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

Photosynthesis

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

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

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

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

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

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)

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

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

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

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.

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

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

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)

Cellular Respiration

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

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

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

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.

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

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.

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

2013 Question 4

Answer