Key stuff - Protists and Amoebae Flashcards
What are protists
eukaryotes
majority are single celled
Cytoskeleton
for trafficking organelles
allow movement of organelles to correct ares, specific areas.
(tubular, actin, throughout cytoplasm)
Photoautotrophic protists
contain plastids (green, red or golden)
green plastid = chloroplast
photosynthesis
Termed ‘Algae’ (some have a cell wall)
Heterotrophic protists
feed on bacteria, fungi and other protists
termed ‘Protozoa’ (‘first animals’) (none have a cell wall)
Bacteria is ‘favourite’ prey.
Mixotrophic bacteria
Feed on bacteria, fungi and other protists and photosynthesise (none have a cell wall)
Direct microscopic count.
easy and fast
Uses special microscope counting slide
-does not differentiate between live and dead bacteria
motile protists have to be killed as easier to count.
Same population growth curve. as bacteria:
Lag phase- Time interval between inoculation and maximal division rate: cells adjust to new environment.
Log phase- constant doubling time, growth rate is maximal
stationary phase- can no longer reproduce but are still alive (e.g no food left)
death (decline) phase- death or cyst formation.
Cysts
Produced under unfavourable conditions
highly resistant to heat, drying and radiation.
very low water content
can survive for 20 years I the environment
good resistance to antibiotics/disinfectants
effective dispersal mechanism (can be transmitted to others via faeces)
Cell walls of protists
Always present in:
non-motile photosynthetic protists
cysts (even if protist that produced them does not have a cell wall)
Not present in:
motile photosynthetic protists
heterotrophic protists
mixotrophic protists
Temperature cut off
60
Oxygen and protist growth
Obligate aerobes
Obligate anaerobes
‘jury’ is out to whether we have microaerophillic eukaryotes (current investigation)
Respiration
Aerobic - mitochondria
anaerobic- hydrogenosomes
(pyruvate to H2, acetate, co2)
What became a mitochondrion after endosymbiosis?
alpha-proteobacterium
hydrogenosome evolved from mitochondria
What became chloroplasts after endosymbiosis
cyanobacterium
Food vacuole (phagosome) dynamics in protists
only certain part of membrane used for feeding.
bacterium to receptors, then phagocytosis stuff, membrane recycling
soluble and insoluble debris released by exocytosis.
if food escapes, it will take membrane of phagosome. will have 2 membranes.
Organellar mixotrophy
-eats algal cells
-does not digest plastids (kleptoplastids)
-plastids fix co2
-plastids do not encode for polymerases
-die and need replenishing (so eats more)
-protist can live without the plastids
-ciliates and amoebae
cellular mixotrophy
-eats algal cells
-no digestion oof algae
-algae fix co2
-algae divide in cell
-protist can live without the algae
constitutive mixotrophs
over time and through complicated genetic transfer events
endosymbiotic algae become true organelles
only seen in flagellates
Ciliates
covered in cilia
most developed protozoan
cytosine (mouth)
cytoproct (anus)
Two types of nucleus:
-macronucleus
-micronuclei
Cilia
Microtuble-based hair-like organelles
used for movement
-go back and forward
-some fuse to form ‘cirri’
very important for feeding
-direct prey towards the mouth are (‘cytostome’
-cytostome contains stiffer cilia (‘membranelles’)
-sieve- correct sized prey enter food vacuoles
-‘filter feeding’
Motile cilia
9+2, dyne motor protein
ciliates
humans (bronchial and oviduct epithelium)
non-motile cilium
9+0, no dyne motor protein
‘primary cilium’ on all human cells.
prey drawn towards cell
vortex at cell mouth
very large feeding currents
‘Mexican wave’ by cilia on top forms vortex of water which draws prey towards oral area. Scared and easily contracts on impact.
vorticella
Suctarian ciliates
numerous microtubule tentacles
each tentacle ends with a cytostome
extrusomes - secrete toxins
dissolve prey contents and suck out.
‘raptorial feeding’
mixotrophic ciliates
do not acquire their own plastids
acquire photoautotrophic ability two ways
organelle mixotrophy and cellular mixotrophy.
Macronuclues
Controls the cell.
Micronucleus
only used for sexual reproduction
Ciliate reproduction
Asexual reproduction:
-transverse ‘binary fission’
-involves mitosis
Sexual reproduction
-conjugation
-involves meiosis and mitosis
-micronuclei swap
-allows for genetic variation.
Flagellates
possesses flagellum/flagella (9+2)
-not backwards and forwards
-in humans- sperm
possesses macronucleus only
-longitudinal ‘binary fission’
mainly aerobic
feed by heterotrophy, photoautotrophy and mixotrophy.
Heterotrophic flagellates
also called ‘zoo flagellates’
most are aerobic
consume pre-formed organic carbon
prey digestion
-organic carbon to inorganic carbon (mineralisation)
use flagella for movement and catching prey
-raptorial feeding
-filter feeding
Naked flagellum
forward swimming
Hipsid flagellum
backwards swimming
Raptorial feeding (with hips flagellum)
create feeding currents due to flagellar movement
prey is drawn towards the base of the flagellum
ingested via cytoplasmic extension (pseudopodia)
more efficient , base of flagella only place of ingestion.
Raptorial feeding (with naked flagellum)
create feeding currents due to flagellar movement
less contact with the base of the flagellum
less efficient capture of prey
Increasing prey capture (with a naked flagellum)
extensions to cell.
catches prey at base of flagellum
covered in scales(drawing pins)
pierce prey and move around surface of cell.
collar of tentacles (microvilli)
contain actin - contractile
Choanoflagellates
only group with a collar of tentacles
all have a single naked flagellum
attach to surface (by means of a stalk)
more closely related to animals than other protists.
silica lorica made only in choanoflagellates, how are they made.
Mother cell makes loads of little glass strips.
Glues together in right places. Bundle produced.
Goes on to divide and daughter cell is pushed into two bundles and then released.
Collar of tentacles grabs top of the bundle, then turns round one and a half 2 times and then tentacles pull everything up.
Bundle now expands and becomes fully built lorica.
biomimetic engineering
due to twist of lorica. gives enhanced strength and rigidity.
photoautotrophic flagellates
also called ‘phytoflagellates’
own plastids - green or golden
all are aerobic
use flagella for movement towards light and nutrients.
Euglena (photoreception)
eyespot/stigma:
organelle containing carotenoid lipid globules. Shading device for photoreceptor to detect direction of light.
Dinoflagellates
contain a second flagellum around the waist.
Amoebae
One macronucleus
most are aerobic
most are heterotrophic
-some mixotrophic
asexual reproduction only
-no specific fission plane (can divide across any part of their membrane, not controlled.
some move, some are stationary
most publicised protozoan.
Naked amoebae
move by cytoplasmic streaming
produce pseudopodia on surface
pseudo phobia used to creep across surfaces
feed by direct interception of prey
raptorial feeding
no specific location of ingestion - can be anywhere.
Naked amoebae - 3 cell forms
Trophozoites - the feeding form
cysts- all produce a resting stage
floating form- stiffened pseudopodia for dispersal
all amoeba produce cysts.
Shelled amoebae
enclosed in shell (‘test’)
shell can be made of anything
intrashellular cytoplasm within test
project extrashellular cytoplasm to move and/ or feed.
raptorial or diffusion feeding
can produce cysts.
Testate amoebae
freshwater, marine and terrestrial
raptorial feeding
made shells out of spent algae
Foraminiferans
marine only CaCO3 tests
diffusion feeding
diffusion feeding
stationary predator captures prey with sticky extrashellular cytoplasm (‘axopodia’)
Radiolarians
marine only
silica tests
diffusion feeding
heliozoans
freshwater
silica tests
diffusion feeding
Good ecological impact of protists
The microbial loop.
predation keeps bacteria in ‘log phase’
Protists cellular C:N:P ratio
50:10:1
has to be maintained at this, excess released.
Bad ecological impact
evolution of pathogens
evident in amoebae as share many similarities with macrophages
bacteria practice evading digestion in amoebae
become pathogenic and evade our immune system.
Evading digestion in amoebae
either change antigens so not recognised by receptors.
be covered in a thick capsule so not detected, receptors cannot bind
or can release chemicals which prevent the digestive enzymes fusing with the phagosome.
How much of human cells are bacterial
90%
one protist naturally present
Visceral
attacks tissues
Cutaneous
infects macrophages and divides within
