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Energy and Reducing Power (Energy enters the biological world through…
Energy and Reducing Power
Energy enters the biological world through photosynthesis
Photosynthesis- a process which converts light energy to chemical energy
Carbon dioxide and water
Very abundant and cheap
Stable and contain little chemical energy
Both reactants and products are nontoxic
These are reduced and energy is supplied, converting it to carbohydrates
Electron source and energy source are necessary
These do not add on carbon dioxide directly
Light dependent reactions
Stroma reactions
ATP and NADPH react with CO2 and produce a carbohydrate
Energy Carriers
Theoretical ways exist of transporting energy
Allow pigment to enter every reaction necessary but but energize pigments are large molecules so they are not very mobile
Energized pigments make one or Several smaller less energetic intermediates that can be easily moved
Substrate-level phosphorylation- high energy phosphate groups force their phosphate on ADP making ATP
Oxidative phosphorylation-ADP is phosphorylated to ATP
Other electron carriers
Cytochromes-small proteins that carry an iron atom which carries electrons
Plastoquinones- transport Electrons over short distances within the membrane
Plastocyanin- proteins that carry electrons on the metal atom
Reducing Power
Oxidation-Reducing Reducing Reaction
NAD+ and NADP are reducing (picking up electrons) becoming NADH and NADPH
Compounds in the environment are predominately in the oxidized state
Light-dependent reactions
The nature of light
Radiation- physically a set of particles called quanta or as a set of waves
The various types of radiation differ from each other only in their wavelengths and and energy
Nature of pigment
Pigment- any material that absorbs certain wavelengths specifically and therefore has a distinctive color
Photosynthetic pigments transfer absorbed light energy to electrons that enter chemical reactions
Chlorophyll
a
absorbs Only some red and some blue ones
Energy in visible light is absorbed by the pigment
An electron is activated- the molecule goes from the ground state to excited state
Photochemical process
Absorption spectrum- graph that shows which wavelengths are most strongly observed by a pigment
Action spectrum- which wavelengths are the most effective at powering a photochemical process
Accessory pigments are molecules that strongly absorbed wavelengths not absorbed by chlorophyll
a
In chlorophyll a and chlorophyll b phytol tail lie parallel to each other making them act as one molecule, transferring energy-resonance
Pigments are held by light harvesting complex proteins
Light strikes the antenna complex the energy is transferred to the reaction center
Antenna complex is helping the chlorophyll absorb thousands of quanta each second
Photosynthetic unit is where the pigment and carriers work together in a granule
Contains little amounts of chlorophyll b- photosystem I
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When chlorophyll b is almost equal to chlorophyll a are photosystem II
The pigment can not be seen or made without the light (Crosslink)
Photosystem I
P700-name of the pair of chlorophyll because they absorb red knight of 700 nm most efficiently
X absorbs an electron from P700 it goes onto ferrdoxin
From the ferrdoxin to an enzyme, ferrdoxin-NADP+ reductase
Photosystem II
Plastocyanin receives an electron from cytochrome b6/f complex
Cytochrome b6/f complex then receives an electron from a molecule of quinone
Quinone receives an electron from phaeophyin
P680
Synthesis of ATP
Takes place in the chloroplast
The chloroplast contain thylakoid and in that is thylakoid lumen
The thylakoid lumen has enzymes and electron carriers of the photosystems
The thylakoid accumulates protons because the reaction that breaks down water and produce oxygen and protons are located on the lumen’s side of the thylakoid membrane
The electron transport between P680 and P700 the electron carrier plastic window moves a proton from the stroma to the thylakoid lumen
Proton begin to flow out of the lumen through special channels called ATP synthetase
Noncyclic electron transport is when electrons flow smoothly from the water to NADPH
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Cyclic electron transport is when the plastoquinones carry electrons along and use their energy to pump more protons into the thylakoid lumen
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Orderliness of life’s two methods
Photoautotrophs- Organisms that gather energy directly from light and use it to assimilate small inorganic molecules in their own tissue
Heterotrophs- take organic molecules and respire them obtaining energy available in them
Stroma Reactions
C3 Cycle
Acceptor molecule reacts with a molecule of carbon dioxide, containing now 6 carbons
Then 3 carbons break off making 3-phosphoglycerate (PGA)
RuBP carboxylase is the enzyme that carries out this reaction it is the largest in the most complex enzymes known
It can constitute up to 30% of the protein in a leaf. Without it there would be almost no life.
The first step of the stroma consist of only carboxylation, electrons and energy are added in step two
Environmental Factors
Light
The quality of sunlight refers to the colors or wavelength contains
The quantity of sunlight refers to light intensity or brightness
Duration of sunlight Refers to the number of hours per day that sunlight is available
Leaf Structure
Temperate and tropical plants have a structure that is excellent for absorbing carbon dioxide but inefficient for conserving water
A plant is in a hot dry habitat has their leaf cells are frequently packed together without intercellular space
Another method of minimizing water loss while maintaining photosynthesis there is to reduce external surface
Water
Most plants keep their stomach open during the day permitting entry of carbon dioxide but water is lost
C4 metabolism
Ideally the ratio for the amount of water lost to carbon dioxide absorbed is low
With relatively high concentration carbon dioxide diffusion into a leaf is slow, and water loss can be high
Occasionally RuBP binds to oxygen producing one molecule of 3-phosphoglycerate and one phosphoglycolate
The phosphoglycolate is transported to perioxisomes and mitochondria
Some of it is converted to amino acids and serine
Much of is broken down to two molecules of carbon dioxede
This is photorespiration
C4 metabolism is a mechanism in which carbon is absorbed and transported through and concentrated in the leaf nad oxygen is kept away from RuBP carboxylase
PEP carboxylase enzymes have a very high affinity for carbon dioxide
PEP carboxylase adds carbon to PEP, then it has 4 carbins
Crassulacean Acid Metabolism (CAM)
A second metabolic adaption that improves conservation of water while permitting photosynthesis
It’s almost identical to the metabolism in C4 plants
The acids are not transported but accumulate to store carbon dioxide
They’re stomata opens only at night, conserving water but lack of light enervy
CAM is selectively advantageous in a hot, dry climate where is survives but does not have rapid growth
C3 and C4 metabolism plants waste water and do not survive in these climates
This two reactions and cycles are very similar in most ways
(Crosslink)
If a plants soil becomes dry and water is not readily available keeps its stomata closed even during the day
Anabolic metabolism
Storage compounds
Short-term storage:ATP and NADPH
Intermediate-term storage: simple sugar glucose and disaccharide
Long-term storage: starch and lipids
The synthesis of polysaccharides
Gluconeogenesis
