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Questions and Answers
What does microbiology study?
What does microbiology study?
Microbiology studies tiny living organisms such as bacteria, fungi, and viruses.
Which of the following organisms are classified as prokaryotes?
Which of the following organisms are classified as prokaryotes?
Eukaryotes include bacteria and archaea.
Eukaryotes include bacteria and archaea.
False
What is absent in prokaryotic cells?
What is absent in prokaryotic cells?
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Bacteria are primarily classified based on their morphology; spherical bacteria are called __________.
Bacteria are primarily classified based on their morphology; spherical bacteria are called __________.
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Match the following bacterial classifications with their descriptions:
Match the following bacterial classifications with their descriptions:
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What role does the cell wall play in bacteria?
What role does the cell wall play in bacteria?
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The presence of a capsule is essential for bacterial life.
The presence of a capsule is essential for bacterial life.
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Gram positive bacteria have a thick layer of ________ in their cell wall.
Gram positive bacteria have a thick layer of ________ in their cell wall.
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What is a common target for antibiotics?
What is a common target for antibiotics?
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Study Notes
General Bacteriology
- Microbiology is the study of small living organisms like bacteria, fungi, and viruses.
- Organisms were classified into Protista (bacteria, fungi, protozoa, and algae) before the electron microscope.
- After the electron microscope, Prokaryotes (Bacteria, Rickettsia, Chlamydia) and Eukaryotes (Fungi, protozoa, plant and animal cells), and Viruses are included.
Bacterial Structure
- Bacteria have a capsule, cell wall, plasma membrane, nucleoid, cytoplasm, and ribosomes.
Classification of Bacteria
- Morphology: Bacteria can be spherical (cocci), rod-shaped (bacilli), or spiral (spirochetes). Specific arrangements exist (diplococci, streptococci, staphylococci).
- Stained according to gram staining: Gram-positive and gram-negative.
- Metabolism and nutrition
- Orders, families, genera, species, and groups
Structure of the Bacterial Cell
- Essential structures: cell wall, cytoplasmic membrane, and protoplasm (cytoplasm and the nuclear material).
- Accessory structures: capsule and slime layer, fimbriae (pili), flagella, spores, and plasmids.
1- Cell Wall
- Rigid structure that maintains bacterial shape.
- Prevents osmotic rupture or lysis.
- Plays a role in cell division.
- Virulence factor: LPS (endotoxin) is present in Gram-negative bacteria; Teichoic acids are in Gram-positive bacteria, enabling adherence to host cells. Protein A (Staph) and Protein M (Strept) are anti-phagocytic.
- Medial importance: Major antigen, important for classification according to staining, and a good target for antibiotics (penicillin and cephalosporins).
Gram-positive vs. Gram-negative
- Gram-positive: Thick peptidoglycan layer (50%), teichoic acid, absent outer membrane.
- Gram-negative: Thin peptidoglycan layer (5-10%), outer membrane with lipopolysaccharide (LPS), periplasmic space.
2- Cytoplasmic Membrane
- Semi-permeable, delicate membrane.
- Maintains constant environment.
- Chemical composition: phospholipid bilayer with proteins.
- Function: -Selective permeability to molecules. -Excretion of hydrolytic enzymes and toxins -Site of respiration, energy production, and electron transport. -Plays a role in DNA replication and cell wall biosynthesis.
Mesosomes
- Invaginations of the cell membrane.
- Play a role in respiration and cell division.
3- Bacterial Cytoplasm
- Viscous, watery, soft gel-like substance.
- Contains cytoplasmic inclusion granules (e.g., meta-polyphosphate).
- Contains ribosomes (70S, 30S and 50S subunits) responsible for protein synthesis.
- Contains other types of RNA (t-RNA, m-RNA).
4- Bacterial Nucleus
- Single, circular, double-stranded DNA.
- Supercoiled to fit within the cell
- Binary fission method of multiplication; chromosome attaches to the mesosome.
- Forms two identical copies of the DNA.
5- Plasmids
- Extra-chromosomal, circular, double-stranded DNA molecules.
- Replicate independently of the host chromosome.
- Multiple copies are present in the cell.
- Do not encode essential bacterial functions.
- Can be classified as conjugative or non-conjugative.
B-Accessory Structures
- Capsule: Firmly attached layer of polysaccharides or polypeptide (mucoid colonies).
- Slime Layer (Glycocalyx): Loosely attached.
- Capsule and slime function as a virulence factor, aiding in attachment and preventing phagocytosis.
- Function:
- Adherence to host surfaces
- Protection against immune system
- Resistance to antibiotics.
Flagella
- Long, thin filaments composed of flagellin protein.
- Enable motility in the bacteria.
- Present in different distributions.
- Different types of flagella distributions exist (monotrichous, amphitrichous, lophotrichous, peritrichous, and atrichous).
Pili (Fimbriae)
- Short, hair-like protein filaments.
- Enable adhesion to host cells, increasing pathogenicity.
- Two types of Pili found; ordinary pili and sex pili.
- Ordinary pili used for colonization.
- Sex pili used for bacterial conjugation.
Spores
- Highly resistant resting stage.
- Formed under unfavorable conditions (e.g., nutrient depletion, heat, dryness).
- Resistant to heat, chemicals, and desiccation.
- Marked by structural components like calcium dipicolinate and impermeable layer.
- Medial Importance -Extraordinary resistance to heat & chemical methods of sterilization and boiling. -Can generate into vegetative forms, causing disease. -Use as indicators of sterilization and as a biological weapon.
Demonstrations
- Various staining techniques for visualizing bacterial structures.
- Capsules can be visualized using special staining techniques.
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Description
Explore the fundamental concepts of general bacteriology, including the classification of bacteria and their unique structures. This quiz covers topics such as morphology, staining techniques, and the components of bacterial cells. Perfect for students delving into microbiology.
