Eukaryotes and Viruses

Chapters 12 and 13

Fungi

Heterotrophic, Mainly Opportunistic Pathogens

Distinguishing Characteristics of

Fungi

• Chemoheterotrophic

• Cells walls composed of Chitin

• Diverse Metabolic Capabilities for Complex

Carbohydrates

• Xerophilic

• Aerobic/Facultative Anaerobes

• Prefer Low pH

Vegetative Growth

• Filamentous Fungi

• Yeasts

• Dimorphic Fungi

Filamentous Fungi

• Hyphae (individual

strands)

– Septate

– Coenocytic

• Mycelium (mass of

hyphae)

• Aerial Hyphae

• Mass of Conidia

Yeast

• Bud

• Bud Scar

• Pseudohyphae

Dimorphic Fungi

• Medically very

important

• Hyphae in the

Environment, Yeast

in the host

• Temperature and

CO2 are common

triggers

Fungal Lifecycle

• Haplodiplontic Lifecycles

• Asexual Cycle

• Sexual Cycle

Haplodiplontic Life Cycle

Gametophyte (n)

Sporophyte (2n)

Egg

Sperm

Zygote

Embryo

Sporangia

Sporocyte

Spores

Haploid

Diploid

Asexual Spores

• Genetically Identical to the parent

• Genetically Haploid

• Several Types

– Conidia

– Blastoconidia

– Arthroconidia

– Chlamydoconidia

– Sporangiospores

Sexual Spores

• Haploid Spores Arising

from a Diploid Cell

• Genetic Recombination

of compatible mating

types

• Fungi are classified on

the basis of their sexual

cycles.

Medically Important Phyla

• Zygomycota

• Ascomycota

• Basidiomycota

• Deuteromycota (Asexual Fungi)

Zygomycota

• Coenocytic Hyphae

• Not a phylogentically

distinct group.

• Sporoangiospores and

Zygospores

• Rhizopus is a common

genus.

Ascomycota

• Septate Hyphae and Yeasts

• Largest group of classified fungi

• Most Deuteromycota are classified in this group by Genetics

• Ascospores (in an ascus) and Conidia

Basidiomycota

• Septate Hyphae

• Basidiospores

produced on Basidium,

some produce conidia

(though this is crude

terminology)

Deuteromycota

• Depreciated, though still used Taxon

• Holding Phyla with no observed sexual state

• Most have been reclassified as Ascomycota

based on Genetics

• Leads to confusion over nomenclature

– Telomorph : Sexual State (preferred name)

– Anamorph : Asexual State (common name)

Fungal Disease

• Mycoses are not common but difficult to

treat.

• Mycoses are defined by the depth of tissue

affected.

• Most fungi are either superficial or

opportunistic pathogens… though overt

pathogens exist.

Examples of Fungal Disease

Protozoa

Diverse Unicellular Eukarya Pathogens

Protozoans

• Phylogenetically, a diverse and ill-defined

group.

• Medically we are worried about the

heterotrophs, not the photosynthetic phyla

• Complex lifecycles with unique stages

– Trophozoite

– Schizogony

– Cyst

Protists Are NOT Monophyletic

Archaezoa

• Lack Mitochondria,

but possess relics

called mitosomes.

• Move by means of

Flagella

• Possess two nuclei.

Giardia intestinalis

Microspora

• No mitochondria

• No microtubules

• Obligate intra-

cellular pathogens

• Common in AIDS

Amoebozoa

• Phylogenetically

these organisms are

not linked to a

definite clade.

• Movement through

pseudopods

Apicomplexa

• Named for the

Apical complex, an

organelle used for

cell penetration.

• Complex Lifecycles

with both a

definitive and

intermediate host

Plasmodium species

Eugelnozoa

• Hemoflagellates, more appropriately called

Kinetoplastids, are the pathogenic

members.

• Possess unique single mitochondrion called

kinetoplasts.

• Many are Parasitic

Helminths

The Worms

Characteristics of Pathogens

• They may lack a digestive system

• They have a reduced nervous system

• Lacking or atrophied movement systems

• Complex reproductive systems

• May be dioecious or monoecious

Platyhelminthes

• Flatworms, so called for overall flat body

plan.

• Actually the Subphylum Neodermata

• All have a Neodermis (also called a cuticle)

to protect them from the host and lack

adaptations such as eyepores (found in

free-living flatworms)

Trematodes

• Flukes

• Ventral and Oral

Sucker to attach to

host tissue.

• Life Cycles involve

more than a single

host and mutiple

developmental stages

Schistosoma Life Cycle

Cestodes

• Tapeworms

• Three body sections,

scolex, neck and

proglottids

• No digestive system

• Mature proglottids

are released through

feces of host.

Phylum Nematoda

• Roundworms, due to the circular body

cross-section.

• Not to be confused with Phylum Annileda,

the segmented worms (i.e. Earthworms)

• Complete digestive systems

• Sexually dimorphic

• Numerous through out the environment

Comparative Anatomy

Nematoda Diseases

Viral Characteristics and Structure

Why Viruses aren’t Alive

General Characteristics of Viruses

• Name derives from the Latin for “poison”

• Obligatory intracellular parasites

• Referred to as filterable

• Contain a single type of nucleic material

• The nucleic material is covered in a protein

coat.

• Use the synthesis machinery of the host to

multiply.

Why are they not Alive?

• No independent metabolism or

reproduction

• No single phylogenetic origin

• No cellular structure

• No ribosomes

• Though they DO evolve and reproduce.

Host Range

• Viruses have a specific subset of cell types

they will infect, referred to as Host Range.

• Most viruses can only infect a single species

• Some viruses can cross species barriers

• Numerous factors influence host range

• Viruses that infect bacteria are referred to

as bacteriophage or simply phage.

Viral Particle Size

Staphylococcus Bacteria 1 μm in diameter

Poxviridae

Lentiviruses

Picornaviridae

Bacteriophage

Viral Structure

• A Virion is a complete, infectious viral

particle and is composed of…

– Nucleic Acid

– Capsid and Envelope

Nucleic Acid

• Only a single type of nucleic acid (RNA or

DNA) is present in any species of virus.

• Unlike cellular life, viral nucleic acid can be

either single or double-stranded (again only

a single type per species)

• Size of the genetic structure can range from

a few thousand base pairs to a quarter of a

million

Capsid and Envelope

• Capsids are regular repeating protein

structures composed of capsomeres.

• Some viral species also have a host-derived

envelope surrounding the capsid

• Some viral species have protein/

carbohydrate “spikes” rising from the

surface that can be used for identification

Viral Morphology

Viral Taxonomy

How do you do a taxonomy of something that isn’t alive?

Viral Taxonomy

• Without a shared phylogeny there is no use for the higher taxons (Domain, Kingdom, Phylum, and Class)

• Typically viral species are referred to by Order, Family, Genus and a descriptive common name (in place of a species epithet)

• Based on – Nucleic Acid type

– Strategy of replication

– Morphology

– Host range

Viral Replication

No, not 1 becomes 2, more like 1 becomes 1000.

Growing Bacteriophage

Growing Animal Viruses

Viral Identification

• Polyphasic Identification

– Morphology

– Detection of Antibodies

– Western Blotting of known viral proteins

– Nucleic Methodologies

• PCR

• RFLP

• RNA PCR

Lytic Bacteriophage Cycle

Attachment

Penetration

Biosynthesis Maturation

Release

Lysogenic Bacteriophage Cycle

Lytic Cycle

Animal Unenveloped DNA Viral

Replication

DNA vs. RNA Viral Replication

• There are various types of RNA viruses.

• Replication of the Genetic Material can be simple or a multistep process. – +RNA, direct translation and replication by viral

protein

– -RNA, indirect translation and replication by viral protein

– dsRNA, direct translation and relication by viral protein

– Retroviruses, conversion of RNA to DNA, integration and then production by host.

Comparison

Bacteriophage

• Attachment to Cell Wall

proteins.

• Viral DNA is injected into

cell

• No removal of capsid

required

• Biosynthesis in cytoplasm

• Lysogeny

• Host cell lysed for release

Animal

• Attachment to plasma

membrane proteins and

glycoproteins.

• Capsid enters cells

• Capsid removed by enzymes

• Biosynthesis in nucleus or

cytoplasm

• Latency

• Enveloped viruses bud and

nonenveloped rupture.

Viruses and Cancer

One of many factors

Oncogenic Viruses

• Some viruses and known to help trigger cancers, called oncogenic viruses.

• These viruses affect oncogenes, natural parts of our genetic structure that can cause cancer.

• The process of becoming cancerous is termed transformation.

• Oncogenic Viruses integrate into the host genetic material.

Known Oncogenic Viruses

Type of Virus Viral Species Associated Cancer

DNA Human Papillomavirus Cervical Cancer

Epstein-Barr Virus Burkitt’s Lymphoma

Hepatitis B Virus Liver Cancer

Kaposi Sarcoma-Associated Hepervirus

Kaposi Sarcoma

Merkel Cell Polyomavirus Merkel Cell Carcinoma

RNA Human T-Lymphotropic Virus 1 Leukemia

Hepatitis C Virus Liver Cancer

Latency, Persistence and the

Prions

Acute, Latent, and Persistent Viral

Infections

• Acute Infections are those that cause

immediate proliferation.

• Latent infections can occur by itself or after

an acute infection, where the viral load

remains undetected for a long period of

time before reemerging quickly.

• Persistent Infections are ones where the

viral load build over a long period of time.

Graph of Acute, Latent and

Persistent Viral Infections

Prions

• Prions are infectious protein particles

• Prions are altered forms of a normal protein in the host that can catalyze the alteration of other “normal” protein particles to the “prion” state

• They cause neurological degradation and death with no known treatment.

• Since each prion protein is infectious, they are extremely resistant to control measures.

Prion Reaction

PrPC + PrPSc 2 PrPSc