Bacteria, Archaea, and Viruses: Key Concepts for Biology

What is a prokaryote?

A cell without a nucleus or membrane-bound organelles; designed for speed and efficiency.

Why are prokaryotes so successful?

Fast reproduction, rapid adaptation, and ability to live in diverse environments.

What is the main advantage of being structurally simple?

Faster growth and reproduction, allowing quick adaptation.

What is the function of the bacterial cell wall?

Protection, maintaining shape, and preventing the cell from bursting.

What is peptidoglycan?

A strong mesh-like molecule in bacterial cell walls that provides strength and rigidity.

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

Gram-positive: thick peptidoglycan. Gram-negative: thin layer + outer membrane (more resistant and toxic).

Why are gram-negative bacteria harder to treat?

Their outer membrane acts as an extra barrier and can contain toxins.

What are the three main bacterial shapes?

Bacilli (rod), cocci (sphere), spirilla (spiral).

What is an example of cocci bacteria?

Staphylococcus aureus.

What is an example of spiral bacteria?

Treponema pallidum.

What do fimbriae do?

Help bacteria attach to surfaces or other cells.

What do pili do?

Transfer DNA between bacteria (conjugation).

What is chemotaxis?

Movement toward or away from chemical stimuli.

What structure allows bacterial movement?

Flagella.

Where is bacterial DNA located?

In the nucleoid region (not inside a nucleus).

What is a plasmid?

Small circular DNA that can carry traits like antibiotic resistance.

How do bacteria reproduce?

Binary fission (one cell splits into two identical cells).

Why do bacteria still have genetic diversity?

Mutation + genetic recombination.

What is transformation?

Uptake of DNA from the environment.

What is transduction?

Transfer of DNA via viruses.

What is conjugation?

Direct DNA transfer between bacteria using pili.

Why does genetic recombination matter?

It increases diversity and spreads traits like antibiotic resistance.

What are extremophiles?

Archaea that live in extreme environments.

What are methanogens?

Archaea that produce methane and live without oxygen.

What is the role of bacteria in ecosystems?

Decomposition, nutrient cycling, and symbiosis.

Why are bacteria both helpful and harmful?

They support ecosystems but can also cause disease.

What is the main goal of a virus?

To replicate its genetic material and spread.

Why can't viruses reproduce on their own?

They lack cellular machinery and must use a host cell.

What are the three main parts of a virus?

Genetic material, capsid, and sometimes an envelope.

What is the capsid?

A protein shell that protects and delivers viral DNA/RNA.

What is the envelope?

A lipid layer from the host that helps viruses enter cells.

What is an advantage and disadvantage of envelopes?

Advantage: easier entry. Disadvantage: easily destroyed.

Why does viral structure matter?

It determines how the virus infects, survives, and spreads.

What type of genome can viruses have?

DNA or RNA.

What is positive-sense RNA?

RNA that can be immediately translated into proteins.

What is negative-sense RNA?

RNA that must be converted to positive-sense first.

What makes retroviruses unique?

They convert RNA into DNA.

What is an example of a retrovirus?

Human Immunodeficiency Virus.

What enzyme do retroviruses use?

Reverse transcriptase.

What is the lytic cycle?

Virus replicates immediately and destroys the host cell.

What is the lysogenic cycle?

Viral DNA integrates into host genome and stays dormant.

What is a prophage?

Viral DNA embedded in bacterial DNA.

What triggers lysogenic to lytic switch?

Stress or DNA damage.

What is the key difference between lytic and lysogenic cycles?

Lytic kills immediately; lysogenic hides first.

How do animal viruses enter cells?

Endocytosis or membrane fusion.

What is uncoating?

Release of viral genome from capsid inside host cell.

How do viruses exit cells?

Lysis or budding.

What is budding?

Virus leaves cell gradually, taking part of the membrane.

Why are retroviruses hard to treat?

They integrate into host DNA and mutate quickly.

How do viruses cause disease?

By disrupting normal cell function or killing cells.