Cellular Respiration

5/31/12

Cellular Respiration

• Obtain energy from the degradation of sugars (and other macromolecules)

_• Uses Oxygen and produces CO₂

• Many steps take place in the mitochondria of cells

• Complementary process to photosynthesis

– Will recognize many of the same molecules

Oxidation-Reduction reactions

• Type of reaction when an electron is transferred from one atom or molecule to another

– Electron donor is reducing agent

– Electron acceptor is oxidizing agent

– The addition of electron to a molecule or atom is called reduction

• Energy is released when electrons are transferred to lower energy state molecules

– Electron transfer chains

Cellular Respiration Mechanisms

• 3 Stages

– Glycolysis-happens in cytosol of cell

– Krebs cycle-happens in matrix of mitochondria

– Electron transport and oxidative phophorylation-cristae

Glycolysis

• Means “sugar splitting”-glucose is split into Pyruvate

• First step of respiration

• Broken into two stages

– Energy investment phase-uses 2ATP

– Energy Payoff Phase-Yields 4 ATP +2 NADH

– Net of 2 ATP

Energy Investment Phase

• Begins with Glucose

• 2 ATPs are used to phosphorylate Carbons 1 and 6

– Activated intermediates

• Isomerase converts glucose to fructose structure

– Isomerase is enzyme that changes one molecule to an isomer

• Eventually yields 2 molecules of glyceraldehyde phosphate

– Enters energy payoff phase

Energy Payoff Phase

• Starts with Glyceraldehyde phosphate

– 2 for every glucose

• Enzyme adds phosphate to GP while 2 NADH molecules are produced

• Phosphates are eventually lost resulting in the production of 4 ATP molecules

• The final product is Pyruvate

– Moves into Krebs cycle

Transition

_• Once Pyruvate enters Mitochondrion it is converted to Acetyl CoA and CO₂

– Acetyl CoA is the starting molecule for the Krebs cycle

Krebs cycle

• Completes the oxidation of organic molecules

• Takes place in matrix of mitochondria

• Cyclic like Calvin cycle

• Produces 1 ATP for each acetyl CoA

– 2 per glucose

_• Many high energy electrons are saved as 3NADH and FADH₂ per cycle

• Also produces 2 CO₂ molecules per cycle

Transition 2

• NADH and FADH2 are used in the electron transport chain

– Happens in cristae of mitochondrion

– Uses Oxygen as ultimate electron acceptor