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PhotosynthesisPhotosynthesis

Let the sun shine…..Let the sun shine…..

Hooray for photosynthesis!!!!Hooray for photosynthesis!!!!

The equations…The equations…

• Cellular respiration-highly exergonicCellular respiration-highly exergonic– C6H12O6 + O2 C6H12O6 + O2 CO2 + H2O + CO2 + H2O +

ATP!!ATP!!– Energy released thru oxidation of Energy released thru oxidation of

glucoseglucose

• Photosynthesis-highly endergonicPhotosynthesis-highly endergonic– Light + CO2 Light + CO2 C6H12O6 + O2 C6H12O6 + O2– Light energy used to reduce CO2Light energy used to reduce CO2

• StromaStroma– ATP produced in stromaATP produced in stroma– Calvin cycleCalvin cycle

• Thylakoid membraneThylakoid membrane– Photosystems Photosystems

embeddedembedded– ETCsETCs– ATP synthaseATP synthase

• Thylakoid spaceThylakoid space– H+ conc. gradientH+ conc. gradient

OverviewOverviewProduce energyRequired for darkreactions

“fix” CO2 into glucose

Highly endergonic

• Light independent reactionsLight independent reactions– Occur in thylakoid space & membraneOccur in thylakoid space & membrane– Light strikes chlorophyllLight strikes chlorophyll– E- are boosted to higher energy level & E- are boosted to higher energy level &

travel down an ETCtravel down an ETC– Released energy captured to form ATP & Released energy captured to form ATP &

NAPHNAPH– Water molecules borken apart to Water molecules borken apart to

replace lost e-replace lost e-

• Light independent reactions-carbon Light independent reactions-carbon fixingfixing– Uses energy captured in ATP & NADPH Uses energy captured in ATP & NADPH

to reduce CO2 to sugarto reduce CO2 to sugar– Occurs in stromaOccurs in stroma

Absorption pigmentsAbsorption pigments• Light energy must be Light energy must be

absorbed to be of any absorbed to be of any benefitbenefit

• Pigments absorb certain Pigments absorb certain wavelengths of light, which wavelengths of light, which causes altered structurecauses altered structure

• Chloroplasts contain Chloroplasts contain several pigmentsseveral pigments– Chlrophyll-absorbs violet, Chlrophyll-absorbs violet,

blue, redblue, red– Carotenoids-absorb blue & Carotenoids-absorb blue &

greengreen– Phycocyanins-absorb greenPhycocyanins-absorb green

What happens when chlorophyll absirbs What happens when chlorophyll absirbs light?light?

• An e- becomes energized & moves to higher orbitalAn e- becomes energized & moves to higher orbital

• This is unstable-e- will normally release energy & This is unstable-e- will normally release energy & move back to its original orbitalmove back to its original orbital

• In photosynthesis, e- is captured by ETCIn photosynthesis, e- is captured by ETC

What is a photosystem?What is a photosystem?

• Located in thylakoid membraneLocated in thylakoid membrane• Composed of a reaction Composed of a reaction

center(chlorophyll), ,accessory(center(chlorophyll), ,accessory(antennae) pigments, & an ETCantennae) pigments, & an ETC

• PSI-PSI-– evolved 1evolved 1stst, , – cotains a dimer of chlorophyll,cotains a dimer of chlorophyll,– can operate independently of PSII, can operate independently of PSII, – its ETC makes NADPHits ETC makes NADPH

• PSIIPSII– Supllies e- to PSISupllies e- to PSI– ETC produces ATP ETC produces ATP

(photophosphorylation)(photophosphorylation)

• Accessory pigments absorb Accessory pigments absorb light & pass it chlorophylllight & pass it chlorophyll

•Only chlorophyll loses e- to ETCs

Light causes e- to become energized in PSIIJump to higher level

Water is split to replace e-

E- captured by cytochromes in ETC

Energy used to push H+ from stroma to space

Gradient used to produce ATP in stroma

E- end up in PSI, which has also lost e-To its ETC

PSI ETC gives its e- to NAD-an e- shuttle, it carries e- to calvin cycle

Cyclic e- flow-used when no NADP is available-Cyclic e- flow-used when no NADP is available-(calvin cycle uses ATP faster than NADPH)(calvin cycle uses ATP faster than NADPH)

This ETC shuts downNo NADPH or O2

RuBP is regenerated

RuBP carboxylase

Reverse reactions of glycolysis

CO2 is reduced

G3P

In stroma

Totals-1 glucose moleculeRequires:6CO218 ATP12 NADPHHow many ATP do we get From 1 glucose in cell resp?

C4 plantsC4 plants

• During hot weather, stoma During hot weather, stoma close to avoid water lossclose to avoid water loss

• Causes build up of O2 Causes build up of O2 which favors which favors photorespiration-rubisco photorespiration-rubisco not selectivenot selective

• This inhibits calvin cycleThis inhibits calvin cycle• C4 plants have 2 C4 plants have 2

adaptations to combat thisadaptations to combat this– Bundle sheath cells in leaf Bundle sheath cells in leaf

interior-less PSII, so less interior-less PSII, so less O2 producedO2 produced

– PEP carboxylase-high PEP carboxylase-high affinity for CO2 despite affinity for CO2 despite O2 levlsO2 levls

– Result is maintenance of Result is maintenance of high level of CO2, with a high level of CO2, with a lower level of O2lower level of O2

CAM plantsCAM plants

• Crusculacean AcidCrusculacean Acid

MetabolismMetabolism

• Open stomata at Open stomata at night-store CO2 as night-store CO2 as CACA

• During day, During day, stomata closed-stomata closed-convert CA back to convert CA back to CO2 & CO2 & photosynthesizephotosynthesize

Terminal phosphatesBreak off fairly easilyDue to instability ofMolecule-provide Enough energy for mostCellular reactions

ADP AMP + Pi

Coupled reactions-energy released Coupled reactions-energy released from exergonic reactions drives from exergonic reactions drives endergonic reactionsendergonic reactions

Nuclear fusion H He + Light energy

EXERGONIC

CO2 + H2O + O2

ENDERGONIC

Sometimes the breakdownOf ATP is coupled toAn endergonic reaction

This reaction is endergonic

This compound is Phosphorylated & Has energy

This bond isBroken & theEnergy releasedDrives the reaction

•ATP is formed through the oxidation ATP is formed through the oxidation (breakdown) of glucose in a series of step (breakdown) of glucose in a series of step wise reactionswise reactions

Redox (oxidation-reduction) Redox (oxidation-reduction) ReactionsReactions• e- pass from one atom/molecule to anothere- pass from one atom/molecule to another• H+ may also be lost or gained as a resultH+ may also be lost or gained as a result• Molecule which loses the e- (H+) is oxidizedMolecule which loses the e- (H+) is oxidized• Molecule which gains e- (H+) is reducedMolecule which gains e- (H+) is reduced• Must always occur togetherMust always occur together• The transfer of an e- to a more The transfer of an e- to a more

electronegative atom releases energyelectronegative atom releases energy

Na + Cl Na+ Cl-

Na is oxidizedCl is reduced

CC66HH1212OO66 + 6O + 6O22 6CO2 + 6H2O

During cellular respiration…..•Glucose is oxidized, oxygen is reduced• e- shift from glucose to highly electronegative O2•Energy released a little at a time

No matter what food is taken inIt can be fed into this processAt some point!

The Reactions…….The Reactions…….

So what’s really So what’s really important aboutimportant aboutglycolysis?glycolysis?

1. Takes place in cytoplasm2. With or without oxygen3. Every living thing on the

planet does it4. Starts with 6C glucose5. Ends with 2, 3C pyruvates6. Gross 4 ATP7. Net 2ATP, & 2 NADH

Nicotinamide adenine diphosphate, Nicotinamide adenine diphosphate, aka NAD, is an electron shuttleaka NAD, is an electron shuttle

So what happens So what happens next?next?That depends on That depends on whether or not O2 is whether or not O2 is present!!!present!!!

•W/ O2, Kreb’s cycle & ETC•W/O O2, fermentation

FermentationFermentation• In the presence of O2, In the presence of O2,

NADH carries its e- to NADH carries its e- to the ETCthe ETC

• NAD is regenerated for NAD is regenerated for use during glycolysisuse during glycolysis– W/o this regeneration, W/o this regeneration,

glycolysis would stop!!glycolysis would stop!!

• If no O2 is present, If no O2 is present, fermentation fermentation regenerates NAD, & regenerates NAD, & keeps glycolysis activekeeps glycolysis active

Hooray forFermentation!

Used by anaerobic microorganisms (bacteria, Used by anaerobic microorganisms (bacteria, yeast), & to make human foodsyeast), & to make human foods

• Used by human Used by human muscles during muscles during vigorous exercise vigorous exercise (oxygen debt)(oxygen debt)

• Allows muscles to Allows muscles to continue working w/o continue working w/o oxygenoxygen

• Build-up forces Build-up forces muscles to slow muscles to slow down until intake of down until intake of O2 catches upO2 catches up

• Lactic acid eventually Lactic acid eventually breaks downbreaks down

• Outer membrane permeable to most small moleculesOuter membrane permeable to most small molecules

• Inner membrane only permeable to ATP & pyruvateInner membrane only permeable to ATP & pyruvate

• Matrix-enzymes, water, Pi-parts of Kreb’s & ETCMatrix-enzymes, water, Pi-parts of Kreb’s & ETC

• Cristae-kreb cycle enzymes, ATP synthetase, ETC Cristae-kreb cycle enzymes, ATP synthetase, ETC embedded in foldsembedded in folds

•Intermediate Step-what’s important…Intermediate Step-what’s important… link between glycolysis & Kreb’slink between glycolysis & Kreb’smoves pyruvate into mitochondria (sometimes ACTIVE transport)moves pyruvate into mitochondria (sometimes ACTIVE transport)happens twice per glucose (2 pyruvate)happens twice per glucose (2 pyruvate)start w/ 2 pyruvatestart w/ 2 pyruvateend with 2 acetyl CoAend with 2 acetyl CoAnet 2 NADH, 2 CO2 (by-product)net 2 NADH, 2 CO2 (by-product)

oxidized

To Krebscycle

Series of redox Reactions whichCompletely finishesThe oxidation ofglucose

So Dunbar, help us So Dunbar, help us out out here! What’s here! What’s important?important?• Each glucose requires 2 turns Each glucose requires 2 turns

of cycle (2 pyruvates)of cycle (2 pyruvates)• Takes place in matrix & Takes place in matrix &

cristaecristae• Oxaloacetate is regeneratedOxaloacetate is regenerated• Start w/ 2 acetyl CoAStart w/ 2 acetyl CoA• End w/ oxaloacetateEnd w/ oxaloacetate• Net, per glucoseNet, per glucose

– 2 ATP2 ATP– 6 NADH6 NADH– 2 FADH2 (another e- shuttle)2 FADH2 (another e- shuttle)– 4 CO2 (by-product)4 CO2 (by-product)

• TOTALS SO FARTOTALS SO FAR– 4 ATP4 ATP– 10 NADH10 NADH– 2 FADH22 FADH2– 6 CO26 CO2

THE BIG PAYOFF!!!!THE BIG PAYOFF!!!!• Totals so far…Totals so far…

– 4 ATP4 ATP– 10 NADH10 NADH– 2 FADH22 FADH2– 6 CO26 CO2

• But I thought you could But I thought you could get 38 ATPs from just 1 get 38 ATPs from just 1 glucose!! What’s the glucose!! What’s the deal yo?deal yo?

• MOST OF THE ATP MOST OF THE ATP COMES FROM THE COMES FROM THE ELECTRON TRANSPORT ELECTRON TRANSPORT CHAIN!!!!CHAIN!!!!

So what is it, So what is it, anyway????anyway????

• A collection of molecules A collection of molecules embedded in the cristaeembedded in the cristae

• Molecules are proteins called Molecules are proteins called cytochromes- they can accept cytochromes- they can accept & pass on e- (just like NAD)& pass on e- (just like NAD)– Heme group alternates Heme group alternates

between reduced & oxidized between reduced & oxidized statestate

• NADH & FADH2 drop off e- to 1NADH & FADH2 drop off e- to 1stst cytochrome, & these are cytochrome, & these are passed down the chain passed down the chain

• Each cytochrome in the chain is Each cytochrome in the chain is more electronegative than the more electronegative than the one before it one before it

• The last e- acceptor is O2 The last e- acceptor is O2

(the most (the most electronegative of electronegative of all!!!)all!!!)

cristae

H+

H+H+ H+

H+H+

H+

H+

H+

H+

1. Energy released as e- move closer to O2-used to pump H+ into intermembrane space

2. Conc. Gradient set up-water behind a dam

3. H+ MUST pass thru here

4. Energy created from H+ moving thru enzyme provides energy toPhosphorylate ADP (chemiosmosis)

How does this How does this enzyme work?enzyme work?Think pinwheel!Think pinwheel!

1.1. Rush of H+ turns the Rush of H+ turns the rotor which spins the rotor which spins the rodrod

2.2. Turning of rod Turning of rod activates catalytic activates catalytic sitessites

3.3. Each NADH makes Each NADH makes 3ATP, each FADH2 3ATP, each FADH2 makes 2 ATPmakes 2 ATP

• 10 NADH10 NADH30 ATP30 ATP• 2 FADH2 2 FADH2 4 ATP 4 ATP

• SO…………..SO…………..

TA-DAAAA!!

The last thing!The last thing!

• How does a How does a cell/organism cell/organism control how much control how much ATP is made?ATP is made?– Second step of Second step of

glycolysis controlled glycolysis controlled thru biofeedbackthru biofeedback

– PhosphofructokinasPhosphofructokinase is an allosteric e is an allosteric enzyme!!!enzyme!!!