Cellular RespirationChapter 9

Organisms need to obtain materials and energy in order to complete necessary reactions for life.

◦ 2 Processes

Cellular Respiration (heterotrophs)

glucose + O2 ---> CO2 + H20 + ATP (heat)

Photosynthesis (autotrophs)

CO2 + H20 (light) ----> glucose + O2

Big Picture...Life is Work.

ATP (adenosine triphosphate)◦ bonds broken via hydrolysis (release energy)◦ molecule that provides energy to drive

cellular work happens via phosphorylation (adding or

removing P from ATP) ATP <--> ADP Producing ATP requires energy

Oxidation-Reduction Reactions (redox)◦ oxidation (losing electrons)

reducing agent (electron donor)◦ reduction (gaining electrons--reduce positive

charge) oxidizing agent (electron acceptor)

Transfer of electrons between compounds...

Redox in Cellular Respiration...

◦glucose oxidized to CO2

◦oxygen reduced to H2O

◦coenzymes are used throughout this process to “help shuttle” the electrons (H+)

NAD+ (nicotinamide adenine dinucleotide)--NADH is reduced state

FAD (flavin adenine dinucleotide)--FADH2 is reduced state

Cellular Respiration does not oxidize glucose in a single explosive step. Instead a series of steps are used to release small amounts of energy.

◦ Glycolysis in the cytosol. Glucose broken to pyruvate. Some ATP

produced.

◦ TCA (Krebs) Cycle and Pyruvate oxidation pyruvate further oxidized and completely broken down to

CO2 in the mitochondria. Some ATP produced.

◦ Electron Transport Chain (oxidative phosphorylation and chemiosmosis)

accepts electrons from carriers (NADH and FADH2) and releases energy. ATP and H20 are produced here.

Cellular Respiration

Through a series of 10 reactions, the 6-carbon sugar (glucose), is broken down into…◦ two molecules of a 3-carbon molecule called pyruvate

◦ net gain of 2 ATP molecules and 2 NADH molecules occurs (inefficient)

Anaerobic process. Does not require oxygen.

Glycolysis

Pyruvate travels into the mitochondria via a transport protein.

Pyruvate then gets oxidized into Acetyl-CoA inside the mitochondria (one is produced per pyruvate molecule)◦ A CO2 molecule is released◦ One NADH molecule is produced

◦ Acetyl-CoA then enters the TCA (Krebs) cycle in the mitochondrial matrix

Pyruvate Oxidation

Begins with one Acetyl-CoA molecule (requries two turns to completely oxidize glucose)

◦ Produces: 2 CO2

3 NADH 1 FADH2

1 ATP

For each Acetyl-CoA molecule

Krebs Cycle (TCA cycle)

Occurs in the inner membrane of the mitochondria (cristae—folds)◦ Oxidative Phosphorylation

Within the membrane are transmembrane proteins to pump H+ ions across (creates gradient)

Electron carriers (NADH and FADH2) donate electrons to drive the passage of H+ ions

Last protein oxidizes oxygen into water

◦ Chemiosmosis At the end of the chain, H+ passes back through the membrane

in ATP synthase, which uses the energy from this process to convert ADP back to ATP.

H+ gradient across a membrane used to drive cellular work (movement of H+ ions)

Electron Transport Chain

Without oxygen pyruvate cannot enter the mitochondria and begin the Krebs Cycle, oxygen is not present to pull electrons down chain, and the process stops.

Instead pyruvate enters into an alternate pathway to oxidize glucose and generate ATP…

◦ Lactic acid fermentation (pyruvate to lactate) Regenerates NAD+ for glycolysis

◦ Alcohol fermentation (pyruvate to ethanol) Regenerates NAD+ for glycolysis

In anaerobic situations…

aerobic respiration: cell respiration that requires oxygen (most organisms)

anaerobic respiration (fermentation): cell respiration that occurs without oxygen

oxidative phosphorylation: ATP synthesis powered by redox reactions in ETC (90% of ATP generated by CR)

substrate level phosphorylation: ATP formed by glycolysis and TCA cycle

chemiosmosis: H+ ions move through a membrane to drive cellular work