Transcript Photosynthesis

6
Pathways that Harvest and
Store Chemical Energy
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological
Energy Metabolism
Five principles governing metabolic pathways:
1. Chemical transformations occur in a series of
intermediate reactions that form a metabolic
pathway.
2. Each reaction is catalyzed by a specific
enzyme.
3. Most metabolic pathways are similar in all
organisms.
Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological
Energy Metabolism
4. In eukaryotes, many metabolic pathways
occur inside specific organelles.
5. Each metabolic pathway is controlled by
enzymes that can be inhibited or activated.
What are the energy processing strategies that autotrophs use to
obtain free energy?
• Use energy from the environment to convert
inorganic molecules into high energy organic
compounds
• They are the producers for all food chains on
Earth!
• Examples: photosynthetic and chemosynthetic
How do photosynthetic organisms obtain free energy?
• Use visible light energy to convert water and
CO2 in to organic compounds and oxygen gas
• Ex: ALL plants, phytoplankton (cyanobacteria
and protists)
Are plants the only photosynthetic organisms?
NO!
Most of the oxygen in the atmosphere was
produced by cyanobacteria and photosynthetic
protists
Photosynthesis Reaction
Water and CO2 are both required for photosynthesis...How do
they get to the sites of photosynthesis?
Photosynthesis is a two part process
Photosynthesis is described as an endergonic redox process
Why endergonic?
What substance is oxidized?
To what is it oxidized?
What substance is reduced?
To what is it reduced?
What is light?
Light is energy!
Photons of specific wavelengths of light are
used in the light reactions
Absorption Spectrum
Questions 9 and 10. What are the major photosynthetic pigments?
Is this the only photosynthetic pigment?
• chlorophyll a and chlorophyll b
• PROTEINS!
• Accessory pigments—additional pigments that
can absorb other wavelengths of light energy
Why are plants green?
Chloroplasts cannot absorb all wavelengths
of light equally and they reflect green
The Chloroplast
• Chloroplasts separate the light reactions
from carbon fixation compartmentalization
• The light reactions - thylakoid
membranes
• Calvin Cycle - stroma
Figure 6.15 An Overview of Photosynthesis
How do photosynthetic prokaryotic organisms carry out
photosynthesis?
Internal folding of the plasma membrane and
presence of chlorophyll provides a
specialized site for photosynthesis to occur
Overview of the Light Reactions
• Occurs: in photosystems (membrane
proteins and pigment proteins) in the
thylakoid membranes of chloroplasts
• Uses: Water, light, NADP+, and ADP
• Produces: O2 (waste), NADPH, and ATP
Figure 6.18 The Molecular Structure of Chlorophyll (Part 1)
Figure 6.18 The Molecular Structure of Chlorophyll (Part 2)
What happens when chlorophyll absorbs light energy?
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What happens when chlorophyll absorbs light energy?
• Chlorophyll molecules in photosystems
produce high energy electrons when exposed
to photons
• Excited Electrons move through electron
transport chains between photosystems
• This releases free energy used to pump
protons across the thylakoid membrane
and into the lumen of the thylakoid
Non-cyclic electron flow
Figure 6.19 Noncyclic Electron Transport Uses Two Photosystems
What is the role of water in the light reactions?
• Water is decomposed (photolysis) at PSII to
supply chlorophyll with replacement electrons
• This produces waste O2
How is ATP produced in non-cyclic electron flow?
• Chemiosmosis!
• The high concentration of H+ in the
thylakoid space passively diffuse through
ATP synthase enzyme
How is NADPH produced? Why is it considered a “final electron
acceptor”
• Electrons in the ETC are used to reduce
NADP+ to NADPH
• NADPH “accepts” the electrons at the
end of the ETC
Figure 6.20 Cyclic Electron Transport Traps Light Energy as ATP
Summary of the Light Dependent Reactions:
Location?
Reactants (4)?
Products (4)?
**The ATP and NADPH produced are needed for
the light independent reactions to take place**
Overview of the Calvin Cycle
• Occurs: in the stroma of the chloroplast
• Uses: CO2, NADPH, and ATP
• Produces: Organic Molecules (G3P),
NADP+, and ADP
How can we describe the process of carbon fixation?
The ATP and NADPH produced during the
L.D. reactions will be used to drive the
incorporation of CO2 in to an organic
sugar building block called G3P
Figure 6.22 RuBP Is the Carbon Dioxide Acceptor
What is the first step of the Calvin Cycle? What is the name of the
enzyme that catalyzes this reaction? This is carbon fixation.
Carbon dioxide is
incorporated into
the Calvin Cycle by
the enzyme
RuBisCo.
This reaction turns a
5-Carbon RuBP
molecule into two
3-Carbon PGA
molecules
How are ATP and NADPH used in the Calvin Cycle?
The energy in ATP
and the electrons in
NADPH are used to
reduce the PGA
molecules into 3Carbon G3P
molecules.
A total of 12 G3P
molecules are
produced
G3P is the 3-Carbon organic compound produced during the
calvin cycle. What are the possible fates of the G3P molecules
produced?
• 10 of the 12 molecules produced are
used to regenerate RuBP…Why?
• 2 G3P molecules exit the stroma and can
be combined to…
• Make sugars and be used in C.R.
• Excess glucose stored as starch
• Make lipids, amino acids, or nucleotides
Why is photosynthesis the most important biological reaction on
Earth?
The C—H bonds generated by the Calvin cycle
provide almost all the energy for life on Earth.
Autotrophs and Heterotrophs rely on this
chemical energy to support their own growth
and reproduction!
Photosynthesis Determines Global Productivity
Summary of the Calvin Cycle:
Location:
Reactants:
Products: