Lecture 7: Prokaryotic cell organization II Flashcards
In gram-positives, the peptidoglycan cell wall contains […], perpendicular to the chains.
Teichoic acid and lipotechoic acid
The function of teichoic acid and lipotechoic acid is […]
Teichoic acid: to solidify the peptidoglycan structure
Lipoteichoic acid: keep it attached to the plasma membrane.
In gram-negatives, the peptidoglycan cell wall contains […]
Braun’s lipoprotein and porins
The function of Braun’s lipoprotein is […]
To anchor the peptidoglycan cell wall to the outer membrane
What is the main function of the outer membrane in gram negatives?
To serve as a selective barrier.
Explain how the outer membrane of gram negatives is selective.
It prevents the entry of toxins and antibiotics, allows water and small molecules in, and has porins for other molecules to use.
Describe the structure of the outer membrane of gram negatives.
Its inner layer is made of phospholipids and its outer layer is made of lipopolysaccharides (hydrophilic) and some phospholipids.
Describe in detail how the outer membrane in gram negatives is anchored to the cell wall.
It is anchored by lipoproteins, which have a lipid part that inserts into the inner layer of the outer membrane.
Poking out of the gram-negative envelope are […]
O-specific side chains (look hairlike)
Describe the structure of a lipopolysaccharide
From top to bottom: has an O side chain, core polysaccharide, and lipid A
Explain the function of the O side chain in lipopolysaccharides
Bacteria can change their O side chain to avoid an immune reaction.
Explain the structure of the Lipid A portion of lipopolysaccharides
They have long fatty acid tails, which are hydrophobic, and heads comprised of a glucosamine molecule with phosphates, which are hydrophilic
Explain the structure and function of porins in the outer membrane of gram-negatives.
The middle of the porins are hydrophilic so molecules can freely flow through, but the outside amino acids of the porins are hydrophobic because they interact with the membrane.
Name three structures that can be found outside of gram-negatives and gram-positives.
The capsule, slime layer, and S-layer
Name 5 possible functions of the capsule, slime layer, and/or S-layer
- Protection from phagocytes and protozoa
- Protection from desiccation, toxic compounds, ions, pH fluctuations, and destructive enzymes
- Reservoir of stored food
- Site for waste disposal
- Helps maintain shape and rigidity
- Prevent infection by bacteriophages or attack by predacious bacteria
- Aid in cell adhesion and motility
How do the capsule, slime layer, and/or S-layer serve as a waste disposal site?
They can use side products of reactions to create a shield against the environment
How to the capsule, slime layer, and S-layer use polysaccharides?
The polysaccharides that make up the capsule and slime layer can be reinternalized and used as a food source when the cell needs more energy.
The capule is also known as the […]
Virulence factor
The capsule is made of […]
Polysaccharides
Describe the appearance and organization of the capsule.
It is easily seen by microscopy and is thick and well-organized. It is difficult to remove.
The slime layer is made of […]
Polysaccharides, glycoproteins, glycolipids
Describe the appearance and organization of the slime layer.
It is not easy to see by microscopy and is thin and less organized. It is easy to remove.
The surface layer is also known as the […]
S-layer
The surface layer is made of […]
Proteins, glycoproteins
Describe the appearance and organization of the surface layer
It is easily seen by microscopy and is highly organized. It is hard to remove
Name the two major surface appendages of bacteria.
Flagella and pili
Flagella are made of […]
Flagellin, a protein polymer
Pili are also known as […]
Fimbriae
Name two purposes for pili
Adherence to solid surfaces and mating
Describe the size and distribution of sex pili
They are larger than typical fimbriae and are present in small numbers, at about 1-10/cell
Explain the functioning of the flagellum.
Its basal structure is embedded in the plasma membrane and doesn’t move. It is connected to a hook which can spin in the environment and produce motion.
Describe the difference in structure between the gram-positive and gram-negative flagellum.
In gram-positives, the base just connects directly to a hook that passes through the peptidoglycan wall and contains a filament that spins. In gram-negatives, from bottom to top, there is the base in the plasma membrane, the S-ring in the periplasmic space below the peptidoglycan layer, the rod, the P-ring in the peptidoglycan layer, the L-ring in the outer membrane, then the hook and filament.
Name the four typical arrangements of bacterial flagella.
Monotrichous, amphitrichous, lophotrichous, peritrichous
Monotrichous bacteria are […]
Bacteria with a single flagellum at one pole
Amphitrichous bacteria are […]
Bacteria with a single flagellum at each pole
Lophotrichous bacteria are […]
Two or more flagella at one or both poles
Peritrichous bacteria are […]
Bacteria with flagella all over their surface
Describe the taxis of monotrichous bacteria.
When the flagella moves counterclockwise, the cell does a forward run. When it moves clockwise, the cell tumbles.
Describe the taxis of peritrichous bacteria.
All the flagella form a single rope-like structure that rotates counterclockwise when doing a forward run. When the flagella spin the other way, they separate and the cell tumbles.
Chemotaxis is […]
Taxis towards or away from specific chemical agents in the environment that have been sensed.
Aerotaxis is […]
Taxis towards (aerobic) or away from (anaerobic) regions rich in oxygen
Phototaxis is […]
Movement towards or away from light.
Magnetotaxis is […]
Taxis to follow magnetic lines of force in the environment.
Describe the motion of chemotaxis.
This bacterium senses that there are nutrients amd starts to run that way then tumbles. It then takes another reading and repeats. Eventually, if it reads that the concentration is decreasing, it can go in the other direction.Through regular sensing, they can tell when the nutrient source is getting closer. Their movement is not random, but is directional.
A bacteria that does magnetotaxis may have […] to help them sense the magnetic field in the environment.
Magnetosomes.
Where do the capsule, S-layer, and slime layer come from?
They are secreted by the cell envelope
