Immunity

Question 1

Phagocytosis

Answer 1

• Phagocyte recognizes antigen
• Pathogen is engulfed into a
• Phagosome
• Lysosome fuses with phagosome forming a phagolysosome
• Lysozyme enzymes
• Hydrolyse pathogen
• Antigens from pathogen may be presented on the surface of the cell

Question 2

Cell mediated immunity

Answer 2

• Antigen is presented by an antigen presenting cell
• Helper T Cells with the complementary receptor binds to the
presented antigen
• Helper T cell is activated and goes through mitosis
• Forming – cytotoxic T cells and more Helper T cells
• Cytotoxic T cells produce perforins to kill cells by making holes in their
cell surface membrane, water enters causing cells to burst

Question 3

Comparison of prokaryote and eukaryote DNA

Answer 3

• Prokaryote DNA is short Eukaryote DNA is long
• Prokaryote DNS is circular Eukaryote DNA is linear
• Prokaryote DNA has no introns Eukaryote DNA has introns
• Prokaryote DNA is free floating Eukaryote DNA is in in the nucleus
(and mitochondria and chloroplasts)

Question 4

Humoural immunity

Answer 4

• T helper cells bind to the complimentary antigens presented by the specific B cell. Clonal selection.
• T helper cells activate specific B cells.
• The B cells rapidly divide by mitosis to produce plasma and memory B cells. This is clonal expansion.
• These cloned plasma cells produce specific complementary antibodies to the antigens on the pathogen
• Antibodies destroy the pathogen

Question 5

Vaccines

Answer 5

• Vaccines contain antigens/weakened pathogen
• Memory B cells are made
• On second exposure memory cells are activated
• Memory cells and plasma cells rapidly produce antibodies
• Antibodies destroy pathogens
• Some vaccines are only effective for a limited time as viruses can change
the tertiary structure of their antigens

Question 6

ELISA

Answer 6

• First antibody binds/complementary to the antigen of interest
• Second antibody with an enzyme is added
• Enzyme binds to substrate (e.g. first antibody/antigen)
• Unbound antibody is washed away
• Solution added and colour change seen

Question 7

HIV replication

Answer 7

• HIV attachment proteins complementary to the receptors on the
helper T cell
• Virus nucleic acid enters the cell
• Reverse transcriptase converts RNA to DNA and inserted into the host
genome
• DNA is transcribed and the HIV capsid (protein) and enzymes are
made by host cell ribosomes.
• Everything is assembled by the host cells RER and Golgi apparatus
into new virus protein, capsid, enzymes.
• Virus are assembled and released