Eukaryotic microorganisms II - Protozoa – 'odds and ends'? Flashcards
the three domains of life?
bacteria
archaea
eukaryota
Protozoa is an informal name used to describe
a polyphyletic group of single-celled eukaryotic organisms (protists) that feed mostly by heterotrophy.
Polyphyletic - (of a group of organisms) derived from
more than one common evolutionary ancestor or ancestral group and therefore not suitable for placing in the same taxon.
The protozoa are a disparate group connected only by
their relatively simple structure – little else in common
Remember organisms evolved in a marine environment where the concentration of ions (Na+, Ca2+, Cl-, etc) is
high
the concentration of solutes in the cytoplasm of cells reflects this somewhat
To counterbalance the different concentration (restore equilibrium) water will…
flow from the environment into the cell across a semi-permeable membrane by osmosis
To maintain a constant ionic concentration the cell must
get rid of excess water - homeostasis
As long as the contractile vacuole has higher osmolarity (higher concentration of ions) then
water will flow into it and out of the cytoplasm
Ions are actively transported across the membrane in …
an energy using process via cation pumps – the vacuole fills with water (diastole) which crosses via osmosis
once filled the vacuole empties (systole)
Food is moved into the cystostome via the movement of
cilia
membrane is pinched off to form a
phagosome (food vacuole)
- lysosomes fuse with
the phagosome releasing their contents -
nucleases, lipases, proteases
glycosidases, phospolipases
Macromolecules are broken down into
absorbable smaller molecules – fatty acids, amino acids, glucose etc
Protozoa may reproduce
sexually or asexually, the frequency of each depends on the organism. e.g. ciliate organisms such as
which protozoa can reproduce sexually?
Tetrahymena and Paramecium can reproduce sexually.
both sexual and asexual reproduction have
adbantages
Sexual reproduction involving meiosis is good for
creating a diverse gene pool that can withstand a dynamic and changing environment.
Asexual reproduction by mitosis is beneficial in
creating a large, uniform population
what are the two dispersal strategies?
dispersal in space
dispersal in time
dispersl in space description
When times are good…
Reproduce quickly.
Asexual reproduction.
dispersal in time description
When times are hard…
Encystment - wait it out.
Sexual reproduction - produce diverse offspring to weather the uncertain future.
how do ciliates reproduce?
asexually by binary fission
However binary fission in the ciliates is more complex than
simple fission
- binary fission in ciliates is
transverse
The macronucleus divides
amitotically
The macronucleus divides amitotically (at least there is no evidence for mitosis) whilst the micronucleus divides
mitotically as it is the repository of genetic information passed onto the next generation asexually or sexually
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In amoeba the cytoplasm is divided into
internal endoplasm and a thicker ectoplasm allowing the cell to retain shape and is important in movement
where is the contractile vacuole located and what is its function?
The contractile vacuole is at the rear of the cell and is used in osmoregulation.
how do amoeba move?
Moves by cytoplasmic streaming and engulfs food items by phagocytosis.
reproduction in amoeba (multiple fission) process?
amoeba pulls in its pseudopodia
amoraba secretes a cyst wall
mitotic division of amoebic cells.
reproduction in amoeba (binary fission) process?
amoeba retracts its pseudopodia and the nucleus divides by mitosis
daughter nuclei separate and cytoplasm constricts
two daughter amoeba cells
Amoeba mitosis takes around
30 minutes on average.
The existing contractile vacuole is inherited by
one daughter cell, the other daughter cell makes a new contractile vacuole
Morphological changes accompany
mitosis with multiple pseudopodia surrounding the spherical cell
Entamoeba has a relatively simple life cycle alternating between
a trophozoite and a cyst (to survive unfavourable environments)
Trophozoites reproduce by
by binary fission and are able to penetrate the intestinal mucosa.
Cysts are evacuated in
faeces and are transmitted by ingestion of unclean water/food.
Dictyostelium is a member of the
‘slime moulds’
Dictyostelium cycles between
a unicellular ‘amoeba-like’ phase and a multicellular phase whereby spores are generated to colonise new habitat with more food
multicellularity here is a
survival strategy (compare with Chlamydomonas and volvox)
in Dictyostelium, over a 24h period the colony develops into a
fruiting body which bursts releasing spores into the environment
research suggests that when bacteria numbers are depleted (i.e. food sources are running low)…..
rather than eating every last one – cells of Dictyostelium take up bacteria and maintain them until after spores are released – farming!
following starvation cells begin to produce
cyclic AMP (cAMP) which is perceived as a signal to migrate to its source
cAMP is radiated from
aggregating colonies in a spiral wave
single cells organise into
streams following the spiral waves of cAMP (C) and (D)
the perception of cAMP is by
cAR1
perception of cAMP by cAR1 results in
increase in cytosolic Ca2+ levels and extension of pseudopodia in the direction of the cAMP gradient
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In order to form a complex structure
cell differentiation is required
Different cells within the developing organism
turn on different genes and secrete different extracellular proteins.
Cell determination is defined by
position and by cues from surrounding cells
Human African trypanosomiasis (HAT) is caused by
protozoan parasites transmitted by infected tsetse flies.
where is Human African trypanosomiasis (HAT) endemic?
in sub-Saharan Africa.
Without treatment, HAT is generally
fatal.
Most exposed people to Human African trypanosomiasis (HAT) live…
in rural areas and depend on agriculture, fishing, animal husbandry or hunting.
How many forms does HAT have
2 forms
HAT takes 2 forms, depending on …
the subspecies of the infecting parasite: Trypanosoma brucei gambiense (92% of reported cases) and Trypanosoma brucei rhodesiense (8%).
Sustained control efforts have reduced the number of new cases of HAT by…
97% in the last 20 years.
Diagnosis and treatment of HAT are
complex and require specific skills.
A kinetoplastid protozoan – Trypanosoma brucei - is the
cause of sleeping sickness.
how is Trypanosoma spread?
Spread by tsetse flies (intermediate host).
describe the life cycle of trypanosoma?
Complex life cycle involving two hosts, this protozoan itself exhibits developmental stages which optimise its ability to live in different host environments
Apicomplexans are a group of
protozoans that are more closely related to Dinoflagellate algae
apicomplexans are a complex…
single cell with an apicoplast which is a degenerate chloroplast now unable to photosynthesise but is essential for infectivity
The rhoptries and micronemes are important in
secreting proteins during intracellular invasion
Apicomplexans are exclusively…
parasites of animals
Apicomplexans are
ex-algae
Malaria is a huge killer (~ 560,000 deaths per year (WHO)) but is confined mainly to
the tropics – related to the population of vectors (Anopheles mosquitoes)
how many malaria deaths per year?
560,000 deaths per year
Presence of malaria in an area is associated with
high incidences of sickle cell anaemia and β-thalassaemia
A female Anopheles mosquito takes
a blood meal from an infected human
who is resistant to maaaria ?
Presence of malaria in an area is associated with high incidences of sickle cell anaemia and β-thalassaemia
Some of the red blood cells ingested will contain
male and female gametocytes
A female Anopheles mosquito takes a blood meal from an infected human
Some of the red blood cells ingested will contain male and female gametocytes
what happens to the red cells?
The red cells burst and these develop into mature flagellated microgametes (male) and macrogametes (female)
The gametes fuse in
the mosquito’s gut forming a motile ookinete which penetrates the gut wall
During sporogyny the oocysts
produce multiple haploid sporozoites which emerge, migrate to the salivary gland and are injected into the next human that the mosquito bites
Development in the mosquito is characterised by
changes in gene expression during different parts of the life cycle
The key to infectivity of the salivary glands is
a surface protein secreted by the micronemes called TRAP – this interacts with a salivary gland receptor called saglin in a species specific manner
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