how is NAD+ regenerated allowing glycolysis to continue with O2 present?
In the presence of O2…
* There is oxidative phosphorylation.
* There is electron transport.
* There is regeneration of NAD +
oxidative phos is performed
how does ETC regenerate NAD+
NADH, FADH 2 from glycolysis, pyruvate oxidation and TCA cycle get oxidized to NAD+ FAD.
Electrons from NADH, FADH 2 transported to respiratory
proteins of increasing electronegativity (yellow arrows)
Oxidation coupled to formation of proton gradient
O2 is the final electron acceptor (most electronegative).
how is NAD+ regenerated during fermentation allowing glycolysis to continue when O2 absent?
In the absence of O2…
* No oxidative phosphorylation.
* No electron transport.
* No regeneration of NAD + by oxidative phosphorylation
But additional reactions can occur in the absence of O2
that regenerate NADH for use in further glycolysis + ATP production
pyruvate reduction
additional reaction that sustains glycolysis during fermentation
NADH recycled to NAD+ (in anaerobic conditions)
lactate causes feedback inhibiton of glycolysis (hexokinase and PFK target enzymes)
heart + liver take up lactate, convert back to pyruvate
anaerobic respiration
involves etc and ox phos; less electronegative e- acceptors can also support respiration
similar to ox phos:
E- from organic energy source; gets oxidized (e.g. lactate).
E- transported down a chain (to acceptors of increasing
electronegativity)
H+ gradient forms; H+ gradient used to produce ATP by
chemiosmosis.
diff to ox phos:
Inputs: Lactate (in this example), vs. NADH.
Related, but distinct electron acceptors in the chain.
SO4–2 , not O2 is the final electron acceptor.
photosynthesis
Redox process: H2O oxidized to O2 (gives up electrons)
CO2 reduced (gains electrons), makes carbohydrates (carbon fixation)
Energy requiring process; the energy is provided by light.
Involves light reactions (require light) and light-independent (dark) reactions
chloroplasts and mitochondria shared features
Key reactions occur in internal membranes
- Redox reactions in electron transport chain create pH
(proton, H + ) gradients. - Reduced compounds (NADH or NADPH)
consumed (mito) or created (chloroplasts) - Reversible ATPase / ATP synthase leads to ATP
production.
photosynthesis in chloroplasts
Occurs in chloroplast membranes.
* Photosystems harvest light energy.
- Light energy drives redox reactions that
1. Produce NADPH
2. Create proton gradients used for ATP synthesis - NADPH and ATP used to make carbohydrates
from CO2 in Calvin cycle
light reactions
Different photosynthetic pigments absorb different wavelengths
carotenoids provide photoprotection; absorb excessive light that would damage chlorophyll
pigments absorb light energy; energy transferred btwn molecules by resonance
energy transfer between pigmentns during light phase - ask tutor
Energy lost from S1 back to S0 by fluorescence (emission of absorbed light) is slow (solid red line).
- Transfer between molecules, from Donor to Acceptor, (needed for photosynthesis), is faster…
- ….occurs when Donor & Acceptor are close (coupled)…
- Donor transfers energy to Acceptor by resonance (blue
line)…electrons and photons not transferred, just the energy. - Acceptor excited from S0 to S1 (green dotted line).
photosystems role in photosynthesis
harvests light during light phase of photosynthesis
light-harvesting complexes
pigment molecules bound to proteins
transfer the energy of photons to the reaction center
reaction center role
creates e- flow during light phase
light reactions: Two routes for electron flow: cyclic and linear.
- Linear electron flow used in plants, involves two photosystems
- Produces ATP and NADPH
- Cyclic electron flow in bacteria
steps for light phase
- PS II starts the process: Light energy transferred
to P680 by upstream pigments (resonance)
excites it to P680+. - P680+ has an excited electron…transferred to the
primary electron acceptor (1 st redox reaction). - Without its electron, P680+ is a very powerful
oxidizer, and it oxidizes H 2 O; electrons given to
P680+ by H 2 O restore it to P680.
- Reverse of respiration where O2 is the
electron acceptor, and it is reduced to H 2 O.
- Electron transport chain in photosynthesis creates proton gradient, as in respiration…
- …is used to make ATP by chemiosmosis, given
the special name, photophosphorylation, - In PS I, P700 accepts electrons from PS II -> activated further by light.
- Further electron transport gives electrons to NADP+ reducing it to NADPH.
cyclic photosynthesis
Used by some bacteria.
- Involves one photosystem.
- There is no terminal electron acceptor.
- Makes ATP, not NADPH
- Photosystems I and II probably evolved from a common ancestor.
- Cyanobacteria first combined the two in a single system.
calvin cycle
Calvin cycle uses ATP and NADPH to reduce CO2 to a simple carbohydrate
- More complex carbohydrates built from simpler ones.
- (Don’t require dark, but can occur without light)
stages of calvin cycle
Carbon fixation (CO2 reacts to form carbohydrate; catalyzed by an enzyme called rubisco)
Reduction (consumes NADPH)
Regeneration of the CO 2 acceptor (RuBP)
