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
2
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
3
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).
4
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
5
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
6
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)
7
•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
8
. 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.
9
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
10
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
11
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
12
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
13
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
14
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)
15
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.
16
ChloroplastChloroplast
GranumThylakoid
STROMA– where Calvin Cycle occursOuter Membrane
Inner Membrane
17
Calvin Cycle (CCalvin Cycle (C33 fixation)fixation)
18
Calvin CycleCalvin Cycle
Remember: CRemember: C33 = Calvin Cycle= Calvin Cycle
C3
Glucose
19
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
20
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
21
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
22
CC44 PlantsPlants
23
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
24
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
27
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
29
Rates of PhotosynthesisRates of Photosynthesis
1.1. Light IntensityLight Intensity
2.2. COCO22
3.3. TemperatureTemperature