Viruses and Protists

Objectives

• Describe the structure of viruses
• Describe how viruses are classified
• Describe the protist kingdom
• Describe animal-like protists

A virus particle consists of DNA or RNA enclosed by a protective protein coat called a capsid.

Types of Virus Structures

• Helical capsids
• Icosahedral capsids
• Complex - may have protein tail or outer wall

Some viruses have an envelope of phospholipids and proteins from the host cell to protect the virus. The envelope may have receptors on it to bind to host cells.

Enveloped viruses

• Better protection from host cell
• More susceptible to environmental agents

Enveloped virus examples

• Influenza
• HIV
• Varicella zoster

The shape of the capsid is used to classify viruses.

Bases of classification

• Capsid shape
• Type of nucleic acid
• Process of replication
• Host organism
• Type of disease caused

Protist Kingdom

Protists include all eukaryotes that are not animals, plants, or fungi.

Protists

• May be unicellular or multicellular
• If multicellular, no specialized tissue
• Term protista first used by Ernst Haeckel

Protist examples

• Giardia lamblia
• Amoeba
• Algae
• Malaria

Originally grouped as:

• Protozoa (animal-like)
• Protophyta (plant-like, mostly algae)
• Slime molds and water molds (fungus-like)
• Now classified based on phylogenetics
• Older terms still used informally

Protist Habitats

• Mostly aquatic
• Need moist environment to survive
• Some are free-living; others are in symbiotic relationships

Protist Motility

• Flagella
• Cilia
• Pseudopod

Protist Reproduction

• Many have sexual and asexual reproduction

Protist Nutrition

• Ingest using a vacuole
• Absorb via diffusion
• Make own organic molecules via photosynthesis

Protozoa

Protozoa are heterotrophs and capable of moving. They are thought to be ancestors of animals

Protozoa Ecology

• Some consume bacteria
• Some consume algae
• Some consume dead organic matter
• Some are parasites
• Many are food sources for insects + worms

Classification based on movement. Only sporozoa cannot move.

Molds

Molds

• Absorbtive feeders on decaying organic matter
• Reproduce with spores
• Cell walls made of cellulose (not chitin like fungi)
• Motile

Slime-molds

• Commonly on rotting logs and compost
• Move slowly in search of decaying matter
• Cells swarm together when food scarce
• Swarm forms blob-like mass that moves
• Two types of swarming

When an acellular slime molds swarm, they fuse together to form one cell with many nuclei.

When cellular slime molds swarm, they remain as distinct cells.

Water Molds

• Common in moist soil and surface water
• Many destroy crops
• Some are fish parasites