Cellular Energetics Flashcards
Git gud
What are ’light’ reactions?
-They are light dependent
-Membrane-bound
-Release O2 from splitting 2H2O molecules, with
H+ from H2O used in the Chemiosmotic synthesis of ATP, and
Hydride ion (H:-) from H2O reduces NADP+ to NADP
What are ‘dark’ reactions?
-Does not require light
-Occur in solution (stroma)
-Reduce gaseous CO2 to carbohydrate
-Require energy of NADPH and ATP
What are Granum?
internal plates stacked of Thylakoids in the chloroplasts, connected by the stroma lamella. Where light reactions take place.
What light capturing pigments are present in plants? And how do they deal with the difference in light and chemical reaction times?
Primarily Chlorophylls such as Chl a and Chl b.
Antenna pigments such as carotenoids, phycocyanin and phycoerythrin are used to extend the range of light capture, especially green.. they exchange light energy with chlorophylls until captured. They pass on electrons.
Where do the light reactions take place?
Takes place in 2 systems: Photosystems; PSI and PSII (which have reaction centres) which operate in series, connected by cytochrome bf complex. Contain many proteins and pigments embedded in the thylakoid membrane.
What is the ‘Z’ scheme? And how does it work?
-path of electron flow and reduction potentials of the components in
photosynthesis
-Absorption of light energy converts P680 at PSII reaction centre and P700 at PSII reaction centre (poor reducing agents) to
excited molecules (good reducing agents)
-Light energy drives the electron flow uphill
-NADP+ is ultimately reduced to NADPH
-For 2 H2O oxidized to O2, 2 NADP+ are reduced to 2 NADPH
What are ATP and NADPH used for in photosynthesis?
To convert CO2 to hexose phosphates
What are phototrophs?
Photosynthetic organisms (some bacteria, algae etc.)
What is the Mitchell’s Chemiosmosis Theory?
conversion of energy from electron transport via formation of a transmembrane electrochemical gradient
What is e- (H+) transferring across a ‘coupling’ membrane required for in chemiososmosis?
Generating proton motive force
What is photophosphorylation?
synthesis of ATP which is dependant upon light energy
What is chloroplast ATP synthase?
Made of 2 major particles:
-CFo: Sits in the membrane, forms a pore from H+
-CF1: Sits on top of CFo, protruding into the stroma and catalyses ATP synthesis from ADP and Pi
How were dark reactions identified?
Using fast CO2 injection, carbon-14 in hydrogen carbonate ion solution - rapid ‘quench’ killing via alcohol or strong acid to stop reactions and a 2D chromatography improves separation of intermediates
What is RuBisCo?
Ribulose-bisphosphate-caboxylase/oxygenase
Is responsible for carbon fixation
also use O2 to catalyse a competing oxygenation reaction, normally carboxylation is 3 times greater than oxygenation
What is the dark reactions cycle in photosynthesis?
The Calvin-Benson cycle
What are the 3 steps in the Calvin-Benson cycle?
Carboxylation, Reduction and Regeneration
What are the required components for the Calvin-Benson cycle?
CO2, RuBisCO, ATP, NADPH
CO2 and the 5-carbon sugar ribulose 1,5-bisphosphate form two molecules of…
3-phosphoglycerate (PGA)
Are the dark reactions reversible?
metabolically irreversible
What is the structure of RuBisCO?
-8 large subunits + 8 small subunits
-Large subunits nuclear-encoded; small subunits chloroplast-encoded
-makes up about 50% of the soluble protein in plant leaves
What is photorespiration?
recycles the (toxic) products of the oxygenation reaction; it
consumes NADH, ATP to give glyoxylate, serine, glycine and CO2
Many organisms have evolved to get around RuBisCO limitations..
What are carboxysomes?
-Produced by cyanobacteria to concentrate CO2 around RuBisCO.
-Semi-crystalline protein structures incorporating RuBisCO
-Cyanobacteria express transport proteins to accumulate CO2 and HCO3
What are pyrenoids?
-membrane-bound structures
found in the chloroplasts of some algae
-include RuBisCO and concentrate CO2
