Immunity

Question 1

Features of non-specific defence mechanisms

Answer 1

• does not distinguish pathogen types
• response always the same
• act immediately

Question 2

Features of specific defence mechanisms

Answer 2

• specific to a type of pathogen
• response dependent on pathogen
• takes time to produce antibodies/long lasting

Question 3

Stages of phagocytosis

Answer 3

• attraction to pathogen by its chem. products + attachment
• pathogen ingested + phagosome formed (endocytosis)
• formation of phagolysosome (lysosome fuses w/ vesicle)
• digestion of pathogens by lysozyme through hydrolysis
• phagocyte either absorbs products or expels them (exocytosis)

Question 4

T lymphocytes

Answer 4

• mature in thymus gland
• cell mediated immunity

Question 5

Cell mediated immunity

Answer 5

• phagocyte presents pathogen antigen on membrane
• receptors on T.H cells fit antigen exactly
• attachment activates T cell replication -> clones

Cloned cells either:

• memory cells -> rapid future response
• stimulate phagocytosis
• stimulate B cell division + secrete antibodies
• activate T.C cells

Question 6

Cytotoxic T cells (T.C cells)

Answer 6

produces perforin which makes holes in cell surface membrane -> permeable to many substances so cell dies

Question 7

B lymphocytes

Answer 7

• mature in bone marrow
• humoral immunity
• concentrate in lymph nodes + spleen

Question 8

Humoral immunity

Answer 8

• B cell processes antigen from pathogen membrane + presents it on its surface
• T.H cell attaches to antigens -> activate B cell
• B cell divides cloning plasma cells
• these produce + secrete specific antibodies for exact antigen of pathogen
• antibodies attach to antigen on pathogen, destroys it
• some B cells develop into memory cells -> divide rapidly, faster response to future infection

Question 9

Differences between cell mediated and humoral immunity

Answer 9

• T cells, B cells
• no antibodies used in cell mediated
• pathogens identified by antigens floating in the blood in humoral vs. antigens on APC in cell mediated

Question 10

Structure of antibody

Answer 10

• 4 polypeptide chains (2 heavy, 2 light)
• 2 identical variable regions (binding sites)
• constant region, bind to receptors of cells
• hinge protein, flexibility when binding

Question 11

Functions of antibodies

Answer 11

• agglutination to clump bacterial cells -> easier for phagocytes to locate/destroy
• act as marker to stimulate phagocytosis

Question 12

Monoclonal antibodies

Answer 12

Single type of antibody that can be isolated and cloned
-> used to target cancer cells by attaching to cancerous cell membranes and blocking chemical signals that stimulate uncontrolled growth

Question 13

Passive immunity

Answer 13

caused by introduction of antibodies from outside source

• > immediate immunity
• > no direct contact w/ pathogen
• > no memory cells produced so not long lasting

Question 14

Active immunity

Answer 14

stimulation of production of antibodies by own immune system

• > long lasting as memory cells produced
• > direct contact w/ pathogen
• > slower immunity

Question 15

What is herd immunity and why is it important?

Answer 15

large proportion of population are vaccinated making transmission of pathogen difficult
-> important as it is never possible to achieve 100% vaccination

Question 16

What do reverse transcriptase and integrase do in HIV replication?

Answer 16

reverse transcriptase - allows production of DNA from RNA (HIV is a retrovirus)
integrase - virus can insert new genetic material into nucleus/DNA of host cell

Question 17

HIV replication

Answer 17

• HIV enters bloodstream, a protein readily binds to CD4 (common on T.H cells)
• capsid fuses w/ cell membrane -> RNA + enzymes enter T.H cell
• RNA -> DNA w/ rev. transcriptase
• new DNA inserted into T.H DNA w/ integrase
• DNA creates mRNA using cell enzymes which has instructions for viral proteins
• mRNA uses cell mechanism to make HIV proteins which break away w/ membrane that forms lipid envelope

Question 18

Use of ELISA test

Answer 18

uses antibodies to detect presence + quantity of a protein eg. HIV, tuberculosis, hepatitis, allergens

very sensitive so detects v. small quantities of a molecule

Question 19

Why are antibiotics ineffective against viruses?

Answer 19

• viruses lack own cell structures, so nothing for antibiotics to disrupt
• viruses have protein coat and no murein cell wall, no site to work at for antibiotics

Question 20

How does HIV cause AIDS?

Answer 20

• kills and disrupts functioning T.H cells
• B cell cannot be stimulated to produce antibodies or secrete T.C cells
• immune system cannot respond effectively to other pathogens

Question 21

Procedure for ELISA test

Answer 21

1. apply sample to slide where antibodies will attach
2. wash surface to remove unattached antigens
3. add antibodies specific to antigen + leave to bind
4. wash surface to remove excess antibodies
5. add 2nd antibody w/ enzyme attached that binds to 1st
6. add colourless substrate of enzyme, enzyme acts on it when bound -> colour change
7. amount of antigen present relative to colour intensity