Biology Unit 3- Domain Bacteria and Domain Archaea

What are prokaryotes?

Unicellular organisms whose cells lack membrane-bound organelles; includes bacteria and archaea

What is a key feature of prokaryotic cells and its function?

The cell wall

Function: protects the cell, maintains its shape, and prevents it from bursting in hypotonic environments

Structure: bacterial cell walls contain peptidoglycan (polymer composed of modified sugars) archaeal cell walls contain polysaccharides and proteins

What is the gram stain used for?

To categorize many bacterial species by the structure of their cell walls

Gram positive: have simple walls composed of thick layer petiodylcan

Gram negative: walls have less peptidoglycan and are more complex, with outer membrane that contains lipopolysaccharides

What is a capsule and its function?

A sticky layer of polysaccharides or protein surrounding some prokaryotic cells that can help cells adhere to surfaces, avoid desiccation, and evade host immune defenses.

What are fimbriae and their function?

Short, numerous protein appendages used primarily for attachment to surfaces or other cells.

What are pili and their function?

Protein appendages that can function in attachment, DNA transfer, or movement. (sometimes referred to as sex pili)

What are endospores?

A highly resistant, dormant structure formed by some bacteria that allows survival under harsh environmental conditions.

How is an endospore formed?

The original cell produces a copy of its chromosome and surrounds it with a tough multilayered structure

What is taxis?

A directed movement toward or away from a stimulus

Prokaryotes that exhibit chemotaxis change their movement pattern in response to chemicals (move toward nutrients or oxygen or away from toxic substances)

What is the flagella used for?

Evolved independently in bacteria, archaea, and eukaryotes (analogous structure) which aids in the movement of cells

Consists of the motor, hook and filament

How do prokaryotic cells different from eukaryotic ones?

Lack complex organization associated with membrane-bound organelles

Have one circular chromosome, whereas eukaryotes have several linear chromosomes

Lack a nucleus; DNA located in nucleoid

Plasmids: smaller rings of independently replicating DNA

How do prokaryotes reproduce?

Binary fission: single prokaryotic cell divides into 2 then 4, 8,16…

Cells eventually exhaust nutrient supply, poison themselves with metabolic wastes, face competition from other microorganisms, or are consumed by other organisms

What is an example of a bacterium that reproduces this way?

Escherichia coli reproduces by binary fission in a human intestine

What can mutations lead to in bacteria?

Though they are rare on a per genebasis, they can increase genetic diversity quickly in a species with short generation times and large populations, leading to rapid evolution

What three mechanisms lead to genetic recombination in prokaryotes?

Transformation: genotype (maybe phenotype) of a prokaryotic cell are altered by the uptake of foreign DNA from its surroundings

Transduction: phages carry prokaryotic genes from one host cell to another

Conjugation: DNA is transferred between two prokaryotic cells (usually the same species) that are temporarily joined

What is the F factor?

The ability to form pili and donate DNA during conjugation

Can either exists as a plasmid or a segment of DNA within a bacterial chromosome

What are the different types of nutritional modes in prokaryotes?

Phototrophs: obtain energy from light

Chemotrophs: obtain energy from chemicals

Autotrophs: obtain energy from CO2 or related compounds in some form of carbon source

Heterotrophs: obtain energy from organic nutrients (glucose) to make other organic compounds

What are the 2 types of combined autotrophs?

Photoautotroph

Energy source: light

Carbon source: CO2, HCO3-, other related compounds

Types of organisms: photosynthetic prokaryotes (cyanobacteria), plants, protists (algae)

Chemoautotroph

Energy source: Inorganic chemicals

Carbon source: same as above

Types of organisms: Unique to certain prokaryotes (sulfolobus)

What are the 2 types of combined heterotrophs?

Photoheterotroph

Energy source: light

Carbon source: organic compounds

Types of organisms: Unique to certain aquatic and salt loving prokaryotes (Rhodobacter)

Chemoheterotroph

Energy source: organic compounds

Carbon source: same as above

Types of organisms: Many prokaryotes ( clostridium), protists, fungi, animals and some plants

What are obligate aerobes and anaerobes?

Aerobes: Use O2 for cellular respiration and cannot grow without it

Anaerobes: poisoned by O2. Some live exclusively in fermentation; others extract chemical energy by anaerobic respiration

What are facultative anaerobes?

Use O2 if it is present but can also carry out fermentation or anaerobic respiration in an anaerobic environment

How do eukaryotes and prokaryotes obtain nitrogen?

Eukaryotes can obtain nitrogen only from a limited group of nitrogen compounds, but prokaryotes can metabolize nitrogen in many forms

Example: cyanobacteria and some methanogens convert N2 to NH3 (nitrogen fixation)

What are nitrogen fixing prokaryotes capable of doing?

They can increase the nitrogen available to plants, which cannot use N2 but can use the nitrogen compounds that the prokaryotes produce from NH3

What is metabolic cooperation in prokaryotes?

Cooperation between cells that allows them to use resources they could not use individually

How does Anabaena demonstrate metabolic cooperation?

Different cells specialize: most perform photosynthesis, while heterocysts perform nitrogen fixation.

Cannot perform photosynthesis and nitrogen fixation simultaneously b/c photosynthesis produce O2 which inactivates enzymes required for nitrogen fixation

What are heterocysts and how are they adapted for nitrogen fixation?

Specialized Anabaena cells that carry out nitrogen fixation, which have a thickened cell wall that limits O₂ entry, protecting nitrogen-fixation enzymes.

What is horizontal gene transfer and how has it played a role in prokaryote evolution?

Movement of genetic material between organisms other than by parent-to-offspring inheritance

Prokaryotes have acquired genes from distantly related species over millions of years, as a result a significant portion of genomes of many prokaryotes are mosaics

What are extremophiles?

Archaea that live in environments so extreme that few other organisms can survive there

What are extreme halophiles and thermophiles?

Halophiles: live in highly saline environments, such as those found in the pool of the Danakil Depression

Thermophiles: thrive in very hot environments. Cells avoid the fate of DNA unwinding and proteins denaturing because they have structural and biochemical adaptations that make their DNA and proteins stable at high temps

What are methanogens?

Archaea that release methane as a by-rpdouct of how they obtain energy. They use CO2 to oxidize H2, which produces both energy and methane waste

Why are methanogens useful?

Inhabit anaerobic environments within the guts of cattle, termites, and other herbivores, playing an essential role in the nutrition of these animals, and useful as decomposers in sewage treatment facilities.

Why are prokaryotes important to nutrient cycling?

They help recycle chemical elements between living organisms and the nonliving environment.

What are decomposers?

Organisms that break down dead organisms and waste, releasing nutrients such as carbon and nitrogen.

How do chemoheterotrophic prokaryotes act as decomposers?

They break down dead organisms and waste products, releasing carbon, nitrogen, and other elements

Why are prokaryotic decomposers essential to ecosystems?

They return nutrients to the environment, making them available for reuse by other organisms.

How do cyanobacteria and other autotrophic prokaryotes contribute to food chains?

They use CO₂ to produce organic compounds such as sugars, which provide carbon for other organisms.

How can prokaryotes affect plant nutrient availability?

They can increase or decrease nutrient availability by transforming or immobilizing nutrients such as N, P, and K.

How are prokaryotes beneficial to humans?

Form microbiome: intestines house 500-1000 species of bacteria which vary in their ability to process different foods (mutualists-digest food our intestines cannot)

How are prokaryotes harmful to humans?

Pathogenic prokaryotes: bacteria cause diseases in humans, transmitted by other species (fleas or ticks)

What are exo and endotoxins?

Exotoxins: proteins secreted by certain bacteria and other organisms (Cholera is caused by an exotoxin secreted by the proteobacterium Vibrio cholerae)

Endotoxin: lipopolysaccharide components of the outer membrane of gram-negative bacteria. Released only when the bacteria die and their cell walls break down (Salmonella typhi-causes typhoid fever)

How have bacteria evolved over the years in response to antibiotics?

Antibiotic resistance has evolved in many bacteria rapidly, which the discovery of new antibiotics not keeping pace with the rate of resistance evolution

What is the rise in antibiotic resistance driven by

Rapid reproduction: enables cells carrying resistance genes to quickly produce large number of resistant offspring

Horizontal transfer: resistance genes spread among bacteria species