood and tissue fluid and divide rapidly into plasma cells which produce the antibodies and memory cells when an antigen that has previously entered the body returns so form part of the secondary immune response

Question 17

Describe the steps of humoral immunity

Answer 17

1. The surface antigens of an invading pathogen are taken up by a specific B
2. The B cell processes the antigen and presents them on its surface
3. Helper T cells from the cell mediated immunity attach to the processed antigens on the B cell hence activating the B cell by releasing cytokines cell causing it to divide by mitosis to give a clone of plasma cells
4. The cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogens surface
5. The antibody attaches to antigens on the pathogens and destroys them through agglutination, opsonisation, neutralisation and inactivation via antigen antibody complexes
6. Some B cells develop into memory cells which can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce antibodies (this is the secondary immune response).

Question 18

What are the 4 ways antibodies work?

Answer 18

• release metabolic toxins
• cause agglutination which makes it easier for phagocytes to locate the pathogen as it isn’t as spread out within the body
• serve as markers in opsonisation as they stimulate the phagocytes to engulf the pathogen to which they are attached
• they inactivate viruses

Question 19

What is antigen variability?

Answer 19

When the mutations of a pathogens DNA means that previous immunity to the pathogen is no longer effective because the antigens shape has changed

Question 20

Why do antibodies have at least 2 antigen binding sites?

Answer 20

So they can bind to more than one pathogen at once to allow for agglutination

Question 21

Explain the formation of an antigen-antibody complex

Answer 21

1. An antigen and its antibody have complementary shapes so are specific to each other
2. When an antibody collides with a foreign cell that has non self antigens with a complementary shape, it binds with one of the antigens and so form an antigen antibody complex

Question 22

Explain the 3 types of immunity

Answer 22

• naturally acquired active immunity - direct contact with the pathogen or its antigen under natural circumstances stimulates the individual’s specific immune response to produce antibodies
• artificially acquired active immunity - direct contact with the pathogen or its antigen through vaccination stimulates the individual’s specific immune response to produce antibodies
• passive immunity - introducing antibodies into individuals from an outside source meaning immediate immunity is acquired but it doesn’t last as no memory cells are formed e.g. immunity acquired by a foetus through antibodies passing across placenta and snake bites treated with anti venom

Question 23

What are the steps to active immunity?

Answer 23

1. Exposure to antigen (naturally or artificially via vaccination)
2. Stimulates specific immune response
3. Produces antibodies
4. Which produce memory B and T cells

Question 24

What are the steps to passive immunity?

Answer 24

1. No antigen exposure as antibodies themselves are introduced into the individuals
2. Antibodies form antigen-antibody complex
3. No memory cells are produced

Question 25

What factors does a successful vaccination program depend on?

Answer 25

• economic viability in sufficient quantities to immunise most of the vulnerable pop.
• few side effects as they discourage individuals from the vaccine
• means of producing, storing and transporting through technologically advanced equipment hygiene and refrigerated transport
• must have the possibility for herd immunity

Question 26

What are the types of vaccines that can form the process of artificially active immunity

Answer 26

• attenuated live vaccine which contains the actual pathogen but is weak
• fragments which are the antigens being the proteins of the specific pathogen
• vaccine that contains the pathogen that has been killed by heat

Question 27

What does endemic mean?

Answer 27

A disease that is always present in the population

Question 28

What is the condition for herd immunity to take effect?

Answer 28

95% of the population needs to be vaccinated

Question 29

What is herd immunity?

Answer 29

1. When a high percentage of the population is vaccinated

2. The probability of contact between affected and unvaccinated individuals reduces

Question 30

Give three reasons why vaccination can’t always eliminate a disease

Answer 30

• It may fail to induce immunity in certain individuals e,g, those with defective immune systems
• antigenic variability in antigenic shift/ drift
• individuals may have objections to vaccination for religious, ethical or medical reasons

Question 31

Why are antibiotics ineffective against viruses?

Answer 31

1. Antibiotics have specific modes of action which all effect cell metabolism e.g. inhibiting cell wall construction, inhibiting protein synthesis and inhibiting nucleic acid synthesis
2. Viruses are acellular non living particles so do not have cell metabolism hence, antibiotics have no effect on them

Question 32

What is antigenic shift?

Answer 32

A complete change in the viruses shape as a result of mutations causing the vaccination to become ineffective causing the antigens to become un recognisable by the immune system

Question 33

What is antigenic drift?

Answer 33

A gradual change in the shape of a virus

Question 34

What makes HIV a retrovirus?

Answer 34

The presence of reverse transcriptase as well as the consequent ability to make DNA from RNA

Question 35

What are features of the structure of HIV?

Answer 35

• phospholipid envelope
• protein capsid
• 2 copies of RNA genome
• gp 120 protein attachments
• reverse transcriptase to catalyse the production of DNA from RNA

Question 36

What are the steps to the replication of HIV?

Answer 36

1. HIV enters the blood stream and circulates around the blood
2. HIV’s gp 120 attachment protein binds to the complementary CD4 protein usually on T helper cells
3. the protein capsid fuses with cell surface membrane so RNA and enzymes of HIV enter the T helper cell
4. HIV reverse transcriptase catalyses the reaction to produce DNA from the viruses RNA
5. the proviral DNA is moved into T helper cell’s nucleus so it’s inserted into the cell’s DNA
6. using the cells enzymes, This creates mRNA which contains the instructions to make new viral RNA and proteins
7. The mRNA passes out of the nucleus via nuclear pore and uses the cell’s protein synthesis mechanisms to make HIV particles
8. The HIV particles break away from the helper T cell which a piece of its cell surface membrane surrounding them to form their lipid envelope

Question 37

How does HIV cause the symptoms of AIDS?

Answer 37

1. Infects the T helper cells/ macrophages causing them to become the host cells
2. This means there are fewer T helper cells
3. No binding to specific B cells
4. No cytokines
5. No clonal expansion
6. No plasma cells
7. Therefor no antibodies

Question 38

What is ‘ELISA”in the ELISA test an acronym for?

Answer 38

Enzyme linked immunosorbant assay

Question 39

What are the steps in the ELISA test?

Answer 39

1. Apply the sample from the patient to a surface to which all the antigens in the sample will attach
2. Wash to remove unattached antigens
3. Add an antibody complementary in shape to the antigen to form antibody antigen complexes causing the antibodies to become immobilised
4. Wash to remove the unbound antibodies
5. Add a second antibody complimentary in shape to the first antibody so it binds to it.
6. The second antibody has an enzyme attached to it whose colourless substrate is added.
7. The enzyme acts on the substrate causing it to change colour into a coloured product and the concentration of antigens present is relative to the intensity of colour that develops

Question 40

What does it mean for HIV if someone has a high CD4 count?

Answer 40

That the HIV isn’t replicating at a high rate

Question 41

What is a cell that monoclonal antibodies can target and what are the two methods is can do this? What is their advantage?

Answer 41

Cancer cells through direct and indirect monoclonal antibody therapy.

Antibodies are non toxic and are highly specific so this causes less side effects than other cancer treatments

Question 42

How does direct monoclonal antibody therapy work?

Answer 42

1. The monoclonal antibodies produced are specific to antigens on cancer cells as their shapes are complementary
2. The antibodies are given to patients and bind to the receptors on their cancer cells
3. They attach to the surface of their cancer cells and inhibit the chemical signals that stimulate their uncontrolled growth

Question 43

How does indirect monoclonal antibody therapy work?

Answer 43

1. Monoclonal antibodies are produced that are specific to antigens on cancer cells
2. A cytotoxic drug is attached to the monoclonal antibody
3. These antibodies with the attached drug is given to the patient and they bind to the receptors on their cancer cells and attach to the surface killing the cancer cells

Question 44

What is the use of monoclonal antibodies in medical diagnosis?

Answer 44

Diagnosis of

• influenza
• hepatitis
• chlamydia
• certain cancers
• pregnancies

Question 45

Give three ethical issues raised by monoclonal antibodies

Answer 45

• production of monoclonal antibodies involves deliberately inducing cancer in mice which some class as animal cruelty
• there have been some deaths associated with the use of monoclonal antibodies in treatments such as multiple sclerosis
• testing for the safety of new drugs could present dangers e.g. volunteers taking part in trials could become very unwell so their are issues about the conduct of drug trials

Question 46

Give 7 questions that have been raised concerning the production and use of vaccines

Answer 46

-how acceptable is it to use animals in vaccination trials?
-how can the risk of the side-effects be balanced against the risk of developing a disease that causes greater harm?
-how, to whom and to what extent should vaccination trials be carried out?
-it is acceptable to trial a new vaccine with unknown health risks only in a country where the targeted disease is common on the basis that the population has the most to gain if successful?
-is it right for vaccination to be compulsory especially when people
may have personal and religious beliefs as well as medical circumstances that suggest otherwise?
-should expensive vaccination programmes continue when the disease is almost eradicated?
-how can individual health risks from vaccination be balanced against the advantages of controlling a disease for the benefit of the pop.?