Bacteria Lectures 1-3 Flashcards
Understand this Shiz
Key distinguishing features of Prokaryotes from Eukaryotes?I
Prokaryotes:
- not compartmentalised (no ER, Mitochondria, lysosome)
- ATP made in plasma membrane via oxidative phosp.
70s ribosomal unit as opposed to the 80s in eukaryotes
Steps of how to Do the Gram Stain
1: Crystal Violet is the primary stain
2: Iodine Solution/ Gram’s Iodine (fixes Violet in cell wall)
3: Decolouriser is applied e.g ethanol
4: Safranin (Counter stain)
How does Gram Stain work??
Gram +ve have thicker peptidoglycan layer (and lower lipid content) and can retain the crystal Violet stain
Gram -ve lose the crystal Violet stain and are instead stained by safranin
How does the Decolouriser work in Gram negative staining
It dissolves the lipid layer from the Gram -ve cells. The removal of lipid layer enhances the leaching of the primary strain from the cells into the surrounding solvent
How does the Decolouriser work on Gram +ve staining
The Decolouriser closes the pores as the cell wall shrinks during dehydration. As a result the diffusion of the violet-iodine complex out of cell is blocked + bacteria remains stained
What does prolonged exposure to Decolourising agent cause?
it will remove stains from both types of bacteria
Bacteria that lose the stain easily appear to be a mixture of gram +ve and gram -ve. This is known as
Gram Variable
what shape do Cocci appear as
Spherical
what shape do bacilli appear as
Rod shape
What shape do Spirillium appear as
Spiral
what shape do Vibric appear as?
curved rod shaped
What additional function do Prokaryotic cells have on their plasma membrane to Eukaryotes
Electron Transport and the Phosphorylation of ADP
3 Key features of the bacteria cytoplasmic matrix
1: Nucleoid - consists of supercoiled
2: Plasmid - Extra Chromosomal DNA often coding for antibiotic chromosome
3: Inclusion bodies - granules of organic/inorganic and may be bound by protein or lipid membranes
Features of a bacterial gram +ve envelope
Cell wall consists of many layers of peptigoglycan formed by alternating units of NAG and NAM cross-linked by short peptides.
NAG and NAM arrangements gives a strong and rigid but semi-permeable structure
State the 3 different Symbiotic Relationships with Microbes and Humans. State examples
Mutualism - e.g Lactobacillus acidophilus
Commensialism - e.g Escherichia Coli
Parasitism - e.g Helicobacter Pylori
What does NAG and NAM stand for
NAG = N-acetylglucosamine and NAM = N-acetylmuramic acid
Features of a bacterial gram -ve envelope
The most inner layer is composed of a phospholipid layer. Outer membrane is made up of lipopolysaccharide (LPS).
In between membrane = periplasmic space
On a gram -ve envelope, what does the periplasmic space consist of
Peptidoglycan layer and Periphrastic proteins
Tell me more about Lipopolysaccharide
Makes up the outer membrane of gram -ve bacteria and is an endotoxin. On destruction of the cell, it is released into the environment. This can be toxic to humans.
What is Acid Fastness?
A physical property that relates to their resistance to decolourisation by acids in the staining procedure
Give an example of an acid fast bacteria. What happens to it in acid-fast testing?
mycobacterium tuberculosis - It is stained red after the decolourisation step during the acid fast staining procedure
Characteristics of a acid-fast bacterium
cell walls contain large amounts of lipid substance (mycolic acid) resulting in a very hydrophobic cell wall. This allows for survival within Macrophages and intrinsic resistance to antimicrobials
External Components of all Bacterium
All bacterium secrete a form of glycocalyx. Having this layer aids adhesion to environment, and allows host to form a colony or bio-film formation. This helps inhibit opsonisation
If glycocalyx is tighly bound to the cell, the bacterium is referred to as..
A Capsule
