Topic 2C: Cells and the Immune System

Question 1

What are antigens?

Answer 1

Molecules which generate an immune response when detected by the body.

Question 2

What are pathogens?

Answer 2

Disease causing organisms which have antigen on their surface.

Question 3

What are abnormal body cells?

Answer 3

Cancerous or pathogen-infected cells which have abnormal antigens on their surface triggering an immune response.

Question 4

What are the different stages of an immune response?

Answer 4

1) Phagocytosis
2) T-cells
3) B-cells
4) Antibody production

Question 5

What is the process of phagocytosis?

Answer 5

1) Phagocyte detects foreign antigens on pathogen.
2) The cytoplasm of the phagocyte engulfs the pathogen.
3) This forms a phagocytic vacuole around the pathogen.
4) A lysosome fuses with the phagocytic vacuole and releases lysozymes which break down the pathogen.
5) The phagocyte then presents the pathogen’s antigens on its surface to activate other immune system cells.

Question 6

What is the role of a T-Cell?

Answer 6

1) The T-Cell binds to the complementary antigens presenter by a phagocyte using receptor proteins.
2) This activates the T-Cell.
3) Helper T-Cells release chemical signals which stimulate phagocytes and B-Cells. Cytotoxic T-Cells kill abnormal and foreign cells.

Question 7

What is the role of a B-Cell?

Answer 7

1) The B-Cell binds to complementary antigens using antibodies on its surface.
2) The chemical signals released by helped T-Cells then activated the B-Cell in a process called clonal selection.
3) The activated B-Cell then divides into plasma cells.

Question 8

How does antibody production fight pathogens?

Answer 8

1) Plasma cell’s secrete many monoclonal antibodies which bind to complementary antigens on the surface of pathogens.
2) This forms antigen-antibody complexes and because each antibody has two binding sites it can bind to two pathogens at the same time.
3) This causes pathogens to be clumped together in a process called agglutination.
4) A phagocyte then binds the antigen-antibody complex and phagocytose many pathogens at once.

Question 9

What is the structure of an antibody?

Answer 9

• 2 variable regions (which determines the antibodies specificity)
• 2 heavy polypeptide chains.
• 2 light polypeptide chains.
• 2 hinge regions.

All of which are held together by disulfide bridges.

Question 10

What is the cellular immune response?

Answer 10

Phagocytosis and the T-Cells.

Question 11

What is the humoral immune response?

Answer 11

B-Cells and antibody production.

Question 12

What is a primary response?

Answer 12

The response which occurs the first time an antigen enters the body and activates the immune system.

Question 13

What are the features of a primary response?

Answer 13

• Slow = because there aren’t many complementary B-Cells.
• Symptoms shown = because it takes time to produce enough of the correct antibody.
• Memory T-Cells produced = remain in the body for a long time to recognise specific antigens.
• Memory B-Cells produced = remain in the body for a long time to record the antibodies needed to bind to the antigen.

Question 14

What is a secondary response?

Answer 14

The response which occurs if the same pathogen enters the body again and activates the immune system.

Question 15

What are the features of a secondary response?

Answer 15

• Fast = clonal selection happens quicker.
• No symptoms = the response is stronger and faster.
• Memory B-Cells activated = produce complementary antibodies to the antigen.
• Memory T-Cells activated = kill the cell carrying antigen.

Question 16

What is active immunity?

Answer 16

The type of immunity you get when your immune system makes it’s own antibodies after being stimulated by an antigen.

Natural = After catching a disease.
Artificial = After receiving a vaccination.

Question 17

What is passive immunity?

Answer 17

The type of immunity you get when you’ve been given antibodies made by a different organism.

Natural = Breast milk containing antibodies from mother.
Artificial = Injections containing someone else’s antibodies.

Question 18

How do vaccinations work?

Answer 18

Vaccines contain antigens causing your body to produce memory cells, without the pathogen causing disease, meaning you gain immunity without showing any symptoms.

Question 19

What is herd immunity?

Answer 19

When people who haven’t been vaccinated gain protection from a disease due to others being vaccinated, reducing the occurrence of a disease.

Question 20

What is the disadvantage of taking vaccines orally?

Answer 20

It could be broken down by enzymes in the gut or the molecules may be too large to be absorbed.

Question 21

Why are booster vaccines provided?

Answer 21

To make sure that more memory cells are produced so a pathogen can be detected and killed quickly.

Question 22

What are the ethical issues surrounding the use of vaccines?

Answer 22

• Vaccines are tested on animals before human trials.
• Unsuccessful testing could lead to people exposing themselves to diseases thinking they are immune.
• Risk of side effects.
• If there was an epidemic of a new disease it would be difficult to decide who receives the vaccination first.

Question 23

What is antigenic variation?

Answer 23

When pathogens change their surface antigens.

Question 24

What are the affects of antigenic variation?

Answer 24

When you’re infected for a second time, your memory cells produced from the first infection will not recognise the different antigens, meaning it takes time to fight the infection and you get ill.

Question 25

What are monoclonal antibodies?

Answer 25

Antibodies which are produced by genetically identical plasma cells, meaning they are all identical in structure.

Question 26

How are monoclonal antibodies used in anti-cancer drugs?

Answer 26

1) Take a biopsy of a tumour and identify any non-self antigens.
2) Produce monoclonal antibodies which are complementary to that antigen.
3) Attach anti-cancer drugs to these monoclonal antibodies.
4) The antibodies then bind to the cancer cell’s antigens and deliver the drug to that region.
5) Therefore, less normal cell’s are killed so side effects are reduced.

Question 27

How are monoclonal antibodies used in pregnancy tests?

Answer 27

1) Dye beads are attached to the monoclonal antibodies (complementary to hCG) on a strip of absorbent paper.
2) The absorbent paper is dipped into the urine sample.
3) If the woman is pregnant, hCG will be present in their urine and bind to the monoclonal antibodies forming an antigen-antibody complex.
4) The urine will then move up the absorbent paper, carrying the monoclonal antibodies with it.
5) If the hCG proteins have bound to the monoclonal antibodies, they will then bind to the immobilised antibodies, forming a line of concentrated dye beads, producing a blue strip.

Question 28

What is the purpose of carrying out an ELISA test?

Answer 28

It allows you to see if a patient has any specific antigens present in their blood.

Question 29

How do you carry out a direct ELISA test?

Answer 29

1) Bind a sample of antigens to a well plate.
2) Add a detection antibody which has an enzyme attached that is complementary to the antigen being tested for.
3) If the antigen being tested for is present the detection antibody will bind to it.
4) The well is then washed to remove any unbound antibodies.
5) A substrate solution is then added which will react with the enzyme attached to the antibodies and change colour.

Question 30

What is HIV?

Answer 30

HIV is a virus which affects the human immune system and eventually causes AIDS.

Question 31

What is AIDS?

Answer 31

A condition caused by the HIV virus where the immune system deteriorated and fails, making you more vulnerable to infections.

Question 32

How does HIV affect the human immune system?

Answer 32

HIV infects and eventually kills helper T-Cells, meaning phagocytes and B-Cells aren’t activated, and therefore the immune system is unable to mount an effective response to infections.

Question 33

What is the initial infection period of HIV?

Answer 33

When HIV replicates rapidly and the infected person experience severe flu-like symptoms.

Question 34

What is the latency period?

Answer 34

The time after the initial infection of HIV where HIV replication slows down, meaning symptoms are no longer showed.

Question 35

What are the symptoms of AIDS?

Answer 35

Initially:
Minor infections of mucous membranes.

During:
Serious infections including severe diarrhoea.

Late stages:
Serious infections leading to death.

Question 36

What is the structure of HIV?

Answer 36

The virus particle has a spherical structure made up of a core containing RNA and reverse transcriptase. It has an outer coating called a capsid which is surrounded by an envelope. Sticking out of the envelope are many attachment proteins.

Question 37

What is the process of HIV replication?

Answer 37

1) HIV uses attachment proteins to bind to a receptor on the host helper T-Cell.
2) It then releases its capsid into cell where it uncoats and releases RNA.
3) Reverse transcriptase is then used to make a complementary strand DNA from the viral RNA template.
4) From this a double-stranded DNA is made and inserted into the human DNA.
5) Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA.
6) The viral proteins then assemble into new viruses which bud from the cell and infect others.

Question 38

What are the factors affecting the progression of HIV into AIDS?

Answer 38

• Age.
• Strain of HIV.
• Accra to healthcare.

Question 39

How are antibiotics used to treat bacteria?

Answer 39

Antibiotics interfere with their metabolic reactions by targeting the bacterial enzymes and ribosomes involved in these reactions.

Question 40

Why can’t antibiotics treat viruses?

Answer 40

Viruses don’t have their own enzymes and ribosomes meaning antibiotics cannot inhibit them as they do not target the human enzymes and ribosomes.