History of Photosynthesis
- Cyanobacteria: 2.4 bya
- Eukaryote Photosynthesis: 1.4 bya
- 1st fossil evidence for photosynthesis in red algae.
Cellular Respiration
This is a complimentary, but reverse, process.
- Cellular Respiration
- Catabolic
- Uses sugar to make ATP.
- Spontaneous electron transport pulled by O2.
Photosynthesis
- Metabolism
- Catabolic (breakdown bonds) & anabolic (building bonds)
- Refers to how macromolecules are broken down or build up.
- Photosynthesis
- Is glucose anabolic
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- Creates carbohydrates.
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- Creates macromolecules.
- Uses light to make sugar.
- Light driven electron transport.
Electron Transport Chain
- Electron Transport Chain
- Creates photon gradient (potential energy).
- Proton Gradient
- Creates potential energy.
- Electron transfers drive H⁺s (hydrogen ions) across the inner membrane.
- Oxidative Phosphorylation
- Makes ATP using the ATP Synthase enzyme.
Molecules
- ATP
- High-energy
- 3 negative phosphates
- NADPH
- Electron carrier
Chloroplasts
- Chloroplast
- Has two membranes.
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- Thylakoid Membranes
- Contains thylakoid lumen.
- When stacked: granum
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- Stroma
- Fluid around thylakoid lumen.
- Light Dependent Reactions
- Occur in the thylakoid membrane.
- Makes ATP and NADPH and O₂ from ADP and NADPH
- Light Independent Reactions Calvin Cycle Depends on Light Dependent Reactions
- Occur in stroma
- Uses ATP and NADPH and CO₂ to make sugar.
Light Dependent Reactions
- Forster Resonance Energy Transfer
- How photons excite electrons.
- Antenna Complex
- Light harvesting
- PQ A lipid
- Accepts electrons
- Reaction Center
- Accepts and donates and electron to and from chlorophyll.
- Water donates an electron to chlorophyll and gives off oxygen.
- Redox Reactions
- Stands for REDuction/OXygen.
- Gains electrons or loses electrons.
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- Reduction
- GAIN electrons +e
- Oxidation
- LOSE electrons -e
Excited molecules must return to their ground state. Light energy can be lost as:
- Transfers to another molecule (chlorophyll)
- Fluorescence (light)
- Heat
PhotoSystem II
Makes ATP. Photons can be scattered, reflected, transmitted, or absorbed.
- Chlorophyll
- Reflects green light
- Absorbs photons.
Photons excite electrons, increasing energy,
- Electron is less stable, more reactive.
- Some electrons escape to the electron transport chain.
PhotoSystem I
Makes NADPH. Goes through electron transport chain again, second photon is used to re-excite the electron.
Light Independent Reactions
_Calvin Cycle
Takes place in the stroma.
- RuBisCO RuBP
- An enzyme that "fixes" carbon.
- Most abundant protein on Earth.
Magnesium counter balances H+ ions in proton gradients.
H+ ions are just protons. Hydrogen has 1 proton, neutron and electron, and when it loses the electron (+) it becomes just a proton. Acidic solution has higher H+ ions than a basic solution.
pH is the concentration of Hydrogen (H+) ions in a solution.
Assignment
| Photosynthesis | Cellular Respiration | |
|---|---|---|
| Takes place in which organisms: bacteria, plants, and/or animals? | Cyanobacteria, plants | Plants, animals |
| Takes place in which organelle in eukaryotic organisms? | Chloroplasts | Mitochondria |
| What is the purpose of this metabolic pathway? | Makes sugars | Makes ATP |
| What source of energy drives this metabolic process? | Sunlight (photons) | Glucose |
| What is the initial electron donor to the electron transport chain? | Chlorophyll | Glucose |
| What is the final electron acceptor in the electron transport chain? | NADP+ | O₂ |
| What are the final products from the electron transport chain? | O2, ATP, NADPH | H₂O, ATP, CO₂ |
| Which type of electron transport is involved? cyclic and/or non-cyclic? | Non-cyclic | Non-cyclic |
| What electron carriers are involved? | NADPH | NADH |
| Is ATP synthesized? How? | Light reactions, photosystem II-photophosphorylation. | Yes, breakdown of glucose in kreb's cycle. |
| What “cycle” is used in this metabolic pathway? What happens during the cycle? | Calvin cycle. Fixes CO₂ using ATP&NADPH into sugar. | Kreb's cycle. Pyruvate oxidizes to make ATP+CO2+H2O. |
Study Guide
- When did photosynthesis first evolve and in what type of cells?
- When did photosynthesis arise in eukaryotes? a. the first fossil evidence of this is from what group of organisms?
- Which major groups of animals photosynthesize, which do not? a. which organisms have photosynthesizing symbionts? b. which organisms 'steal' chloroplasts from prey algae?
- What is the overall reaction for photosynthesis?
- How does this compare to cellular respiration?
- Fill out the chart comparing photosynthesis and respiration (last slide!).
- Compare photophosphorylation and oxidative phosphorylation a. where do they happen, what drives each one.
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How is photosynthesis split into two sets of reactions?
a. What are they called?
b. Where does each take place? - Describe the structure of the chloroplast and the compartments within. What was the origin of the chloroplast again? a. Where do light-dependent reactions take place? b. Where do light-independent reactions take place? c. Why do both stop in darkness
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What is light?
a. Describe its properties.
b. How is the wavelength related to light energy? c. How is light energy related to the visible spectrum colors? - What kinds of molecules absorb light?
- What happens when a photon of light is absorbed in terms of electrons?
- Understand all the forms of chlorophyll in the reaction centers
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Where is Chlorophyll, within the cell?
a. How is it anchored in place? b. What molecule regenerates chlorophyll? - How many photosystems are there in plants?
- What wavelengths of light are useful in photosynthesis? a. what wavelengths are absorbed by plant pigments b. what wavelengths are not c. how is this related to the visible color of photosynthetic organisms?
- Understand the following terms and what role they play in the light reactions of photosynthesis: a. Chlorophyll b. Photosystem II (P680) and Photosystem I (P700) c. Plastoquinone/Cytochrome/ d. NADP+/NADPH e. ATP synthase
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Describe the Z-scheme of photosynthesis: is the light dependent/independent?
a. What is the sequence of events?
b. What are the final products?
c. What is the role of H2O?
d. What role do H+ protons play? e. How does pH change in different compartments? f. How is ATP synthesized? (there are TWO places) -
What happens during the light-independent reactions?
a. Describe the Calvin Cycle (C3).
b. How do the light-independent reactions relate to the light reactions? -
What is Rubisco?
a. What does it do in the cell? b. Where does it do its job? c. What factors affect Rubisco activity? - What are the two main classes of biochemical pathways in Metabolism.
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How are glycolysis and photosynthesis related?
a. What are the energy carriers for each? - How are the metabolic processes in the plant cell inter-related?