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Ch.11: Phototrophic Energy Metabolism: Photosynthesis
Cell Biology
63
Biology
Undergraduate 3
10/17/2011

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Term
photosynthesis
Definition

the use of solar energy to drive the anabolic pathways that produce the building blocks of life

 

the conversion of light energy to chemical energy and its subsequent use in synthesizing organic molecules

Term
phototrophs
Definition
organisms that convert solar energy to chemical energy in the form of ATP and the reduced coenzyme NADPH
Term
NADPH
Definition
the electron and hydrogen carrier for a large number of anabolic pathways and is closely related to NADH of catabolic pathways
Term
photoheterotrophs
Definition

organisms that acquire energy from sunlight but depend on organic sources of reduced carbon

 

 

ex: halobacteria

Term
photoautotrophs
Definition

organisms that use solar energy to synthesize energy-rich molecules from simple inorganic starting materials such as carbon dioxide and water

 

ex: plants, algae, bacteria

 

replenish reduced carbon in the biosphere and provide the oxygen in the atmosphere used by aerobic organisms to oxidize these reduced compounds for energy

Term
energy transduction reactions
Definition

 a process in which light is captured by chlorophyll molecules and converted to chemical energy in the form of ATP and NADPH

 

ATP and NADPH provide energy and reducing power for the carbon fixation reactions (calvin cycle)

Term
carbon assimilation reactions (Calvin Cycle)
Definition

a process in which fully oxidized carbon atoms from carbon dioxide are fixed (reduced and covalently joined), forming carbohydrates

 

take place in the chloroplast of the eukaryotic phototrophs

Term
chlorophyll
Definition

light energy from the sun is captured by a variety of green pigment molecules known as  ______.

 

light absorption by this molecule excites one of its electrons, which is then ejected from the molecule and flows energetically downhill through an electron transport system (ETS)

 

the primary energy-transduction pigment that channels solar energy into the biosphere

Term
oxidative phosphorylation
Definition
ATP synthesis driven by energy derived from the oxidation of organic compounds
Term
photophosphorylation
Definition
ATP synthesis driven by energy derived from the sun
Term
oxygenic phototrophs
Definition

plants, algae, and cyanobacteria

 

water is the electron donor, and light energy absorbed by chlorophyll powers the movement of two electrons from water to NADP+ , which is reduced to NADPH

Term
anoxygenic phototrophs
Definition

green and purple photosynthetic bacteria

 

compounds such as sulfide, thiosulfate, or succinate---> serve as electron donors, then...

oxidized forms of these compounds are released

Term
photoreduction
Definition
in both oxygenic and anoxygenic phototrophs, the light dependent generation of NADPH
Term
reaction for photosynthesis
Definition
light + 6CO2 + 6H2O --> C6H12O6 + 6O2
Term
chloroplast
Definition

the organelle responsible for most of the events of photosynthesis in eukaryotic phototrophs

 

found in most plants, but not all

Term
protoplastids
Definition
small, double-membrane enclosed , plant cytoplasmic organelle that can develop into several kinds of plastids, including chloroplasts
Term
plastids
Definition

any of several different types of plant cytoplasmic organelles derived from protoplastids

 

chloroplasts, amyloplasts, chromoplasts, proteinplasts, elaioplasts

Term
structure of the chloroplast
Definition

the structure of this organelle is comprised of an outer membrane and an inner membrane often separated by a narrow intermembrane space.

 

the inner membrane encloses the stroma, a gel like matrix teeming with enzymes for carbon, nitrogen, and sulfur reduction and assimilation

 

the outer membrane contains transmembrane proteins called porins that permit the passage of solutes

Term
thylakoids
Definition

a third membrane system inside the chloroplast that creates an internal compartment

 

saclike structures suspended in the stroma

 

arranged in stacks called grana (interconnected by a network of longer thylakoids called stroma thylakoids)

 

grana and stroma thylakoids enclose a single continuous compartment called the thylakoid lumen

Term
endosymbiont theory
Definition
suggests mitochondria and chloroplasts evolved from bacteria that were engulfed by primitive cells
Term
photosynthetic energy transduction I: light harvesting
Definition

the first stage of photosynthetic energy transduction in which  light energy is captured from the sun

 

light has both wave-like and particle-like properties

 

light behaves as a stream of discrete particles called photons, each photon carrying a quantum of energy

Term
photoexcitation: 1st step in photosynthesis
Definition
when a photon is absorbed by a pigment, the energy of the photon is transferred to an electron, which is energized from its ground state in a low energy orbital to an excited state in a high energy orbital
Term
absorption spectra
Definition
because each pigment has a different configuration of atoms and electrons, pigments display characteristic ____ that describe the particular wavelengths of light absorbed by a pigment
Term
resonance energy transfer
Definition

mechanism whereby the excitation of energy of a photoexcited molecule is transferred to an electron in an adjacent molecule, exciting that electron to a high-energy orbital

 

important means of passing energy from one pigment molecule to another in photosynthetic energy transduction

Term
photochemical reduction
Definition
act of transferring photoexcited electrons from one molecule to another
Term
bacteriochlorophyll
Definition
a subfamily of chlorophyll molecules restricted to anoxygenic phototrophs and is characterized by a saturated site not found in other chlorophyll molecules
Term
accessory pigments
Definition

absorb photons that cannot be captured by chlorophyll and then transfer the energy of these photons to a chlorophyll molecule by resonance energy transfer

 

2 types: carotenoids and phycobilins

 

variations in the amounts and properties of _____ often reflect a phototroph's adaptation to a specific environment

Term
photosystems
Definition
chlorophyll molecules, accessory pigments, and associated proteins are organized into functional units called ______ which are localized to thylakoid or photosynthetic bacterial membranes
Term
chlorophyll-binding proteins
Definition
proteins that stabilize the chlorophyll within a photosystem and modify the absorption spectra of specific chlorophyll molecules
Term
antenna pigments
Definition
most pigments of a photosystem serve as light-gathering _______ which collect light energy much like a radio antenna collects radio waves
Term
reaction center of a photosystem
Definition
portion of a photosystem containing the 2 chlorophyll molecules that initiate electron transfer, using the energy gathered by other chlorophyll molecules and accessory pigments
Term
light-harvesting complex
Definition

collects light energy

 

does not contain a reaction center. instead passes the collected energy to a nearby photosystem by resonance energy transfer

Term
photosystem complex
Definition
together, a photosystem and the associated light harvesting complexes are referred to as ______
Term
Emerson enhancement effect
Definition
acheivement of greater photosynthetic activity with red light of 2 slightly different wavelengths than is possible by summing the activities obtained with the individual wavelengths
Term
photosystem I (PSI)
Definition

photosystem containing a pair of chlorophyll molecules (P700) that absorbs red light

 

light of this wavelength can excite electrons derived from plastocyanin to an energy level that allows them to reduce ferredoxin, from which the electrons are then used to reduce NADP+ to NADPH

Term
photosystem II (PSII)
Definition

photosystem containing a pair of chlorophyll molecules (P680) that absorb red light

 

light of this wavelength can excite electrons donated by water to an energy level that allows them to reduce plastoquinone

Term
special pair
Definition

in the reaction center of each photosystem is a distinctive ______ of chlorophyll a molecules that have the electrons that will be photoexcited following photon absorption

 

designated P680 for PSII and P700 for PSI to reflect their specific absorption maximum

 

the photosystems are somewhat mobile in the membrane and thus able to move to allow the cell to adapt to changing conditions of light quantity (brightness) and quality (wavelength)

Term
NADP+
Definition

the second stage of photosynthetic energy transduction uses a series of electron carriers to transport excited electrons from chlorophyll to the coenzyme _____, forming NADPH

 

this process is known as photoreduction and involves a chloroplast electron transport system

Term

noncyclic electron flow in oxygenic phototrophs

--->

 

continuous, unidirectional flow of electrons from water to NADP during the energy transduction reactions of photosynthesis, with light providing the energy that drives the transfer

Definition
[image]
Term
major energy transduction complexes within the thylakoid membrane
Definition
[image]
Term
light harvesting complex II (LHCII)
Definition

in plants and green algae, PSII is usually associated with _________, which contains about 250 chlorophyll and numerous carotenoid molecules

 

energy captured by this complex is funneled to the reaction center by resonance energy transfer

 

P680 becomes a better electron donor

Term
plastoquinone
Definition
nonprotein molecule associated with photosystem II, where it receives electrons from a modified type of chlorophyll called pheophytin during the light requiring reactions of photosynthesis
Term
plastoquinol
Definition

fully reduced form of plastoquinone, invovled in the light requiring reactions of photosynthesis

 

present in the lipid phase of the photosynthetic membrane, where it transfers electrons to the cytochrome b6/f complex

Term
oxygen evolving complex
Definition
assembly of manganese ions and proteins included within photosystem II that catalyzes the oxidation of water to oxygen
Term
cytochrome b6/f complex
Definition
multiprotein complex within the thylakoid membrane that transfers electrons from a plastoquinol to plastocyanin as a part of the energy transduction reactions of photosynthesis
Term
plastocyanin
Definition
copper-containing protein that donates electrons to chlorophyll P700 of photosystem I in the light requiring reactions of photosynthesis
Term
light harvesting complex I
Definition
the harvesting complex associated with photosystem I
Term
Ferredoxin
Definition
iron-sulfur protein in the chloroplast stroma involved in the transfer of electrons from photosystem I to NADP+ during the energy transduction reactions of photosynthesis
Term
ferredoxin-NADP+ reductase (FNR)
Definition
enzyme located on the stroma side of the thylakoid membrane that catalyzes the transfer of electrons from ferredoxin to NADP+
Term
photophosphorylation
Definition
light dependent generation of ATP driven by an electrochemical proton gradient established and maintained as excited electrons of chlorophyll return to their ground state via an electron transport system
Term
ATP Synthase
Definition
alternative name for an F-type ATPase when it catalyzes the reverse process in which the exergonic flow of protons down their electrochemical gradient is used to drive ATP synthesis
Term
proton translocator
Definition
channel through which protons flow across a membrane driven by an electrochemical gradient
Term
cyclic electron flow
Definition
light driven transfer of electrons from photosystem I through a sequence of electron carriers that return them to a chlorophyll molecule of the same photosystem, with the released energy used to drive ATP synthesis
Term
review page 308-309 summary
Definition
Term
stomata (singular-stoma)
Definition
pores on the surface of a plant leaf that can be opened or closed to control gas and water exchange between the atmosphere and the interior of the leaf
Term
mesophyll cells
Definition
outer cell in the leaf of a C4 plant that serves as the site of carbon fixation by the Hatch-Slack Cycle
Term
3 stages of the calvin cycle
Definition
pg 309
Term
rubisco
Definition

enzyme that catalyzes the carbon dioxide-capturing step of the calvin cycle

 

forms 2 molecules of 3-phosphoglycerate

Term
isoenzymes
Definition
any of several, physically distinct proteins that catalyze the same reaction
Term
phosphoglycolate
Definition

two-carbon compound produced by the oxygenase activity of rubisco

 

it cannot be metabolized during the next step of the calvin cycle and thus, the production of _____ decreases photosynthetic efficiency

Term
glycolate pathway/photorespiration
Definition

light-dependent pathway that decreases the efficiency of photosynthesis by oxidizing reduced carbon compounds without capturing the released energy

 

 

Term
leaf peroxisome
Definition
special type of peroxisome found in the leaves of photosynthetic plant cells that contain some of the enzymes involved in photorespiration
Term
hatch-slack cycle
Definition
series of reactions in C4 plants in which carbon dioxide is fixed in the mesophyll cells and transported as a 4-carbon compound to the bundle of sheath cells, where subsequent decarboxylation results in a higher concentration of carbon dioxide and therefore a higher rate of carbon fixation by rubisco
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