Lecture 6: External Structure and Motility Flashcards
What is the capsule in relation to polysaccharide layers?
Well organized layer of polysaccharides, not easily removed
The capsule serves various functions including protection and adherence.
What distinguishes a slime layer from a capsule?
Less well organized layer of polysaccharide, diffuse and easily removed
The slime layer is more loosely structured compared to the capsule.
What is the glyocalyx?
Sugar shell that encompasses both the capsule and slime layer
It plays a role in protection and adherence.
What are biofilms?
Communities of microoragnisms that stick to surfaces
Protected by and attached by layers of polysaccharide
Biofilms can form on various surfaces and are significant in medical contexts.
What is quorum sensing in biofilms?
Bacteria communicate to change gene expression
This includes increasing polysaccharide production and antibiotic resistance.
List three functions of polysaccharide layers.
Help adhere to host
Help avoid immune system (phagocytosis) Protect against bacterial viruses
Additional functions include conferring growth advantages and preventing dehydration.
What is an S-layer?
Patterned layer that helps give cell shape and protects against changes in pH and osmotic pressure
The S-layer also aids in virulence
What is the mycolic acid layer?
Waxy outer layer in Mycobacterium, stains poorly with Gram stain
It is associated with diseases like TB and Leprosy.
What is the significance of a positive PPD test?
Usually leads to a chest x-ray
If positive, antibiotics are prescribed and contacts are notified and tested.
What are pili and fimbriae?
Small, short hair-like appendages (3-10 nm diameter)
They help bacteria adhere to hosts and are usually not involved in motility.
What is the function of a sex pilus?
Connects bacteria for transfer of genetic material during ‘mating’
Only bacteria with plasmids carrying sex pili genes have sex pili.
What is the structure of flagella?
Hollow tube of protein with three parts: filament, basal body, and hook
Each part plays a role in the movement of bacteria.
Name the types of flagellar arrangements.
Monotrichous: 1 flagellum
Amphitrichous: 1 flagellum at each pole
Lophotrichous: tuft of flagella at one or both ends
Peritrichous: flagella evenly spread
These arrangements affect how bacteria move.
What is chemotaxis?
Movement towards food (attractants) or away from toxins (repellents)
Chemotaxis requires motility and the presence of chemoreceptors.
What are the requirements for bacteria to be chemotactic?
- Be motile * Have chemoreceptors
Chemoreceptors are proteins located in the plasma membrane or periplasmic space.
True or False: Brownian motion is a form of bacterial motility.
False
Brownian motion is shaking movement due to water molecules hitting bacteria, not a form of motility.
