Week 13 / Microbiology 3 Flashcards
What are bacterial colonies, and how can they differ in appearance?
Bacterial colonies are aggregates of individual bacteria that form visible clusters on a large scale. They can vary in shapes, colors, and sizes depending on the species. While the appearance of colonies can provide clues, it is an inaccurate method for classification.
What are the common bacterial cell shapes?
What are there sizes?
and how are they observed?
cocci (spheres), bacilli (rod-shaped), and spiral bacteria.
They range in size from 1 to 10μm
must be observed under a microscope due to their small size.
Question:
What are the different arrangements of cocci bacterial cells, and can you provide examples?
- Monococcus: single cells (e.g., Micrococcus flavus)
- Diplococcus: paired cells (e.g., Neisseria gonorrhoeae)
- Staphylococci: grouped cells (e.g., Staphylococcus aureus)
- Streptococci: chained cells (e.g., Streptococcus pyogenes)
- Tetrads: groups of 4 cells in the same plane (e.g., Micrococcus luteus)
- Sarcina: cuboidal arrangements of 8 cells (e.g., Sarcina spp.).
What are the different arrangements of bacilli bacterial cells, and can you provide examples?
- Bacillus: single rod (e.g., Bacillus cereus)
- Diplobacilli: two bacilli side by side (e.g., Coxiella burnetii)
- Streptobacilli: chains of bacilli (e.g., Streptobacillus moniliformis - Rat Bite Fever).
What are the different types of spiral bacteria, and can you provide examples?
- Spirillum: a rigid, spiral-shaped Gram-negative bacterium (e.g., Campylobacter jejuni or Helicobacter pylori)
- Spirochete: a thin, long, and more flexible bacterium (e.g., Treponema pallidum).
What are the key structural differences between eukaryotic and prokaryotic cells?
Eukaryotic cells have a membrane-enclosed nucleus and organelles such as mitochondria.
Prokaryotic cells lack a membrane-bound nucleus, instead having a nucleoid region. Some prokaryotes have a capsule, and they may possess a flagellum for movement.
Both types of cells have ribosomes and a cell membrane, but prokaryotes also have a cell wall, which is only present in some eukaryotes.
How do prokaryotic cells differ from eukaryotic cells, and why can they adapt more readily to environmental changes?
Prokaryotic cells are simpler in structure than eukaryotic cells and can adapt more readily to environmental changes.
They have the ability to metabolize a wider range of substrates, which allows them to survive in more diverse environments.
prokaryotic cells are more flexible and efficient in responding to environmental changes than eukaryotic cells.
What are the general categories of bacterial cell components, and what functions do they serve?
- Structural: includes the cell wall and plasma membrane
- Genetic material: includes the nucleoid (chromosomal DNA) and plasmids
- Protein production: carried out by ribosomes
- Motility: involves structures like flagella and pilli
- Specialist structures: such as endospores (for survival) and capsules/slime layers (for protection).
What is the role of the bacterial cell wall, and how do Gram-positive and Gram-negative bacteria differ?
Answer:
The bacterial cell wall, made of peptidoglycan, provides shape and protects the cell from osmotic lysis.
Bacteria are divided into two major groups based on their cell wall structure:
- Gram-positive bacteria have a thick peptidoglycan layer with a single plasma membrane.
- Gram-negative bacteria have a thinner peptidoglycan layer but possess two plasma membranes.
What is peptidoglycan, and what are its key characteristics and differences between Gram-positive and Gram-negative bacteria?
Peptidoglycan is a polymer composed of sugars and amino acids, specifically alternating residues of β-(1,4) linked N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). Key characteristics include:
- A chain of 3 to 5 amino acids is attached to NAM.
- It allows particles of approximately 2 nm to pass through in both Gram-positive and Gram-negative bacteria.
- The thickness of the peptidoglycan layer varies between Gram-positive (90% of cell weight) and Gram-negative bacteria (10% of cell weight).
What are the key components and functions of the plasma membrane in bacteria?
- Lipid bilayer: Forms the fundamental structure.
- Proteins: Embedded in the bilayer, providing various functions.
- Lipopolysaccharides: Present in Gram-negative bacteria, contributing to membrane structure.
Key functions include:
- Retention of cytoplasm: Maintains the internal environment of the cell.
- Segregation of internal environment: Separates cellular components from the external environment.
- Support for proteins: Anchors proteins that play roles in transport and signaling.
- Selectively permeable: Regulates the movement of substances in and out of the cell.
What are the two main types of membrane proteins in the plasma membrane, and what are their key characteristics and functions?
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Integral Proteins:
- Comprise approximately 75% of membrane proteins.
- Are tightly attached to or stretched across the lipid bilayer.
- Function primarily in ion transport and can form channels or transporters.
-
Peripheral Proteins:
- Make up about 25% of membrane proteins.
- Are soluble in aqueous environments, meaning they do not span the membrane.
- Can include enzymes like cholesterol oxidases, which deplete eukaryotic cells of cholesterol.
- Often involved in signaling pathways or serve as enzymes
What is lipopolysaccharide (LPS), and what are its structural components and implications for health?
Lipopolysaccharide (LPS) contributes to the structural integrity of bacterial cells and consists of three domains:
- O Antigen: The outermost part that varies among different bacterial species.
- Core Antigen: A central region that connects the O antigen to Lipid A.
- Lipid A: Anchors the LPS to the bacterial membrane and is responsible for many of its biological activities.
Key implications include:
- Pro-inflammatory immune response: LPS can stimulate a strong immune reaction.
- Health risks: Small amounts can cause illness, leading to conditions like endotoxemia, which may result in septic shock.
- Manufacturing control: LPS content is highly regulated in sterile manufacturing processes.
- Limulus Amebocyte Lysate (LAL) Assay: A test used to detect the presence of LPS in products, indicating potential contamination.
What are flagella in bacteria, and what roles do they play in bacterial motility and pathogenesis?
Flagella are external structures in bacteria involved in motility (movement) and have the following characteristics:
-
Positioning and Quantity: The number and arrangement of flagella depend on the bacterial species.
- Monotrichous: A single flagellum (e.g., Vibrio cholerae).
- Lophotrichous: Multiple flagella at one end.
- Amphitrichous: A flagellum at both ends.
- Peritrichous: Flagella distributed around the cell (e.g., Escherichia coli).
- Size: Flagella are long compared to the bacterial cell, measuring approximately 10 μm.
- Power Source: They are powered by H⁺ ion flow (occasionally Na⁺ ions).
-
Pathogenic Role:
- Flagella are crucial for the virulence of V. cholerae.
- In Helicobacter pylori, flagella help propel the bacteria through the mucus lining in the stomach, aiding in infection.
What are pili (fimbriae) in bacteria, and what are their types and functions?
Pili, also known as fimbriae, are external components primarily found in Gram-negative bacteria. They serve various functions and are categorized into two main types:
-
Conjugative Pili:
- Facilitate the transfer of DNA between two bacteria during a process called conjugation.
- Play a critical role in horizontal gene transfer, contributing to genetic diversity.
-
Type IV Pili:
- Involved in twitching motility, allowing bacteria to move across surfaces.
- Essential for adhesion to surfaces and in processes such as biofilm formation.
Overall, pili enhance bacterial adhesion, motility, and genetic exchange, contributing to their adaptability and survival.
