[5.1-2] defence mechanisms and phagocytosis

Question 1

what will proteins embedded in the cell membrane act as a mechanism for?

Answer 1

• identifying cells as ‘self’, rather than ‘non-self’
• this is the basis of the immune response (recognition system)

Question 2

how does the immune system recognise the proteins?

Answer 2

because they have a specific tertiary structure

Question 3

what is an immune response triggered by?

Answer 3

the presence of a ‘non-self material’ eg.

1. pathogens (bacteria, viruses)
2. human cells from another individual
3. tumour cells
4. toxic molecules from pathogens

• these will all be covered in proteins that will act as ‘non-antigens’

Question 4

what is the 5 step process of phagocytosis?

Answer 4

1. bacteria engulfed due to membrane fluidity of phospholipid bilayer
2. bacterium now contained in a ‘phagosome’
3. lysosomes fuse with phagosome to form a ‘phagolysosome’
4. therefore, lysozymes can hydrolyse bacterial molecules
5. the hydrolysis products of the bacterium are absorbed by the phagocyte

Question 5

what are some examples of products of bacterial digestion?

Answer 5

• amino acids
• nucleic acids
• monosaccharides
• fatty acids / glycerol

BUT bacterial antigens are often retained intact by the phagocyte

Question 6

what is an antigen?

Answer 6

any part of an organism or substance that is recognised as non-self (foreign) by the immune system and stimulates an immune response