Photosynthesis
Energy and Reducing Power
Photophosphorylation
light energy in photosynthesis
animals, fungi, nonchlorophyllous plants
these 3 can't perform photophosphorylation due to the fact they lack pigments and organelles
Substrate-level phosphorylation
respiration of high-energy compounds
it is consumed as food or imported by phloem
Compounds work with high-energy phosphate groups
Compounds force their phosphates onto ADP which makes ATP
Oxidative phosphorylation
last stage of respiration
ADP phosphorylated into ATP
Reducing Power
Oxidated
atom doesn't carry as many electrons as it could
Reduced
electrons added to an atom
reduction reaction
reduces positive charge
oxidation reaction
increases positive charge
oxidized compounds
contain great deal of oxygen
reduced compounds
contain hydrogen
reducing power
ability to force electrons onto compounds
important to plants
takes in carbon dioxide and water
then turns them into carbohydrates, fats and other compounds that are very reduced
oxidizing agents
NAD+ NADP+
take away electrons
reducing agents
NADH NADPH
place electrons on compounds
Electron Carriers
Cytochromes
small portion that contains a cofactor: heme, which holds an iron atom
integral part of chloroplast's thylakoid membrane
carry electrons between sites extremely close together
Plastoquinones
like cytochromes, transport electrons over short distances
pick up 2 electrons bind 2 protiens
long hydrocarbon tail allows for them to dissolve easily into lipid component of chloroplast membrane
Plastocyanin
small portions that carry on metal atom
loosely associated with chloroplast membrane
move short distance along surface but doesn't travel far
Light Dependent reactions
also referred to as Thylakoid Reactions
Dark Reactions
Stroma Reactions
ATP and NADPH interact with Carbon Dioxide
produces carbohydrate
Water and Light
dont't interact with CO2
create Intermediates ATP and NADPH
Light is a small segment on the Electromagnetic Radiation Spectrum
Radiation can be thought of and treated as a set of particles called Quanta
also referred to as Photons
Pigments
Any material that absorbs a certain wavelength specifically has a distinctive color
Photosynthetic pigments transfer absorbed light to electrons
Chlorophyll a
absorbs some red and blue light
lets the rest pass through especially high-energy radiation
when quanta is absorbed by the pigment, an electron is activated
the molecule goes from a ground state to an excited state
the release of light by pigment is called fluorescence
Accessory Pigments
molecules that strongly absorb wavelengths not absorbed by chlorophyll a
Chlorophyll b and carotenoids
carotenoids and 300 chlorophylls are called antenna complex
when light strikes the antenna complex the energy is transferred to the reaction center
Photosystems
photosystem 1
little chlorophyll b
each contain an antenna complex and reaction center
some have an abundance of chlorophyll b and some have a lack of it
P700= reaction center
absorb red light of 700nm most efficiently
excites an electron, which is absorbed by a membrane-bound electron acceptor known as Fx
no bonding orbitial formed
the transferred electron is extremely unstable and the reduced Fx passes it to ferredoxin
electrons are passed from the ferrodoxin to an enzyme ferrodoxin-NADP+ reductase
then reduces NADP+ converting it to NADPH
photosystem 2
reduces P700
best described as working backwards from photosystem 1
molecule of plastocynanin, donates an electron to the chlorophyll a of the photosystem 1 reaction center
plastocyanin is oxidized
lacks an electron, receives one from cytochrome b6/f complex
a molecule of Q (quinone) which in turn receives electrons from phaeophytin
phaeophytin is oxidized as it donates an electron to Q
reaction center named p680
electrons stripped off, protons are used, and oxygen is discarded through stomata.
both systems are efficient
electrons are passed from water to P680 in photosystem 2
their energy is boosted by light, then they move down the electron transport chain
to p700 in photosystem 1
where energy is boosted again and they pass through a second ETC to NADP+
reducing to NADPH
P680 and P700 are needed to make ATP
The Synthesis of ATP
The necessary ATP is created by light reactions , but the process is indirect
Chemiosmotic phosphorylation
involves the thylakoids, and when they are formed in a region they become known as grana
Thylakoid Lumen
important because some of the enzymes and electron carriers are embedded in the membrane of this
the molecules of ferredoxin-NADP reductase that generate NADPH
Water is broken down
There is a strong difference between the concentration of protons inside the thylakoid lumen and exterior the storm quickly becomes powerful
protons begin to flow out of the lumen through special channels in the membrane
these channels are complex sets of enzymes that can synthesis ATP from ADP and phosphate
Calvin/Benson Cycle
reactions take place in the storma, mediated by enzymes that are not bound to the thylakoid membrane
acceptor molecule(ribulose-1,5 bisphosphate) reacts with a molecule of CO2
carbon count up to 6
two new molecules created, 3-phosophoglycerate, each contain 3 carbons
the enzyme that carries out this reaction is called RuBP carboxylase
one of the largest and most complex enzymes known, a giant complex of two kinds of protein subunits
first step of storma reactions is carboxylation only
electrons and energy are added in the next two steps
ATP donates a high energy phosphate group to the 3-phosphoglycerate
it is then converted to 1,3-diphosphoglycerate which is then reduced by NADPH to PGAL
a phosphate comes off in this step, as well as carbon being reduced and energized
the rest of the storma reactions are complex
key points
the operate some 3-phosphoglyceraldehyde can be taken out of the chloroplast and be used for building anything the plant needs
the rest of the PGAL remains in the chloroplast and undergo's several more storma reactions, which converts it to RuBP
Anabolic Metabolism
basis that all animal metabolism cause animals eat plants or eat other animals that eat plants
most biological molecules are larger than 3-phosphoglyceradehyde, so it's rearranged and altered in the cytoplasm to build larger molecules
this constructive metabolism is called anabolism, and consists of anabolic reactions
two important pathways
the synthetic pathways of polysaccharides and fats, which are storage forms of energy and carbon
The NADPH and ATP produced by photosynthesis are excellent sources of energy
can only be stored for a short amount of time, cause they are reactive and unstable
Synthesis of Polysaccharides
the anabolic synthesis of glucose is gluconeogenesis
in similar reactions to those of C3 metabolism, part of the PGAL exported to the cytoplasm is converted to dihydroxyacetone phosphate
one molecule of this condenses with one molecule of unconverted 3-phosphoglyceraldehyde to form a sugar( fructose-1,6-bisphosphate
this loses a phosphate to become fructose-6-phosphate, this becomes rearranged converting it to glucose-6-phosphate
Environmental and Internal Factors
Light
three important factors
quality
quantity
duration
refers to the colors or the wavelengths it contains
refers to the light intensity or brightness, is affected by several factors
refers to the number of hours per day the sunlight is available
Leaf Structure
most standard is palisade parenchyma above and mesophyll below
good for absorbing carbon dioxide, bad for conserving water
Water
the amount of water greatly impacts photosynthesis
the small amount of carbon dioxide produced during respiration can be reused photsynthetically