Lecture 15 - Eukaryotic Microbes (Protozoan parasites)

Define the various kinds of organismal interactions (mutualism, cooperation, commensalism, predation, parasitism, ammensalism, competition). What is parasitism and how does it differ from predation or ammensalism?

Mutualism = relationship that benefits both organisms and is obligatory

• obligatory → both organisms need each other to survive

Cooperation = relationship benefits both, but is not obligatory

Commensalism = one organism is helping the other and gets no benefit in return

Predation = one organism kills another for its benefit

Parasitism = intimate association with another organism

• Parasites benefit at the expense of the host

• a longer-lived relationship than predation

Ammensalism = one organism causes harm to another and does not benefit

• eg. antibiotics

Competition = 2 species competing for the same resources

• relationship where 1 organism wins or both organisms coexist at lower levels of resource

Can organisms switch between relationships?

Yes, relationships are not inherent to the characteristic of the organism

Some relationships are obligatory (required) or facultative (capable, but not restricted to)

What relationships are beneficial?

• Mutualism

• Cooperation

• Commensalism

• Parasitism

Can a parasite be beneficial to the host?

NO! By definition, a parasite will harm the host, not help it

What is an intermediate host vs a definitive host for a parasite? Distinguish between sexual reproduction and asexual reproduction.

Intermediate host = parasite does not undergo sexual reproduction while living in this host

• can only undergo asexual reproduction (just cell division) 

Definitive host = the host in which sexual reproduction occurs

• formation of 2 different gametes that combine and mix to form 1

• the benefit of sexual reproduction is that a lot more diversity is generated

• sometimes, death of the intermediate host may facilitate transmission to the definitive host that ate the intermediate

What is an example of an organism that uses death to jump between intermediate and definitive hosts?

Toxoplasma gondii

• this parasite infects mice (intermediate host)

• cats then eat mice and become the definitive host

Compare and contrast 4 fundamental processes that are conserved in both prokaryotes and eukaryotes

1. Both cell types evolved from LUCA

• central dogma is the same in both, except their mechanisms differ

2. Fundamentals of metabolism still apply

• central pathways are the same

• ATP is needed to carry out important functions

• macromolecules are the same

3. Membrane permeability is still controlled

• channels and transporters are still present

• secretion pathways with signal peptides are still present but different

4. Sensing and signaling mechanisms are different, but still present 

• phosphorylation is still a common signal transduction

• eukaryotes don’t have simple 2-component systems

  • their secretion systems are much more complex, with multiple components

• still regulate protein amount and activity

Compare and contrast 4 fundamental qualities that are unique to eukaryotes (not found in any prokaryotes)

1. Eukaryotes have a nucleus and organelles

2. Transcription and translation are not coupled 

• transcription occurs in the nucleus

• translation occurs in the cytoplasm at the rough ER

  • RNA cannot have a short half-life

  • there are 5’ and 3’ modifications to provide mRNA stability

3. Cytoskeleton inside eukaryotes

• provides stability and structure to the cell

• made up of actin, microtubules, or another flexible protein

  • can be remodeled constantly due to being in the interior of the cell, as it has better access to enzymes and machinery

  • can be broken down when needed

4. Sexual reproduction - all eukaryotes are diploid

• can have haploid stages in complex life cycles

• parasite in intermediate host = asexual (haploid)

Explain, from an evolutionary and geological time perspective, why there are qualities that are unique to protists, and why protists are so diverse as a group.

• Protists evolved long before the modern eukaryotes

• Because of their “early” evolution, they have had time to evolve into many different groups, one of which is the protozoa

What distinguishes apicomplexans? Define apical complex, rhoptry, and microneme. Are these secretion organelles similar to bacterial secretion systems? Do you think they evolved from a single secretion system? Why or why not.

Apicomplexons are named such due to the presence of the apical complex, which is used to deliver things into a cell and for invasion of the host cell

• The apical complex is formed really specifically at one end of the cell

• most notable components are micronemes and rhoptries → secretory organelles secrete things needed to take over the host cell

Functionally, the secretory organelles are similar to bacterial secretion systems type 3 and 4 because they inject proteins directly into the host cell cytoplasm, but mechanistically…

NO! The apical complex is very different and much more complex compared to a bacterial secretion system

• Apical complex is a large multi-organellar complex that involves the coordinated, regulated exocytosis (release of vesicle contents) of multiple organelles into the extracellular environment or host cell membrane.

• Bacterial secretion systems actively pump or inject specific proteins through a channel in a one-step or two-step process, one at a time

Protozoan parasites often have complex life cycles and have different morphologies depending on its life cycle stage. Give an example of a parasite that changes shape depending on its life cycle.

1. What do you think this means regarding cell biology (where fundamental processes take place)?

2. Would you expect all the organelles will be present in all stages, or that they disappear in some stages?

Plasmodium is a protozoan that changes morphology depending on its life cycle stage

Intermediate host = humans

Definitive host = mosquito

• infected mosquito bites a host and releases sporozoites

• sporozites target the liver and turn into merozites

• Merzouites released from the liver infect RBCs

• the parasite then undergoes asexual reproduction and multiple morphologies in the RBC cycle and bursts out of RBCs

  • the RBC cycle causes all the symptoms to form

• mosquito then gets infected with human blood

• sexual reproduction occurs in the mosquito gut, and the cycle continues

Asexual reproduction in the intermediate host is usually what causes the disease to manifest

1. This means, as a parasite goes through different life cycles, different cues and signals are expressed, which affect the genes that are being made which dictate what the cell does (its shape and function)

   1. Fundamental processes like metabolism, motility, secretion, and replication are regulated differently across morphologies.

2. It is unlikely that all organelles are present for every stage, as it depends on the cues being expressed and the function of each life stage, meaning some aren’t needed for certain processes

What is the defining feature of the kinetoplastids? What is contained in the kinetoplast?

*we did not discuss the function of the kinetoplast, you do not need to know this, only what it contains.

Kinetoplastids are defined by the prescence of kinetoplasts = extended large network of DNA inside a large/expanded mitochondria (kDNA)

• contain multiple copies of the mitochondrial genome

• have circular DNA in varying sizes - maxicircles and minicircles

Name two apicomplexan parasites and two kinetoplastid parasites. (genus species)

Ampicomplexan:

• plasmodium = malaria

• toxoplasm gondii = toxoplasmosis (sexual reproduction in cats)

Kinetoplastids:

• trypanosomes = have a flagella that spans the length of the cell

• leishmania = infects skin wounds

Compare and contrast prokaryotic and eukaryotic flagella. How do their structures and function differ?

Prokaryotic flagella:

• use flagellin protein

• proton motive force as energy source

• move in a clockwise motion

• no membrane → external apendage

• use a 2 component system to change direction 

Eukaryotic flagella:

• structure is more similar to cillia and more complex

• consists of microtubule filaments with motor proteins and actin, and uses motor proteins for flagella movement (side-to-side)

• uses ATP hydrolysis as energy source

• moves in waves rather than rotation

• membrane-bound extension of the cell

• can also do gliding through focal adhesions → more directed because can control where focal adhesions go

What determines the shape of eukaryotes and bacteria?

Eukaryotes = cytoskeleton

• not fixed, can be broken and remodeled if needed

Bacteria = cell wall

• shape is inherent to the cell and will not change