32 Questions
What happens to the pores in the cell walls of gram-positive bacteria when treated with alcohol?
They close
What happens to the crystal violet-iodine complex in gram-negative bacteria after alcohol treatment?
It is extracted from the cell
What is the function of the outer membrane in gram-negative bacteria?
To keep proteins outside the cell
What is the periplasm?
The region between the outer and cytoplastic membranes
What is the consistency of the periplasm contents?
Gel-like
What type of molecules are not permeable through the outer membrane?
Enzymes
What is the function of glycocalyx?
To protect the cell and adhere to surfaces
What is a capsule?
A dense, tightly bound glycocalyx
What percentage of the total cell wall of gram-negative bacteria consists of peptidoglycan?
10%
What is the function of porins in the outer membrane of gram-negative bacteria?
To form channels for the entrance and exit of hydrophilic low-molecular-weight substances
What is the term for the toxic component of LPS?
Endotoxin
What is responsible for the differences in the Gram stain reaction between gram-positive and gram-negative bacteria?
The structural differences between the cell walls
What is the other name for the outer membrane of gram-negative bacteria?
Lipopolysaccharide layer
What is the purpose of the Gram stain?
To distinguish between gram-positive and gram-negative bacteria
What is the name of the polysaccharide portion of LPS?
Both A and B
What is the consequence of the structural differences between the cell walls of gram-positive and gram-negative bacteria in the Gram stain reaction?
The complex is not extracted by alcohol from gram-negative bacteria
What is the primary function of the cell envelope in prokaryotic cells?
To protect the cell from its environment
What is the structure of the plasma membrane?
Phospholipid bilayer with embedded proteins
What is the selective barrier function of the plasma membrane?
To control the movement of molecules into and out of the cell
What is the role of the cell wall in bacterial cells?
To provide structural support and maintain cell shape
What is the main component of the cell wall in most bacteria?
Peptidoglycan
What is the function of peripheral proteins in the plasma membrane?
To facilitate the transport of molecules into the cell
What is the function of lysozyme in animal secretions?
To break down peptidoglycan
What is the function of electron transport in bacterial respiration?
To generate ATP
What is the percentage of peptidoglycan in the cell wall of gram-positive bacteria?
90%
What is the role of the cell wall in some species of bacteria causing disease?
It contributes to the ability of some species to cause disease
What is the chemical composition of the cell wall used for?
To differentiate major types of bacteria
What is the function of teichoic acids in the cell wall?
To bind Ca2+ and Mg2+ for transport into the cell
What is the result of lysozyme breaking down peptidoglycan?
The cell wall becomes weaker
What is the structure of peptidoglycan?
A mesh-like layer of sugars and amino acids
What happens to the cell when the cell wall is weakened by lysozyme?
The cell swells and eventually bursts
What is the charge of the cell surface due to teichoic acids?
Negatively charged
Study Notes
Cell Envelope
- The cell envelope is the boundary layer of bacteria, lying outside the cytoplasm
- It has a structure comprising a cell wall and a cytoplasmic membrane
- Gram-positive bacteria have a two-layer cell envelope, while Gram-negative bacteria have a three-layer cell envelope
Plasma (Cell) Membrane
- A barrier that separates the cell from its environment
- Composed of a phospholipid bilayer with embedded proteins
- Has an inner and outer hydrophilic face, and a hydrophobic interior, forming a barrier to hydrophilic molecules
- Functions:
- Protects the cytoplasm and inner structure of the cell
- Acts as a selective barrier for material entering and exiting the cell
- Important for nutrient breakdown, energy production, and bacterial respiration
- Involved in chromosomal segregation during replication
Cell Wall of Bacteria
- Responsible for the shape of the cell
- Protects the interior structure of the cell from environmental changes
- Prevents bacterial cells from rupturing due to osmotic pressure
- Contributes to disease causation in some species
- Site of action for some antibiotics
- Cell wall structure is used to differentiate major types of bacteria
- Peptidoglycan (murein) is a key component of the cell wall
Peptidoglycan (Murein)
- A polymer consisting of sugars and amino acids
- Forms a mesh-like layer outside the cell membrane
- Composed of alternating residues of β-(1,4) linked N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
- Subunits are covalently joined to form glycan chains
- Can be destroyed by certain agents, such as lysozyme
- Lysozyme breaks the β-1,4-glycosidic bonds between NAG and NAM, weakening the wall and leading to cell lysis
Gram-Positive Cell Wall
- In Gram-positive bacteria, the cell wall consists of multiple layers of peptidoglycan
- Teichoic acids are embedded in the cell wall, giving it a negative charge
- Teichoic acids bind Ca2+ and Mg2+ for transport into the cell
Gram-Negative Cell Wall
- In Gram-negative bacteria, the cell wall consists of a thin layer of peptidoglycan
- The outer membrane is composed of a lipopolysaccharide layer, with a complex of lipid and polysaccharide
- The lipopolysaccharide layer is toxic and responsible for the pathogenicity of Gram-negative bacteria
- Porins are proteins in the outer membrane that function as channels for hydrophilic substances
Periplasm
- A region between the outer surface of the cytoplasmic membrane and the inner surface of the outer membrane
- Contains proteins, including hydrolytic enzymes, binding proteins, and chemoreceptors
- Proteins in the periplasm are involved in initial food molecule degradation, substrate transport, and chemotaxis response
Glycocalyx
- A coating of repeating polysaccharide, protein, or both
- Protects the cell and helps with attachment to the environment
- Can form a loose shield (slime layer) or a dense layer (capsule)
- Involved in protection, attachment, and biofilm formation
This quiz covers the structure of a prokaryotic cell, including the cell envelope, plasma membrane, and differences between gram-positive and gram-negative bacteria.
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