Overview of Viruses, Bacteria, Archaea, and Fungi

Virus structure

A virus consists of a nucleic acid core (DNA or RNA) surrounded by a protein coat called a capsid, and sometimes an envelope.

Size of viruses

Viruses range in size from 20 to 300 nm.

Viral capsids

Viral capsids determine the shape of viruses and may be helical, polyhedral, or a combination of both.

Complex/combination viruses

Viruses that have capsids with both polyhedral and helical characteristics.

Bacteriophages

Examples of complex viruses with a polyhedral 'head' and a helical 'tail.'

Enveloped viruses

Viruses surrounded by an outer envelope of plasma membrane derived from the host cell.

Example of an enveloped virus

HIV is an example of an enveloped virus.

Lytic cycle

A viral reproductive cycle where the virus forces the host cell to replicate viral particles and then lyses (destroys) the host cell to release new viruses.

Stages of the lytic cycle

Includes attachment, penetration, biosynthesis, maturation, and release.

Lysogenic cycle

A viral reproductive cycle where the viral genome becomes integrated into the host DNA and is replicated along with bacterial DNA without immediately destroying the host.

Temperate viruses

Viruses that do not always destroy their hosts and can undergo a lysogenic cycle.

External conditions affecting temperate viruses

External conditions like UV or X-rays can cause them to revert to a lytic cycle.

Retroviruses

RNA viruses that have an enzyme called reverse transcriptase, which transcribes the viral RNA genome into DNA.

Example of a retrovirus

HIV is an example of a retrovirus.

Human diseases caused by DNA viruses

Smallpox, herpes, warts, chickenpox.

Human diseases caused by RNA viruses

Influenza, polio, measles, mumps, rubella, rabies, COVID-19.

Human diseases caused by retroviruses

AIDS (caused by HIV).

Prokaryotic cell structure

Prokaryotic cells lack a nucleus and membrane-bound organelles.

Components of prokaryotic cells

They have a cell wall, cell membrane, ribosomes, and genetic material in a nucleoid region.

Common shapes of bacteria

Bacilli: rod-shaped, Cocci: spherical, Spirochete: spiral-shaped.

Gram-positive cell walls

Have a thick peptidoglycan layer and stain purple with Gram stain. Lack an outer membrane.

Gram-negative cell walls

Have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides (LPS). Stain pink with Gram stain.

Transformation

A genetic recombination mechanism where bacteria take up DNA from their environment and incorporate it into their genome.

Conjugation

A genetic recombination mechanism where bacteria transfer DNA directly between cells through a pilus connecting two bacteria.

Transduction

A genetic recombination mechanism where bacterial DNA is transferred from one bacterium to another by a virus (bacteriophage).

Autotrophs

Synthesize their own food using light (photoautotrophs) or chemicals (chemoautotrophs).

Heterotrophs

Obtain energy from organic compounds.

Saprotrophs

Decompose dead organic matter.

Parasites

Live off other organisms.

Antibiotic resistance

The ability of bacteria to withstand antibiotics, often through mutation or acquisition of resistance genes.

Contributing factors to antibiotic resistance

Include overuse of antibiotics and improper medical treatments.

Crenarchaeota

Mostly extremophiles that live in very hot or acidic environments, like hot springs and hydrothermal vents.

Euryarchaeota

Includes methanogens (produce methane), halophiles (live in high salt concentrations), and thermophiles (live in high temperatures).

Monophyletic group

A group of organisms that includes the most recent common ancestor and all its descendants.

Paraphyletic group

A group of organisms that includes the most recent common ancestor but not all of its descendants.

Coenocytic

A multinucleate cell or hypha that lacks septa (cross walls), allowing cytoplasm and nuclei to flow freely.

Pseudopodia

Temporary projections of the cell membrane used by some protists for movement and feeding.

Flagellum

A long, whip-like structure used for movement by some cells and organisms.

Cilia

Short, hair-like structures found on the surface of some cells, used for movement or to move substances across the cell surface.

Gametangia

Structures or organs that produce gametes in fungi, algae, and plants.

Hyphae

Filamentous structures that make up the body of a fungus.

Mycelium

The network of hyphae that forms the body (thallus) of a fungus.

Plasmogamy

The fusion of the cytoplasm of two cells without the immediate fusion of nuclei, a step in fungal sexual reproduction.

Karyogamy

The fusion of nuclei, typically following plasmogamy in fungal sexual reproduction.

Unikonta

Includes animals, fungi, and some amoebas.

Archaeplastida

Includes land plants, green algae, and red algae.

Excavata

Includes various flagellated protists.

SAR

Includes brown algae, golden algae, diatoms, ciliates, and foraminiferans.

Ascomycota

Fungi characterized by the production of ascospores, which are produced in a microscopic sac called an ascus.

Basidiomycota

Fungi characterized by the production of basidiospores on club-shaped structures called basidia.

Chytridiomycota

The only fungi with flagellate cells, most are decomposers.

Zygomycota

Fungi that produce zygospores.

Dikaryotic hyphae

Hyphae that contain two genetically distinct nuclei within each cell (n + n).

Lichens

A mutualistic relationship between a fungus (usually an ascomycete) and a photoautotroph (green alga, cyanobacterium, or both).