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Ch. 10 Photosynthesis (Photosynthesis :recycle: (combination of carbon…
Ch. 10 Photosynthesis
Photosynthesis :recycle:
combination of carbon dioxide and water
Both abundant resouces
Cheap and occur almost everywhere
CO2 & water are stable
Also, contain little chemical energy
Can deposit large amount of energy on them
From carbohydrates, good for storing energy
Both reactants & products are nontoxic
Light-Dependent Reactions
Intermediates ATP & NADPH act on CO2
Act on CO2 by water and light
Pigment
Any material that absorbs certain wavelengths
Pigments, like melanin, absorb light
Pigments in flowers/fruits are important for what they do not absorb
Gives pigments color, which attracts pollinators
Chlorophyll doesn't use high energy quanta
They already have too much energy
Each can knock electrons off pigment
This disrupts bonds, causing the molecule to break
Our atmosphere absorbs high-energy molecules
This saves ATP and the molecule from breaking
Energy Carriers
Energy enters the world through photosynthesis
Converts light to chemical energy
Captured by certain pigments in plants
use the energy in chemical reactions
can only enter 2 reactions
Ways transporting energy from pigments
Allow pigments to enter every reaction
Problem is energized pigments are large
Don't move across membranes
Also, too energetic
Would react with anything
Allow energized pigments to be smaller
These are less energetic
This has evolved, photosynthesis produces ATP
These produce enough energy for reactions
Other energy carrier,
guanosine triphosphate
, carries energetic bonds
And easier to control
Each ATP molecule is an energy carrier
3 ways ADP turns to ATP
photophosphorylation
involves light energy in photosynthesis :star:
Animals, fungi, etc. cannot perform this
lack necessary pigments
Substrate-level phosphorylation
Compounds w/ high energy are produced
These force phosphate groups on ADP
This then turns to ATP
Oxidative phosphorylation
Last stages of respiration
ADP turned to ATP
The Stroma Reactions :black_flag:
Conversion of CO2 to carbohydrates
take place in stroma
First step,
acceptor molecule
reacts with CO2
RuBP combines with CO2 to have 6 carbons
the new molecule breaks down fast by enzyme
two identical molecules are formed, called
3-phosphoglycerate
the enzyme,
RuBP carboxlase
, carries out the reaction
can constitute up to 30% of protein in leaves
is only carboxylation
Electrons and energy are added in the next steps
ATP donates high-energy phosphate group
Converts it to
1,3-diphosphoglycerate
reduced by NADPH to
3-phosphoglyceraldehyde
(PGAL)
carbon is now reduced and energized
Reducing Power
Earth's atmosphere is 21% oxygen
Many compounds are found in oxidized form
Carbon as CO2
Sulfur as sulfate
nitrogen as nitrate
Oxidated
- can hold more electrons
Oxygen pulls electrons away
Whatever oxygen takes, is now in an
oxidation state
But, still shares because covalent
Oxidized compounds
usually contain tons of O2
NAD+ and NADP+ are
oxidizing agents
take electrons away
Electrons added = being
reduced
Reduced compounds
contain hydrogen
Most compounds in animals are in reduced state
Organisms need
reducing power
ability to force electrons on compounds
NADH and NADPH are
reducing agents
place electrons on other molecules
they reduce molecules. but oxidize themselves
redox potential
- tendency to accept or donate electrons
Photosystem I
P700
- pair of chlorophylls in reaction center
energy excites a P700 electron
absorbed by membrane-bound electron acceptor
the reduced Fx passes onto
ferredoxin
located in thylakoid membrane
small protein, with active site of two iron atoms bound to two sulfur
electrons are passed to
ferredoxin-NADP+ reductase
this reduces NADP+, to NADPH
Photosystems 1 & 2 are efficient
1 more item...
Photosystem II
Reduces P700 in Photosystem I
Works backwards from other
plastocyanin
- contains copper and donates electron to chlorophyll
a
must reacquire electron
receives new electron from
cytochrome b6/f complex
Phaeophytin
becomes oxidized when it donates to
Q
Obtains electron from chlorophyll
a
and is named
P680
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