Bacteria, Archaea, and Viruses (ch 18)

What are the three major groups (domains) of life?

Bacteria, Archaea, and Eukarya (plants, animals, fungi, protists).

What is the main cellular difference between Prokaryotes (Bacteria/Archaea) and Eukaryotes?

Prokaryotes do not have a nucleus or other membrane-bound organelles.

Are all prokaryotes closely related? (Are they a monophyletic group?)

They are a paraphyletic group. Archaea are more closely related to Eukarya than to Bacteria.

______ share a more recent ancestor with Archaea

Eukaryotes

• most successful organisms on Earth (in terms of number of individuals)

• found in every type of habitat on Earth

Prokaryotes

How do prokaryotes (bacteria and archaea) differ from eukaryotes?

• All are unicellular

• divide by binary fission, not mitosis

• cellular organization is different: DNA is often circular & not in a nucleus, few or no membrane-enclosed organelles (they are rare!)

What unique molecule is found in the cell walls of Bacteria but not Archaea?

Peptidoglycan.

Many Archaea are known as "extremophiles." What does this mean?

They thrive in extreme environments like very hot, salty, or acidic places.

What is the difference between Gram-positive and Gram-negative bacteria?

It's a staining test.

• Gram-positive bacteria have a thick peptidoglycan wall that stains purple.

• Gram-negative bacteria have a thin wall and an outer membrane, and don't hold the purple stain.

What are the three common shapes of prokaryotes?

Cocci (spheres), Bacilli (rods), and Spirilla (spirals).

______ can make their own food (photosynthesis)

Autotrophs

• Ex. photoautotrophs (get energy from sun) and chemoautotrophs (get energy from chemicals)

What is an organism that gets energy from light and carbon from CO₂ called?

A Photoautotroph (e.g., cyanobacteria).

______ consume other organisms to get food/energy

Heterotroph

What is an organism that gets energy and carbon from organic compounds (like food) called?

A Chemoheterotroph (e.g., E. coli, animals).

What is "Lateral Gene Transfer"?

When genes move "sideways" from one species to another, not from parent to offspring.

What genes are transferred and retained? Why?

Those that result in new adaptations that confer higher fitness.

Example: genes for antibiotic resistance are often transferred among bacterial species, especially under strong selection pressure

Why does Lateral Gene Transfer make it hard to build a simple Tree of Life?

It creates discordant gene trees, where the history of one gene doesn't match the history of the organism.

What are dormant, tough structures that some bacteria form to survive harsh conditions?

Endospores.

What is a slimy community of bacteria that sticks to a surface?

• Prokaryotes live in complex communities known as ______

Biofilms (e.g., dental plaque).

What is the name for the process bacteria use to communicate and coordinate as a group?

Quorum Sensing.

What vital role do some bacteria play in the nitrogen cycle?

Nitrogen-fixing bacteria convert nitrogen gas from the air into a form plants can use.

What is the human microbiome?

The community of trillions of microbes (bacteria, etc.) that live in and on our bodies.

Are viruses considered living organisms?

Generally, no. They cannot reproduce on their own and don't have a metabolism.

What is a virus that infects bacteria called?

A bacteriophage.

What is a retrovirus?

An RNA virus that uses an enzyme called reverse transcriptase to make DNA from its RNA. (HIV is a retrovirus).

What is a "provirus"?

Viral DNA that has been inserted into the DNA of a host cell.

What are "endogenous retroviruses" in our DNA?

Ancient viral DNA that is now a permanent, inherited part of our genome.