Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

ch5 - photosynthesis
photosynthesis​: the process of capturing free energy in sunlight and storing that energy in
chemical bonds (especially glucose); chemical equation:
6CO​2​ + 6H​2​O + light = C​6​H12​O6​ + 6O​2​ (1 )
​ ​
interconnection with cellular respiration: energy stored in chemical bonds by photosynthesis is
extracted from those bonds by respiration to make ATP (which is then used to do cellular work
through metabolic processes)
beginning of photosynthesis:
- light absorbing pigments in chloroplasts of plant cells absorb the energy from sunlight
within certain wavelengths (the dominant pigment is the green chlorophyll a; others
​
​
include chlorophylls and various red, orange, and yellow carotenoids; together, energy
absorption across the spectrum is maximized)
- the energy from the light is incorporated into electrons within the atoms that make up the
pigment molecule; these energized/excited electrons are unstable, and thus quickly
re-emit the absorbed energy, which is reabsorbed by a nearby pigment molecule; this
continues until it is absorbed by one of the two special chlorophyll a molecules (P​680​ and
​
​
2
P​700​) , which are different from other chlorophyll molecules because of their association
with various nearby pigments: chlorophyll P​700​ clusters with other pigments to form a
pigment cluster called photosystem I (PSI); chlorophyll P​680​ clusters and forms PSII
...
noncyclic phosphorylation​ and ​cyclic phosphorylation​: use H​2​O and energy from sunlight
to generate ATP, NADPH, and O​2
2
...
photosystem II: electrons trapped by P​680​ in PSII are energized by light
2
...
electron transport chain (ETC): electrons pass through an ETC, which consists of
​
proteins in the thylakoid membrane of the chloroplast that pass electrons from one
carrier protein to the next3
4
...
5 ATP molecules
5
...
NADPH: the two electrons pass through a short ETC; after, they combine with NADP​+
and H​+​ to form NADPH, which is a coenzyme, electron acceptor, and forms an
energy-rich molecule (like NADH in respiration)4
7
...
carbon fixation​: 6 CO​2​ combine with 6 RuBP to produce 12 PGA: (the enzyme ​rubisco
catalyzes this merging); the first product formed (PGA) contains three carbon atoms,
thus the calvin cycle is referred to as ​C3​ photosynthesis
​
2
...
regeneration​: 6 ATP are used to convert 10 G3P to 6 RuBP (thus regenerating the 6
RuBP originally used to combine with 6 CO​2​, allowing the cycle to repeat)
4
...
outer membrane​: made of a double layer of phospholipids (like the plasma membrane)
2
...
inner membrane​: the second membrane (also a double phospholipid bilayer)
4
...
thylakoids​: stacks of pancake-like membranes suspended within the stroma (an entire
stack is called a ​granum​); thylakoid membranes contain the protein complexes (including
PSI and PSII), cytochromes, and other electron carriers of the light-dependent reactions
6
...
H+ ions (protons) accumulate inside thylakoids: H​+​ are released into the thylakoid lumen
when water is split by PS II; H​+​ are also carried from the stroma into the lumen by a
cytochrome in the ETC between PSII and PSI
2
...
ATP synthase generates ATP: potential energy (in the form of the pH and electrical
gradients) produces energy through ​channel protein ATP synthase​ when H​+​ flows
through the thylakoid membrane and out to the stroma; the energy produced provides
energy for the ATP synthase to phosphorylate ADP to ATP6
4
...
with NADPH,
ATP, and CO​2​, 2 G3P are generated and subsequently used to make carbohydrates
(such as glucose)

5
6

the calvin cycle occurs here, fixing carbon from CO​2​ to generate G3P, the precursor to glucose
the passage of ~3 H​+​ is required to generate 1 ATP

photorespiration
rubisco​: the most common protein on earth due to its critical function in catalyzing the fixation of
CO​2​ in all photosynthesizing plants (however, not a particularly efficient molecule); it is also able
to fix oxygen (a process called photorespiration​), leading to two problems:
​
1
...
the products formed when O​2​ is combined with RuBP do not lead to the production of
useful/energy-rich molecules like glucose; instead, the plants spend considerable
amounts of effort to rid the cell of the products of photorespiration, through specialized
cellular organelles called peroxisomes​ (found near chloroplasts) that function to break
​
down these products
it is hypothesized that the early evolution of rubisco was not influenced by its O​2​-fixing handicap,
as the early atmosphere contained little oxygen, and this is when primitive plants originated
capturing free energy without light
photoautotrophs​: organisms that use sunlight as a source of free energy (to drive
photosynthesis and produce carbohydrates)
chemoautotroph​ (or ​chemolithoautotroph​): a type of prokaryote that is able to use inorganic
substances as a source of energy to generate organic molecules
- chemosynthesis​: the process which chemoautotrophs use to generate free energy, using
H​2​S (hydrogen sulfide), NH​3​ (ammonia), or NO​2​- (nitrite)
- ex: symbiotic bacteria found growing in giant tubeworms at deep ocean depths
near hydrothermal vents, which use free energy from H​2​S to produce
carbohydrates (CH​2​O): CO​2​ + 4 H​2​S + O​2​ = CH​2​O + 4 S + 3 H​2​O



---