Honors Biology

Halophiles

Archaea that thrive in extremely high-salt environments containing $12\text{--}15\%$ salt.

Thermoacidophiles

Archaea adapted to survive in environments that are both extremely hot and acidic, such as hot aquatic springs.

Methanogens

Obligate anaerobic Archaea that consume carbon dioxide and hydrogen to generate energy, releasing methane gas as a byproduct.

Structural traits distinguishing Archaea from Bacteria

Archaea feature cell walls lacking peptidoglycan (composed instead of polysaccharides or proteins) and plasma membranes containing a lipid monolayer with branched hydrocarbon chains.

Gram-positive bacteria

Bacteria with a thick outer layer of peptidoglycan in their cell wall that retains crystal violet dye, staining purple during Gram staining.

Gram-negative bacteria

Bacteria with a thin peptidoglycan layer surrounded by an outer lipopolysaccharide membrane that stains pink or red with safranin counterstain.

Chemoheterotroph vs. Photoheterotroph

Chemoheterotrophs obtain both energy and carbon from organic compounds, whereas photoheterotrophs capture energy from sunlight but must obtain carbon from organic compounds.

Chemoautotroph vs. Photoautotroph

Chemoautotrophs synthesize organic compounds using chemical energy from inorganic reactions, while photoautotrophs utilize solar energy and carbon dioxide via photosynthesis.

Obligate aerobes vs. Obligate anaerobes

Obligate aerobes strictly require oxygen for survival and cellular respiration, whereas obligate anaerobes are poisoned by oxygen and thrive only in anaerobic environments.

Facultative anaerobes

Bacteria capable of growing with or without oxygen, though they metabolize more efficiently and grow better when oxygen is present.

Binary fission

An asexual reproductive process in bacteria where a single parent cell replicates its DNA and divides into two genetically identical daughter cells.

Conjugation (bacteria)

The direct horizontal transfer of genetic material between two bacterial cells joined by an elongated protein tube called a pilus.

Bacterial endospore formation

The production of a dehydrated, thick-walled, dormant structure by a bacterium to withstand extreme environmental stress such as desiccation or heat.

Dimitri Ivanowski's viral discovery

Discovered that the causative agent of tobacco mosaic disease passed through porcelain filters fine enough to trap all known bacteria, demonstrating the existence of submicroscopic pathogens.

Molecular basis of influenza subtypes (e.g., H1N1, H5N1)

Variations in the specific types of surface glycoprotein spikes: hemagglutinin (H) and neuraminidase (N).

Five steps of the lytic viral reproduction cycle

1. Attachment to host receptors; 2. Penetration of viral genome into the cell; 3. Biosynthesis of viral proteins and nucleic acids; 4. Maturation and assembly of virions; 5. Release via cell lysis or budding.

Lysogenic cycle

A viral life cycle in which viral DNA integrates directly into the host bacterial chromosome as a prophage, replicating passively alongside host division until induction into the lytic cycle.

Retrovirus mechanism of action

RNA viruses that carry the enzyme reverse transcriptase to transcribe their single-stranded RNA genome into complementary DNA before host cellular transcription can take place.

Viroids

Small, infectious, circular naked RNA molecules that lack a protein capsid and primarily cause disease in plant species.

Prions

Infectious, misfolded protein particles that cause fatal neurodegenerative diseases in animals by inducing normal native cellular proteins to adopt the misfolded conformation.