Microalgae and Cyanobacteria Flashcards
What are microalgae and cyanobacteria?
Micro-organisms, but non-plant life.
Microalgae are eukaryotic, oxygenic photosynthesisers with chlorophyll.
Microalgae are polyphyletic group, as they do not share one unique common ancestor.
Cyanobacteria are prokaryotic, and can be photosynthetic or not.
Why should we learn about Microalgae?
Produce 50% of earth’s O2
Fix atmospheric CO2 and N2 to produce Oxygen, sugar, Ammonia for AAs and Nucleotides.
Have evolved over 3 billion years and still survived numerous different climate changes.
Microalgae led to the Great Oxidation event 2.4 billion years ago which enables aerobic life on earth to thrive.
How have microalgae evolved?
Primary, secondary and tertiary endosymbiosis:
Primary eukaryotic host endocytosed a cyanbacterium 1.6 BYA, evolving into chloroplasts. (Though cytoskeletal similarity suggests may have been archae)
BUT THIS EVENT HAS HAPPENED AT DIFFERENT TIMES WITH DIFFERENT CYANOBACTERIA AS MICROALGAE ARE POLYPHYLETIC:
Depending on the cyanobacteria, gave rise to Green, red and Blue algae
Secondary endosymbiosis event where a secondary eukaryotic host endocytosed the primary endosymbiote, to evolve into complex eukaryotic microalgae (1.2 BYA) and retaining its plastids = Leading to complex Red and Green Microalgae.
Tertiary endosymbiosis where a complex eukaryotic cell itself already having obtained its plastids via secondary endosymbiosis, becomes engulfed by another eukaryote.
What is the evidence for endosymbiosis occurring today?
Nitrogen fixing protists (Eukaryotes) have been found to house cyanobacteria, Suggesting a modern-day endosymbiosis.
Who are the most primitive microalgae
Blue microalgae are most primitive in terms of evolution from a primary endosymbiotic event.
What are common features of microalgae?
Unicellular micro-organisms.
Photosynthetic with chlorophyll.
Can live individually or in colonies.
Tend to be aquatic, but ubiquitous, can be not. (Desert, snow, in symbiosis with other organisms e.g Zooxanthelles in corals).
Carry out oxygenic photosynthesis.
What is the process for Light reaction of Microalgae photosynthesis?
Occurs in Thylakoid membranes of chloroplasts.
PSII chlorophyll pigments absorbe photons in the reaction centre (P680), with this energy used in photolysis of water and transfer of electrons along the electron chain.
PSII transfers an electron to Plastoquinon (PQ), which transfers electron to Cytochrome b6f (pumps 1H+ into lumen), Cyt b6f trasnfers 1 electron to Plastocyanin (PC), which goes to PSI.
PSI absorbes photon in P700 reaction centre, an electron is transferred to Ferreodxin, and then to Ferredoxin NADP reductase, which reduces NADP to NADPH.
Photolysis of water, and H+ flow via cytb6f generates a PMF, where H+ flow through ATP synthase into the chloroplast lumen, generating ATP
What are in PS1 and PSII?
PSII contains reaction centre P680, whereas PSII contains reaction centre P700.
Light harvesting complex contains chlorophyll pigments, but chlorophyll a within reaction centre.
PSI and PSII contain photosynthetic pigment, aswell as carotenoids to protect from harmful ROS and UV.
What are phycobilisomes?
Phycobilisomes are structures associated with PSI/PSII above the thylakoid membrane.
Containing Phycoerythrin, Phyocyanin and/or Allophyocyanin.
ONLY FOUND in microalgae and some photosynthetic cyanobacteria.
Pigments capture wavelengths different from chlorophyll
Enable cameleon cyanobacteria
How can cyanobacteria adapt to different light wavelengths?
Synechoccus and Synechocystis can adapt the expression of pigments in their phycobillisomes to adapt to different wavelengths of light.
In red light, enhance expression of PC (Phycocyanin) to increase red wavelength absorption = appear blue.
In Green light, express more Phycoerythrin (PE) to absorbe more green wavelength = appears red.
Which microalgae and Cyanobacteria have phycobillisomes?
Green microalgae contain phycobillisomes.
RED ALGAE NO!
Synechococcus and Synechocystis contain phycobilisomes.
Whereas Prochlorococcus do not.
How does the Dark reactions of Photosynthesis occur in Microalgae?
Where?
CO2 is reduced to form carbohydrated via the Calvin Cycle.
Inside of Carboxysomes in Cyanobacteria.
Inside Stroma of chloroplasts in Microalgae, or Pyrenoid of Green microalgae.
Pyrenoid = Green algae
Chloroplast stroma = Red algae
Carboxysomes = cyanobacteria.
JUST NEEDS RUBISCO AND CARBONIC ANHYDRASE>
What are Carboxysomes?
Micro-compartments within Cyanobacteria cytoplasm.
An icosahedric protein shell housing:
Containing RuBisCO and Carbonic anhydrease required for Dark reaction of photosynthesis.
= CO2 fixation.
What is the CO2 fixation process?
RUBISCO carries out CO2 fixation to RuBP (5C), forming 2 lots of 3-phosphoglycerate (3C).
Reduction occurs to form Glyceraldehyde-3-phosphate (3C), utilising NADPH and ATP energy.
Then RuBP is regenerated using ATP from G3P.
6 cycles needed, so forms 10 G3P which are used to regenerate RuBP, and 2 used to form glucose.
Each use of CO2 requires 3 ATP and 2 NADPH. Therefore each Glucose requires 18ATP and 12 NADPH
What are Cyanobacteria?
Prokaryotes, lacking organelles.
No Mitochondria, No chloroplasts.
Highly diverse: Can be single, or form colonies or be multicellular filamentous,
However contain thyalkoids! Just beneath the PM, where Light reaction occurs in oxygenic photosynthesis with ETC.
Prochloroccus DO NOT HAVE PHYCOBILISOMES.
Only thick layer f Thyalkoids beneath PM.
Synechococcus and Synechocystis contain Phycobilisomes.
Contain free circular DNA and 70s Ribosomes.
Across 1 micron in size.
All Gram negative bacteria, containing a thin Peptidoglycan cell wall and an outer membrane.
Asexual reproduction.
How are carboxysomes arranged and happens to Carboxysomes during cell division
Found in the Cytoplasm, and spatially ordered in linear pattern.
During cell division, they become segregated.
Assemble via Rubisco clustering and assembly of icosahedral shell around.
