Cellular Respiration

Principles of Energy Harvest

Ultimately, the NRG in an ecosystem begins as sunlight and leaves as heat

Chemical elements are recycled

Photosynthesis and Respiration are essential processes that allow NRG to flow through an ecosystem

NRG from food Catabolic pathways

produce ATP from organic compounds

Fermentation Partially degrades sugars Occurs when no O2

present Cellular Respiration

C6H12O6 + 6O2 6CO2 + 6H2O + E (ATP + heat)

Redox reactions In order to make ATP,

electrons must be rearranged

Oxidation/Reduction LEO the lion says GER

Lose Electrons = Oxidation

Gain Electrons = Reduction

Reducing agent: e- donor

Oxidizing agent: e- acceptor

Oxidizing agent in Respiration

NAD+ (nicotinamide adenine dinucleotide)

Removes electrons from food (series of reactions)

NAD+ is reduced to NADH

Enzyme action: dehydrogenase (removes 2 e- and 2 H+)

NRG in NADH is used to make ATP (controlled production of NRG)

Electron Transport Chains

Electron carrier molecules (membrane proteins)

Shuttle e- that release NRG used to make ATP

Sequence of reactions that prevents NRG release in one explosive step

Electron route: food NADH ETC O2

Oxygen is the final e- acceptor

Cellular respiration Glycolysis:

cytosol degrades glucose into

pyruvate Citric Acid (Kreb’s)

Cycle: mitochondrial matrix pyruvate into CO2

Electron Transport Chain: inner membrane of

mitochondrion electrons passed to

oxygen NRG trapped to make

ATP

Glycolysis 1 Glucose ---> 2 pyruvate

molecules Energy investment phase:

cell uses 2 ATP to phosphorylate fuel

Energy payoff phase: 4 ATP produced by substrate-level phosphorylation and NAD+ is reduced to NADH by food oxidation

Net NRG yield per glucose: 2 ATP, 2 NADH

Kreb’s Cycle If molecular O2 is present… Each pyruvate (2 from

glycolysis) converted into acetyl CoA CO2 released NAD+ ---> NADH coenzyme A (from B vitamin)

attached; makes molecule very reactive

In each turn, 2 C atoms enter (pyruvate) and 2 exit (CO2)

For each pyruvate: 3 NAD+ reduced to NADH 1 FAD+ reduced to FADH2 1 ATP molecule

Electron Transport Chain e- carriers, NADH

and FADH2 donate e- to the chain

e- passed “downhill” to more electronegative molecules as they move on

Most carrier molecules are cytochromes have a heme group

that accepts and donates e-

Chemiosmosis Electron Transport chain

sets up a H+ concentration gradient

e- flow is exergonic; released NRG is used to pump protons across the membrane “proton-motive force”

As H+ diffuses back in, ATP synthase makes ATP

Chemiosmosis: energy coupling mechanism NRG of H+ gradient

drives cellular work

ATP Production ATP synthase:

produces ATP using the H+ gradient

harnesses flow of H+ back into matrix

phosphorylates ADP to ATP (oxidative phosphorylation)

Produces 32-34 molecules of ATP

Review: Cellular Respiration

Glycolysis: 2 ATP (substrate-level phosphorylation)

Kreb’s Cycle: 2 ATP (substrate-level phosphorylation)

Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6 ATP 2 NADH (acetyl CoA) = 6 ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP

38 TOTAL ATP/glucose

Fermentation Occurs when no O2 is present Produces some ATP and replenishes NAD+

Keeps glycolysis going so some ATP can be produced

Facultative anaerobes (yeast/bacteria) can survive off of fermentation alone

Types of fermentation Alcoholic

pyruvate to ethanol Bacteria, yeast, most

plants Production of bread and

alcoholic beverages Lactic acid

pyruvate to lactate Fungi, bacteria, human

muscle cells Production of cheese

and yogurt Causes muscle fatigue

and pain during strenuous exercise

Other Metabolic Pathways

Proteins broken down into amino

acids Converted into

intermediates used in glycolysis and Kreb’s

Lipids Broken down into glycerol

and fatty acids Glycerol transformed into

an intermediate in glycolysis

Fatty acids broken down by beta-oxidation and transformed into Acetyl Co-A