3.2.3 Cell Recognition and the Immune System

Question 1

Answer 1

Question 2

How does the HIV virus replicate?

Answer 2

Attaches to receptor molecule on host cell membrane. Capsid is released into cell and it uncoats and releases nucleic acid. Reverse transcriptase is used to make a complementary strand of DNA from the viral RNA template. Double stranded DNA is made and inserted into the human DNA (using integrase). Host cell enzymes are used to make viral proteins from the viral DNA within the human DNA. The viral proteins are assembled into new viruses and releases from the cell via cell lysis

Question 3

What is AIDS?

Answer 3

When the immune system deteriorates and eventually falls

Question 5

How does the human body distinguish between self & non-self cells?

Answer 5

Marker molecules (proteins) are present on the membrane of cells, enabling the body to recognise these as ‘self’ cells.

Question 6

What is a toxin?

Answer 6

A protein (antigen) released by pathogens which are poisonous to the body.

Question 7

What is phagocytosis?

Answer 7

When foreign cells are engulfed by phagocytes, digested by lysozymes released by lysosomes in the cell.

Question 8

Describe the role of T-helper cells.

Answer 8

Recruit & signal to phagocytes AND activate B cells

Question 9

Describe the role of T-cytotoxic cells.

Answer 9

Kill abnormal & foreign cells (produces proteins to do this e.g. perforin)

Question 10

What is a B plasma cell?

Answer 10

A type of B cell which secrete LOTS of monoclonal antibodies (all complementary to a specific antigen)

Question 11

Describe the importance of the variable region of an antibody.

Answer 11

Has a unique protein structure, which provides specificity to one type of antigen.

Question 12

What does the humoral immmune response consist of?

Answer 12

B cells- antibodies, clonal selection.

Question 13

What does the cellular immune response consist of?

Answer 13

T cells- phagocytes, cell signals etc.

Question 14

Describe the primary response of the immune system.

Answer 14

When the body first detects a type of pathogen, a slow response, which creates memory cells. The body will show symptoms until enough antibodies are made.

Question 15

Explain why the secondary response is quicker than the primary immune response.

Answer 15

B- memory cells are activated and divide into plasma cells, producing antibodies. T-memory cells are activated and produce T-cells to kill the pathogen. FEWER STEPS!

Question 16

What is active natural immunity?

Answer 16

When a person is immune, after naturally contracting an infection.

Question 17

What is passive immunity?

Answer 17

When a person is immune, by being given antibodies rather than making them. e.g. natural from breastfeeding.

Question 18

Give 2 differences between passive & active immunity.

Answer 18

Active- lasts longer, memory cells are produced, response takes longer to happen, needs antigen to trigger response.

Question 19

What is a vaccine?

Answer 19

A low dose of an inactive/dead pathogen are injected- contain antigens to trigger immune response, creating protective memory cells.

Question 20

What is herd immunity?

Answer 20

When more members of a population have had a vaccine/are immune, so more people are protected asthe disease can spread less rapidly, even if they haven’t had the vaccine themselves.

Question 21

What is antigenic variation?

Answer 21

Where a pathogen can change the antigens on its surface (e.g. different strains of flu)

Question 22

Explain why people must receive a different flu vaccine annually.

Answer 22

The flu virus undergoes antigenic variation, so memory cells from one vaccine will not always protect against new strains.

Question 23

What are monoclonal antibodies?

Answer 23

Antibodies which are all made from identical B plasma cells- complementary to the same specific antigen.

Question 24

Describe how monoclonal antibodies can be used in anti-cancer drugs.

Answer 24

Antibodies are specific to antigens on cancerous cells (tumour markers)- the drug bind s& accumulates in specific area (much fewer side effects than conventional cancer treatments).

Question 25

What is an ELISA test?

Answer 25

Where antibodies are attached to an enzyme, which produces a coloured substrate- used in diagnosis.

Question 26

Which part of the immune system does HIV initially affect?

Answer 26

T cells

Question 27

Explain why antibiotics cannot be used on HIV.

Answer 27

Antibiotics are specific to bacteria e.g. murein cell walls, so would be ineffective on viral structure.

Question 28

Why is aseptic technique important?

Answer 28

prevents contamination of cultures by unwanted microorganism

Question 29

What is phagocytosis?

Answer 29

Phagocyte recognises the antigens on a pathogen. endocytosis. pathogen is contained in a phagocytic vacuole. lysosomes, containing digestive enzymes fuse with the vacuole, enzymes are released and they destroy the pathogen. phagocyte presents antigen on its surface

Question 30

What do the receptors on T cells do?

Answer 30

bind to antigens displayed by antigen presenting cells

Question 31

How are T cells activated?

Answer 31

When their receptors bind to complementary antigens on the surface of antigen presenting cells. once activated by this binding each t helper cell produces a clone of active t helper cells and a clone of t memory cells

Question 32

Describe the antibody structure

Answer 32

Four polypeptide chains, 2 heavy and 2 light. each chain has a variable region and a constant region

Question 33

State the variable region on an antibody

Answer 33

Form the antigen binding site. The shape is complementary to a particular antigen, its shape varies between antibodies

Question 34

What are B memory cells?

Answer 34

They bind to the antigen. They remain or months or years in the body, enabling the individual to respond more quickly to the same antigen in the future.

Question 35

If the zone of inhibition is wider, what does this indicate about the antibiotic?

Answer 35

the wider the clear zone, the more effective the antibiotic is at preventing growth