BI 2: Electron Transport Chain & Chemiosmosis

Making ATP:
Electron Transport Chain
& Chemiosmosis
Electrons' Role in Photosynthesis
and Cellular Respiration
*remember that electrons are responsible for the bonding properties of atoms
both photosynthesis & respiration involve a series of reactions where energized electrons are transferred between molecules when bonds are broken and formed
Redox Reactions
OXIDIZED molecule gives electrons to REDUCED molecule
Redox in Photosynthesis
Light + CO2 + H2O --> C6H12O6 + O2
e-
oxidized
reduced
Redox in Cellular Respiration
C6H12O6 + O2 --> ATP + CO2 + H2O
e-
oxidized
reduced
Of course the story isn't that simple!
Electron Carrier Molecules: molecules that temporarily hold electrons during the reactions of photosynthesis and respiration
oxidized carriers (without e-) are readily available in cell (NADP+, NAD+, FAD)
reduced forms are created during the course of P & CR (NADPH, NADH, FADH)
Redox Reaction: any chemical reaction involving the transfer of electrons from one reactant to another

Oxidation: loss of electrons from a molecule (becomes more positive)
Reduction: gain of electrons on a molecule (becomes more negative)
Overview: Photosynthesis
Overview: Cellular Respiration
Stage 1: Light Reaction
uses sun's energy to excite electrons and produce NADPH and ATP

Stage 2: Calvin Cycle
uses energy in NADPH and ATP to affix carbons together to make glucose
Stage 1: Glycolysis/Krebs Cycle
breaks apart glucose to release potential energy

Stage 2: ETC/Oxidative Phosphorylation
uses energy released from glucose to assemble ATP from ADP and Pi
ATP Production during P & CR
ATP: (adenosine triphosphate) molecule storing energy used to do all work within living cells
produced during photosynthesis (Light Reaction) and cell respiration (ETC/Chemiosmosis)
Methods for Making ATP
phosphorlyation: addition of a phosphate group (Pi) to ADP to create ATP in order to store energy

two methods:
substrate-level phosphorylation: direct transfer of phosphate group from one molecule onto ADP to make ATP
oxidative phosphorylation: creation of ATP (from ADP & Pi) using energy released during electron transport chain and chemiosmosis
Electron Transport Chain
Step 1A:
e- "jump" along a series of cytochrome (protein) molecules in membrane
ENERGY is released
Step 1B:
ENERGY released from e- is used to actively transport H+ (protons) across membrane
photosynthesis: along thylakoid membrane
cell respiration: along inner membrane
Chemiosmosis
Step 2A:
H+ are allowed to diffuse back across membrane through ATP synthase (transport protein & enzyme)
ENERGY is released
Step 2B:
ENERGY released from H+ diffusion is used to attach ADP & Pi to make ATP at ATP synthase
photosynthesis: ATP made in stroma
cell respiration: ATP made in matrix
http://vcell.ndsu.nodak.edu/animations/energyconsumption/movie-flash.htm
http://vcell.ndsu.nodak.edu/animations/etc/movie-flash.htm
http://vcell.ndsu.nodak.edu/animations/atpgradient/movie-flash.htm
To start your notes, write out the equations for P & CR.
Leave three lines of space below each.
Photosynthesis:
Cellular Respiration:
Photosynthesis: NADPH carries e- from light reaction to Calvin cycle
Cellular Respiration: NADH, FADH2 carry e- from glycolysis/Krebs cycle to electron transport chain