Chloroplasts & Photosynthesis (23) Flashcards
heterotrophs
depend on an external source of organic compounds which were produced abiotically
autotrophs
utilize CO2 to manufacture their own organic molecules
chemoautotrophs
utilize the energy stored in inorganic molecules (ex: hydrogen sulfide) to convert CO2 into organic compounds
Ex: found around thermal vents
photoautotrophs
utilize radiant E of the fun to convert CO2 into organic compounds
what organisms carry out photosynthesis?
higher plants
eukaryotic algae
various flagellated protists
variety of prokaryotes (ex: blue-green bacteria)
photosynthesis
sunlight is transformed into chemical E & used to form carbs
what is the chemical formula of photosynthesis?
6CO2 + 6H2O –> C6H12O6 + 6O2 (coupled with light)
how is light E captured?
with pigment molecules including chlorophylls & accessory pigments (carotenes & phycobilins)
cytochromes
method plants capture electrons & produces a reducing power in the form of NADPH (plant version of ETC PROs)
NADH is used for _____ & NADPH is used for ______
catabolism
anabolism
light rxns
photochemical rxns
Products: ATP & NADPH
Occurs in thylakoid membranes of chloroplasts
darks rxns
thermochemical rxns
ATP & NADPH are used to synthesize carbs, conversion of CO2 into carbs
Occurs in stroma of chloroplasts
what are the 3 types of membranes of a chloroplast?
Outer membrane: freely permeable
Inner membrane: contains transporters which involves the transport in & out of the chloroplast of:
Small molecules like sugars
PROs synthesized in the cytoplasm
Thylakoid membranes
thylakoid membranes
enclose a lumen containing a sys of vesicles
System of vesicles are stacked in an array called a grana Carry out light rxns Contains 4 types of PROs that are embedded in the membranes: Photosystem I: includes chlorophyll & carotenoid molecules Photosystem II: also includes chlorophyll & carotenoid molecules Cytochromes b & f ATP synthase
stroma
fluid surrounding thylakoid membranes
Contains enzymes involved in dark rxns Contains the complete chloroplast genome which encodes most of the molecules required for chloroplast function
where are the molecules required for chloroplast function made?
stroma of the chloroplast
transcribed in the nucleus & translated in the cytoplasm
chloroplast genome
total gene set found within the chloroplast
Encodes about 100 chloroplast specific PROs Uses its own RNA polymerase & ribosomes
how many PROs for the chloroplast are encoded in the nucleus?
900
they’re made in the cytoplasm & transported into the chloroplast
how do chloroplasts divide?
Arise from pre-existing chloroplasts
Chloroplasts pinch themselves into 2 equal parts like bacteria (binary fission)
FtsZ PRO (in chloroplasts & bacteria) polymerize & form a contractile ring on the inside of the chloroplast –> constrict & divide the organelle
There is also a ring on the outside of the chloroplast called the plastid-dividing ring
PROs are derived from the host
describe the process of the absorption of light?
E from sun is in the form of electromagnetic radiation
Radiation travels in photons
When a photon is absorbed the compound is converted to a higher E state (excited state)
Ground state is re-established in 3 ways:
Dissipated as heat
Re-emitted as a longer wavelength
Transferred to another molecule (occurs in photosynthetic pigments)
pigments
molecules containing chromophores
chromophore
chemical group capable of absorbing light of a particular wavelength
absorption spectrum
plot intensity of light absorbed vs. wavelength
action spectrum
plot of physiological response vs wavelength
what does the action spectrum follow?
absorption spectrum of chlorophylls & carotenoids
carotenoid
long hydrocarbon chains containing alternating double bonds
protects photosynthetic machinery from damage caused by reactive oxygen species
how do carotenoids increase their efficiency?
absorbing light in regions where the chlorophyll absorbs light inefficiently
carotenoids absorb what colour light & of what wavelengths?
light blue & green (400-550nm)
carotenoids reflect what colour light & of what wavelengths?
yellow, orange & red (>550nm, <700nm)
how do animals obtain carotenoids?
diet
how do animals use carotenoids?
ornamental colourings:
Pink of flamingos, pigment in feathers
Pink colour of salmon
Red colour of lobsters
Antioxidants –> reduces risk of cancer when consumed carotenoids
Ex: lycopene in tomatoes is linked to reduced lipid peroxidation, reduced heart attacks, improved male fertility & longevity
Steps of electron transfers in photosynthesis
- rxn center chlorophyll P680 absorbs photons & gives up the electrons to the primary electron acceptor (pheophytin)
- P680 replenishes its electrons from H2O, H2O is oxidized releasing O2 (photolysis)
- Electron is passed from PSII to PSI via the ETC & produces ATP (used in calvin cycle)
- P700 chlorophyll uses light to excite the electron to its own primary acceptor
- Electron is sent down another chain to create NADPH
- NADPH is used in the calvin cycle
what are the 2 fates of the excited electrons in PSI?
can pass down:
a short electron transport chain to NADP+ to form NADPH
or
back to P700 to form ATP
cyclic photophosphorylation
electrons are excited, pass down the chain creating ATP & then land back on 9700 to be reused
Electrons move from P700 to ferredoxin & back to P700
Electrons return to ground state
Use PSI only
Formation of ATP
noncyclic photophosphorylation
electrons aren’t recycled back to ground state, they end up on NADH
Electrons move in a linear path from H2O to NADP+
Electrons don’t return to ground state
Uses PSI & PSII
Formation of: ATP, NADPH & O2
Z scheme or pathway steps
- 2 photosystems acting in series
- Electron flow occurs in 3 steps:
a. B/w H2O & PSII
b. B/w PSII & PSI Electron transport chain
c. B/w PSI & NADP+ - As electrons flow along Z-pathway, H+ ions are moved from stroma to inner compartment of thylakoids
- Important end result is proton gradient proton concentration:
a. High in lumen of thylakoid
b. Low in stroma
calvin cycle steps
- Carboxylation
a. CO2 combines with ribulose-1, 5-bisphosphate (RuBP)
b. Forms a transient 6-carbon compound
c. This breaks down to form 2 3-carbon molecules of 3-phosphoglycerate (PGA)
d. Catalyzed by ribulose-1, 5-bisphosphate carboxylase (“Rubisco”) - ATP and NADPH are used to form (in a couple of steps) glyceraldehyde 3-phosphate (G3P)
some G3P is used to make glucose & some gets cycled to re-make more RuBP
what is the most abundant PRO in the world?
Rubisco
endosymbiotic theory with chloroplasts
suggests that chloroplasts started as a photosynthetic bacterium which later got assimilated in a larger cell
how do chloroplasts resemble bacteria in structure & composition? (3)
own circular genome
double membranes
share highly similar photosynthetic enzymes
what are the similarities b/w mitochondria & chloroplasts? (3)
Method of replication
Generation of chemical E electron transport coupled to a proton gradient
Similar ATPases
what are the diffs b/w mitochondria & chloroplasts? (2)
conduct opposing rxns –> one uses glucose (chloroplasts) & the other produces it (mitochondria)
diff electron acceptors
Artifical photosynthesis
Attempt to replicate the natural process of photosynthesis
Replace fossil fuels
Artificial light rxns hopes to generate H as a new E source
Done in 2 ways:
Cyanobacteria are genetically altered so that they release H instead of using it to make carbs in bioreactors
Engineered enzymes on solar cells
