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!