electron transportelectron transport /photosynthesis chapter 14 electron transport • reduced...
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electron transport /photosynthesis
chapter 14
electron transport• Reduced coenzymes
• NADH and FADH2
• used to produce ATP-
• oxidative phosphorylation• energy from redox
reactions used to produce ATP
• chemiosmosis
electron transport• electron tranport chain
• multiprotein complexes• accept and donate
electrons• each time, electrons
lose free energy• H+ pumped out
• chemiosmosis• potential energy
stored in H+ gradient used to synthesize ATP
electron transport• types of electron carriers
• flavoproteins• cytochromes• three copper atoms• ubiquinone• iron sulfur proteins
electron transport• complex I
• NADH dehydrogenase• flavin
mononucleotide• iron-sulfur protein
• complex II (TCA cycle)• succinate
dehydrogenase• FADH2 - lower energy
• complex III• cytochrome bc1
• complex IV• cytocrome c oxidase
2 H+2 H+
-2
4 4 2
proton differential = 12 ( per pair of e- )
proton motive force• ATP-synthase
• F0
• 10-14 subunits• H+ flows into half channel• binds with rotor subunits• rotor turns
• F1 • internal rod spins• catalytic portion fixed
F1
F0
INTERMEMBRANE SPACE
Rotor
StatorH+
Internal rod
Catalytic knob
ADP
+P
iATP
MITOCHONDRIAL MATRIX
F1
F0
H+
binding change mech.• catalysis of ATP
• three binding sites• three conformations (active site)
• loose• binds with ADP and P
• tight• ATP formed
• open• ATP released
energy accounting• about 32 ATP molecules produced from glucose
• uncoupling proteins• brown fat
2 2 26
2 2 26 or 28TOTAL: ~30-32 max
• what if there is no O2?• fermentation
• glycolysis -> pyruvate / NADH• pyruvate ->
• reduced to lactate• no release of CO2
• OR• pyruvate ->
• reduced to EtOH• release of CO2
anaerobic anaerobic• eukaryotes
• if O2 not available - • pyruvate undergoes fermentation
photoautotrophs• photosynthesis
• low energy electrons converted to high energy electrons• used to chain carbon
atoms together• electron donors
• H2S• H2O
• cyanobacteria
plant structure• leaves
• eudicots• two layers of
mesophyll• palisade• spongy
• stomata• monocots
• single layer of mesophyll
eudicot
monocot
palisade mesophyll
spongy mesophyll
chloroplasts• plastids
• special organelles found in plants
• involved in various metabolic processes and storage
• develop from proplastids in meristem
• chloroplasts• specialized plastids involved
in the process of photosynthesis
Mesophyll
Leaf cross sectionChloroplasts Vein
Stomata
Chloroplast Mesophyll cell
CO2
O2
20 μm
Outer membrane
Intermembrane space
Inner membrane
1 μm
Thylakoid space
ThylakoidGranumStroma
chloroplasts• outer membrane
• intermembrane space• inner membrane
• stroma• thylakoid
• grana• thylakoid space
Outer membrane
Intermembrane space
Inner membrane
1 μm
Thylakoid space
ThylakoidGranum
Stroma
Chloroplast
photosynthesis• light-dependent
• energy from sunlight absorbed• stored as ATP and NADPH
• light-independent• CO2 converted to carbs• uses energy from ATP and NADPH
Light
Light Reactions
Calvin Cycle
[CH2O]
(sugar)
CO2
Chloroplast
ATP
NADPH
NADP+
ADP+ P
i
H2O
O2
Figure 10.17
Mitochondrion Chloroplast
MITOCHONDRION STRUCTURE
CHLOROPLAST STRUCTURE
Intermembrane space
Inner membrane
Matrix
Thylakoid space
Thylakoid membrane
Stroma
Electron transport
chain
H+ Diffusion
ATP synthase
H+
ADP + P i
Key Higher [H+ ]
Lower [H+ ]
ATP
harvesting light• chlorophyll structure
• porphyrin ring• hydrocarbon tail
• hydrophobic• carotenoids
• accessory pigments• absorb blue & green light
Phytol tail
Porphyrin ring
CH3
CH3 in chlorophyll a
CHO in chlorophyll b
harvesting light• photosystems
• photosynthetic unit• antenna
• reaction-center
Thy
lako
id m
embr
ane
Photon
Photosystem
STROMA
Light- harvesting complexes
Reaction- center
complex
Primary electron acceptor
Transfer of energy
Special pair of chlorophyll a
molecules
Pigment molecules
THYLAKOID SPACE (INTERIOR OF THYLAKOID)
e−
photosystems• photosystem II
• boosts electrons energy level to midpoint• reaction center (P680)
• photosystem I• boosts electrons energy level to above
NADP+
• reaction center (P700)• Z scheme -
Primary acceptor
P680
Light
Pigment molecules
Photosystem II (PS II)
1
2
e−
splitting water• photosystem II
• light-harvesting complex II• contains most of the antenna pigments• light energy transmitted to core of PS2
splitting water• photosystem II
• transfers electron to pheophytin1. primary electron acceptor
• pheo + P680+ (powerful oxidizing agent)2. pheo- donates electron to PQA —> PQB
3. with next photon, plastoquinone reduced to plastoquinol (PQH2)
• photolysis • requires 4 electrons (2
for each O atom)
production of NADPH• bridging the gap
• PQH2 -> cytochrome b6f (multiprotein complex)• electrons passed to plastocyanin• plastocyanin passes electrons to P700+
1 μm
Thylakoid space
ThylakoidGranum
production of NADPH• photosystem I
• electron passed -> lumen side to stroma side1. P700 transfers electron to
A0
2. A0- passes to A1
3. A1- passes electron through 3 Fe-S clusters
4. passed to ferredoxin5. 2 ferredoxins interact with
ferredoxin NADP+ reductase
• FAD group - accepts 2 e-
• NADPH
photophosphorylation• production of ATP
• pH gradient established• ATP synthase pumps H+ out of lumen• noncyclic phosphoryation
• cyclic photophosphorylation• sometimes electrons from ferredoxin passed back
plastoquinone• then to cyt b6f
• pump H+ into lumen• mainly in lamellae• cuts PSII out of loop
actual locations• PSI and PS II are not located in the same areas
• PSII is located in the stacked grana• PSI is located outside stacked grana
GRANA
3 Co2 (one at a time) 1
Carbon fixationP P
short-lived intermediate
x3
P
3-Phosphoglycerate
x6
3Regeneration of
CO2 acceptor
3 ADP
3 ATP
2
Reduction
P
Glyceraldehyde 3-phosphate (G3P)
x66 NADPH
6 NADP+
6 P
P
Glyceraldehyde 3-phosphate (G3P)
CALVIN CYCLE
Ribulose bisphosphate
(RuBP)
P Px3
Rubisco
P
Glyceraldehyde 3-phosphate (G3P)
x5
PP1,3-bisphosphoglyceratex6
6 ADP
6 ATP
carbohydrate synthesis• GAP molecules
• exported into cytoplasm• exchanged for
phosphate • used to synthesize
sucrose• can remain in
chloroplast
Light
Light Reactions:
Photosystem II Electron transport chain
Photosystem I Electron transport chain
NADP+
ADP+ P
i
RuBP
ATP
NADPH
3-Phosphoglycerate
Calvin Cycle
G3P
Starch (storage)
Sucrose (export)
Chloroplast
H2O CO
2
O2
photorespiration• when stomata are closed
• rubisco --> O2 --> 2-carbon compound • 2-phosphoglycolate
• consumes O2, releases CO2• glycolate -> glycoxylate ->
glycine (CO2 released)• perhaps evolutionary relic
• limits buildup of damaging light reaction products
• problem for plants when hot and dry
C4 plants• adaptation to hot climate
• C4 pathway works well with low CO2
• CO2 combined with PEP • produce 4-carbon compounds
• passed to bundle sheath cell and calvin cycle• mainly found in monocots
• mainly grasses• corn, sorghum, sugar cane
bundle sheath cells
mesophyll
The C4 pathwayMesophyll
cellPEP carboxylaseCO
2
Oxaloacetate (4C) PEP (3C)
Malate (4C)
Pyruvate (3C)
CO2
Bundle- sheath
cell
Calvin Cycle
Sugar
Vascular tissue
ADP
ATP
CAM plants• crassulacean acid metabolism
• open stomata at night• fix CO2
• close stomata during day• use CO2 from CAM pathway
• examples• orchids, bromeliads, pineapple, ferns, cycads, some dicots
Temporal separation of steps
CO2
Organic acid
CO2
Calvin Cycle
Sugar
Day
Night
CAMCO
2 incorporated
(carbon fixation)
CO2 released
to the Calvin cycle
2
1