Bio 2C

Front 1

Define antigens

Back 1

Molecules (usually proteins) which generate an immune response when detected by the body; usually on the surface of cells

Front 2

What does the immune system use antigens to identify?

Back 2

Pathogens, abnormal body cells (like cancer), toxins, cells from other individuals

Front 3

Describe the role of the phagocyte

Back 3

Phagocytes recognise foreign antigen on a pathogen, forms pseudopodia around it and engulfs it by moving it into the cytoplasm, forms a phagocytic vacuole, a lysosome fuses with this and lysozymes hydrolyse the pathogen. The phagocyte then presents the antigens on its CSM (antigen-presenting cell), and the rest of the debris is expelled via exocytosis

Front 4

Describe how helper T-cells are activated

Back 4

The receptor proteins bind to complementary antigens presented by phagocytes, activating the T-cell to stimulate other cells via chemicals.

Front 5

Describe the cellular response

Back 5

T-cells and other immune cells they interact with, e.g. the helper T-cell response stimulates phagocytes to engulf foreign cells and activates cytotoxic T-cells which kill foreign cells

Front 6

What is the humoral response?

Back 6

B-cells, clinal selection and monoclonal antibodies

Front 7

Explain the role of B-cells in the immune response

Back 7

B-cells activate with chemicals from the T-helper cell and when antibodies covering the B-cells binds to a complementary antigen. The B-cells undergo clonal selection to divide into genetically identical plasma cells, which then release many antibodies all complementary to the same specific antigen

Front 8

Describe the structure of antibodies

Back 8

They are proteins with 2 identical specific variable regions which form antigen binding sites - very specific to one antigen due to unique tertiary structure that is only complementary to one shape. Have the same constant regions which are bonded by 2 disulfide bridges. Constant region also known as heavy region, variable is light region. Also has hinge proteins.

Front 9

Describe how antibodies deal with antigens

Back 9

2 binding sites mean they can bind to 2 pathogens at the same time, which clumps them together (agglutination) and so makes it easier for phagocytes to find and engulf them, leading to the destruction of the pathogen

Front 10

Describe the role of memory B-cells

Back 10

B-cells also differentiate into memory B-cells which are activated when the same antigen is encountered again - stimulates a faster secondary response as clinal selection happens faster and the correct T-cells can be immediately activated

Front 11

Explain why the secondary immune response is faster than the primary

Back 11

Primary response is slow as not many B-cells around specific to that antigen so have to undergo clonal selection - finding correct helper T-cell also takes time

Front 12

Define a vaccination

Back 12

A dead or inactive form of a pathogen containing the antigens to stimulate the immune response without causing active infection to the individual

Front 13

Explain how vaccinations cause immunity

Back 13

The antigens trigger the immune response as normal, activating B-cells to make memory cells for the antigen so that if live pathogen infects the secondary immune response is triggered and person does not show symptoms

Front 14

Explain how herd immunity comes abot

Back 14

Vaccines reduce the occurrence of the disease so those unvaccinated are less likely to catch the disease as there are fewer people to catch it from

Front 15

How does HIV cause disease?

Back 15

HIV kills helper T-cells, and when their level falls beyond a certain point it means that an immune response can not be mounted against foreign antigens, and so body can’t fight off simple infections (developing into AIDS) and person dies from them - e.g. pneumonia

Front 16

How does HIV replicate?

Back 16

Attachment proteins bind to receptors on helper T-cell, capsid releases into cell and uncoats to release RNA into cytoplasm, reverse transcriptase makes a complementary strand of DNA from viral RNA template, from this double stranded DNA is made and inserted into human DNA, causes host cell enzymes to make viral proteins which assemble into new viruses and bud from the cell to infect more cells

Front 17

Why may a HIV infected person not show symptoms for a period of time?

Back 17

HIV initially replicated rapidly causing flu-like symptoms, then the replication drops during latency period - until activated again person won’t show any symptoms

Front 18

Why don’t antibiotics work against viruses?

Back 18

Antibiotics kill bacteria by targeting bacterial enzymes and ribosomes - but viruses do not have those, so use host cell’s - cannot target them as would cause significant damage to the host:

Front 19

How do antiviral drugs work?

Back 19

Target virus-specific enzymes, like reverse transcriptase in HIV, and since humans don’t use these it does not affect the host cell. Called reverse-transcriptase inhibitors.

Front 20

How can HIV spread be reduced?

Back 20

Educating about risks of unprotected sexual intercourse, injecting bodily fluids and mothers taking antiviral drugs to reduce chance of baby being HIV positive

Front 21

How can pathogens evade the immune system?

Back 21

Antigen variability means that the memory cells do not recognise the new form of the antigen, so the slower primary response occurs which means symptoms are shown

Front 22

Define active immunjty

Back 22

When the immune system makes its own antibodies when stimulated by an antigen

Natural - antigens from catching a disease

Artificial - vaccinations

Front 23

Define passive immunity

Back 23

When given antibodies made by a different organism

Natural - antibodies in breast milk and placenta

Artificial - injected with someone else’s antibodies

Front 24

Give advantages of active immunity

Back 24

Memory cells are produced, protection is long-term as complementary antibodies already present

Front 25

Describe the advantages of passive immunity

Back 25

Doesn’t require exposure to antigen, protection is immediate

Front 26

Define monoclonal antibodies

Back 26

Proteins produced by genetically identical B-cells which are all complementary to the same specific antigen - all identical in structure

Front 27

Why are monoclonal antibodies useful in medicine?

Back 27

You can make monoclonal antibodies that bind to anything.

Can be used to target drugs to particular cells like cancer cells by making them complementary to their antigens and attaching the drug

Can target a particular substance for diagnosis, like bind to hCG to show pregnancy

Front 28

Describe how to make an ELISA test

Back 28

Bind antigen in well, add sample of blood, if antibodies present (from fighting the disease) then will bind to antigen, well washed out to remove unbound antibodies, secondary antibody with enzyme added to well which binds to primary antibody so of present will bind, well washed out, a solution with substrate to the enzyme added, if enzyme present a colour change will occur to indicate a positive result

Front 29

Describe the HIV structure

Back 29

Spherical, has core of RNA genetic material and some proteins (e.g. enzymes like reverse transcriptase), a protein coating called a capsid, extra outer layer called an envelope from stolen membrane of host cell, attachment proteins complementary to helper T-cells