Topic 6 - Phototrophy - Biology 241 - University of Calgary

• 6CO2 + 6H2O ---> C6H12O6 + 6O2

What is the overall reaction for photosynthesis?

• Polar covalent bonds in the reactants.

What bonds are broken during photosynthesis?

• Non-polar covalent bonds in the products.

What bonds are formed during photosynthesis?

• H2O is oxidized and it becomes O2 since the bonding electrons between the oxygen and hydrogen have moved further away from the O atoms in O2.

What reactant in photosynthesis is oxidized? What is its product?

• Carbon is reduced and it becomes CO2 since the bonding electrons between the carbon and oxygen in the carbon dioxide have moved closer to the C atoms in glucose.

What reactant in photosynthesis is reduced? What is its product?

• Photosynthesis.

What occurs in the chloroplast?

• Outer membrane.
• Inner membrane.

What two membranes does the chloroplast consist of?

• Space around the thylakoids.

Stroma

• One of the stacks of thylakoids found in chloroplasts.

Granum

• Membrane-bound compartments inside chloroplasts that are the site of light-dependent reactions of photosynthesis.

Thylakoids

• To allow for pigments, ETC complexes, and ATP synthase.

Why do thylakoid structures contain high SA?

• Light dependent reactions.
• Light independent reactions.

What are the two photosynthetic processes?

• Reactants: Sunlight + H2O + NADP+ + ADP
• Products: ATP + NADPH + O2

What are the reactants and products in light dependent reactions?

• Reactants: ATP + NADPH + CO2
• Products: Glucose + NADP+ + ADP

What are the reactants and products in light independent reactions?

• High energy.

A small wave length results in what type of energy?

• Low energy.

A long wavelength results in what type of energy?

• Photon.
• Frequencies.

Light is a _________ that resonates as different ____________.

• Reflected (what we see).
• Transmitted (pass through).
• Absorbed (photons absorb electrons, gaining energy).

When a photon strikes an object, it can be... (3)

• Those efficient in absorbing photons.

What types of molecules produce pigments?

• Their chemical structure allows their electrons to absorb solar energy.

How does a molecule that can efficiently absorb photons produce pigments?

A) Specific

Pigments absorb photons of _________ wavelengths.

A) Specific.
B) Similar.
C) Varying.

• Must exactly match the energy needed to excite the electron to a higher orbital.

What requirements must a wavelength meet to be absorbed?

• Electrons can jump 2 energy levels.

Blue Light (450nm) Characteristics

• Nothing.
• Doesn't absorb photons, so they are reflected or transmitted instead.

Green Light (550nm) Characteristics (2)

• Electrons jump 1 energy level.

Red Light (700nm) Characteristics

• Falls back down to ground state and releases heat/light.
• Transferred to different pigment molecule.
• Transfers to electron acceptor.

What are the three fates of an excited electron?

• Thylakoid membrane.

Where are photosynthetic pigments embedded?

• Main pigment.
• Capture of energy.

Chlorophylls (2)

• Accessory pigments.
• Extends wavelength range absorbed.
• Protects from sunburn.

Carotenoids (3)

• Shows what pigments absorb what wavelengths.

Absorption Spectrum (Spectrophotometry)

• What wavelengths the chloroplasts are photosynthesizing.

Action Spectrum

• Photosystems.

What are pigment molecules organized into?

• A reaction center pigment.

Antenna pigments are grouped around...

• Reaction center in which not all electrons are transferred and electrons fall back.

When excited, the antenna pigments channel energy to the...

• Transfer of solar energy from one pigment molecule to other in an antenna complex.

Inductive Resonance

• Jump.

Photons do not leave the pigment, instead they __________ around.

• Light is absorbed by the antennae pigments.
• Energy is passed to the reaction center.
• The reaction center reduces a primary electron acceptor.

What happens when reaction centers reduce a primary electron acceptor? (3)

• The reduction of a primary electron acceptor.

What powers light dependent reactions?

• Photosystem II.

Which photosystem produces PMF?

• Prokaryotes.

Does anoxygenic photosynthesis occur in eukaryotes or prokaryotes?

• At a time before oxygen was present in the atmosphere and when there were less organic molecules.

How did anoxygenic photosynthesis evolve?

• Anoxygenic photosynthesis.

What was the first metabolism that utilized an ETC?

• Cyclic electron flow (does not split the water for oxygen).

What type of process does anoxygenic photosynthesis use?

• Cytosol and on the cell membrane.

Where does oxygenic photosynthesis in prokaryotes occur?

• Chloroplasts.
• PSII, PSI, Calvin Cycle.

Cyanobacteria have a photosynthetic mechanism similar to what? What makes them similar?

• Oxygenating the entire planet.

Oxygenic photosynthesis is responsible for...

G3P (3C) + G3P (3C) ---> Glucose (6C)

What is the formula for the conversion of G3P to glucose?

• Used in glycolysis for aerobic respiration.
• Polymerized into starch/cellulose for cell walls.
• Used to synthesize amino acids, nucleic acids, and lipids for us to eat.

What is glucose used for? (3)

• It uses energy to raise an electron to a higher energy level (P680*), and through oxidation and reduction processes from P680* to electron acceptors, it finally leaves behind P680+ which is highly oxidizing and can split apart water molecules. The oxidization of water molecules allows for P680 to regenerate.

When photosystem II is hit with solar energy, what happens in the reaction center P680?

• P680* reduces the primary electron acceptor that passes electrons to PQ.
• PQ (taxi) grabs H+ from the stroma.
• PQ reduces the cytochrome b6f complex and releases H+ into the thylakoid lumen.
• b6f reduces plastocyanin (taxi).

How is the PMF produced by photosystem II? (5)

• Hydrophobic.

Is PQ hydrophobic or hydrophilic?

• Hydrophilic.

Is b6f hydrophobic or hydrophilic?

• The antenna.

Where does photosystem I get its energy from?

• It uses the energy from each photon to raise an electron to a higher energy level (P700*), and through oxidation and reduction processes, from P700* to electron acceptors, it finally leaves behind P700+, which then oxidizes plastocyanin, regenerating P700.

What happens when the energy from the antenna reaches photosystem I?

• The inner surface of the thylakoid.

Thylakoid Lumen

• P700* donates electrons to a primary electron acceptor which passes electrons to the protein ferredoxin.
• Ferredoxin reduces NADP+ reductase which in return, reduces NADP+ to NADPH in the stroma.

How does photosystem I produce NADPH? (2)

• Hydrophilic.

Is ferredoxin hydrophobic or hydrophilic?

• Thylakoid membrane.

Where can we find photosystem II inside the chloroplast?

• Stroma.

Where can we find photosystem I inside the chloroplast?

• Nothing happens.

What happens if a wavelength is not exact and specific?

• Collection of proteins that interact with pigments.

Reaction Center

• Pigments that are grouped around reaction center (RC).

Antenna Pigments

• It reaches the reaction center.

Inductive resonance occurs until...

• It grabs a H+ from the stroma when reduced.

What does PQ do?

• Passes electrons to P700.

What does plantacyanin (PC) do?

• False.

Photosystem 2 does not produce the PMF, true or false?

• True.

P680 replaces its lost electrons by splitting H2O, true or false?

• True.

Photosystem I produces NADPH, true or false?

• Reduces NADP+ reductase.

What does ferredoxin do?

• Reduces NADP+ to NADPH.

What does NADP+ reductase do?

• Releasing protons in the thylakoid lumen when H2O is oxidized.
• Moving protons from the stroma into the lumen when PQ shuttles electrons.
• Using protons in the stroma to reduce NADP+ to NADPH.

Both photosystems produce a strong proton electrochemical gradient, they do this by: (3)

(Hint: Think about the functions of PQ, b6f, ferredoxin, and NADP+ reductase.)

• The use of solar energy to generate PMF to power ATP synthase.

Photophosphorylation

• Stroma side of the membrane.

ATP is generated on the...

• Chemical energy.

What type of energy is in ATP and NADPH?

• Creates the PMF.
• Reducing powers.

The electron transport chain performs two actions:

• False, the energy from PSII generates enough energy to power the ETC only.

The energy from photosystem II is enough to power an ETC and generate enough energy to reduce NADP+, true or false?

• True.

Photosystem I reenergizes electrons enough to reduce NADP+, true or false?

• The stroma.

The Calvin cycle occurs in...

• ATP.
• NADPH.

What two products of the light-dependent reaction does the Calvin cycle use?

• ATP.

Does the Calvin cycle use more NADPH or ATP?

• Cyclic electron flow.

What is the solution to a buildup of NADPH in the Calvin cycle?

• To generate balance between the ATP and NADPH energy budget.
• Protects both photosystems from damage due to stromal overreduction.

What is the function of the cyclic electron flow? (2)

• Fixation.
• Reduction.
• Regeneration.

What are the three phases in the Calvin Cycle?

• 3 CO2.
• 9 ATP.
• 6 NADPH.

What are the reactants of the Calvin cycle?

• 1 G3P.
• 9 ADP.
• 6 NADP+.

What are the products of the Calvin cycle?

• Use carbon dioxide to create sugar for plants.

What is the purpose of the Calvin cycle?

• Hydrophilic

Is PC a hydrophobic or hydrophilic electron taxi?