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)
What is the function of teichoic acids in Gram-positive bacteria?
Anchor the cell wall to the membrane and promote adhesion.
What is a key characteristic of a Gram-negative cell wall?
Very little peptidoglycan is present and has a second, outer membrane
What is the space between the inner and outer membranes of Gram-negative bacteria called?
Periplasm/periplasmic space; This is where the small amount of peptidoglycan is located
What is the outer membrane of Gram-negative bacteria made up of?
Lipopolysaccharide (LPS).
What is LPS known for?
It is toxic to humans and other animals. It is referred to as an endotoxin. LPS causes endotoxic shock in gram-negative infections.
What are the three components of lipopolysaccharide (LPS)?
- Lipid A- a toxic, modified phospholipid
- Core polysaccharide
- O antigen polysaccharide side chain- major surface antigen of gram negative cells with repeating units
What is an ‘acid-fast cell wall’?
A bacterial cell wall with a high lipid content, primarily composed of mycolic acid, which makes the bacteria resistant to decolorization by acids during staining procedures. Mycolic acid is a waxy lipid that binds to the peptidoglycan.
What is the primary stain used in acid-fast staining?
Carbol fuchsin.
The primary stain used in acid fast staining, carbol fuchsin, is lipid-soluble and contains phenol, which helps the stain penetrate the cell wall. This is further assisted by the addition of heat in the form of heat (steam).
What bacteria are typically associated with acid-fast cell walls?
Mycobacterium tuberculosis.
What do mycoplasmas lack?
Cell walls.
What allows Gram-positive bacteria like Clostridium and Bacillus to form endospores?
The thick peptidoglycan layer. Spores allow bacteria to withstand conditions that are not ideal, such as high temperature or lack of nutrients.
True or False: An outer layer of lipopolysaccharide is only seen in the cell envelope of Gram-negative bacteria.
True.
What is the role of porins in Gram-negative bacteria?
Form pores for substances to pass through the outer membrane. Porins are a type of protein.
What structural feature of peptidoglycan is only found in Gram-positive bacteria?
Pentaglycine cross-bridges.
What is the purpose of the bacterial cell wall?
To prevent osmotic lysis of the cell.
What structure is used to identify different Gram-negative bacterial species and strains?
The O antigen within the lipopolysaccharide.
What structures lack a cell wall?
Mycoplasmas.
Acid-fast cells cell walls are like Gram-positive cells. Gram-negative bacteria and Gram-positive bacteria contain cell walls.
What is the primary component of prokaryotic cell walls?
Peptidoglycan
True or False: All prokaryotic cells have a cell wall.
False
Fill in the blank: The cell wall of Gram-positive bacteria is characterized by a thick layer of __________.
peptidoglycan
What distinguishes Gram-negative bacteria from Gram-positive bacteria?
Gram-negative bacteria have a thinner peptidoglycan layer and an outer membrane.
Which stain is used to differentiate between Gram-positive and Gram-negative bacteria?
Gram stain
What is the function of the cell wall in prokaryotic cells?
To maintain cell shape, protect against osmotic pressure, and provide structural support.
True or False: The outer membrane of Gram-negative bacteria is composed of lipopolysaccharides.
True
What is the role of teichoic acids in Gram-positive bacteria?
Teichoic acids help maintain cell wall integrity and are involved in cell division.
Multiple Choice: Which of the following is NOT a component of the prokaryotic cell wall? A) Peptidoglycan B) Cellulose C) Lipopolysaccharide
B) Cellulose
What is the effect of penicillin on prokaryotic cells?
Penicillin inhibits the synthesis of peptidoglycan, weakening the cell wall.
Fill in the blank: The __________ is a protective outer layer found in Gram-negative bacteria.
outer membrane
What is the main difference in the cell wall structure between Archaea and Bacteria?
Archaea often have pseudopeptidoglycan or other polysaccharides, while Bacteria have peptidoglycan.
True or False: Prokaryotic cell walls can be targets for antibiotics.
True
What type of bacteria typically has a periplasmic space?
Gram-negative bacteria
Multiple Choice: Which of the following structures is found in the cell walls of some Archaea? A) Peptidoglycan B) Pseudomurein C) Chitin
B) Pseudomurein
What is the role of the periplasmic space in Gram-negative bacteria?
It contains enzymes and proteins involved in nutrient acquisition and cell wall maintenance.
Fill in the blank: The __________ layer of Gram-negative bacteria contains lipopolysaccharides.
outer membrane
What are the two main types of prokaryotic cell walls?
Gram-positive and Gram-negative
True or False: Peptidoglycan is unique to prokaryotic cells.
True
What is the consequence of a damaged prokaryotic cell wall?
The cell may burst due to osmotic pressure.
Fill in the blank: The __________ is a complex of proteins and carbohydrates that forms the cell wall in bacteria.
peptidoglycan
What is the primary function of lipopolysaccharides in Gram-negative bacteria?
To act as an endotoxin and contribute to the structural integrity of the outer membrane.
Multiple Choice: Which of the following is a characteristic of Gram-positive bacteria? A) Thin peptidoglycan layer B) Thick peptidoglycan layer C) Presence of outer membrane
B) Thick peptidoglycan layer
What is the significance of the Gram stain in microbiology?
It helps identify and classify bacteria based on their cell wall properties.
