Lab 4-6 exam 2 biology 006

• Prokaryotes were the first organisms on Earth (~3.5 billion years ago)

• Still, the most abundant and diverse

• Found in:

  • Extreme environments

  • Human body

  • Soil, oceans, atmosphere

• Two domains:

  • Bacteria: peptidoglycan

  • Archaea: NO peptidoglycan

Key Characteristics of Prokaryotic Cells

• No nucleus

• No membrane-bound organelles

• Usually 0.5–5 µm

• Single circular chromosome in nucleoid region

• Reproduce by binary fission

Common Shapes

• Coccus → spherical

• Bacillus → rod-shaped

• Spirillum → spiral

External Structures: Cell Wall

• Maintains shape

• Prevents osmotic lysis

• Usually contains peptidoglycan (Bacteria)

External Structures: Capsule (if present)

• Sticky protective layer

• Functions:

  • Adhesion

  • Protection

  • Immune evasion

External Structures: Fimbriae

• Attachment to surfaces

External Structures: Pili(sex pili)

• DNA transfer during conjugation

Motility

• Flagella

  • Different structure than eukaryotic flagella

  • Rotary motion

• Non-Motile

• Pseudopodia (Amoeba like movement)

Internal Organization

• Plasma membrane

• Nucleoid (DNA region)

• Ribosomes (smaller than eukaryotic)

• Inclusion bodies (storage)

Binary Fission

• Very fast reproduction

• Can double population in minutes/hours

Genetic Variation

Even without meiosis:

1. Mutation

• Rapid evolution

2. Horizontal Gene Transfer

• Transformation → uptake of free DNA

• Transduction → bacteriophage transfer

• Conjugation → sex pilus DNA transfer

Endospores

• Dormant, resistant cells

• Survive:

  • Heat

  • Desiccation

  • Chemicals

Molecular Systematics

• Based on rRNA sequences

Domain Bacteria

Major groups:

• Proteobacteria

• Cyanobacteria

• Gram-positive bacteria

• Chlamydias

• Spirochetes

Domain Archaea

• No peptidoglycan

• Unique lipids

• Many are extremophiles

Groups:

• Methanogens

• Extreme halophiles

• Extreme thermophiles

Role in Ecosystems

Decomposers

Producers : make their own organic food using an external energy source like sunlight, forming the base of the food chain.

Nitrogen fixers : convert atmospheric nitrogen gas into a usable form like ammonia for other organisms.

Symbiosis : mutualism, commensalism, or parasitism.

Symbiotic Relationships

1. Mutualism

Example:

• Human gut microbiome

2. Commensalism: one organism benefits while the other is neither helped nor harmed, such as harmless bacteria living on human skin without affecting the host

3. Parasitism (pathogens)

Biofilms

• Surface-attached communities

• Resistant to antibiotics

• Dental plaque example: Biofilm formed when bacteria attach to the tooth surface and multiply within a protective matrix they secrete. This biofilm structure makes the bacteria more resistant to saliva, brushing, and antimicrobial agents than they would be as free-floating cells.

Beneficial Prokaryotes

• Food production

• Bioremediation

• Biotechnology

• Normal microbiota

Pathogenic Bacteria

1. Exotoxins: Proteins secreted by living bacteria (both Gram-positive and Gram-negative) that damage host cells or disrupt their normal function.

• Secreted proteins

2. Endotoxins: Lipopolysaccharide components of the outer membrane of Gram-negative bacteria that are released when the bacterial cell dies or lyses, triggering a strong immune/inflammatory response.

• Lipopolysaccharide from the outer membrane

Antibiotics & Resistance

• Resistance evolves rapidly

• Misuse accelerates selection

How do mutations contribute to genetic diversity in prokaryotic populations, even though they reproduce by binary fission?

Since binary fission is asexual and produces genetically identical offspring, mutations are the primary source of new genetic variation in prokaryotic populations. These random changes in DNA sequence occur during replication and can alter traits, creating diversity even without sexual reproduction. Over many generations, accumulated mutations can lead to significant genetic differences within a population.

Why can mutations spread rapidly through a prokaryotic population? Be sure to include the role of the reproduction rate in your explanation.

Prokaryotes have extremely short generation times, allowing them to reproduce by binary fission in as little as 20 minutes under ideal conditions. This rapid reproduction rate means a beneficial mutation can be passed on to enormous numbers of offspring in a very short period. As a result, favorable mutations can quickly become widespread throughout the population through natural selection.

Give one example of how a beneficial mutation can increase the survival of prokaryotes in a changing environment.

A mutation that alters the structure of a bacterial protein targeted by an antibiotic can prevent that antibiotic from binding effectively, making the bacterium resistant. Bacteria carrying this mutation survive and reproduce even when exposed to the antibiotic, while non-resistant bacteria die off. Over time, this leads to a population dominated by antibiotic-resistant strains, as seen in the development of antibiotic resistance discussed in your notes.

Structural Characteristics of Fungi

• Body composed of hyphae (threadlike filaments).

• A mass of hyphae forms a mycelium (feeding network).

• Hyphae may be:

  • Septate – divided by cross walls

  • Coenocytic – continuous cytoplasm with many nuclei

• Cell walls contain chitin.

• Fungi obtain nutrients by extracellular digestion followed by absorption.

Reproduction in Fungi: Asexual

• Production of spores

• Budding (common in yeasts)

• Fragmentation of mycelium

Reproduction in Fungi: Sexual

Sexual reproduction (three stages)

1. Plasmogamy – fusion of cytoplasm from two parents

2. Karyogamy – fusion of nuclei

3. Meiosis – produces haploid spores

• Often includes a dikaryotic stage (n + n).

Chytridiomycota (chytrids) FUNGI

• Mostly aquatic

• Only fungi with flagellated spores (zoospores)

Zygomycota (zygote fungi) FUNGI

• Example: bread molds

• Sexual reproduction forms zygosporangia

Glomeromycota FUNGI

• Form arbuscular mycorrhizae with plant roots

• Important for plant nutrient uptake

Ascomycota (sac fungi) FUNGI

• Largest fungal group

• Produce ascospores inside asci

• Examples: yeasts, morels, truffles

Basidiomycota (club fungi) FUNGI

• Produce basidiospores on basidia

• Includes mushrooms, puffballs, shelf fungi

Mycorrhizae FUNGI

• Mutualism between fungi and plant roots

• Fungi increase water and mineral absorption.

Lichens

• Symbiosis between fungus + photosynthetic partner (alga or cyanobacterium).

• Important pioneer species in ecosystems.

Beneficial roles FUNGI

• Food production: bread, cheese, beer

• Medicine: antibiotics (Penicillium)

• Biotechnology and fermentation

Harmful roles FUNGI

• Plant diseases (rusts, smuts)

• Human diseases (athlete’s foot, ringworm)

• Crop loss and food spoilage

What Are Protists?

• Protists are diverse eukaryotic organisms

• Most are unicellular, though some are multicellular

• Protists do not form a natural clade

• They are grouped together mainly because they are not plants, animals, or fungi

Protists include organisms that are:

1. Photosynthetic

2. Heterotrophic

3. Mixotrophic

Examples:

• Algae

• Protozoans

• Slime molds

• Water molds

• Phytoplankton produce about half of Earth’s oxygen

Protist cells may contain:

• Nuclei:

• Contractile vacuoles: collect excess water from the cell and expel it to prevent the cell from bursting.

• Food vacuoles: Membrane-bound sacs formed during phagocytosis that contain and digest ingested food particles.

• Chloroplasts: capture light energy to carry out photosynthesis.

• Flagella or cilia: enable movement and, in some cases, feeding.

• Paramecium uses cilia for movement and feeding

Protists may have:

Pellicle: A flexible, protein-based layer beneath the plasma membrane that supports the cell while still allowing it to bend and move (as seen in organisms like Euglena).

Cell wall: A rigid outer structure that surrounds the cell membrane, providing shape and protection for the protist.

Silica shell: A hard, glass-like outer covering made of silicon dioxide that protects certain protists, such as diatoms.

• Diatoms have silica cell walls

Photoautotrophs: Use photosynthesis

• Diatoms

• Dinoflagellates

• Euglenids

Heterotrophs

Consume organic material by:

• Phagocytosis

• Absorption

Examples:

• Amoebas

• Paramecium

Mixotrophs

Combine both strategies.

Example:

• Euglena

• Can photosynthesize or ingest food