Communicable diseases part 3 Flashcards
How does aggulitinis work?
each antibody has two identical binding sites so is able to cross link by binding an antigen on one pathogen with one binding site and another pathogen with the other binding site this clumps them together then a phagocyte can engulf them at once
Whate are the advantages of aggulitinins
physically impedes them from carrying out some fuctions such as invading host cells
can easily be destroyed and recongnised
very effective against viruses
Why does the primary immune response take time
when first infected the immune system takes time to
- clonally expand
- clonal selection
- differentiation
- APC
- Lack of memory cells
why doesn’t the secondary immune response take time
there are T and B memory cells so they regonise them more quickly and produce an immune response they are quicker and there is a higher concentration therefore no symptoms are felt
draw the graph on immune response times
see revision guide
What makes plants attractive to pathogens
plants have a wide range of sugars in photosynthesis these convert those sugars to many compounds such as proteins and oils which make the plant attractive to organisms
what are passive defences
passive defences are defences are defences that are present before an infection, they prevent entry and spread of pathogen by the chemical and physical ways
what are the physical defences of plants
cellulose cell wall lignin thickening of cell walls waxy cuticles bark stomatal closure callose formation of tylose
describe what role cellulose in the cell wall plays (plant passive physical defences)
it acts as a physical barrier but most plant cell walls contain a variety of chemical defences that are induced when a pathogen is detected
Describe what role the lignin thickening of the cell wall plays (plant passive physical defences)
waterproof and almost completely indigestible
Describe what role waxy cuticles play (plant passive physical defences)
prevent water collecting on cell surfaces therefore waterborne pathogens cannot survive
describe what role bark plays (plant passive physical defences)
bark contains a variety of chemical defences that work against pathogenic organisms
Describe what role stomatal closure plays (plant passive physical defences)
stomata are points of entry therefore when pathogens are detected in a part of the plant the guard cells close the stomata and trap the pathogen preventing it from spreading
Describe what role callose plays (plant passive physical defences)
large polysaccharide polymers are deposited in sieve tube elements at the end of the growing system in the sieve tube elements around sieve tube plates this blocks the flow in the sieve tube and can prevent a pathogen from spreading around the plant
Describe what role tylose plays (plant passive physical defences)
a tylose is a balloon like swelling that fills the xylem vessel, the vessel can no longer carry water and this prevents the spread of pathogens, tylose contains a high concentration of terpenes that are toxic to the pathogen
Name some chemical passive defences
some chemicals are passive such as terpenes but a lot of chemicals are active as it requires a lot of energy to make them
What are active defences
when pathogens attack specific chemicals in pathogenic cell walls, for example proteins and glycolipids, are detected by the plant cell. this increases the passive defences and secretes chemicals
Describe some active defences
- cell wall are stronger and more thickened with more cellulose
- oxidative bursts that produce highly reactive oxygen molecules are capable of damaging the cells of invading organisms
- callose between the plant cell wall and membrane near the invading pathogen, they deposit polysacchiraride polymers which impede cell wall penetration at the site of infection as well as strengthening the cell wall and blocking the plasmodesmata
- terepenoids, phenols, alkaloids, defensive proteins, and hydrolytic enzymes
- necrosis - deliberate cell suicide, this is activated by intracellular enzymes that are activated by injury they turn the leaves brown. this is when a few cells are sacrificed for the rest of the plant to survive (around the infected area), this traps the pathogen and stops it from getting nutrients and water therefore stops it from spreading
- canker - this is a sunken necrotic lesion in the woody tissue, it causes the death of cambium tissue in the bark and prevents spreading and entry
What do terepenoids do (active chemical defence)
these are essential oils that have antibacterial and antifungal properties
what do defensive proteins do (active chemical defence)
small cysteine rich proteins that have broad antimicrobial activity that act on molecules in plasma membranes of pathogens inhibiting action of ion transport channels
What do phenols do? (active chemical defences)
have antibiotic and antifungal properties, tannins found in bark inhibit attack by insects
the tannins bind to the salivary proteins and digestive enzymes such as trypsin and chymotrypsin and deactivate them.
If insects digest a high concentration of these then it stops growth and the insect eventually dies
What do alkaloids do? ( active chemical defences)
Nitrogen containing compounds such as caffeine give a bitter after taste this stops herbivores from feeding on them
also acts on metabolic reactions inhibiting or activating enzyme action this inhibits protein synthesis
What do hydrolytic enzymes do? (active chemical defences)
found in spaces between cells, they include chitinases this breaks down the chitin in fungal walls, glycanases which hydrolyse the glyosidic bonds in glycan and lysozymes which are capable of degrading bacterial cell walls
Why are new drugs needed
- new diseases are emerging
- still many diseases with no treatments
- some antibiotics treatments are becoming less effective
