Prokaryotes Study Notes

Prokaryotes Overview

  • Prokaryotes are single-celled organisms that lack a nucleus. They are one of the two primary domains of life, with the other being Eukarya.

Grand Prismatic Spring: Prism of Light, Spectrum of Life

  • The Grand Prismatic Spring is the largest and one of the most brilliant hot springs in Yellowstone National Park.

    • Spans approximately 200 feet (61m) across.

    • Water temperature is around 160°F (70°C), resulting in frequent steam coverage.

    • Heated by magma from an active volcano, causing water to rise through fissures in rocks.

    • It discharges almost 500 gallons of hot water per minute into the Firehole River.

    • Minerals in the hot water create terraced formations over time.

Did You Know?

  • Definition of Prismatic: Brilliantly colored.

  • Intense blue color at the center of the spring arises from sunlight scattering by suspended particles in the water.

  • The surrounding yellow, orange, and brown colors are due to thermophiles (heat-loving microorganisms).

    • These microbes have colorful pigments enabling them to utilize sunlight for energy and to thrive in high-temperature conditions.

  • Billions of thread-like filaments and sausage-shaped cyanobacteria such as Phormidium, Synechococcus, and Calothrix form colorful mats near the hot spring.

Prokaryotes: Who Are They?

  • Prokaryotes are explored in terms of their classification, appearance, and survival mechanisms.

Prokaryotes: The First Life on Earth

  • Prokaryotes are considered one of the earliest forms of life on the planet.

Habitat and Lifestyle of Prokaryotes

  • Prokaryotes inhabit a wide range of environments:

    • Normal Habitats: Soil, water, and even inside other organisms.

    • Extremophiles: Adapted to extreme conditions.

Extremophiles and Their Preferred Conditions

  • Acidophiles: Thrive at a pH of 3 or below.

  • Alkaliphiles: Prefer a pH of 9 or above.

  • Thermophiles: Live optimally between 60-80 °C (140-176 °F).

  • Hyperthermophiles: Survive at temperatures of 80-122 °C (176-250 °F).

  • Psychrophiles: Grow at temperatures between -15 to 10 °C (5 to 50 °F) or lower.

  • Halophiles: Require a salt concentration of at least 0.2 M to grow.

  • Osmophiles: Thrive in environments with high sugar concentrations.

Uncultured Prokaryotes

  • It is estimated that over 99% of prokaryotes cannot be cultured in laboratory settings.

Prokaryote Structure

Cellular Components

  • Prokaryotes have a simple cellular structure:

    • Cell Wall: Provides structure.

    • Cell Membrane: Regulates what enters and leaves the cell.

    • Pili: Hair-like structures for attachment.

    • Capsule: A protective layer.

    • Ribosomes: Sites of protein synthesis.

    • Chromosome: Circular DNA located in the nucleoid region.

    • Flagellum: A tail-like structure for movement.

Internal Components

  • Prokaryote structure lacks membrane-bound organelles but contains:

    • DNA in the nucleoid region.

  • Main components are similarly structured among various prokaryote groups.

Prokaryote Groups

  • Domain Bacteria: Includes several subgroups.

  • Domain Archaea: Features include extreme environments that bacteria do not typically occupy.

    • Sub-groups include Euryarchaeotes, Crenarchaeotes, Nanoarchaeotes, and Korarchaeotes.

  • Domain Eukarya: Includes all eukaryotic organisms.

Phospholipid Structures

  • Differences in phospholipids and membranes between Archaea and Bacteria:

    • Archaea: Phytanyl sidechain with ether linkages.

    • Bacteria and Eukarya: Fatty acids with glycerol and ester linkages.

Prokaryote Cell Wall Structure

  • Differences in Gram-positive and Gram-negative bacteria:

    • Gram-Positive:

    • Thick peptidoglycan layer, no outer membrane.

    • Gram-Negative:

    • Contains lipopolysaccharides, periplasmic space, and two membranes.

Summary of Structural Differences

  • Prokaryotic characteristics compared across domains:

    • Cocci, bacilli, and spirilla are common morphological forms.

    • Cell walls in bacteria contain peptidoglycan, whereas archaea lack this component.

    • Chromosomes in both domains are typically circular.

Prokaryote Reproduction

  • Modes of prokaryotic reproduction include:

    • Transformation: Uptake of foreign DNA from the environment.

    • Transduction: Transfer of DNA via bacteriophages.

    • Conjugation: Direct transfer of DNA between bacteria through pili.

Prokaryote Metabolism

  • Carbon Cycle: Prokaryotes play a key role in:

    • Photosynthesis: Converting CO₂ into organic compounds.

    • Decomposition: Recycling organic carbon.

    • Metabolism: Utilizing various carbon substrates, especially in anoxic environments.

Prokaryotes in the Ecosystem: Nitrogen Cycle

  • Functions of prokaryotes in the nitrogen cycle include:

    • Nitrogen-Fixing Bacteria: Change atmospheric nitrogen (N₂) into usable forms.

    • Decomposition: Converting organic nitrogen to ammonium (NH₄⁺).

    • Nitrification: Converting ammonium to nitrites (NO₂⁻) and nitrates (NO₃⁻) via nitrifying bacteria.

    • Denitrifying Bacteria: Return nitrogen to the atmosphere by converting nitrates back to N₂.