Topic: Topic: Photosynthesis-Ch 6Photosynthesis-Ch 6

Cellular Respiration-Ch 7Cellular Respiration-Ch 7

American biochemist and Nobel laureate Albert Szent-Gyorgyi, “What American biochemist and Nobel laureate Albert Szent-Gyorgyi, “What drives life is thus a little electric current, set up by the sunshine.” drives life is thus a little electric current, set up by the sunshine.”

• Occurs in chloroplastsOccurs in chloroplasts

Light AbsorptionLight Absorption

•VISIBLE LIGHT (roygbiv)VISIBLE LIGHT (roygbiv)..

•Each color = a specific wavelengthEach color = a specific wavelength

•Pigments: compound that absorbs light (specific Pigments: compound that absorbs light (specific pigments absorb specific wavelengths in pigments absorb specific wavelengths in nanometers)nanometers)

• Surrounded by a double membraneSurrounded by a double membrane• Inside a chloroplast:Inside a chloroplast:

–Flattened membranes = Flattened membranes = thylakoidthylakoid–Stacks of thylakoids = Stacks of thylakoids = granagrana–StromaStroma = liquid = liquid

in the space in the space

surrounding surrounding

the granathe grana

Chloroplast StructureChloroplast Structure

• Found in thylakoidsFound in thylakoids• Chlorophyll Chlorophyll aa = Most important pigment, = Most important pigment,

absorbs the most light (absorbs red, blue; absorbs the most light (absorbs red, blue; reflects green)reflects green)

• Chlorophyll Chlorophyll bb = absorbs slightly different = absorbs slightly different wavelengthwavelength

• CarotenoidsCarotenoids, , XanthophyllsXanthophylls = = red, red, orange, and yellow absorb orange, and yellow absorb additional additional wavelengthswavelengths

PigmentsPigments

Structure of ChlorophyllStructure of Chlorophyll

• Converts inorganic compounds into organic ones using the energy from sunlight & Converts inorganic compounds into organic ones using the energy from sunlight & biochemical pathwaysbiochemical pathways• 2 Stages2 Stages

1. Light 1. Light DependentDependent (capturing light energy or (capturing light energy or “Light”)“Light”) stage stage• releases oxygen for us to breathereleases oxygen for us to breathe• makes ATP and NADPH to run Calvin Cycle makes ATP and NADPH to run Calvin Cycle

2. Calvin cycle (Light 2. Calvin cycle (Light IndependentIndependent or or “Dark")“Dark") stage stage• Makes organic cmpds (sugar for plant)Makes organic cmpds (sugar for plant)

PhotosynthesisPhotosynthesis

• Autotrophs: Make their own organic Autotrophs: Make their own organic compounds (food) ex. plants, algaecompounds (food) ex. plants, algae

• Heterotroph: cannot make their own foodHeterotroph: cannot make their own food

• Cluster of pigment molecules w/ a Cluster of pigment molecules w/ a specific jobspecific job

• Photosystem IPhotosystem I• Photosystem IIPhotosystem II

PhotosystemsPhotosystems

• 6CO6CO22 + 6H + 6H22O + light CO + light C66HH1212OO66 + 6O + 6O22

Photosynthesis EquationPhotosynthesis Equation

• Occurs in the thylakoid membraneOccurs in the thylakoid membrane• Step 1Step 1

–Light energy (from sun) excites Light energy (from sun) excites electrons in chlorophyll electrons in chlorophyll aa molecules, these excited molecules, these excited electrons leave the chlorophyll electrons leave the chlorophyll aa molecule (photosystem II)molecule (photosystem II)

• This is oxidation reaction…..PS II lost an electronThis is oxidation reaction…..PS II lost an electron

Light Reactions - a 5 step Light Reactions - a 5 step processprocess

• Step 2Step 2–Excited electrons leave the chlorophyllExcited electrons leave the chlorophyll

a a & go to the & go to the Primary Electron Acceptor Primary Electron Acceptor (2)(2)

• This is reduction reaction…it gained electronThis is reduction reaction…it gained electron

• Step 3Step 3–Primary electron acceptor gives the Primary electron acceptor gives the

electrons to the electrons to the electron transport chainelectron transport chain• Protons move INTO thylakoid from low to Protons move INTO thylakoid from low to

highhigh

Light Reactions - a 5 step Light Reactions - a 5 step processprocess

• Step 4Step 4–In photosystem I electrons gets In photosystem I electrons gets

excited again by light energy (more excited again by light energy (more sunlight)sunlight)

• Oxidation reaction…lost electronsOxidation reaction…lost electrons

–These electrons go to another These electrons go to another primary primary electron acceptor (1)electron acceptor (1)

–These lost electrons are replaced by the These lost electrons are replaced by the electrons that came from photosystem IIelectrons that came from photosystem II

Light Reactions - a 5 step Light Reactions - a 5 step processprocess

• Step 5Step 5–Primary electron acceptor (I) gives the Primary electron acceptor (I) gives the

electrons to another ETC (I).electrons to another ETC (I).–This ETC (I) moves electrons to the stroma This ETC (I) moves electrons to the stroma

side of the memb.side of the memb.–Electrons combine w/ a proton (HElectrons combine w/ a proton (H++) & ) &

NADP+ this becomes NADPHNADP+ this becomes NADPH• Reduction…gains electronsReduction…gains electrons

–NADPH is nicotinamide adenine NADPH is nicotinamide adenine dinucleotide phosphate…..HOLDS ENERGYdinucleotide phosphate…..HOLDS ENERGY

Light Reactions - a 5 step Light Reactions - a 5 step processprocess

• Where do the electrons come from?Where do the electrons come from?

• An enzyme splits 2 An enzyme splits 2 molecules of water molecules of water into 4 protons, 4 into 4 protons, 4 electrons and 1 electrons and 1 molecule of oxygen molecule of oxygen (O(O22)- this is where )- this is where

oxygen is given off oxygen is given off in photosynthesisin photosynthesis

Replacing Electrons in PS IIReplacing Electrons in PS II

• The process by which ATP is made in the The process by which ATP is made in the light reactionlight reaction

• Happens in between PSII and PSIHappens in between PSII and PSI• More protons accumulate inside the More protons accumulate inside the

thylakoid than stroma = conc. Gradient is thylakoid than stroma = conc. Gradient is high to lowhigh to low

• Some protons came from water splitting, Some protons came from water splitting, others were pumped in using energy others were pumped in using energy generated by ETCgenerated by ETC

ChemiosmosisChemiosmosis

• Protons flow out to Protons flow out to stroma through ATP stroma through ATP synthase enzyme in synthase enzyme in membrane, this releases membrane, this releases energy energy

• ATP synthase uses ATP synthase uses released energy to released energy to convert ADP to ATPconvert ADP to ATP

• ATP synthase = ATP synthase = multifunction protein!multifunction protein!

ChemiosmosisChemiosmosis

ChemiosmosisChemiosmosis

ChemiosmosisChemiosmosis

• Oxygen (given off)Oxygen (given off)• ATP made (used in calvin ATP made (used in calvin

cycle/dark rxn)cycle/dark rxn)• NADPH made (used in calvin NADPH made (used in calvin

cycle/dark rxn)cycle/dark rxn)• Water is consumedWater is consumed

Components of the Components of the light reactionlight reaction

• Where COWhere CO22 is incorporated is incorporated

• Occurs in stroma of chloroplastOccurs in stroma of chloroplast• Makes 3C sugars (carbohydrate)Makes 3C sugars (carbohydrate)

Calvin CycleCalvin Cycle

Calvin CycleCalvin Cycle

• Step 1Step 1

–3CO3CO22 diffuses into stroma from diffuses into stroma from

cytosol, CO2 gets added to cytosol, CO2 gets added to

RuBPRuBP (ribulose biphosphate) (ribulose biphosphate) by enzyme Rubisco by enzyme Rubisco which is a 5 carbon carbohydrate to which is a 5 carbon carbohydrate to equal a 6-Carbon molecule that equal a 6-Carbon molecule that immediately splits into 2 3-carbon immediately splits into 2 3-carbon molecules (PGA)molecules (PGA)

• phosphoglyceratephosphoglycerate

Calvin CycleCalvin Cycle

• Step 2Step 2–PGA converted into G3P PGA converted into G3P (glyceraldehyde 3-(glyceraldehyde 3-

phosphate) phosphate) by adding P by adding P (from ATP) (from ATP) & H & H (from NADPH) (from NADPH)

to the 3-carbon molecules.to the 3-carbon molecules.• Then the ADP, NADP and P are used Then the ADP, NADP and P are used again in light reactions to make more again in light reactions to make more ATP and NADPHATP and NADPH

– In other words…..Binds H carried by NADPH to Carbon from CO2, with the help of ATP….all this was produced in light reactions…

Calvin CycleCalvin Cycle

• Step 3Step 3–Most G3P is converted back into Most G3P is converted back into

RuBP (keeps cycle going), but RuBP (keeps cycle going), but some G3P leaves cycle & is used some G3P leaves cycle & is used to make organic compoundsto make organic compounds

–Plants using Calvin cycle are C3 Plants using Calvin cycle are C3 plants (for the 3 Carbon plants (for the 3 Carbon compound produced)compound produced)

Calvin CycleCalvin Cycle

• ATPATP• NADPHNADPH• CO2CO2

Calvin Cycle RequiresCalvin Cycle Requires

• Pores on leaves through which COPores on leaves through which CO22

enters & Oenters & O22 exits exits

• Low COLow CO22 & High O & High O22 stop calvin stop calvin

cyclecycle

StomataStomata

• Hot dry climateHot dry climate• Partially close stomata during dayPartially close stomata during day• Make a 4 C compound first even though Make a 4 C compound first even though

COCO22 is low and O is low and O22 is high is high

• Lots of grasses do this + corn, sugar caneLots of grasses do this + corn, sugar cane• They lose about half as much water as C3 They lose about half as much water as C3

plants when producing same amount of plants when producing same amount of carbscarbs

Alternative Pathways, C4Alternative Pathways, C4

• Open stomata @ night and incorporate Open stomata @ night and incorporate C into a bunch of other compounds C into a bunch of other compounds they then use for photosynthesis they then use for photosynthesis during the day…grow slowly; lose less during the day…grow slowly; lose less waterwater

• Ex: cactus, pineappleEx: cactus, pineapple

–CAM stands for crassulacean acid CAM stands for crassulacean acid metabolismmetabolism

Alternative Pathways, CAMAlternative Pathways, CAM

• Light Dependent ReactionsLight Dependent Reactions– In thylakoidIn thylakoid– Collect lightCollect light– Produce ATP, NADPHProduce ATP, NADPH– Release OxygenRelease Oxygen– Consume waterConsume water

• Calvin Cycle/Dark Rxn/Light independentCalvin Cycle/Dark Rxn/Light independent– In stromaIn stroma– Take in Carbon dioxideTake in Carbon dioxide– Produce carbohydrate (G3P)Produce carbohydrate (G3P)

REVIEWREVIEW

REVIEWREVIEW

• Varies based on:Varies based on:

–amount of light (increase amount of light (increase level level off)off)

–amount of carbon dioxide amount of carbon dioxide (increase (increase level off) level off)

–Temperature (increase Temperature (increase decrease)decrease)

Factors affecting Factors affecting photosynthesis ratephotosynthesis rate

How do you get the How do you get the energy out of the organic energy out of the organic

compounds?compounds? Cellular Respiration = Cellular Respiration =

CH 7!CH 7!

Cellular RespirationCellular Respiration• Energy is generated by a series of Energy is generated by a series of

reactions ultimately used to form reactions ultimately used to form ATP from ADPATP from ADP

• CC66HH1212OO66 + 6O + 6O2 2 →→ 6CO6CO22 + 6H + 6H22O + energyO + energy

2 steps are:2 steps are:1. Glycolysis 1. Glycolysis

2. Aerobic Respiration2. Aerobic Respiration

GlycolysisGlycolysis• First Step in RespirationFirst Step in Respiration• Occurs in the cytosolOccurs in the cytosol• Splits Splits ONE glucoseONE glucose into into

TWO pyruvateTWO pyruvate moleculesmolecules

• Does not require oxygen= Does not require oxygen= anaerobicanaerobic

• Uses 2 ATP process and 2 Uses 2 ATP process and 2 NADNAD++

• Makes 4 ATPMakes 4 ATP• Net yield = 2 ATP Net yield = 2 ATP

After After Glycolysis:Glycolysis:If If OO22 present present

= aerobic = aerobic resp.resp.If If nono O O22 = =

fermentationfermentation

FermentationFermentation• Glycolysis + an anaerobic pathway = Glycolysis + an anaerobic pathway =

fermentationfermentation• Produces NADProduces NAD++ which keeps glycolysis which keeps glycolysis

going..w/out NADgoing..w/out NAD++ then glycolysis then glycolysis would stop and no ATPwould stop and no ATP would be madewould be made• Anaerobic processAnaerobic process• Does not produce ATPDoes not produce ATP• Lactic acid pathwayLactic acid pathway• Ethyl alcohol pathwayEthyl alcohol pathway

Lactic Acid fermentationLactic Acid fermentation• Pyruvic acid is converted into Pyruvic acid is converted into

lactic acid, forming NAD+lactic acid, forming NAD+• Yogurt, cheese, muscle cellsYogurt, cheese, muscle cells• Produced when strenuous exercise Produced when strenuous exercise

exceeds immediate demands of exceeds immediate demands of muscle tissuesmuscle tissues

Alcoholic fermentationAlcoholic fermentation• Pyruvic acid Pyruvic acid

ethyl alcoholethyl alcohol• Creates NAD +Creates NAD +• Yeast, wine, Yeast, wine,

breadbread

Efficiency of anaerobic Efficiency of anaerobic pathwayspathways

• Not very efficientNot very efficient• Cannot sustain large multicellular Cannot sustain large multicellular

organismsorganisms• OK for bacteria & early life on EarthOK for bacteria & early life on Earth

Aerobic RespirationAerobic Respiration

• If oxygen is present, the pyruvic If oxygen is present, the pyruvic acid from glycolysis undergoes acid from glycolysis undergoes cellular respiration cellular respiration

• Pyruvic acid still has a lot of Pyruvic acid still has a lot of energy in itenergy in it

Aerobic Respiration - 2 Aerobic Respiration - 2 stepssteps

• Step 1: Krebs cycleStep 1: Krebs cycle• Step 2: Electron transport chain & Step 2: Electron transport chain &

chemiosmosischemiosmosis• In Eukaryotes these occur in In Eukaryotes these occur in

mitochondriamitochondria• In Prokaryotes these occur in the In Prokaryotes these occur in the

cytosolcytosol

Krebs CycleKrebs Cycle• Pyruvic acid diffuses into Pyruvic acid diffuses into

mitochondria MATRIX & forms mitochondria MATRIX & forms acetyl CoAacetyl CoA

Krebs CycleKrebs Cycle• 4 carbon 4 carbon beginning product is beginning product is

regenerated at the end of the cycle regenerated at the end of the cycle

Krebs CycleKrebs Cycle• If what you start with is the same If what you start with is the same

as what you end with, what is the as what you end with, what is the point of the Krebs cycle?point of the Krebs cycle?

–It generates other “stuff” while It generates other “stuff” while going through the cyclegoing through the cycle

Krebs CycleKrebs Cycle• Acetyl CoA does a bunch of stuff and generates: (1 Acetyl CoA does a bunch of stuff and generates: (1

glucose = 2 turns of Krebs cycle) glucose = 2 turns of Krebs cycle) – 4 molecules of 4 molecules of CARBON DIOXIDE (is given off as CARBON DIOXIDE (is given off as

waste)waste), , – 6 molecules of 6 molecules of NADHNADH, ,

– 2 molecules of 2 molecules of FADHFADH22

– 2 molecules of 2 molecules of ATPATP

– Krebs still only makesKrebs still only makes

2 ATP like glycolysis…2 ATP like glycolysis…

So rest of products go into So rest of products go into

Mitochondrial inner membrane to make more!Mitochondrial inner membrane to make more!

Electron Transport ChainElectron Transport Chain

Electron Transport ChainElectron Transport Chain• Series of Series of electron carrierselectron carriers accept accept

electrons from NADH and electrons from NADH and FADH2 FADH2

Electron Transport ChainElectron Transport Chain• Chemiosmosis creates ATP from ADP - Chemiosmosis creates ATP from ADP -

just like in photosynthesis!just like in photosynthesis!

The Role of OxygenThe Role of Oxygen• What does the end of the ETC do What does the end of the ETC do

with its electrons?with its electrons?

–Oxygen is “final electron Oxygen is “final electron acceptor”acceptor”

• Oxygen combines with protons & Oxygen combines with protons & electrons that were part of NADH electrons that were part of NADH and FADH2 to create water!!!!!!!!and FADH2 to create water!!!!!!!!

Aerobic RespirationAerobic Respiration• Much more efficient than anaerobicMuch more efficient than anaerobic• Produces 38 ATP (glycolysis + Produces 38 ATP (glycolysis +

krebs + ETC)krebs + ETC)• CC66HH1212OO66 + 6O + 6O2 2 6CO6CO22 + 6H + 6H22O + O +

ATPATP

Summary of Cellular Summary of Cellular RespirationRespiration

Cellular Respiration SummaryCellular Respiration Summary

ETC and Chemiosmosis!ETC and Chemiosmosis!