Cellular Energetics 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 2 nd 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!