Structure and function of features external to the cell wall (prokaryotes) Flashcards
What is the Glycocalyx?
A thin, carbohydrate-rich layer that covers the surface of cells in many organisms, composed of glycoproteins, proteoglycans, and glycolipids.
Contributes to virulence by preventing phagocytosis, preventing complement activation, and assisting in the formation of biofilms.
What are the two types of Glycocalyx?
- Capsule: neatly organized and firmly against the cell wall
- Slime layer: loose and unorganized
How does Glycolyx contribute to virulence?
By preventing phagocytosis, preventing complement activation (Complement activation is a process that occurs when the body’s complement system recognizes and destroys foreign invaders), and assisting in the formation of biofilms
What is the primary function of Flagella?
Responsible for the motility of the cell (taxis). They are long, whip-like appendages external of the cell that are made up of protein flagellin.
What are the four types of flagellar arrangements?
- Monotrichous: single flagellum at one end
- Amphitrichous: single flagellum at each end
- Lophotrichous: multiple flagella from the same point
- Peritrichous: multiple flagella distributed over the entire surface
What are Pili?
Hair-like projections on the surface of some prokaryotes, with some involved in twitching motility and others specialized for attachment. Up to a thousand on each cell.
Sex pili are involved in horizontal gene transfer (conjugation).
What are Fimbriae?
Hair-like projections on the surface of some prokaryotes that are usually shorter than pili; responsible for attachment and not involved in motility.
What is the function of siderophores?
Compounds produced by bacteria that bind iron from outside the cell for growth. The iron/siderophore complex is then transported inside the cell so the iron can be used for growth.
What process does binary fission describe?
The process of replication in bacteria.
Which structure is responsible for the motility of bacteria?
Flagella are long, thin, whip-like structures made of flagellin. The ATPs generated by the cells provide the flagella its energy to move. The flagellum of the bacteria can only be recognized when stained, and not when observed under the microscope. One of its primary purposes is motility, particularly to propel the bacteria towards sources of nutrition. Another function of this structure is to move to the ideal site for infection, such as when the Escherichia coli is transferring from the urethra towards the bladder. The flagella also serve an important role in identifying the types of microorganisms based on the pattern of its movement and the response to certain antibodies.
What type of bacterium has a single flagellum at opposite poles?
Amphitrichous bacteria
What type of arrangement of flagella does a peritrichous bacterium have?
Flagella distributed throughout the surface.
How are exotoxins classified?
Soluble proteins produced and secreted from live cells that act at a site farther away from where they were secreted.
What is the sole purpose of Fimbriae?
To aid in surface adherence.
Cilia are used in motility.
Flagella are used in motility.
Pili aid in surface attachment; sex pili can be used in the process of conjugation.
True or False: Cilia are used in motility.
True.
What is the role of sex pili?
Involved in the process of conjugation where bacteria transfer genetic material to each other through direct contact. It’s a type of horizontal gene transfer.
What is the prokaryotic cell wall?
A rigid structure external to the cell membrane that protects against mechanical disruption and osmotic lysis; also plays a role in determining the shape of the cell.
What is the main component of most bacterial cell walls?
Peptidoglycan
How can bacterial cell walls be categorized?
As gram-positive or gram-negative.
What are the two major components of a Gram-positive cell wall?
- Peptidoglycan (Only found in prokaryotes)
- Teichoic acids
What are the two alternating sugars in peptidoglycan?
- N-acetylglucosamine (NAG)
- N-acetylmuramic acid (NAM)
These glycan chains are cross-linked into sheets by peptide bonds (vital links that connect amino acids to form polypeptide chains, which fold into functional proteins). This forms a rigid, 3D matrix.
What forms a rigid, 3D matrix in the Gram-positive cell wall?
Cross-linked glycan chains by peptide bonds.
Glycan chains are carbohydrate chains made of sugar molecules linked together. Peptide bonds connect amino acids to form polypeptide chains, which fold into functional proteins.
What enzyme is peptidoglycan resistant to?
Most mammalian enzymes, except lysozyme.
What happens if the cell wall is lost?
Osmotic lysis occurs (AKA Cytolysis which occurs when a cell bursts due to an osmotic imbalance that has caused excess water to diffuse into the cell)
