A Level Biology - Microbiology

A Level Biology - Microbiology
Covers:
Important definitions,
Bacteria classification,
Gram stain test,
Bacterial reproduction,
Toxins.

Transcript

1. Microbiology
2. Important definitions • Aseptic – without infection • Bacilli – rod shaped • Cocci – spherical shaped • Facultative anaerobes – grow better in the presence of oxygen but can survive without it • Obligate aerobes – can not survive (grow and reproduce) in the absence of oxygen • Obligate anaerobes – can not survive (grow and reproduce) in the presence of oxygen • Spirillum – spiral shaped • Total count – includes both living and dead cells • Viable count – only includes living cells
3. Bacterium (typical) Cell wall Cell membrane Flagellum Photosynthetic membranes Circular DNA Capsule Mesosome Small ribosomes Glycogen granules and lipid droplets
4. Classification by shape Bacilli (Rod shaped) Cocci (Spherical shaped) Spirillum (Spiral shaped)
5. Classification by cell wall composition Gram positive (+ive) Gram negative (-ive)
6. Gram stain test Gram positive > • Thick peptidoglycan layer • Contains teichoic acid in its structure • Crystal violet in Gram strain binds to the teichoic acid • Resists decolourisation, leaving a purple/blue colour Gram negative > • Thin peptidoglycan layer • Does not contain teichoic acid in its structure • Crystal violet in Gram strain cannot bind so readily • Decolourised, leaving a pink/red colour
7. Reproduction Asexually > • Binary fission (split apart) • When a certain size is reached, DNA is replicated • Old cell wall begins to break down around the middle to split into two Sexually > • No formation or transfer of gametes • Transformation (short piece of DNA released by a donor and taken up by a recipient) • Transduction (small amount of DNA transferred by a bacteriophage) • Conjugation is most common (donor produces a sex pilus, cytoplasmic bridge, between two cells which DNA is transferred into recipient)
8. Toxins produced by bacteria Endotoxins > • Lipopolysaccharides • Outer layer of Gram negative bacteria • Rarely fatal • Cause symptoms such as fever, vomiting and diarrhoea • Examples: Salmonella and E.coli Exotoxins > • Soluble proteins • Produced as they metabolise, reproduce and are released into the body • Most dangerous and fatal disease causing • Many different types have many different effects • Internal bleeding, inhibit neurotransmitters, poison cells etc • Example: Bacterial meningitis