Energy Metabolism: Photosynthesis
Photosynthesis
Energy and Reducing Power
Reducing power
Other electron carriers
Energy carriers
Stroma reactions
Anabolic metabolism
Light-dependent reactions
Environmental and Internal Factors
Water
C4 metabolism #
Leaf structure
Crassulacean acid metabolism
Light
Concepts
Photoautotrophs #
Heterotrophs
Entropy
Increasing within the universe constantly
Get energy directly from sunlight
Include all green plants, cyanobacteria, and few bacteria
Take in organic molecules and respire them
Include animals, protozoa, fungi, and most bacteria
Ways of transporting energy into endergonic reactions
Cytochromes
Plastoquinones
Plastocyanin #
Carries electrons on a metal atom
Small proteins that contain a cofactor heme
Transport electrons within a membrane
Allow pigments to enter into every reaction
Allow pigments to make smaller intermediates
Problem: large molecules are not very mobile and never move across membranes
Photosynthetic reactions produce ATP
Relatives of ATP (ADP) are involved
ADP carries high-energy phosphate bonds
Three methods ADP is phosphorylated to ATP
Photophosphorylation
Substrate-level phosphorylation
Oxidative phosphorylation
Involves light energy so animals cannot do this
Produces compounds with high-energy phosphate groups, animals can do
Last stage of respiration and occurs in the mitochondria
Oxidized
Reduced
Atoms are not carrying as many atoms as it can
Electrons are added to an atom
Reduction reaction
Reduces the positive charge of an atom
Oxidation reaction
Increases the positive charge of an atom
Ability to force electrons onto compounds
NADH and NADPH are strong reducing agents
NAD+ and NADP+ are oxidizing agens
Redox potential
Tendency to accept or donate electrons, varies greatly
Integral part of the chloroplast's thylakoids
Cannot be removed without destroying membrane
Hydrophobic, can dissolve easy into chloroplast membrane
Can travel short distances on chloroplast membrane
Water and light cannot act on CO2 directly
ATP and NADPH interact with CO2 to produce a carbohydrate
Creates intermediates-ATP and NADPH
Nature of Light
Light is a small segment of the electromagnetic radiation spectrum
Radiation as a set of particles are a quanta also called photons
Nature of Pigment
Photosystem I
Photosystem II
Synthesis of ATP
Anabolsim is a constructive metabolism
Synthesis of polysaccharides
Pigment are substances that absorb light
Chlorophyll a only absorbs some red and some blue
Visible light is absorbed and an electron is activated
The molecule goes from ground state to excited state
Action spectrum shows which wavelengths are most effective at powering photochemical processes
Absorption spectrum shows which wavelengths are absorbed by a pigment
Accessory pigments absorb wavelengths not absorbed by chlorophyll a
Most common accessory pigment is chlorophyll b
Resonance occurs to transfer energy from chlorophyll b to a
Contains little chlorophyll b
Reaction center is called P700, absorbs red light of 700 nm
Then absorbed by electron called Fx which is unstable
Then passes electron to ferredoxin
Electrons are then passed to ferredoxin-NADP+ reductase
Located in thylakoid membrane
Converts to NADPH after NADP+ is reduced
Reduces P700
Chlorophyll b levels are almost equal to chlorophyll a
Described as working backwards from PSI
Plastocyanin donates an electron to chlorophyll a of PSI reaction center
Receives new electron from cytochrome b6/f complex
In turn receives an electron from plastoquinone
Receives electrons from Q (molecule of quinone
Receives electrons from phaeophytin (chlorophyll a w/o Mg+ atom)
Phaeophytin is the reaction center for PSII and is called P680
Electrons are passed from water to P680, move through ETC to P700
Important electron carrier in PSII
Chemiosmotic phosphorylation in chloroplast
Granum consist of stacks called thylakoids
Liquid surrounding thylakoids is the stroma
Where noncyclic electron transport occurs
Where cyclic electron transport occurs
Electrons can flow smoothly from H2O to NADPH
Used to make more ATP w/o making extra NADPH
Called the Calvin/Benson cycle or C3 cycle
RuBP reacts with CO2
Forms two C3 molecules called 3-phosphoglycerate (PGA)
RuBP carboxylase (RUBISCO) carries out this reaction
Most abundant protein in the world
Used to rearrange molecules larger than PGAL
Synthesis of glucose is gluconeogenesis
This is just glycolysis in reverse
Three types of storage that have evolved
Intermediate storage
Short term storage
Long term storage
Quanity
Duration
Quality
Light intensity or brightness
Colors of wavelengths the light contains
The number of hours sunlight is available
Lithops of African desserts conserve water by having two leaves
Haworthia cooperi also of Africa have many leaves
The amount available greatly affects photosynthesis
If limited water is available, plants keep stroma closed during the day
Utilized when water is scarce
Phosphoglycolate is broken down into two CO2 molecules
That break down is called photorespiration
Uses enzyme PEP carboxylase when O2 levels are low
Examples of plants that use this
Grasses, ice plants, and spurges
Second adaptation when water is scarce
First discovered in the family Crassulacceae
Stomata is only open at night
ATP and NADPH cannot be stored
CO2 is stored on acids until daytime
Examples of plants that use this
Grapes, cacti, orchids, and agaves
Cannot use this when water is scarce
Uses photosynthesis to utilize energy from sunlight