Photosynthesis (Light Reactions + Calvin Cycle)

Week 7 - Midterm #2

Photosynthesis is the production of _____ using the energy in _____. The oxygen in H20 come from ____ while oxygen in O2 come from _____.

sugars, sunlight, CO2, H20

____________ and __________ are two types of light absorbing pigments located on the thylakoid membrane. They are organized with other proteins to form two _________.

Chlorophyll a, Chlorophyll b, photosystems

Photosystem I is most efficient at absorbing at 680nm (P680) while photosystem II is most efficient at absorbing light at 700nm (P700). (True or False)

FALSE

What are the 3 phases of the Calvin Cycle?

Phase 1: Carbon Fixation - rubisco catalyzes the breakdown of RuBP to form 3PG

Phase 2: Reduction - Two 3PG’s are phosphorylated by ATP to form two 1,3BPG’s and NADPH to G 3P

Phase 3: Regeneration of RuBP - GeP is phosphorylated via ATP to form RuBP and the cycle continues

G3P can either move onto phase 3 of the calves cycle, or it can be used for storage and energy. In terms of sugar production……

(1) 1/3 end up as: _______

(2) 2/3 are converted to: _______

(1) Starch (storage for plants)

(2) Sucrose (used for energy)

What are the characteristics of the light reaction in photosynthesis?

• It occurs only in the presence of light

• NADP+ and ADP + Pi are used as reactants

• It splits water, releasing O2 and sending electrons to chlorophyll

• ATP and NADH are produced

• An electron transfer chain is involved

What are the characteristics of the dark reaction in photosynthesis?

• It produces carbohydrates through CO2 fixation/reduction

• It is oftentimes referred to as the Calvin cycle

What is the first sugar produced in photosynthesis?

Glyceraldehyde-3-phosphate

What is the role of water (H20) in the light reaction of photosynthesis?

Donate electrons to photosystem II releasing ½ O2 and two protons into the thylakoid space

Which of the following is true about the photosystems?

Photosystem I received higher energy electrons than Photosystem II and is found later in the ETC

Pheophytin passes its electrons onto which carrier?

Plastoquinone

What are the steps of the light reaction in photosynthesis?

(1) A photon of light provides energy to a chlorophyll molecule

(2) Resonance/vibrational energy is transferred throughout the light harvesting complex

(3) Vibrational/resonance energy excites P680, causing it to release an electron

(4) P680 is reduced by the oxygen-evolving complex using two water molecules, producing oxygen

(5) Plastoquinone is reduced by pheophytin and travels to the cytochrome complex

In what way does the cyclic electron flow differ from non-cyclic electron flow of the light reactions in one important way

Cyclic electron flow forms ATP but not NADPH

When would a plant want to prioritize non-cyclic electron flow and when would it prioritize cyclic electron flow?

If the plant has plenty of ATP, it may shift towards noncyclic electron flow.

For cyclic electron flow it is performed when the cells wants to prioritize ATP production over NADPH production because there is not enough ATP.

The Calvin cycle uses more NADPH molecules than ATP molecules (T/F)

FALSE

Describe the flow of protons through ATP synthase in chloroplasts and mitochondria.

Mitochondria - protons flow from the IMS to the matrix

Chloroplasts - protons flow from the thylakoid space to the storm

What components of the light reaction’s electron transport chain contribute directly to creating the proton gradient across the thylakoid membrane?

• Photosystem II

• Cytochrome complex

• NADP+ reductase

• ATP synthase

The thylakoid space will have a(n) ___ pH compared to the storm of chloroplast in a dark environment.

Equal

In the mitochondria, pumped H+ flow from ___ to ___. In chloroplasts, they flow from ____ to ____.

matrix, inter membrane space, stroma, thylakoid