Post on 30-Dec-2015
Cellular Energetics
Fermentation and Cellular Respiration
Fermentation and Cellular Respiration
• Both reactions are catabolic/anabolic?• Chemical equation for respiration:
– C6H12O6 + 6O2 6CO2 + 6H2O + ATP
• Both involve redox reactions (LEO says GER): – LEO: glucose to CO2– GER: O2 to H2O
• Electrons = energy!
Cellular Respiration
• In respiration there are 2 e- carriers:– NAD+ and FAD (oxidized forms)– NADH and FADH2 (reduced forms)
• These help carry the energy from glucose to the mitochondria where it will be harnessed
Cellular Respiration
Cellular Respiration: 4 parts
• 1. Glycolysis (splitting of sugar)– Takes place in cytoplasm– Glucose (6-C sugar) is split into 2 pyruvates
(3-C molecules)– NAD+ is reduced to NADH– From 1 glucose: produces 2 (net) ATP, 2
NADH, 2 pyruvate
Gycolysis
Cellular Respiration: 4 parts
• 2. Shuttle Step – Takes place in mitochondria– Pyruvate is decarboxylated (take off a
carboxyl group) to form acetate (2-C compound)
– CoA is attached to form Acetyl-CoA– Produces 1 NADH and 1 CO2 (waste)
Shuttle Step
Cellular Respiration: 4 parts
• 3. Krebs Cycle– Takes place in the mitochondrial matrix– Produces the majority of NADH, FADH2, and
CO2 (waste)– The 2-C fragment from acetyl-CoA is added to
oxaloacetate to make 3-C citrate (citric acid)
• Produces (x2) 3 NADH, 1 FADH2, 1 ATP and CO2 (waste)
Krebs Cycle
Cellular Respiration: 4 parts
• 4. Electron Transport Chain and Oxidative Phosphorylation
• ETC proteins embedded in the inner mitochondrial membrane
• ETC membrane proteins accept e- from NADH and FADH2
• e- are passed down the ETC via redox reactions until they reach the final e- acceptor (O2) to form water
• No ATP is made by ETC; must be coupled to oxidative phosphorylation via chemiosmosis (diffusion of H+ across the membrane)
Cellular Respiration: 4 parts
• 4 cont’d. Electron Transport Chain and Oxidative Phosphorylation
• As NADH and FADH2 are oxidized, H+ inside the mitochondrial matrix is transported to the intermembrane space. This creates a proton-motive force and H+ moves back across the membrane thru ATP synthase and ATP is produced
ETC
Fermentation
• What if O2 is not present?
• Objective of fermentation is to replenish NAD+ so that glycolysis can proceed again
• Takes place in the cytoplasm
Lactic Acid Fermentation
• Prokaryotes and humans
• Pyruvate (product of glycolysis) is converted to lactate (lactic acid). In this process NADH gives up its e- to form NAD+, which can now be used again for glycolysis
• Produces only 2 ATP and 2 NADH (better than zero)
Alcoholic Fermentation
• Fungi (yeast)
• Pyruvate converted to acetaldehyde and then ethanol (ethyl alcohol) producing NAD+ which can now be used again for glycolysis
• Produces only 2 ATP, 2 NADH, and 2 CO2 (carbonation in beer!)
Fermentation
Photosynthesis
• Used by producers (autotrophs)
• Takes place in the chloroplast
• 2 parts: – light-dependent (the photo part- produces
NADPH, ATP, and O2 (waste) – light-independent or Calvin Cycle (the
synthesis part- carbon fixation- produces sugar)
Photosynthesis
Photosynthesis- the light reactions
• Occurs in thylakoids• Chlorphyll a and b, in the photosystems, absorb photons
of light and become excited when their e- gain energy• Photosystem 2 (P680) absorbs light and e- are excited• e- are now boosted to a higher level and must be
replaced• H2O is split (photolysis) and the e- are replaced (and
oxygen is produced)• e- pass down an ETC and ATP is produced by
chemiosmosis • e- are passed to photosystem 1
Photosynthesis- the light reactions
• e- are passed from P680 to Photosystem 1 (P700) where they are again boosted to a higher level
• e- are passed down a 2nd ETC that produces NADPH
Light Reactions
Calvin Cycle
• Occurs in stroma
• Uses e- from NADPH and energy from ATP produced in the light reactions
• One molecule of G3P exits the cycle per 3 CO2 molecules fixed and is converted to glucose
• ADP and NADP+ are returned to the light reactions
Calvin Cycle
All together now!