Introduction to Bacteria (1) Flashcards
Name bacterial structures A-G
How would you view a bacteria?
Bacteria are visible using light microscopy but to see the ultrastructure of the cell we need to use an electron microscope
Do bacteria have a nucleus?
no
Describe the cytoplasmic membrane
(aka plasma membrane) is a very thin, elastic and semi-permeable membrane around the bacterial cell contents.
Describe the cell wall of a bacteria
cell wall -rigid, giving the cell strength and shape but it is permeable.
Between the plasma membrane and cell wall, which is permeable and semi-permeable?
cell wall - permeable
plasma membrane - semi-permeable
What component do gram-negative bacteria have?
outer-membrane
Is this the cell wall of a Gram-negative or -positive bacteria?
positive
Is this the cell wall of a gram positive or negative bacterium?
negative
What bacteria has a thin cell wall/peptidoglycan?
Gram-negative
Which type of bacteria has a cell wall?
Gram-negative
What is the periplasm?
the space between the inner and outer membrane in Gram-negative bacteria
Name structures A-C and decide if this is a Gram positive or -negative bacterium
Name structures A-D and decide if this is a Gram positive or -negative bacterium
What are the components of the outer membrane of Gram-negative bacteria?
lipopolysaccharides and protein
What colours in light-microscopy identify a Gram-negative/positive bacterium?
+ purple
- red
What bacterium appears red in light microscopy?
Negative
What shape are cocci bacteria?
spherical
What shape are bacilli?
rod-shaped
What bacteria are shown here an dhow do they exist?
white cells (multilobed nuclei showing up red) as well as cocci that are in pairs
Gram- positive
What ways can bacteria exist?
single cells
pairs
chains
clusters
What bacteria are shown here an dhow do they exist?
cocci in longer chains look under the electron microscope
Is bacilli Gram-positive or negative?
negative
Is cocci Gram-positive or negative?
positive
What bacteria does the red stain indicate here?
see rod shaped bacteria that have stained red so these are Gram-negative rods, also known as Gram-negative bacilli
what is shown in the electron microscopic image?
see rod shaped bacteria that have stained red so these are Gram-negative rods, also known as Gram-negative bacilli
How thick is the cytoplasmic membrane?
5-10 mm thick
What are the components of the cytoplasmic membrane?
phospholipids (40%) and proteins (60%).
What does the cytoplasmic membrane allow?
It allows the passage of water and uncharged small molecules but otherwise forms a barrier
Do charged or uncharged molecules pass through the plasma membrane?
uncharged small molecules
What are the roles of proteins in the plasma membrane?
- Transport systems for specific nutrients and ions
- As enzymes involved in processes such as energy generation, cell wall synthesis and DNA replication
- Sensing proteins that measure concentrations of molecules in the environment
What makes up the cell wall in bacteria?
Made of peptidoglycan
How thick is the cell wall?
10-25mm thick
What are the 2 components of the peptidoglycan?
N-acetylglucosamine acid and N-acetylmuramic acid molecules linked alternately in a chain, with short peptides forming cross-links
Describe the structural features of the peptidoglycan
Thick, strong and relatively rigid- maintains shape
Can antibiotics effect the cell wall peptidoglycan?
YES
interfere with construction
burst/lysis
e.g. penicillin
What happens if the cell wall is weakened or ruptured?
osmosis means the cell will swell and burst –termed lysis
How is the cell wall involved in cell division?
The cell wall plays an important part in cell division ie cross-walls form prior to separating into 2 daughter cells
What is the component of the outer membrane?
lipopolysaccharides LPS
What type of bacteria have lipopolysaccharides?
Gram-negative (small peptidoglycan)
What is the role of the peptidoglycan?
- Protects peptidoglycan from bile salts (in the gut), also from lysozyme
- Blocks many antibiotics getting into the cell
What makes Gram-negative bacteria toxic?
Lipid A is a lipid component of an endotoxin held responsible for the toxicity of gram-negative bacteria. It is the innermost of the three regions of the lipopolysaccharide (LPS), also called endotoxin molecule, and its hydrophobic nature allows it to anchor the LPS to the outer membrane.
Lipid A (within LPS) forms endotoxin, which, when released into the bloodstream (when multiplying or when lysed), may give rise to endotoxic shock –fever and low blood pressure
What characterises endotoxic shock?
fever and low blood pressure
What lipid is responsible for endotoxic shock?
Lipid A, component of the LPS
What bacteria will cause endotoxic shock?
Gram-negative e.g. cocci
Describe the capsule of bacteria?
usually a hydrated polysaccharide structure that covers the outer layer of the cell wall
Are the LPS layer of Gram-negative bacteria hydrophobic?
YES
What are the 2 types of capsule?
rigid
slimy
What is the role of a rigid capsule?
prevent phagocytosis
What is an example of a bacteria with a rigid capsule?
Streptococcus pneumoniae
Describe a slimy capsule
secretory substance secreted by bacteria
less well defined, form a slime layer or biofilm
What is the role of a slime layer/slimy capsule?
used to adhere to surfaces
provides a protective environment
enhanced as bacteria divide and form microcolonies
What is an example of a bacteria forming a slimy capsule?
S. mutans (Gram-positive) form a biofilm on teeth and make plaque
What is the role of the flagella?
movement
Do bacteria always have 1 flagella?
No, can have 1-20
What are the different categories of flagella?
A-Monotrichous Vibrio cholerae (1);
B-Lophotrichous Spirillum spp (One point);
C-Amphitrichous Rhodospirillum rubrum (both sides);
D-Peritrichous (all over)
What type of flagella does V. cholerae have?
monotrichous
What is lophotrichous?
many flagella form one point
e.g. Spirillum spp
What is amphitrichous?
flagella form both sides
e.g. Rhodospirillum rubrum
What is peritrichous flagella?
flagella all over
e.g. E.coli and Salmonella
Why is motility important for bacteria?
increase ability to cause disease
pathogenesis
Can flagella be seen with a light microscope?
No - use a staining method
What are fimbriae?
long filamentous polymeric protein structures located at the surface of bacterial cells. They enable the bacteria to bind to specific receptor structures and thereby to colonise specific surfaces.
- e.g. adhering to host surfaces
- bacterial to bacterial .. conjugation
- adherence
Can fimbriae been seen under a light microscope?
No
