26 Questions
What is the main function of the cell wall in bacterial cells?
Prevention of osmotic lysis
Which structure in bacterial cells lacks sterols, as opposed to eukaryotic cells?
Cytoplasmic membrane
What is the role of membrane-associated proteins in bacterial cells?
Transport of molecules
Which component allows the differentiation of the two main groups of bacteria?
Bacterial envelope
What is the function of peptidoglycan in the cell wall of bacteria?
Protection against mechanical damage and osmotic lysis
Which structure is responsible for stabilizing the bacterial membrane?
Membrane-associated proteins
What is the main function of the cytoplasmic or plasma membrane in bacterial cells?
Selective transport of substances
Which structure is NOT found in bacterial cells?
Lysosomes
What is a unique feature of the cytoplasmic membrane in bacterial cells compared to eukaryotic cells?
Presence of sterols
Which component is responsible for electron transport during bacterial respiration?
Membrane-associated proteins
Which component of the bacterial cell envelope is only found in Gram-negative bacteria?
Lipopolysaccharide
What is the function of transporter proteins in bacterial cells?
Nutrient transport
Which bacterial species lack a cell wall and are considered the smallest bacteria described?
Mollicutes (Mycoplasma)
What is the function of a bacterial capsule?
Protection
Which structure in bacterial cells is responsible for locomotion or motility?
Flagella
What is the main function of pili/fimbriae in bacterial cells?
Adhesion to host tissues
Which state represents a cryptobiotic state of dormancy in some Gram-positive bacteria?
Endospores
What is the role of mycolic acids in the bacterial envelope?
Maintain cell shape and impermeability
In bacterial cells, what does the periplasmic space contain?
Lipopolysaccharide, porins, and transporter proteins
Which component of the bacterial cell structure acts as an immunogenic molecule known as endotoxin?
Lipopolysaccharide
What is the main function of plasmids in bacterial cells?
Provide additional genes like virulence factors and antibiotic resistance
Which of the following components is NOT found in all bacterial cells?
Plasmids
What is the function of ribosomes in bacterial cells?
Manufacture cellular proteins
In a bacterial cell, where is the DNA primarily located?
In the nucleoid
Which of the following is NOT a component of the bacterial envelope?
Ribosomes
What distinguishes prokaryotic cells from eukaryotic cells?
Presence of a true nucleus
Study Notes
Bacterial Cell Structure
- Cytoplasmic membrane: Flexible structure composed of phospholipids and proteins, no sterols, with hydrophilic outer faces and hydrophobic interior.
- Membrane-associated proteins: Stabilize membrane, transport molecules, and facilitate electron transport for respiration, and contain enzymes.
Cell Wall (Peptidoglycan Layer)
- Peptidoglycan: Chain of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) crosslinked with short peptides.
- Functions: Protection against mechanical damage and osmotic lysis, non-selective transport, and differences in structure and chemical composition affect pathogenicity and staining properties.
Bacterial Envelope
- Allows characterization of two main groups of bacteria: Gram-positive and Gram-negative.
- Gram-staining technique: Gram-negative bacteria have an outer membrane, while Gram-positive bacteria do not.
Alternative Structural Bacterial Envelopes
- Mycobacteria: Contains mycolic acids, has a thick waxy hydrophobic cell wall, and is acid-fast for identification.
- Mollicutes (Mycoplasma): Lack a cell wall (peptidoglycan layer), are highly pleomorphic and osmotically unstable, and are the smallest bacteria described.
Capsule (Glycocalyx)
- Extracellular polymeric matrix present in some bacterial species.
- Functions: Protection (environment, phagocytosis), cell adherence, and nutrient reserve.
Flagella
- Anchored to the bacterial cell envelope, multi-protein structure with varied number and position between bacteria.
- Functions: Locomotion or bacterial motility.
Pili/Fimbriae
- Fine, straight, hair-like appendages attached to the cell wall, known as “adhesins”.
- Functions: Adhesion to host tissues (specificity) and contribute to antigenicity.
Endospores
- Cryptobiotic state of dormancy and most durable type of cell found in nature.
- Produced by some Gram-positive bacteria, ensuring survival during adverse environmental conditions.
Bacterial Characteristics
- Bacteria are ubiquitous, essential for life on Earth, and have diverse morphologies and arrangements.
- Sizes range from 1 µm to 5 µm in diameter, with the largest bacterium known being Thiomargarita magnifica (2.0 cm long).
Cell Structure
- Prokaryotes: Unicellular organisms lacking membranous organelles and true nucleus.
- All bacteria have cytoplasm, ribosomes, nucleoid (DNA), and plasma membrane, while some have additional structures.
Nucleoid
- Contains the bacterial chromosome, a double-stranded DNA that is mostly single (haploid) and circular.
- Functions: Contains essential genes for bacterial life (core-genome).
Plasmid
- Circular DNA molecule containing additional genes that are not essential for bacterial life.
- Functions: Provide virulence factors (genes), antibiotic resistance (genes), and other genes.
Ribosomes
- Cellular protein factory composed of proteins and rRNA with two subunits (large 50S and small 30S).
- Functions: Applications in therapy and phylogeny.
Test your knowledge on the components of a bacterial cell structure including the cytoplasmic membrane, membrane-associated proteins, and cell wall. Learn about the characteristics and functions of each component.
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