Chloroplasts (10)

Joseph Priestly/Benjamin Franklin

Joseph Priestly - showed that plants release oxygen during photosynthesis needed for animal survival

• sealed a mouse in chamber with a mint and mouse survived longer, then died

Benjamin Franklin - in response to Priestly’s experiment, determined that green part on plants produce oxygen and can purify air in the presence of light.

Theodore Engelman

Theodore Engelman - Worked with spirogya (had similar ribbon structure to chloroplast), made pure chloroplast by:

• Squashing alga in between slides in a sucrose solution (to allow for bacteria to grow) and under microscope you can find chloroplast

• Bacteria migrated to chloroplast, positive aerotaxis (going to a source of oxygen)

• Determined that chloroplast created oxygen

• Teamed up with Carl Zess who made a microscope to analyze this in a quantitative/qualitative way (different wavelengths of light)

• Concluded that red and violet light were the best for promoting photosynthesis

Robert Hill and Cornelius Van Niel

Robert Hill and Cornelius Van Niel - Discovered that oxygen is produced by water used in photosynthesis

• Found this by comparing reaction process to sulfur producing reaction of purple sulfur bacteria

• Haters said what if the purple sulfur bacteria also produce oxygen

  • Took the bacteria, placed in cell culture dish, in a solution

  • Bubble introduce oxygen to bactera

  • Negative aero taxis occurs (bacteria move away from oxygen bubbles

  • Used light in another dish that showed positive aero taxis (bacteria moved to light)

Melvin Calvin

Melvin Calcvin - Discovered Calvin cycle (citric acid cycle, KREBS)

• Politicians delayed studies on photosynthesis

Barack Obama

Barack Obama - Allocated funding into photosynthesis research (JCAP)

• Started interest in artificial photosynthesis (reverse engineering) to make photosynthesis more efficient

• Can be made to produce fuels

• Can be scaled up to reverse climate change

Cyanobacteria

Photosynthetic bacteria capable of producing oxygen:

• Make more energy than consumed

• Prokaryotes that perform photosynthesis (simpler genome to work with)

• Sequenced DNA (transgenic cyanobacteria have been made)

• Several strains of this bacteria with unique properties have been made

• One variant can be used as fuel

• Cyanomediation - remediates polluted environments by utilizing their photosynthetic processes and ability to metabolize various compounds.

• Used to model circadian clocks

• Cyanobacteria is suitable for growth on Mars

Neoplants

Claims to remove volatile compounds from the air and converts into better things

Bioengineered plants

Plants are low-cost platforms to generate monoclonal antibodies (mAbs), vaccines, and biologics, examples:

• Medicago: COVID-19 vaccine in tobacco plants

• Kentucky Bioprocessing: KBP-201 vaccine in plants

• Transgenic lettuce used for virus-trapping chewing gum

Chloroplasts

Chloroplasts are the site of photosynthesis in plants.

• Thylakoid membranes contain chlorophyll, which absorbs light to produce ATP and NADPH.

• Stroma uses this energy to fix CO₂ into sugars.
  Chlorophyll a and b absorb light mostly in blue and red regions, while accessory pigments (like carotenoids) expand the usable spectrum.

• In deep-sea organisms, specialized pigments allow absorption of green light where red/blue light is scarce.

• Chloroplast autofluorescence helps visualize their structure under a microscope.

Beta-carotene

Could it work against cancer as a vitamin to take?

No, however… 2 clinical trials show:

1) ATBC study in Finland:

• Gave male smokers beta-carotene and vitamin e to take to see if lung cancer can be prevented

• Lung cancer increases by 16%

2) CARET study

• Gave male and female smokers beta-carotene and vitamin a

• Lung cancer increases by 28% (even worse)

Photosynthesis Basics

Photosynthesis begins when light-harvesting complexes (LHCs) capture light and transfer energy via resonance energy transfer to reaction centers.
There, chlorophyll a donates electrons to a primary acceptor, initiating electron transport across the thylakoid membrane.

Four stages:

1. Light absorption & water splitting (PSII → O₂ release)

2. Electron transport chain → NADPH

3. ATP synthesis via proton gradient

4. Carbon fixation in the stroma → sugar production

This process converts light energy into chemical energy (ATP, NADPH) for plant growth and metabolism.

Land plants can use both linear and cyclic photosynthesis

Cyclic Photosynthesis (electron flow)

Occurs in Photosystem I (PSI) and recycles electrons back to the cytochrome b₆f complex without producing NADPH

• Purpose: Generates extra ATP without making NADPH or releasing O₂.

• Pathway: Excited electrons from PSI → ferredoxin → cytochrome b₆f → plastocyanin → back to PSI.

• Boosts the proton gradient, driving more ATP synthesis through the F₀F₁ complex.

• Helps balance the ATP/NADPH ratio needed for the Calvin cycle.

Linear Photosynthesis (electron flow)

Uses both Photosystem II (PSII) and Photosystem I (PSI).

• Light excites electrons in PSII → water is split → O₂ released

• Electrons move through the cytochrome b₆f complex → proton pumping

• Electrons reach PSI, get re-excited by light, and reduce NADP⁺ → NADPH

• ATP is generated by the proton gradient via F₀F₁ ATP synthase

End result: Produces ATP, NADPH, and O₂ needed for the Calvin cycle.

Photoinhibition/Recovery

• Photoinhibition is a protective response where Photosystem II is damaged by excess blue light.

• The D1 protein in PSII is targeted. When its synthesis is blocked, photosynthesis efficiency declines.

• Increased light intensity reduces photosynthesis due to photoinhibition.

• HSP70 (a chaperone protein) helps PSII recover by assisting D1 protein turnover.

  • Overexpressing (OE) HSP70 boosts recovery.

  • Underexpressing (UE) mutants recover poorly.

• Studied in Chlamydomonas, showing the importance of protein repair in light stress adaptation.

RUBISCO

• Carbon Fixation is favored when CO₂ is high and O₂ is low. It produces glyceraldehyde-3-phosphate, a useful sugar.

• Photorespiration occurs when O₂ is high and CO₂ is low, leading to CO₂ release—a wasteful process.

• RUBISCO catalyzes both processes but has a low affinity for CO₂.

• In photorespiration, energy is consumed without fixing carbon, making it inefficient

C4 plants live in hot, arid climates where CO₂ is limited.

Problem: RUBISCO can bind to O₂ instead of CO₂, triggering photorespiration.

• Solution: C4 plants use PEP carboxylase, an enzyme with higher CO₂ affinity.

  • It captures CO₂ in mesophyll cells and converts it to malate.

  • Malate transports CO₂ to bundle sheath cells, where CO₂ levels are higher—ideal for RUBISCO and the Calvin cycle.