Endosymbiotic

Theory p. 427-428

The Endosymbiotic Theory Review:

What is a theory?

What is the difference between prokaryotic and

eukaryotic cells?

The endosymbiotic theory is the idea that a

long time ago, prokaryotic cells engulfed

other prokaryotic cells by endocytosis. This

resulted in the first eukaryotic cells.

First proposed by Lynn Margulis

Explains the origin of eukaryotic cells

Explains the origin of certain membrane-bound

organelles

What Exactly Happened?

Heterotrophic

bacteria

Ancient Prokaryotes

Ancient Heterotrophic

Prokaryote

Primitive Heterotrophic

Eukaryote

Primitive Autotrophic

(Photosynthetic) Eukaryote

Chloroplast

Photosynthetic

bacteria Nuclear

envelope

evolving Mitochondrion

Plants and

plant-like

protists

Animals, fungi, and

animal-like protists

Membrane-Bound Organelles

Mitochondria =

membrane-bound

organelle that produces

energy for the cell

Chloroplast =

membrane-bound

organelle that captures

sunlight and uses it to

make food for the cell

Evidence in support of the

endosymbiotic theory: Both mitochondria and chloroplasts contain DNA,

which is fairly different from that of the cell nucleus, and that is similar to that of bacteria (circular and smaller).

They are surrounded by two or more membranes, and the innermost of these shows differences in composition compared to the other membranes in the cell. The composition is like that of a prokaryotic cell membrane.

New mitochondria and chloroplasts are formed only through a process similar to binary fission (prokaryote cell division).

Evidence in support of the

endosymbiotic theory:

Much of the internal structure and biochemistry of chloroplasts, for instance the presence of thylakoids and particular chlorophylls, is very similar to that of cyanobacteria.

The size of both organelles is comparable to bacteria.

These organelle's ribosomes are like those found in bacteria (70s).

Adenine Ribose 3 Phosphate groups

Cell Energy:

• Cells usable source of energy is called ATP

• ATP stands for adenosine triphosphate

• ADP stands for adenosine diphosphate

Adenine Ribose 2 Phosphate groups

•All energy is stored in the bonds of compounds—breaking the bond releases the energy

•When the cell has energy available it can store this energy by adding a phosphate group to ADP, producing ATP

• ATP is converted into ADP by breaking the bond between the second and third phosphate groups and releasing energy for cellular processes.

PHOTOSYNTHESISPHOTOSYNTHESISPart IIPart II

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Two Parts of PhotosynthesisTwo Parts of Photosynthesis

Two reactions make up Two reactions make up photosynthesis:photosynthesis:

1.1.Light Reaction or Light Light Reaction or Light Dependent ReactionDependent Reaction --

Produces energy from solar Produces energy from solar power (photons) in the form of power (photons) in the form of ATP and NADPH.ATP and NADPH.

SUNSUN

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Two Parts of PhotosynthesisTwo Parts of Photosynthesis

2. 2. Calvin Cycle or Light Calvin Cycle or Light Independent ReactionIndependent Reaction

•• Also called Also called Carbon FixationCarbon Fixationor or CC33 FixationFixation

•• Uses energy (Uses energy (ATP and ATP and NADPHNADPH) from light reaction ) from light reaction to make sugar to make sugar (glucose).(glucose).

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Light Reaction (Electron Flow)Light Reaction (Electron Flow)

•• Occurs in the Occurs in the Thylakoid Thylakoid membranesmembranes

•• During the During the light reactionlight reaction, there , there are are twotwo possible routes for possible routes for electron flow:electron flow:

A.A.Cyclic Electron FlowCyclic Electron Flow

B.B. Noncyclic Electron FlowNoncyclic Electron Flow

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Cyclic Electron FlowCyclic Electron Flow•• Occurs in the Occurs in the thylakoidthylakoid membrane.membrane.•• Uses Uses Photosystem I onlyPhotosystem I only•• P700P700 reaction centerreaction center-- chlorophyll a chlorophyll a •• Uses Electron Transport Chain Uses Electron Transport Chain (ETC)(ETC)

•• Generates Generates ATP onlyATP only, more ATP , more ATP required for required for

ADP + ADP + ATPATPP

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Adenosine Triphosphate – ATPA. Because cells need a steady supply

of energy to carry on cellular processes they store energy by bonding a third phosphate moleculeto ADP (adenosine diphosphate)forming ATP (adenosine triphosphate)

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•What makes up ADP (adenosine diphosphate)?

Adenine base, ribose sugar and 2 (di)phosphates

• ATP consists of an adenine base, a ribose sugar and 3 phosphate molecules

Adenosine Adenosine TriphosphateTriphosphate

AdenosineAdenosineDiphophateDiphophate

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. Energy stored in the bonds betweenphosphate molecules is released when a phosphate molecule breaks off. Sinceevery activity an organism performs requires energy, this cycle is repeatedagain and again throughout the life ofthe cell.

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Cyclic Electron FlowCyclic Electron Flow

P700

PrimaryElectronAcceptor

e-

e-

e-

e-

ATPATPproducedby ETC

Photosystem I

AccessoryPigments

SUN

Photons

Pigments absorb light energy & excite ePigments absorb light energy & excite e-- of of Chlorophyll a to produce ATP Chlorophyll a to produce ATP

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Noncyclic Electron FlowNoncyclic Electron Flow•• Occurs in the Occurs in the thylakoidthylakoid membranemembrane•• Uses Uses PhotosystemPhotosystem II II and and PhotosystemPhotosystem II

•• P680 P680 reaction center reaction center (PSII)(PSII) --chlorophyll achlorophyll a

•• P700P700 reaction center reaction center (PS I)(PS I) --chlorophyll achlorophyll a

•• Uses Electron Transport Chain Uses Electron Transport Chain (ETC)(ETC)

•• Generates Generates OO22, ATP and NADPH, ATP and NADPH

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Noncyclic Electron FlowNoncyclic Electron Flow

P700

Photosystem IP680

Photosystem II

PrimaryElectronAcceptor

PrimaryElectronAcceptor

ETC

EnzymeReaction

H2O

½½ OO22 + 2H+

ATPATP

NADPHNADPHPhoton

2e-

2e-

2e-

2e-

2e-

SUN

Photon

HH22O is split in PSII & ATP is made, while the energy carrier O is split in PSII & ATP is made, while the energy carrier NADPH is made in PSINADPH is made in PSI

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Noncyclic Electron FlowNoncyclic Electron Flow

•• ADP +ADP + →→→→→→→→ ATPATP

•• NADPNADP++ + H + H → → → → → → → → NADPHNADPH

•• OxygenOxygen comes from the splitting comes from the splitting of Hof H22O, not COO, not CO2 2 (Photolysis)(Photolysis)

HH22O O →→→→→→→→ ½½ OO22 + 2H+ 2H++

PP

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ChemiosmosisChemiosmosis

•• Powers Powers ATP synthesisATP synthesis•• Located in the Located in the thylakoid thylakoid membranesmembranes

•• Uses Uses ETETC and C and ATP synthase ATP synthase (enzyme)(enzyme) to make ATPto make ATP

•• Photophosphorylation:Photophosphorylation:addition of phosphate to ADP addition of phosphate to ADP to make ATPto make ATP

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ChemiosmosisChemiosmosisH+ H+

ATP Synthase

H+ H+ H+ H+

H+ H+ high Hhigh H ++

concentrationconcentration

H+ADP + P ATP

PS II PS IE

TC

low Hlow H ++

concentrationconcentration

H+ThylakoidThylakoidSpaceSpace

ThylakoidThylakoid

SUN (Proton Pumping)

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Calvin CycleCalvin Cycle•• Carbon Fixation Carbon Fixation (light independent (light independent reaction)reaction)

•• CC33 plants (80% of plants on earth)plants (80% of plants on earth)•• Occurs in the Occurs in the stromastroma•• Uses Uses ATP and NADPHATP and NADPH from light from light reaction as energyreaction as energy

•• Uses Uses COCO22

•• To produce To produce glucoseglucose: it takes : it takes 6 6 turns and uses 18 ATP and 12 turns and uses 18 ATP and 12 NADPH. NADPH.

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ChloroplastChloroplast

GranumThylakoid

STROMA– where Calvin Cycle occursOuter Membrane

Inner Membrane

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Calvin Cycle (CCalvin Cycle (C33 fixation)fixation)

18

Calvin CycleCalvin Cycle

Remember: CRemember: C33 = Calvin Cycle= Calvin Cycle

C3

Glucose

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PhotorespirationPhotorespiration

•• Occurs on hot, dry, bright daysOccurs on hot, dry, bright days

•• Stomates closeStomates close

•• Fixation of OFixation of O22 instead of COinstead of CO22

•• Produces Produces 22--C molecules instead of C molecules instead of 33--C sugar moleculesC sugar molecules

•• Produces Produces no sugarno sugar molecules or molecules or no no ATPATP

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PhotorespirationPhotorespiration

Because of photorespiration, plants Because of photorespiration, plants have special adaptations have special adaptations (alternative pathways) to limit the (alternative pathways) to limit the effect of photorespiration:effect of photorespiration:

1.1. CC44 plantsplants

2.2. CAM plantsCAM plants

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CC44 PlantsPlants•• Hot, moist Hot, moist environmentsenvironments

•• 15% of plants 15% of plants ((grasses, corn, grasses, corn, sugarcane)sugarcane)

•• Photosynthesis Photosynthesis occurs in 2 placesoccurs in 2 places

•• Light reactionLight reaction --mesophyll cellsmesophyll cells

•• Calvin cycleCalvin cycle -- bundle bundle sheath cellssheath cells

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CC44 PlantsPlants

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CAM PlantsCAM Plants

•• Hot, dry environmentsHot, dry environments•• 5%5% of plants (cactus and ice of plants (cactus and ice plants)plants)

•• Stomates closed during dayStomates closed during day•• Stomates open during the nightStomates open during the night•• Light reaction Light reaction -- occurs during occurs during the daythe day

•• Calvin Cycle Calvin Cycle -- occurs when COoccurs when CO22 is is presentpresent

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Stomata OpenStomata Open Stomata ClosedStomata Closed

25

CAM PlantsCAM PlantsNight (Stomates Open) Day (Stomates Closed)

Vacuole

C-C-C-CMalate

C-C-C-CMalate Malate

C-C-C-CCO2

CO2

C3

C-C-CPyruvic acid

ATPC-C-CPEP glucose

26

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Question:Question:

Why do CAM Why do CAM plants close plants close their stomata their stomata during the day?during the day?

Cam plants close Cam plants close their stomata in their stomata in the hottest part the hottest part of the day to of the day to conserve waterconserve water

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Rates of PhotosynthesisRates of Photosynthesis

1.1. Light IntensityLight Intensity

2.2. COCO22

3.3. TemperatureTemperature