5.1 Antigens & Phagocytosis Flashcards
What is a pathogen?
A microorganism that causes disease
An invading bacteria is recognised as ‘foreign’ by our bodies because…
They contain molecules that are different from those in our own body called antigens
Antigens are…
Large molecules usually proteins or polysaccharides - either free or on surface of microorganism
In response to antigens, our immune system makes…
Antibodies
Antibodies are…
- Proteins that have a specific shape to fit on to the foreign antigen
- Y shaped
- 4 polypeptide chains
- same basic shape (constant region) but there is a ‘variable region’ at one end of the molecule
Antibodies are made by…
A white blood cell called a B-lymphocyte
The ‘variable’ region of the antibody is different to each antibody because…
It is a specific shape so that it can bind to one specific kind of antigen
When a microorganism enters the body, antibodies attach to the antigens on its surface, these act like a ‘marker’ and…
Lead to the bacterium being destroyed - phagocytosis
When body cells & tissues have been damaged, they release certain chemicals which cause…
Inflammation
The redness and swelling of inflammation is because the capillaries have become more ‘leaky’ so that…
More antibodies and white blood cells can reach the site of infection
Phagocytes can engulf bacteria by…
Phagocytosis
Phagocytosis stage 1:
The phagocyte is attracted to the bacterium by chemicals
-It moves towards the bacterium along the concentration gradient
Phagocytosis stage 2:
Phagocytes bind themselves to the bacterium
Phagocytosis stage 3:
- The cytoplasm of the phagocyte flows around the bacterium engulfing it.
- A membrane pocket (phagosome) forms around the bacterium
- Inside the phagocyte are lysosomes which contain powerful digestive enzymes
- The lysosomes move towards the phagosome
Phagocytosis stage 4:
- The lysosomes fuse with the phagosome, releasing their digestive enzymes
- The enzymes break down the bacterium
