Lecture 7: Anatomy of Bacteria Flashcards
(36 cards)
Shapes of individual bacteria cells
-coccus (spheres)
-bacillus (rods)
-Vibrio (crescent)
-Spiral
arrangement of cells: coccus
- Coccus: single cell, alone
- Diplococcus: two cells
- Streptococcus: many cells
in a chain - Staphylococcus: many cells
in a cluster
arrangement of cells: bacillus
- Bacillus: single cell, alone
- Streptobacillus: many cells in a chain
- Many bacteria are named after their shape Bacillus subtilis, etc.
is bacterial shape a good trait to use in regards to classification?
Bacterial shape is not
a very good, homologous trait for classification
morphological features of a bacterial cell
- Plasma membrane and the
bacterial cell wall - Capsule/slime layer
- Flagella and pilus
- Sub-cellular compartments
- Endospores
plasma membrane is a __ made up of ___
lipid bilayer
phospholipids
the head of a phospholipid is __ and the tail is ____
hydrophilic (as its polar)
hydrophobic (non-polar)
how does a phospholipid interact with water?
In water, the heads face
water while tails ‘hide’ from
water, facing each other
the plasma membrane in terms of permeability is
semi-permeable: (of a material or membrane) allowing certain substances to pass through it but not others
what kind of molecules can diffuse freely?
very small molecules: O2, N2, CO2 etc (non-polar)
which small molecules diffuse more slowly?
polar molecules
H2O, glycerol, urea and ethanol etc
which molecules can not diffuse at all?
- Molecules larger than 3 – 4 carbons
- Charged molecules (i.e., negatively or positively
charged)
what type of cell walls do bacteria have?
peptidoglycan cell walls
peptidoglycan structure
- Peptidoglycan is made of two types of sugars in attached in a long,
unbranched chain (backbone) - One of the sugars have a short peptide attached (3 - 5 amino acids)
- Different peptidoglycan backbones can attach via their peptides cross-
linking
where does peptidoglycan exist?
Peptidoglycan exists outside the plasma membrane, surrounding the entire cell
How do peptidoglycan and the plasma membrane work together to make the cell wall stronger?
- Peptidoglycan is rigid and gives
mechanical strength to the cell wall - But peptidoglycan is not a permeability barrier; it has large openings which lets many molecules diffuse freely
- Plasma membrane is a permeability
barrier - But plasma membrane is ‘soft’ and is not mechanically strong
what does peptidoglycan protect the cell from in regards to the environment?
osmotic pressure => the concentration of chemicals in cytoplasm is higher compared to that of surrounding environment, creates osmotic pressure for water to
move from the environment into the cell
what are the two types of bacterial cell walls?
Gram positive cell wall
Gram negative cell wall
Gram positive cell wall
- Thick layer of peptidoglycan
- Relatively simpler structure
Gram negative cell wall
- Thin layer of peptidoglycan
- A second lipid bilayer surrounds the
peptidoglycan layer (outer membrane)
gram stain procedure
Procedure
1. Stain all cells with dark purple dye, crystal violet
2. Destain with ethanol
* Gram negative cells becomes clear because the thin peptidoglycan does not retain the purple dye
* Gram positive cells remains purple because the thick peptidoglycan retains the dye
3. Stain again with lighter, pink dye, safranin
* Gram positive cells appear purple
* Gram negative cells appear pink
examples of gram negative bacteria
- Proteobacteria (such as E. coli)
- Chlamydias
- Spirochetes
- Cyanobacteria (the photo-autotrophs)
examples of gram positive bacteria
- Such as S. aureus and B. subtilis
why does a gram negative stain not indicate the bacteria in question is gram negative?
- Some group such as Chlamydias don’t have a peptidoglycan cell wall
- Chlamydias still stain pink in Gram stain
