Microbial Evolution Chapter 1

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Questions and Answers

What effect does a shorter focal length have on magnification?

It increases the magnification. (correct)

It has no effect on magnification.

It decreases the total magnification.

It only affects resolution, not magnification.

Which type of microscope is best suited for observing living, unstained specimens?

Fluorescence microscope

Phase-contrast microscope

Dark-field microscope (correct)

Bright-field microscope

What is the primary purpose of immersion oil in microscopy?

To stain the specimen for better visibility

To reduce light refraction and enhance resolution (correct)

To preserve the specimen's morphology during observation

To increase the overall size of the specimen

What is the main advantage of fluorescence microscopy?

It allows for the identification of specific structures using fluorescent dyes. Signup and view all the answers

What is a characteristic of phase-contrast microscopy?

It uses phase shifts in light to create contrast. Signup and view all the answers

What does differential staining primarily allow scientists to do?

Classify organisms into specific groups based on structure. Signup and view all the answers

During the Gram staining process, what is the function of iodine?

It acts as a mordant to fix the crystal violet dye. Signup and view all the answers

What is the primary purpose of fixation in microscopy?

To preserve the structure of specimens for observation. Signup and view all the answers

What is the primary function of the Endospore Stain?

To identify spore-forming bacteria Signup and view all the answers

Which electron microscope provides images based on the internal structure of a specimen?

Transmission Electron Microscope (TEM) Signup and view all the answers

Which statement about Scanning Probe Microscopy is most accurate?

STM can visualize individual atoms by measuring current fluctuations Signup and view all the answers

What defines a prokaryote according to traditional classification?

They lack a defined nucleus and membrane-bound organelles Signup and view all the answers

Which bacterial shape is described as pleomorphic?

Variable in shape Signup and view all the answers

Which of the following is a characteristic of Bacillus-shaped bacteria?

Can be in chains or single Signup and view all the answers

What distinguishes Scanning Electron Microscopy (SEM) from other electron microscopes?

It produces 3D images based on surface interactions Signup and view all the answers

What is the function of a capsule in bacteria?

To protect against environmental stresses Signup and view all the answers

What is one characteristic that differentiates prokaryotes from eukaryotes?

Absence of a true membrane-delimited nucleus Signup and view all the answers

Which of the following microbes is known to thrive in geothermal vent environments?

Deferribacter desulfuricans Signup and view all the answers

What does LUCA refer to in the context of microbial evolution?

Last Universal Common Ancestor Signup and view all the answers

What is primarily stored in bacterial inclusions?

Nutrients and energy Signup and view all the answers

Which principle is associated with the endosymbiotic hypothesis regarding eukaryotic evolution?

Mitochondria evolved from free-living prokaryotes that were engulfed. Signup and view all the answers

Which structure is responsible for providing buoyancy in aquatic environments for bacteria?

Gas vacuoles Signup and view all the answers

Which infectious agent is characterized as containing only RNA?

Viroid Signup and view all the answers

What is the primary function of the S-layer in bacterial cells?

Environmental protection and structural integrity Signup and view all the answers

Which of the following best describes the composition of bacterial ribosomes?

70S composed of 30S and 50S subunits Signup and view all the answers

What type of cellular organization do fungi represent in microbial classification?

Eukaryotic Signup and view all the answers

Who was the first to observe microorganisms, significantly impacting microbiology?

Antony van Leeuwenhoek Signup and view all the answers

Which type of bacterial movement is driven by the presence of flagella?

Swimming Signup and view all the answers

Which statement about microbial diversity is true?

Microbes can photosynthesize, respire aerobically, or utilize inorganic matter for energy. Signup and view all the answers

What is the function of the bacterial cell wall?

Maintains shape and provides protection Signup and view all the answers

Which statement about passive diffusion is accurate?

It happens from high to low concentration Signup and view all the answers

Which of the following correctly describes Gram-positive bacteria?

Contain teichoic acids that contribute to cell wall rigidity Signup and view all the answers

What role do siderophores play in bacterial iron uptake?

They bind ferric ions to aid in iron transport Signup and view all the answers

In Gram staining, which reagent removes the primary dye from Gram-negative cells?

Alcohol Signup and view all the answers

How are molecules transported in group translocation?

They are chemically altered during transport Signup and view all the answers

What distinguishes the plasma membrane from the cell wall in bacteria?

The plasma membrane is selectively permeable and involved in nutrient transport Signup and view all the answers

Which component of the bacterial envelope contributes to pathogenicity?

Capsule Signup and view all the answers

Study Notes

Life on Earth

Earth is approximately 4.5 billion years old, with the first microbes emerging around 3.5 billion years ago.

Microbial Diversity

Microbes exhibit metabolic diversity, allowing aerobic respiration, photosynthesis, or utilizing inorganic substances for energy.
Adapted to extreme environments, such as geothermal vents and Arctic regions.
Examples include:
- Deferribacter desulfuricans: thrives in geothermal vents.
- Polaribacter: found in Arctic environments.
- Thiobacillus ferrooxidans: lives in varied pH environments.

Characteristics of Microorganisms

Typically microscopic, with exceptions like Thiomargarita magnifica and some filamentous fungi.
Structurally simple, lacking complex cells and tissues.

Types of Microbes

Prokaryotes: No membrane-bound nucleus; an example is bacteria.
Eukaryotes: Contain membrane-enclosed nuclei; examples include fungi.

Classification Systems

Classification influenced by electron microscopy and molecular biology.
Three Domain System:
- Bacteria: Single-celled with peptidoglycan cell walls, no membrane-bound nucleus.
- Archaea: Distinct rRNA, lack peptidoglycan, unique membrane lipids.
- Eukarya: Encompasses animals, plants, fungi, and protists.

Acellular Infectious Agents

Viruses: Smallest microbes, require hosts for replication.
Viroids: Composed solely of infectious RNA.
Prions: Infectious proteins causing disease.

Origin of Life and RNA World Hypothesis

Early life may have been RNA-based for genetic storage, replication, and catalysis.
LUCA (Last Universal Common Ancestor) gave rise to Bacteria, Archaea, and Eukarya.

Evolution of Eukaryotes

Endosymbiotic hypothesis suggests eukaryotic organelles (e.g., mitochondria) originated from bacteria engulfed by ancestral cells.

Microscopy and Early Discoveries

Antony van Leeuwenhoek was the first to observe microorganisms.
Louis Pasteur disproved spontaneous generation using the swan-neck flask experiment.

Germ Theory and Disease

Heinrich de Bary demonstrated that fungi can inflict diseases on crops.
Understanding focal length is key for microscope magnification, which involves objective and ocular lenses.

Resolution

Critical for distinguishing closely spaced objects.
Immersion oil enhances resolution by reducing light refraction, matching the refractive index.

Types of Light Microscopes

Bright-field: Dark image against a bright background, usable with stained or unstained specimens.
Dark-field: Bright image on a dark background, suited for living, unstained specimens, e.g., Treponema pallidum.
Phase-contrast: Converts phase shifts into light intensity differences, ideal for living cells.
Fluorescence: Detects fluorescent light from specimens stained with fluorochromes.

Fixation and Staining

Fixation preserves specimen structure; methods include:
- Heat fixation: Common for microbial specimens.
- Chemical fixation: Used for fragile organisms.
Staining improves visibility of structures using chromophores for color and binding.

Types of Staining

Simple Staining: Single dye to assess size, shape, and arrangement of microbes.
Differential Staining: Multiple dyes differentiate structures:
- Gram Staining: Classifies bacteria as Gram-positive (purple) or Gram-negative (pink).
- Acid-fast and Endospore Stains: Target specific cellular components.
- Capsule and Flagella Stains: Visualize protective features and motility structures.

Electron Microscopy

Utilizes an electron beam for high resolution.
Transmission Electron Microscope (TEM): Reveals internal structure through thin specimens.
Scanning Electron Microscope (SEM): Produces 3D surface images but requires metal coating.

Scanning Probe Microscopy

Scanning Tunneling Microscope (STM): Magnifies up to 100 million times, visualizes individual atoms.
Atomic Force Microscope (AFM): Maintains distance from the surface, ideal for non-conductive specimens.

Prokaryotes vs. Eukaryotes

Definitions of prokaryotes remain contentious; includes bacteria and archaea.
Some archaea possess membrane-bound structures, indicating complexity.

Bacterial Shape and Arrangement

Shape categories include:
- Coccus: Round (e.g., Neisseria gonorrhea).
- Bacillus: Rod-shaped (e.g., Bacillus megaterium).
- Vibrio: Comma-shaped (e.g., Vibrio cholerae).
- Spirochete: Flexible spiral (e.g., Treponema pallidum).

Bacterial Cell Size

Smallest reported size: 0.3 μm (Mycoplasma).
Largest known bacterium: Up to 1 cm (Thiomargarita magnifica).

Bacterial Cell Envelope

Composed of plasma membrane, cell wall (provides structure and protection), and outer layers (capsules, slime layers, S-layers).

Plasma Membrane Structure

Lipid bilayer with embedded proteins, functioning as a barrier and for transport.

Movement of Molecules In and Out of the Cell

Mechanisms include passive diffusion, facilitated diffusion, and active transport (primary and secondary).

Group Translocation and Iron Uptake

Group translocation chemically modifies molecules during membrane transport.
Siderophores assist in iron uptake by binding ferric ions.

Bacterial Cell Wall

Composed of peptidoglycan, which varies in thickness between Gram-positive (thick, purple stain) and Gram-negative (thin, pink stain) bacteria.

Gram Staining

Key steps include crystal violet to stain, iodine as a mordant, alcohol as a decolorizer, and safranin as a counterstain.

Layers Outside the Cell Wall

Capsule: Polysaccharide layer resisting phagocytosis.
Slime Layer: Less organized, related to motility.
S-layer: Regular protein layer for structural integrity.

Bacterial Cytoplasm

Contains cytoskeletal elements, inclusions, ribosomes, nucleoid, and plasmids.

Cytoskeleton

Functions similarly to eukaryotic cytoskeletons, aiding in shape maintenance and cell division.

Inclusions

Storage components for nutrients and resources, including glycogen and gas vacuoles for buoyancy.

Ribosomes

Bacterial ribosomes are 70S, crucial for protein synthesis.

Nucleoid

Region containing a single circular DNA strand; plasmids can carry additional genetic information.

Bacterial Motility

Movement in response to environmental stimuli through modes like swimming, swarming, twitching, and gliding.

Pili/Fimbriae and Flagella

Pili/Fimbriae: Hair-like structures for surface attachment and DNA exchange.
Flagella: Appendages for locomotion, varying in arrangement.

Endospores

Dormant structures formed by specific bacteria for survival in extreme conditions, highly resistant to environmental stressors.

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Explore the origins of life on Earth and the evolution of microbes in this quiz. Discover how microbes diversified in terms of metabolism and environmental conditions, thriving in extreme habitats and showcasing remarkable adaptability.