Why do phycologists call cyanobacteria algae?

Why do phycologists call cyanobacteria algae?

• Eukaryotic algae acquired the ability to conduct oxygenic photosynthesis from cyanobacteria

• Photosynthesis occurs on thylakoid membranes in cyanobacteria and eukaryotic algae

• All photosynthetic algae use the same apparatus to conduct oxygenic photosynthesis

• Cyanobacteria are the only bacteria that conduct oxygenic photosynthesis

Describe the endosymbiont theory

1. An endosymbiotic relationship was first set up between an ancient microbial cell, most likely an Archaeal cell, and a bacterial cell

2. Over time, the endosymbionts evolved into mitochondria found in all eukaryotes today

3. Later in evolutionary time, an endosymbiotic relationship was set up between a mitochondrial-containing heterotroph and a cyanobacterium

4. Eventually, the cyanobacterium lost the ability to live independently and evolved into a chloroplast but maintained the ability to conduct photosynthesis

What are thylakoids?

Intracellular flattened membranous sacs that are often arranged in stacks

Where does algal photosynthesis occur?

• In cyanobacteria, photosynthesis occurs on thylakoid membranes

• In eukaryotic algae, photosynthesis occurs on thylakoid membranes inside the chloroplast 

What is the photosynthetic apparatus in algae?

• A large, complicated set of proteins and protein complexes

• Consists of 2 photosystems, a cytochrome complex with an electron transport chain, and an ATP synthase

What is the formula for photosynthesis?

6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂

What are the photosystems?

• Large complexes that contain chlorophyll, accessory pigment molecules, proteins and other compounds

• The pigments and proteins in the photosystems act as antennae that absorb light at different wavelengths and transfer the excitation energy to reaction centers in the photosystems

What are phycobilisomes?

• Antennae-like structures on the surfaces of thylakoids in cyanobacteria and many red algae

• Where light-harvesting pigments are found

• Increase the efficiency of light harvesting and the transfer of energy to reaction centres

What are the functions of accessory pigments?

• Extend an organism’s ability to absorb light for photosynthesis

• Can provide protection from light-induced damage to cells

Describe the oxygen-producing step of oxygenic photosynthesis

1. Light is absorbed by Photosystem II

2. Light energy gathered by the antennae is transferred to chl a molecules that donate energized electrons to acceptor molecules (plastoquinone)

3. Electrons lost from chl a are replaced by low-energy electrons obtained from the splitting of water

4. H+ ions are released into the thylakoid space

Describe the process of electron transport and the creation of a proton gradient

1. The electron carrier molecule plastoquinone shuttles energized electrons to the cytochrome complex

2. Energized electrons move through the cytochrome complex

3. Energy is released and used to move protons from outside the thylakoid to the inner thylakoid space, creating a proton gradient across the thylakoid membrane

4. Electrons are transferred to a second electron carrier (plastocyanin) that brings them to Photosystem I 

Describe Photosystem I

1. The light absorbed by Photosystem I excites the electrons it receives from plastocyanin

2. Electrons are transferred to ferredoxin (Fd), which carries them to NADP+ reductase

3. NADP+ reductase reduces NADP+ to NADPH

4. NADPH supplies the electrons needed to convert CO2 to carbohydrates in the carbon-fixing reactions

Describe ATP synthesis

1. ATP synthase translocates protons across the thylakoid membrane from a region of high concentration (thylakoid space) to a region of low concentration (bacterial cytoplasm or chloroplast stroma)

2. It uses the energy released to drive ATP synthesis

What is ATP?

A high-energy molecule used in the reactions that convert CO2 to carbohydrates

Describe the carbon-fixing reactions

1. Carbon fixation: the enzyme ribulose 1,5-bisphosphate carboxylase oxygenase (RuBisCO) fixes CO2 into precursor molecules that are used to synthesize glucose and regenerate ribulose 1,5-bisphosphate

2. Reduction: NADPH generated in the light reactions is used

3. Regeneration of ribulose 1,5-bisphosphate

• ATP is needed in the reduction steps and to regenerate ribulose 1,5-bisphosphate

How did Melvin Calvin discover how CO2 is converted into carbohydrates during photosynthesis?

• Used radioactive Carbon 14 as a tracer to follow the path of carbon during photosynthesis:

  • Green algae were placed in a glass “lollipop” with a light shining on them

  • Carbon-14 labelled CO2 was injected into the stream of nonradioactive CO2 for different amounts of time, and the algae were killed

  • The compounds into which the radioactive carbon had entered were analyzed by paper chromatography

How do cyanobacteria differ from purple bacteria?

• Type I and II reaction centers VS Type II reaction center

• Electrons extracted from water VS reduced compounds from the environment (H2S and other sulfur compounds, organic matter)

• O2 is generated VS not generated

• Possess chlorophyll a and b VS bacteriochlorophyll

• Photosynthetic apparatus located on thylakoid membranes VS non-thylakoid membranes

How do cyanobacteria differ from green sulfur bacteria? 

• Type I and II reaction centers VS Type I reaction center

• Electrons extracted from water VS reduced sulfur compounds (H2S)

• O2 is generated VS not generated

• Possess chlorophyll and b VS bacteriochlorophyll

• Photosynthetic apparatus located on thylakoid membranes VS non-thylakoid membranes

Where does photosynthesis occur in purple bacteria?

On chromatophores (intracellular membrane vesicles) or stacked invaginations continuous with the plasma membrane

Where does photosynthesis occur in green sulfur bacteria?

Chlorosome membranes