6.2RadjewskiAP Biology

Cellular Respiration

• Catabolism (break down) of organic molecules within cells

• Key ways cells get energy• 4 steps

1. Glycolysis2. Formation of Acetyl CoA (pyruvate oxidation)3. Krebs Cycle (Acetyl CoA oxidation)4. Electron Transport/Chemiosmosis

• Occurs in a bunch of small steps to allow for more energy to be made

Glycolysis

• Takes place in the cytosol in the cytoplasm– All organisms have cytoplasm, so all organisms

can do glycolysis

• 10 steps• Glucose is oxidized releasing stored energy– To break down glucose, cells need to invest 2

ATP’s (endergonic)

ATP is required because glucose has covalent bonds, which are strong. The phosphate from the ATP’s are basically being added to glucose in these steps.

The 6 carbon molecule is broken in half, creating two 3C sugars.

Later steps are exergonic and release energy, forming ATP and NADH. ATP is made through substrate level phosphorylation

Glycolysis Ins/Outs

• Requirements: 1 glucose, 2 ATP, 2 NAD+,4 ADP, 4 Pi

• Products: 2 Pyruvates, 4 ATP,2 NADH, 2 ADP, 2 Pi

• Net ATP Production is 2ATP• In the presence of oxygen, further oxidation

can occur.

Formation of Acetyl CoA (Pyruvate Oxidation)

• Takes place in the mitochondria matrix• Pyruvate gets oxidized to a 2C acetate

molecule and CO2

• Then Acetate is bound to Coenzyme A (CoA), forming acetyl coenzyme A or Acetyl CoA

» It is a carrier of acetyl groups» Vitamin B

• Exergonic reaction (released NADH) and decarboxylation occurred (release of CO2)

Formation of Acetyl CoA (Pyruvate Oxidation)

• Requirements: pyruvate, NAD+, Coenzyme A• Products: Acetyl CoA, NADH, CO2

• The main role of Acetyl CoA is to donate its acetyl group to the 4C compound oxaloacetate, forming a 6C compound, citrate

Krebs Cycle

• Citric Acid Cycle• 8 steps• 2C Acetyl CoA combines with 4C oxaloacetate to

form 6C citrate• Citrate changes to its isomer isocitrate in step 2

(water was added and released)• In step 3, isocitrate undergoes decarboxylation to

form 5C alpha-ketoglutarate.– This releases CO2 and forms NADH

Krebs Cycle

• In step 4, alpha ketoglutarate undergoes decarboxylation to form 4C succinyl CoA– NADH is formed and CO2 is released

• In step 5, succinyl CoA loses it’s CoA to form succinate– This is a coupled reaction where GDP + Pi forms

GTP, which then transfer its high energy phosphate to form ATP

Krebs Cycle

• In step 6, succinate undergoes dehydrogenation to form fumarate– This forms FADH2, which is similar to NADH

• In step 7, fumarate adds water forming malate• In step 8, malate undergoes dehydrogenation

forming oxaloacetic acid (which started the cycle!)– NADH was made!

Krebs Cycle

• Requirements: Acetyl CoA, 3 NAD+, 1 GDP, 1Pi, FAD, Water, CoA, Oxaloacetate

• Products: 3 NADH, Water, 2 CO2, 1 ATP, FADH2

• So far, we only made 3 ATP (2 from glycolysis, and 1 from Krebs) This isn’t a lot. How do we make all the energy?

Electron Transport Chain

• Occurs on the cristae of the mitochondria• NADH and FADH2 are oxidized and it is

exergonic– The protons get pumped through proton channels

on the cristae and go through chemiosmosis• Remember this creates a proton gradient and then

they go back through ATP synthase, driving the reaction to create ATP from ADP and Pi

– The electrons pass through proteins and then add to oxygen (with protons)

Oxidative Phosphorylation

• Requirements: NADH, FADH2, Oxygen

• Products: Yields a lot of ATP and H20

• For each NADH or FADH2, 2-3 ATP molecules are formed