1. Photosynthesis & Cellular Respiration
By: Zainab Arif, Xena Nam, Alliza Castillo, Reniba Babu

2. Photosynthesis

3. Light Dependent Reaction
Vocabulary:
Chlorophyll - pigment that absorbs blue and red wavelengths
ETC - proteins embedded in thylakoid membrane
ADP - when phosphate group from ATP breaks off, energy is released
ATP - energy-containing molecule
NADP+ - stores electron energy
NADPH - product of LDR and is taken to the Calvin Cycle

4. Light Dependent Reaction
Photosystem II
(Part 1):
Photon activates chlorophyll molecules in the Light-Harvesting Complex
Vibration energy is transferred to P680 molecules in the Reaction Center
An electron is lost from P680 and donated to QA and then QB (plastoquinones)
Plastoquinone - plant substance that occurs in chloroplasts of plants and functions as an electron carrier

5. Light Dependent Reaction
Photosystem II
(Part 2)
P680 is reduced (electron) when water splits at the Oxygen-Evolving Complex
Oxygen is a product
A second photon of light is required since QB needs two electrons to be mobile
Once QB has two electrons, it carries them to cytochrome b6f

6. Light Dependent Reaction
Cytochrome b6f
Enzyme - transfers electrons from Photosystem II to Photosystem I
Pushes H+ ions into thylakoid space, which creates an electrochemical gradient.
This gradient stores energy for ATP synthesis
Photosystem I
Absorbs photons of 700 nm wavelength
Provides high-energy electrons which reduces NADP+ and produces NADPH for the Calvin Cycle

7. Light Dependent Reaction
ATP Synthase
Accumulation of H+ ions in the thylakoid lumen creates an electrochemical gradient
This gradient pushes protons through the ATP Synthase
Protons accumulate in the stroma
When the ATP Synthase rotates, ADP phosphorylates to ATP (energy)
Process known as photophosphorylation

8. Were You Paying Attention???
LDR REQUIRES light to occur!
Photons hit Photosystem II, which oxidizes P680 molecule
P680 is then reduced as water splits and an electron is added
Process repeats for a second time until QB has 2 electrons
Cytochrome b6f creates electrochemical gradient
Delivers electrons to Photosystem I
Photosystem II absorbs P700 nm
Converts NADP+ to NADPH by adding electrons
Electrochemical gradient pushes protons through ATP Synthase
Phosphorylates ADP to ATP
ATP and NADPH are taken to the Calvin Cycle (Light Independent Reaction)

9. Light Independent Reaction
Calvin Cycle
Takes place in stroma of
chloroplasts
Carbon enters in the form of CO2
and leaves in the form of a
sugar
Uses ATP and NADPH

10. Light Independent Reaction
Phase 1: Carbon Fixation
CO2 becomes 5 carbon sugar, RuBP (ribulose bisphosphate)
Rubisco catalyzes step.
Product is a 6 carbon intermediate which breaks into 2 molecules of 3-phosphoglycerate

11. Light Independent Reaction
Phase 2: Reduction
ATP and NADPH2 from light reactions are used
Convert 3-phosphoglycerate to glyceraldehyde 3 phosphate (precursor to glucose)

12. Light Independent Reactions
Phase 3: Regeneration
ATP converts some of the of the pool of glyceraldehyde 3-phosphate back to RuBP, the acceptor for CO2, thereby completing the cycle.

13. Light Independent Reactions
Net Output
Every 3 molecules of CO2 = 1 G3P molecule
1 G3P synthesized = 9 molecules of ATP and 6 molecules of NADPH2 used up

14. C4 Plants
Uses PEP carboxylase instead of rubisco (less affinity for O2)
CO2 taken up by mesophyll cells and converted to 4 carbon sugar, Oxaloacetate/Malate.
Malate transfers CO2 to Calvin cycle and becomes pyruvate which regenerates PEP and continues cycle
WHY? Hot and dry conditions > Stomata closed for long periods > O2 buildup > Photorespiration

15. CAM Plants Night: Stomata open and buildup of Oxaloacetate
Day: Stomata closed and CO2 enters Calvin Cycle
WHY? Desert Conditions (Can’t keep stomata open during the day to prevent dehydration)

16. Cellular Respiration

17. Cellular Respiration: Glycolysis
Breakdown of glucose into pyruvate
Occurs in the cytoplasm
Net output: 2 ATP (produces 4 but uses 2) , 2 NADH
does not require O2

18. Fermentation Glucose → Pyruvate → NADH oxidized to NAD+ → Lactic Acid
To allow glycolysis to continue
Lack of oxygen → no aerobic respiration thus body relies on lactic acid
Glucose→ Pyruvate → one carbon lost → Acetaldehyde → NADH oxidized to NAD+ → Ethanol
Allow glycolysis to continue when no oxygen

19. Cellular Respiration: Pyruvate Oxidation
Pyruvate is turned into Acetyl-CoA
The carboxyl group leaves as carbon dioxide
Remaining fragment forms acetate NAD+ into NADH
Coenzyme A attaches binds is sulfur atom to acetate and forms Acetyl-CoA

20. Cellular Respiration: Krebs Cycle
Acetyl group binds to oxaloacetate and is turned into citrate, As each carbon compound changes into a different carbon compound, it produces CO2 , NADH, ATP, and FADH2 , which can be used for oxidative phosphorylation.

21. Electron Transport Chain
FADH2 and NADH are oxidized and thus transfer their electrons to the carrier molecules
Electrons move from molecule to molecule
Last electron acceptor is O2

22. Cellular Respiration: Oxidative Phosphorylation
The energy from the electrons passing through the carrier molecules allows for the carrier molecules to transfer a proton from one side of the membrane to the other.
This creates a gradient, which creates energy for ATP synthesis.

23. Cellular Respiration: ATP Synthase
generates one ATP per H+ ion
uses the energy of the ion gradient to power ATP synthesis
powered by the flow of hydrogen ions

24. 2013 Question 4

25. Answer