How Cells Acquire Energy Chapter 6. Photoautotrophs –Carbon source is carbon dioxide –Energy...
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Transcript of How Cells Acquire Energy Chapter 6. Photoautotrophs –Carbon source is carbon dioxide –Energy...
![Page 1: How Cells Acquire Energy Chapter 6. Photoautotrophs –Carbon source is carbon dioxide –Energy source is sunlight Heterotrophs –Get carbon and energy by.](https://reader035.fdocuments.net/reader035/viewer/2022062805/5697bff11a28abf838cbb5a0/html5/thumbnails/1.jpg)
How Cells Acquire Energy
Chapter 6
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• Photoautotrophs
– Carbon source is carbon dioxide
– Energy source is sunlight
• Heterotrophs
– Get carbon and energy by eating
autotrophs or one another
Carbon and Energy Sources
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Photoautotrophs
• Capture sunlight energy and use it to carry out photosynthesis
– Plants
– Some bacteria
– Many protistans
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T.E. Englemann’s Experiment
Background
• Certain bacterial cells will move toward places where oxygen concentration is high
• Photosynthesis produces oxygen
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T.E. Englemann’s Experiment
Hypothesis
• Movement of bacteria can be used to determine optimal light wavelengths for photosynthesis
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T.E. Englemann’s Experiment
Method
• Algal strand placed on microscope slide and illuminated by light of varying wavelengths
• Oxygen-requiring bacteria placed on same slide
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T.E. Englemann’s Experiment
![Page 8: How Cells Acquire Energy Chapter 6. Photoautotrophs –Carbon source is carbon dioxide –Energy source is sunlight Heterotrophs –Get carbon and energy by.](https://reader035.fdocuments.net/reader035/viewer/2022062805/5697bff11a28abf838cbb5a0/html5/thumbnails/8.jpg)
T.E. Englemann’s Experiment
Results Bacteria congregated where red and violet wavelengths illuminated alga
ConclusionBacteria moved to where algal cells released more oxygen--areas illuminated by the most effective light for photosynthesis
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Linked Processes
Photosynthesis
• Energy-storing pathway
• Releases oxygen
• Requires carbon dioxide
Aerobic Respiration
• Energy-releasing pathway
• Requires oxygen
• Releases carbon dioxide
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Organelles of photosynthesis
Chloroplasts
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Photosynthesis Equation
12H2O + 6CO2 6O2 + C2H12O6 + 6H2Owater carbon
dioxideoxygen glucose water
LIGHT ENERGY
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Two Stages of Photosynthesis
sunlight water uptake carbon dioxide uptake
ATP
ADP + Pi
NADPH
NADP+
glucoseP
oxygen release
LIGHT INDEPENDENT-
REACTIONS
LIGHT DEPENDENT-REACTIONS
new water
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• Continual input of solar energy into
Earth’s atmosphere
• Almost 1/3 is reflected back into space
• Of the energy that reaches Earth’s
surface, about 1% is intercepted by
photoautotrophs
Sunlight Energy
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Electromagnetic Spectrum
Shortest Gamma rays
wavelength X-rays
UV radiation
Visible light
Infrared radiation
Microwaves
Longest Radio waves
wavelength
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Visible Light
• Wavelengths humans perceive as different colors
• Violet (380 nm) to red (750 nm)
• Longer wavelengths, lower energy
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Photons
• Packets of light energy
• Each type of photon has fixed amount of energy
• Photons having most energy travel as shortest wavelength (blue-green light)
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Pigments
• Light-absorbing molecules
• Absorb some wavelengths and transmit others
• Color you see are the wavelengths NOT absorbed
Wavelength (nanometers)
chlorophyll b
chlorophyll a
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• Light-catching part of molecule often has alternating single and double bonds
• These bonds contain electrons that are capable of being moved to higher energy levels by absorbing light
Pigment Structure
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Excitation of Electrons
• Excitation occurs only when the quantity of energy in an incoming photon matches the amount of energy necessary to boost the electrons of that specific pigment
• Amount of energy needed varies among pigment molecules
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Variety of Pigments
Chlorophylls a and b
Carotenoids
Anthocyanins
Phycobilins
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Chlorophylls
Main pigments in most photoautotrophsW
avel
eng
th a
bso
rpti
on
(%
)
Wavelength (nanometers)
chlorophyll b
chlorophyll a
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Carotenoids
• Found in all photoautotrophs
• Absorb blue-violet and blue-green that chlorophylls miss
• Reflect red, yellow, orange wavelengths
• Two types– Carotenes - pure hydrocarbons
– Xanthophylls - contain oxygen
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Anthocyanins & Phycobilins
Red to purple pigments
• Anthocyanins– Give many flowers their colors
• Phycobilins– Found in red algae and cyanobacteria
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Pigments in Photosynthesis
• Bacteria– Pigments in plasma membranes
• Plants– Pigments embedded in thylakoid membrane
system– Pigments and proteins organized into
photosystems– Photosystems located next to electron
transport systems
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Photosystems and Electron Transporters
water-splitting complex thylakoidcompartment
H2O 2H + 1/2O2
P680
acceptor
P700
acceptor
pool of electron
transporters
stromaPHOTOSYSTEM II
PHOTOSYSTEM I
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• Pigments absorb light energy, give up e- which enter electron transport systems
• Water molecules are split, ATP and NADH are formed, and oxygen is released
• Pigments that gave up electrons get replacements
Light-Dependent Reactions
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Photosystem Function: Harvester Pigments
• Most pigments in photosystem are harvester pigments
• When excited by light energy, these pigments transfer energy to adjacent pigment molecules
• Each transfer involves energy loss
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Photosystem Function: Reaction Center
• Energy is reduced to level that can be captured by molecule of chlorophyll a
• This molecule (P700 or P680) is the reaction center of a photosystem
• Reaction center accepts energy and donates electron to acceptor molecule
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Pigments in a Photosystem
reaction center (a specialized chlorophyll a molecule)
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Electron Transport System
• Adjacent to photosystem • Acceptor molecule donates electrons
from reaction center
• As electrons flow through system, energy they release is used to produce ATP and, in some cases, NADPH
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Cyclic Electron Flow
• Electrons – are donated by P700 in photosystem I to
acceptor molecule
– flow through electron transport system and back to P700
• Electron flow drives ATP formation
• No NADPH is formed
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Cyclic Electron Flow
electron acceptor electron transport system
e–
e–
e–
e–
ATP
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Noncyclic Electron Flow
• Two-step pathway for light absorption
and electron excitation
• Uses two photosystems: type I and
type II
• Produces ATP and NADPH
• Involves photolysis - splitting of water
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Machinery of Noncyclic Electron Flow
photolysis
H2O
NADP+ NADPH
e–
ATP
ATP SYNTHASE
PHOTOSYSTEM IPHOTOSYSTEM II ADP + Pi
e–
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Energy ChangesP
ote
nti
al
to t
ran
sfer
en
erg
y (v
oid
s)
H2O 1/2 O2 + 2H+
(PHOTOSYSTEM II)
(PHOTOSYSTEM I)
e–
e–
e–e–
secondtransport
system
NADPHfirst
transport
system
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Chemiosmotic Model of ATP Formation
• When water is split during photolysis, hydrogen ions are released into thylakoid compartment
• More hydrogen ions are pumped into the thylakoid compartment when the electron transport system operates
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Chemiosmotic Model of ATP Formation
• Electrical and H+ concentration gradient exists between thylakoid compartment and stroma
• H+ flows down gradients into stroma through ATP synthesis
• Flow of ions drives formation of ATP
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• Synthesis part of
photosynthesis
• Can proceed in the dark
• Take place in the stroma
• Calvin-Benson cycle
Light-Independent Reactions
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Calvin-Benson Cycle
• Overall reactants
– Carbon dioxide
– ATP
– NADPH
• Overall products
– Glucose
– ADP
– NADP+
Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated
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Calvin- Benson Cycle
CARBON FIXATION
6 CO2 (from the air)
6 6RuBP
PGA
unstable intermediate
6 ADP
6
12
12ATP
ATP
NADPH
10
12PGAL
glucoseP
PGAL2
Pi
12 ADP12 Pi
12NADP+
12
4 Pi
PGAL
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Building Glucose
• PGA accepts– phosphate from ATP
– hydrogen and electrons from NADPH
• PGAL (phosphoglyceraldehyde) forms
• When 12 PGAL have formed– 10 are used to regenerate RuBP
– 2 combine to form phosphorylated glucose
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Using the Products of Photosynthesis
• Phosphorylated glucose is the building block for:
– sucrose• The most easily transported plant carbohydrate
– starch• The most common storage form
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• In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGA
• Because the first intermediate has three carbons, the pathway is called the C3 pathway
The C3 Pathway
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Photorespiration in C3 Plants
• On hot, dry days stomata close
• Inside leaf – Oxygen levels rise– Carbon dioxide levels drop
• Rubisco attaches RuBP to oxygen instead of carbon dioxide
• Only one PGAL forms instead of two
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C4 Plants
• Carbon dioxide is fixed twice
– In mesophyll cells, carbon dioxide is fixed to
form four-carbon oxaloacetate
– Oxaloacetate is transferred to bundle-sheath
cells
– Carbon dioxide is released and fixed again
in Calvin-Benson cycle
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CAM Plants
• Carbon is fixed twice (in same cells)
• Night – Carbon dioxide is fixed to form organic
acids
• Day– Carbon dioxide is released and fixed in
Calvin-Benson cycle
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• Fissures in sea-floor where seawater
mixes with molten rock
• Complex ecosystem is based on energy
from these vents
• Bacteria are producers in this system
Hydrothermal Vents
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Light and Life at the Vents
• Vents release faint radiation at low end of visible spectrum
• These photons could be used to carry out photosynthesis
• Nisbet and Van Dover hypothesize that the first cells may have arisen at hydrothermal vent systems
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Supporting Evidence
• Absorption spectra for ancient photosynthetic bacteria correspond to wavelengths measured at the vents
• Photosynthetic machinery contains iron, sulfur, manganese, and other minerals that are abundant at the vents
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Summary of Photosynthesislight
6O212H2O
CALVIN-BENSON CYCLE
C6H12O6
(phosphorylated glucose)
NADPHNADP+ATPADP + Pi
PGA PGAL
RuBP
P
6CO2
end product (e.g. sucrose, starch, cellulose)
LIGHT-DEPENDENT REACTIONS