Microbial Eukaryotes Flashcards
1
Q
What are ‘Prtotists”, etc?
A
‘Protists’: The eukaryotes (mostly microbial) that are NOT animals, land plants or (true) fungi
- e.g. ‘Protozoa’ : usually heterotrophic & unicellular
- “(heterotrophic) flagellates”; “amoebae (amoebas)”
- e.g. ‘Algae’: usually photosythetic
- Many unicellular or simple colonies (microalgae)
- Some large, complex (macroalgae)
2
Q
Some example unicellular protists
A
- Raphidophyte (flagellated microalga)
- Diatom (microalga)
- Gefionella (‘protozoan flagellate)
- Paramecium (a large ciliate)
- Tetrahymena (a ciliated ‘protozoan’)
- Trypanosome (parasitic ‘protozoan’ flagellate)
- Acanthamoeba (an amoeba)
3
Q
Archaias
A
A foraminiferan ‘shelled’ amoeba. cell is ~2 mm diameter; (some foraminifera are >1 cm)
4
Q
Macrocystsis giant kelp
A
A multicellular macroalga (NOT closely related to land plants)
5
Q
Components of eukaryotic cells
A
- Cytoskeleton
- Flagella
- Endomembrane system
6
Q
Eukaryotic Cytoskeleton
A
- Microtubules; actin microfilaments; other systems
- Often define cell shape
- Essential fro mitosis, phagocytosis, etc
- Cell *motility structures
- e.g. *Pseudopodia and *eukaryotic flagella
7
Q
Eukaryotic Flaglla (=cilia)
A
- *not homologous to bacterial flagella (or archaella)
- Membrane-enclosed
- Powered by ATP-consuming dyneins along flagellum
- Bending motion; *variety of beating patterns possible
- Flagellar hairs, vanes etc in some protists
8
Q
Endomembrane system
A
- Golgi apparatus
- Nucleus (w. nuclear envelope)
- Endoplasmic reticulum
- Food vacuole (with fusing lysososmes)
- Contractile vacuole
9
Q
Phagocytosis
A
- Endocytosis of particles (especially other cells)
- Most ‘protozoa’ are phagotrophic (= **mixotrophy)
- *Key eukaryote innovation?
- “true” predators
- facilitated *endosysmbiosis?
10
Q
**Bdellovibrio
A
- ‘Predator’ (?) of other Gram-negative bacteria
- check slides for figure
11
Q
Chromosomes and mitosis etc.
A
- Nucleus, bounded by nuclear envelope
- DNA packaged around histone proteins
- Multiple linear chromosomes
- Nucleus ‘divides’ by mitosis (usually!)
- Diploid life history stages common -> meiosis & sexuality
12
Q
Nuclues division and asexual reproduction
A
a) Normal binary fission
b) Multiple fission
c) Multinucleate cells (instead of reproduction; inc. ‘plasmodial’/’coenocytic’ organisms etc.)
13
Q
Number of cells in a eukaryote organism
A
- Unicellular - Colonial (form colony)
- Plasmodial (blob of cells)
- Coenocytic (blob in a line)
- Multicellular (multiple *types of cells and/or cells organized into tissues)
14
Q
Sexual cycles of protists
A
- Often many asexual cycles between each sexual cycle
- So sex and reproduction not always linked
- Main form can be diploids, or haploids (or both)
- Alternation of generations in some (esp. macroalgae)
15
Q
Haploid phase dominates example
A
Chlamydomonas life cycle:
haploid phase dominates, haploid asexual cycle
- Sexual cycle: two fuse, make diploid cell, meiosis, make new haploid cells
16
Q
Organelles of endosymbiotic origin
A
- Mitochondrion
- Plastid (chloroplast)
17
Q
Mitochondria and Plastids
A
- Own genomes
- Own bacterial-like ribosomes
- 2 membranes*; represent cell- & outer- membrane
18
Q
Plastids (~chlorplasts)
A
- in many eukaryotes
- Bounded by 2,3 or 4 membranes
- Descended from cyanobacteria, with same basic photosynthesis:
- Oxygenic; two-photosystem
- Chlorophyll a - based
- Thylakoid membranes
19
Q
Primary endosymbiosis: origin of plastids as example (mitochondrion similar)
A
- Engulfment of a cyanobacterium by a heterotrophic eukaryote
- Gave rise to a primary alga
- Organelle genome reduced
20
Q
Secondary endosymbiosis (plastids only)
A
- A primary alga is engulfed by another eukaryote and reduced to an organelle
- Result: ‘secondary alga’
- ‘Complex plastid’ with 4 (or 3) membranes
21
Q
Related Primary algae
A
- Chloroplastida (green alga)
-> secondary endosymbiosis
-> Euglenid - Rhodophyte (red alga)
-> Different Secondary endosymbiosis
-> Stramenopile
22
Q
Archaeplastida
A
Clade with plastids of primary endosymbiotic origin,
- Chloroplastida (green algae + land plants
- Rhodophyta (red algae) - mostly macroalgae
- Almost all are not phagotrophic
23
Q
Rhodophyte plastids
A
Phycobilisomes containing phycobilins (inc. phycoerythrin)
‘starch’ in cytoplasm
24
Q
Chloroplastida plastids
A
Chlorophyll b, not phycobilins
- Green pigmentation
- Starch is plastid
25
Chloroplastida
- Diverse - ~7000 algal species (plus 200,000+ plants)
- Algae range from small flagellated cells to large macroalgae
- Most with well walls or scales of carbohydrate (e.g. cellulose)
- Unicellular (aflagellate), Filamentous form, Macroalgae
26
'Prasinophytes'
- Mostly small flagellates
- Important in marine plankton
- Many have carbohydrate scales
27
Chlorophyceae
- Mostly freshwater
- Usually with continuous cell wall
- withstand osmotic pressure
- Includes a range of *colonial forms
28
Chlorophycaea colonial forms
- Desmodesmus (4 cells)
- Gonium (16 cells)
- Volvox - 100s of cells; daughter colonies
29
Secondary algae groups (Chlorophyll c algae)
- Haptophytes
- Stramenopile algae (e.g. diatoms)
- Dinoflagellates (part of 'alveolates')
30
Chlorophyll c plastids
- All derived ultimately from secondary endosymbiosis of red alga
- 4 (or 3) bounding membranes
- Chlorophyll c (AS WELL AS CHLOROPHYLL A)
- Large amounts of other accessory pigments, especially carotenoids
- but *not phycobilisomes
- Stacked thylakoids
Ex: dinoflagellates plastid: 3 bounding membranes + stacked thylakoid
31
Haptophytes
- Usually small flagellates (<10 micrometres)
- many with aflagellate stages
- mostly marine
- Usually with Haptonema**
- microtubular tentacle
- sensing; food capture in some
- Usually carbohydrate scales or mineralized *'coccoliths'
32
Coccoliths
- Calcium carbonate (CaCO3) scales
- In major *marine group
- Geological burial of carbon
- Massive blooms of Emiliania
- especially in North Atlantic
33
Coccolith formation
- Calcium carbonate deposited on organic scale base *within endomembrane vesicle
34
Stramenopiles (Heterokonts)
Very diverse:
- 1.2-micrometre flagellates to 50 m macroalgae
- Algae; protozoa; 'pseudo-fungi'
- Unique *flagellar hairs (mastigonemes)
- On one flagellum
- 'Reverses' effect of 'flagellar beat'
E.g. Diatoms, brown algae
35
Diatoms (Bacillariophyta)
- Unicellular / colonial
- < 10 micrometres - hundreds of micrometers
- Non-flagellated
- Characteristic silica *frustule
- Centrics (mostly planktonic) vs, Pennates (mostly benthic)
36
Diatom frustule
- Extracellular
- *'Box with lid' construction (Epitheca and Hypotheca)
- Valves (single continuous pieces of silica) and girdle bands (series of strips of silica, on top of each other)
- Tiny holes in valves: areolae, for gas exchange
- grow by adding girdles, limited by size of frustule
37
Diatom frustules and cell division
- Parental epitheca and hypotheca retained: Each becomes *epitheca in a daughter cell
- New valves & girdles produced *intracellularly, within confines of parental frustule
- gradual fall in average cell size
38
Diatom life cycle (centric diatom example)
- Diploid-dominant
- Key role of sex in resetting cell size
- smallest cell size, appropriate environment, acts as a trigger for sexual reproduction, resets size
- male gametes with *flagellar hairs
39
Ecological importance of diatoms
- Major 'large' algae in ocean
- e.g. Coastal 'spring bloom' of 'micro phytoplankton' (20-200 micrometres); [unicellular & colonial centrics, mostly]
- Pennates often dominate lit sediments
40
Alveolates (Alveolata)
Three very different groups
- Dinoflagellata: type of 'algae'
- Apicomplexa: parasites
- Ciliophora: mostly free-living 'protozoa'
With cortical alveoli
- Flattened vesicles under the cell membrane
41
Dinoflagellata (dinoflagellates)
- Most are flagellates (dino=whirling)
- 2 micrometres - 2 millimetres
- ~1/2 have plastids
- Many/most are *phagotrophic (even those with plastids)
- Ecologically important microalgae
- inc. algal symbionts; toxic algae
42
'Armoured' dinoflagellates
have cellulose 'thecal plates' within the alveoli
- The plates are BENEATH the cell membrane
43
Apicomplexa
Major group of parasites of animals
- malaria, toxoplasmosis, others
Usually *invade host cells (i.e. intracellular)
Often complex lifecycles
- (sexual; often with two hosts)
44
Apicomplexan Lifecycle
- Example of *Haploid-dominant lifecycle
- May involve more than one host species
Three main cell types:
- Sporozoites (key transmission phase)
- Merozoites
- Gametes
- Sporozoite production includes *meiosis
- Reproduction by *multiple fission
45
Ciliophora (ciliates)
- Important & diverse 'protozoan' group
- <10 micrometres to 3+ mm
Cilia
- Often with simple somatic ('body') cilia
- *Complex ciliary structures common too (esp. in oral apparatus)
Nuclear dualism
46
Nuclear Dualism
Micronuclei (mic)
- Diploid
~ inactive; germ line
Macronucleus (mac)
- Tens-to-thousands of copies of (parts of) the mic genome
- Transcriptionally active
47
Nuclear Dualism reproduction
Micronuclei (mic)
- Can undergo mitosis and meiosis
Macronucleus (mac)
- Divides in *asexual reproduction
- Degenerates in *sexual process ('conjugation')
48
Some ciliate diversity
1. Cells with even covering of individual somatic cilia:
- Tetrahymena
- Paramecium
2. With few somatic cilia, but huge oral apparatus (ocean plankton)
- Oligotrich
- Tintinnid
49
Amoeba (main groups)
- captures food with actin-based or microtubule pseudopodia
- no cilia
- Alveolates
- Rhizaria
- Discoba (Euglenozoa, heterobosea)
- nucleariids
50
Foramininfera ('forams')
Almost all marine
- Benthic or planktonic
- Often 'huge' (some mm-cm)
- Elongate network of pseudopodia
- Usually with multi-chambered 'test' (shell) of calcium carbonate
51
Foraminiferan pseudopodia
- Supported by microtubules
- Rapidly shuttles organelles along microtubules
52
Amoebozoa
- Actin-based pseudopodia; usually thick, or broad and flat
- Cells 4 micrometers - 5 mm (plasmodia can be larger)
- Important in sediments, soil
53
Slime moulds
- Amoeba (or plasmodium (large cell with multiple nucleii)) that makes *fruiting bodies
- Fruiting body -> spores -> dispersal
**Terrestrial: soil, rotting timber, dung, etc.
54
'Cellular' slime mould - Life Cycle
- Many individual amoebae *aggregate as a *'pseudoplasmodium' shortly before fruiting
- Most cells *transform into spores
- Other cells *sacrificed to form stalk of fruiting body
55
Heterotrophic flagellates
The 'default' eukaryotes
- Choanoflagellates
- Metamonada
- Stramenopiles
56
Choanoflagellates
- *Example group of heterotrophic flagellates
- Also, closest relatives of animals (Metazoa)
- Best known 'protozoan' opisthokonts
- Small cells; some colonial
- *collar surrounding flagellum
- Important *bacterivores (especially marine plankton)
57
Collar (choanoflagellates)
- Ring of actin-supported microvilli around the flagellum
- Function: capture of food particles
58
A traditional view of the ocean
- Primary production: phytoplankton (e.g. colonial diatom, dinoflagellates)
- Copepods
- Small fish, etc
- Big fish, etc
59
Prokaryotes in the ocean
- 10^5-10^6 + cells/ml (in much of euphotic zone)
- More biomass than *all the marine animals
- Cyanobacteria: ~50% of total ocean photosynthesis
- Heterotrophic prokaryotes: Exploit most of the dissolved organic material (DOM)
59
Who 'eats' prokaryotes in the Ocean?
- Mainly, *protists; especially *heterotrophic flagellates (and mixotrophic flagellates!)
- Plus viruses (phage):
(typically cause 10-40% of prokaryotes mortality
