Protists

PART 1:

Importance:

• widespread

  • live everywhere

  • medical uses

• significant part of the food chain

  • pseudoplankton

• make up 40% of global photosynthesis

• mutualistic symbiosis with other organisms

• models of multicellularity

van Leeuwenhoek:

• looked at pond water and saw the “little animals”

Their Diverse Morphologies:

• grouped based on general similarities

  • defined by what they are not:

    • NOT related to plants, animals, or fungi

• last eukaryotic common ancestor (LECA) was a protist

• now classified through DNA:

  • extraction, amplification, and analysis

• plant-like: but do not protect gametes from drought

• fungi-like: lack flagella, but no chitin in cell walls

• animal-like: heterotrophs, but no embryonic development

• make up most of the Eukaryotic tree

• most activity stays within their membranes

• high complexity

• life cycle:

  • asexual reproduction, but may have sexual if the conditions of their environment are not favorable.

  • some have simple, some have complex

Eukaryotic Features:

• nucleus with nuclear envelope

• chromosomes organized by histones

• cytoskeleton: microtubules + microfilaments

• mitochondria

• cilia + flagella (evolved independently from bacteria and archaea)

• mitosis + meiosis

• cell walls (cellulose, chitin)

Qualities of All Protists:

• require water-based environments

• most are obligate aerobes

• most are unicellular

Different Qualities of Protists:

• obtaining nutrition:

  • photosynthesis

  • phagocytosis

  • absorption of nutrients

  • symbiosis

• how they move:

  • pseudopodia

  • cilia

  • flagella

Red Algae (archaeplastida):

• usually multicellular

• light red/ dark green

• mostly marine

  • near shores but can be deeper

• some filamentous, most branched + flat

• economic importance:

  • agar

  • carrageen - emulsifier for food and consmetics

  • sushi

Green Algae (archaeplastida):

• over 7K species

• variety of habitats

• many symbiotic w/ plants, fungi, and animals

  • ex: turtle shells

• usually unicellular

  • many filamentous/ colonial

• some multicellular (look like lettuce)

• plants are thought to be derived from Charophytes (type of green algae)

  • have cell walls with cellulose

  • have chlorophylls a + b

  • stores excess food as starch

Amoebae - Loboseans + Heteroloboseans - (amoebozoa):

• protists that move + ingest food w/ pseudopods

  • phagocytes

  • pseudopods - form when the cytoplasm streams forward in a certain direction

• Entamoeba Histolytica - parasite of human colon

  • causes amoebic dysenterie

  • can be fatal

• Naegleria Fowleri - “brain eating amoeba”

  • causes primary amoebic meningoencephalitis (PAM)

    • amoeba in the brain

  • fatal water-born disease

Slime Moulds (amoebozoa):

• not actually mould

• can be:

  • plasmodial - single multinucleated cells

    • the maze mould that emit chemicals trails to recall where it has gone

    • find best routes for Japanese transit

  • cellular - single cells that can aggregate to form a multicellular organism

    • emit chemical signal when food is low, attracting more moulds to form a cluster

    • preform altruism - selflessness

      • sacrifices for the better of the population, not the individual

PART 2:

Blood is a Hazardous Environment:

• Immune cells - work together to identify and destroy a pathogen.

  • T-cells

  • Macrophages

  • Neutrophils

• Compliment - clearing foreign matter in the immune response.

  • Antibodies

Malaria: “Bad Air”:

• named because they thought it was from the air

• Hippocrates described clinical symptoms in 500 BC

• The bark of the cinchona tree was a successful medicine against malaria, but it is too bitter

  • resulted in the creation of Gin and Tonic

• caused by Plasmodium Parasites

  • two forms

    • Plasmodium DNA in red blood cell

    • Plasmodium Cell in another - dormant sexual malaria cells

      • become active once blood cools

• targets human liver cells, multiplies, then targets red blood cells

4 Species of Plasmodium Cause Disease in Humans:

• Falciparum - affect the brain, main cause of cerebral malaria, majority of deaths globally.

  • 90% cases in Africa, 50% in Southeast Asia

• Vivax - immunity for people with Duffy antigen, can cause severe malaria in 1/5 cases.

  • 90% cases in Asia, South America, 50% cases in Southeast Asia

• Malariae - milder symptoms

  • 2% in Africa, sporadic in Asia + South America

• Ovale - milder symtoms

  • 8% in Africa.

Global Imact:

• kills a child every 2 minutes.

• 300-500 million cases each year, mostly affecting pregnant women and children under the age of 5

• mainly in Africa

• Increase resistance to anti-malaria drugs.

  • antigenic variation

• 2021 - first malaria vaccine successfully created.

• 2023 - second vaccine introduced

• Tu YouYou and Wilhelm Rohl - contributed to defense against malaria.

Malaria is a Vector-Borne Disease:

• insect vector and human host.

• transmitted by female anopheline mosquitoes

• Plasmodium needs to be passed through a mosquito and human in order to complete its lifecycle.

• no animal reservoir

Malaria Life Cycle:

• Sporozoites - in salivary glands of mosquitoes, injected with saliva

invade liver cells within 30-60 minutes.

• Sporozoites are long.

• in hepatocyte divide asexually, leading to schizonts in 6-7 days

• each schizont gives birth to thousands of merozoites released into the blood from ruptured hepatocytes

• Merozoites actively invade RBCs

• Merozoites - a non-motile stage. Invade, divide, repeat.

Pros and Cons of Life in a Red Blood Cell:

• Advantages:

  • Rigid cells, combats physical stressors

  • parasite is hidden from the immune system

• Disadvantages:

  • nutrient-poor environment

  • cells have a relative short life

  • cells that are continuously recycled in the liver/spleen and therefore exposed to the immune system.

• the malaria combat the nutrient-poor environment by putting its own proteins on the outside of the infected RBC to take nutrients from other RBCs

• the infected blood cells stick along the wall of the blood vessel so that it isn’t transported to the liver and removed from the body.

Plasmodium Escapes Immune Destruction Using Antigenic Variation:

• A protein that the parasite places on the RBC surface has 60 different genes producing the same protein

  • key in avoiding destruction

  • antigenic variation:

    • immune system will recognize the foreign protein, create specific antibodies, and kill it, but the variation in protein means that there are slightly different versions of the protein, which then survive because they were not targeted by the antibodies.

Excavate: Diplomonads and Parabasalids:

• Diplomonads - Giardia lamblia

  • most common flagellate in human digestive tract

  • causes severe diarrhea, nausea, cramping

Euglenoids and Kinetoplastids (Excavate):

• Kinetoplastids - related organisms, different diseases.

  • trypanosoma:

    • Brucei - human African trypanosomiasis - “Sleeping Sickness”

    • Cruzi - American form - Chugs Disease

    • Leishmania spp. - transmitted by sandflies, found all over

• The difference between sleeping sickness and malaria: sleeping sickness survives and thrives freely in the bloodstream.

  • makes it most deadly, needing only one pathogen to infect.

• the parasite uses antigenic variation, changing its own appearance to stay alive.

  • changes its surface coat protein on a regular basis (in under two minutes)

    • immune system can’t recognize and keep up

Infections are Characterized by Waves of Parasitaemia:

• all due to antigenic variation

Sleeping Sickness is a Two-Stage Disease Always Lethal if Untreated:

• Stage 1: (where treatment must start in order to survive)

  • parasite replicates in the bloodstream

  • flu-like symtoms

  • fever

  • anorexia

  • joint pain

• Stage 2:

  • parasite crosses blood-brain barrier

  • lethargy

  • disturbance of circadian rhythms

  • weight-loss

  • coma

• depending on the location in Africa, it can take up to 6 months to kill, or 1-5 years.