UNIT 3: Part 2

UNIT 3:Part 2Cellular Respiration andphotosynthesisHillis Textbook Chapter 6

Cellularrespiration is a major catabolic pathway.Glucose is oxidized:carbohydra te 6O2 6CO2 6H 2O chemical energy Photosynthesisis a major anabolic pathway. Lightenergy is converted to chemical energy:6CO2 6H 2O light energy 6O2 carbohydra te

Cellular Respiration is AEROBIC (uses oxygen) A lot of energy is released when reducedmolecules with many C—C and C—H bonds arefully oxidized to CO2. Oxidationoccurs in a series of small steps in threepathways, followed by generation of ATP:1. Glycolysis2. Pyruvate Oxidation3. Citric Acid Cycle4. Electron Transport Chain

CELLULAR RESPIRATION:REACTANTS: Glucose and oxygenLEARN THENAMES OF THESTEPS ANDWHERE ITTAKES PLACE!OxygenATPPRODUCTS: Carbon Dioxide,water and ATP

STEP ONE: GLYCOLYSISGlycolysis: ten total reactions. Takes place in the cytosol. Starts with glucose Finalproducts:2 molecules of NADH2 molecules of ATP2 molecules of pyruvate(pyruvic acid)These ATP molecules wereproduced, however they don’tcount because we USED twomolecules at the beginning

STEP TWO: PYRUVATE OXIDATIONPyruvate Oxidation: Happens in the mitochondria Starts with TWO separate pyruvates from glycolysis Products: CO2 and acetate; acetate is then boundto coenzyme A (CoA)2pyruvateinResults in:2 CO2 and 2Acetyl CoAtotal

STEP THREE: CITRIC ACID CYCLE CitricAcid Cycle: Takes place in the mitochondrial matrix 8 reactions Starts with the two Acetyl CoA produced bypyruvate oxidation So, the cycle operates twice for every ONEglucose molecule that enters glycolysis Each acetyl group is oxidized to two CO2. Oxaloacetate is regenerated in the last step to bere-used again when another acetyl CoA comesalong. Energycarriers are produced: 6 NADH, 2 FADH2, 2 GTP

STEP THREE: CITRIC ACID CYCLEEvery glucose formsTWO acetyl CoA frompyruvate End result 4CO2, 6 NADH, 2FADH2 and 2 GTP

ALERT!!!The Citric AcidCycle is also knownas The Kreb’s Cycleand the TCA cycle

STEP FOUR: ELECTRON TRANSPORT CHAINElectron transport/ATP Synthesis: NADH is reoxidized to NAD and O2 is reduced to H2O in aseries of steps. Respiratory chain—series of redox carrier proteins embeddedin the inner mitochondrial membrane. Electron transport—electrons from the oxidation of NADH andFADH2 pass from one carrier to the next in the chain.

STEP FOUR: ELECTRON TRANSPORT CHAIN Theoxidation reactions are exergonic; theenergy is used to actively transport H ions out ofthe mitochondrial matrix, setting up a protongradient. ATP synthase in the membrane uses the H gradient to synthesize ATP by chemiosmosis. About 32 molecules of ATP are produced foreach fully oxidized glucose. Therole of O2: most of the ATP produced isformed by oxidative phosphorylation, which isdue to the reoxidation of NADH.

Under anaerobic conditions (NO OXYGEN IS AVAILABLE), NADH is reoxidized byfermentation. The overall yield of ATP is only two—the ATP made in glycolysis.Lactic acid fermentation:End product is lactic acid (lactate).Alcoholic fermentation:End product is ethyl alcohol (ethanol).

Metabolicpathways arelinked. Carbon skeletons(molecules withcovalently linkedcarbon atoms) canenter catabolic oranabolicpathways.

How do youthink prokaryotesperformrespiration?

Photosynthesis involves two pathways:1. Light reactions convert light energy into chemicalenergy (in ATP and the reduced electron carrierNADPH).2. Carbon-fixation reactions use the ATP and NADPH,along with CO2, to produce carbohydrates.

LIGHT REACTIONS: Lightis a form of electromagnetic radiation,which travels as a wave but also behaves asparticles (photons). Photons can be absorbed by a molecule, addingenergy to the molecule—it moves to an excitedstate. Inplants, two chlorophylls absorb light energychlorophyll a and chlorophyll b.

LIGHT REACTIONS:The lightreactions useCHLOROPHYLLto trap energyfrom the sun!That is why theyare considered“light” reactions.Chlorophyll molecule

LIGHT REACTIONS: When chlorophyll (Chl) absorbs light, it enters an excited state(Chl*), then rapidly returns to ground state, releasing anexcited electron.Chl* gives the excited electron to an acceptor and becomesoxidized to Chl .The acceptor molecule is reduced. Chl * acceptor Chl acceptor The electron acceptor is first in an electron transport system inthe thylakoid membrane.Final electron acceptor is NADP , which gets reduced: NADP H 2e NADPH ATP is produced chemiosmotically during electron transport(photophosphorylation).

LIGHT REACTIONS:Two photosystems: Photosystem I absorbs light energy at 700 nm, passes anexcited electron to NADP , reducing it to NADPH. Photosystem II absorbs light energy at680 nm, produces ATP, and oxidizes water molecules.

CALVIN CYCLE: TheCalvincycle: CO2fixation. Itoccurs in thestroma of thechloroplast. Each reactionis catalyzed bya specificenzyme.

1. Fixation of CO2: CO2 is added to ribulose 1,5-bisphosphate (RuBP). Ribulose bisphosphate carboxylase/oxygenase(rubisco) catalyzes the reaction. A 6-carbon molecule results, which quickly breaksinto two 3-carbon molecules: 3-phosphoglycerate(3PG).2. 3PG is reduced to form glyceraldehyde 3phosphate (G3P).3. The CO2 acceptor, RuBP, is regenerated fromG3P. When glucose accumulates, it is linked to formstarch, a storage carbohydrate.

The C—H bonds generated by the Calvin cycleprovide almost all the energy for life on Earth! Photosynthetic organisms (autotrophs) use mostof this energy to support their own growth andreproduction. Heterotrophs cannot photosynthesize anddepend on autotrophs for chemical energy.Do we rely on plants?Do plants rely on us?

ALCOHOL PRODUCTION USING RESPIRATION: Catabolism of the beet sugar is a cellular process,so living yeast cells must be present. With air (O2) yeasts used aerobic metabolism tofully oxidize glucose to CO2. Without air, yeasts used alcoholic fermentation,producing ethanol, less CO2, and less energy(slower growth).

PATHWAYS THAT HARVEST ENERGY

RESPIRATION OVERVIEW:

RESPIRATION OVERVIEW:

GLYCOLYSISRESPIRATION OVERVIEW:PYRUVATE OXIDATIONFOR EACH PYRUVATEKREB’S CYCLEFOR EACHACETYL CoAELECTRON TRANSPORTCHAINUSES ALL THE ENERGYCARRIERS ANDOXYGEN TO MAKE ATP

Photosynthesis Overview:

Photosynthesis Overview:Light Reactions in thethylakoidmembranesCalvin Cycle in thestroma

STEP THREE: CITRIC ACID CYCLE . ALERT!!! The Citric Acid Cycle is also known as The Kreb’s Cycle and the TCA cycle . Electron transport/ATP Synthesis: . The C—H bonds generated by the Calvin cycle