Lecture 7: Anatomy of Bacteria Flashcards
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
what do antibiotics target in the bacteria?
- Peptidoglycan is the target for many antibiotics
- Beta-lactams such as penicillin
- Vancomycin
- Stopping peptidoglycan synthesis stops bacterial growth
how does the effectiveness of antibiotics change depending on the structure of the cell wall?
- Gram positive have peptidoglycan exposed to environment, antibiotics has easy access
- Gram negative have outer membrane, blocking many
antibiotics from accessing the peptidoglycan
how long does a gram stain take?
~10 minutes to do
capsule and slime layer structure
- A layer outside the bacterial cell wall
- Made of sugars and/or peptides
(species dependent) - Can be rigid (capsule), or more soft
and flexible (slime layer) - Resists de-hydration, resists immune system of host organism, adherence to surfaces
sub cellular structures
- Bacteria does not have an organelle
- They still can have complex, sub-cellular structures, made of lipid bilayers, protein shells, etc.
examples of sub cellular structures?
Thylakoid membranes
* Multiple folds of lipid bilayer inside cyanobacteria
* Conversion of light energy to chemical energy (ATP)
Carboxysomes
* Polygonal structures made of protein shell, found inside cyanobacteria
* Fixation of CO 2 into organic molecules
flagella structure
- Long, whip-like structure attached to the bacterial cell wall
- Rotation of flagella makes the cell
move - Very dissimilar structure from a
eukaryotic flagella - Analogous structures due to convergent evolution
what is the process that makes bacteria move toward “good things” and away from “bad things”?
Chemotaxis
fimbriae and pilus structure
- Other string-like structures are also
found on bacterial surfaces
fimbriae structure
- Shorter and more numerous
- Attachment to surfaces and to other cells
pilus structure
- A longer tubular structure
- Connects two bacterial cells to facilitate exchange of genetic materials (this is a form of horizontal gene transfer)
endospores function
- Ultimate survival mechanism deployed by Gram positive bacteria
- Vegetative cells (normally growing cells) form endospores to survive unfavourable environmental condition
- Endospores grow back to vegetative cells once environmental condition restore
