Kreb’s CycleStep 2 in Cellular Respiration

Life needs energy in order to survive and function

efficiently.

Mitochondrion,-a• “ATP Powerhouses”• Produce most of energy

needed by cell• Some cells have 10, some

have thousands(muscle cells)

• Remember: glycolysis and fermentation are in cytoplasm

• Kreb’s cycle(2) and electron transport system(3) take place in mitochondria

Mitochondrion,-a• “ATP Powerhouses”• Produce most of energy

needed by cell• Some cells have 10, some

have thousands(muscle cells)

• Remember: glycolysis and fermentation are in cytoplasm

• Kreb’s cycle(2) and electron transport system(3) take place in mitochondria

Mitochondrion Structure

• Two membranes

• Outer

• Inner

• Lipid Bilayer

• Inner membrane

• Many enzymes

• Folds into matrix(interior space)

http://ebiomedia.com/gall/cellimgs/mito_320.jpg

Outer membrane

Inner membrane

matrix

Kreb’s Cycle

• Named after Sir Hans Kreb• Oxford University in England• a.k.a “citric acid cycle”

• Citrate or citric acid is produced in this cycle

• Purpose: Take pyruvate from glycolysis and break down completely into carbon dioxide.

PyruvateCarbon Dioxide

Kreb’s Cycle

Prep 1

• Preparing for Kreb’s cycle• Pyruvate is sent from cytoplasm into

mitochondria

C C C

Prep 2:

• Enzymes break off a molecule of CO2 from pyruvate

• Now acetate (2 carbon acid)• Also known as aceitic acid• NADH+ becomes NADH

C C CNAD+

Pyruvate

Prep 2:

• Enzymes break off a molecule of CO2 from pyruvate

• Now acetate (2 carbon acid)• Also known as aceitic acid• NAD+ becomes NADH

C C CNAD+

NADH Acetate Carbon dioxide

Prep 3:

• CoA(Coenzyme A) binds to acetate• A carrier molecule• Carries acetate to the Kreb’s cycle

C C

Acetate

CoA

Prep 3:

• CoA(Coenzyme A) binds to acetate• A carrier molecule• Carries acetate to the Kreb’s cycle• Overall: Produces 1 NADH and 1 CO2

C C

Acetate

CoAKreb’s Cycle

Kreb’s Cycle: Step 1

• Acetate Group of Acetyl/CoA combines with oxaloacetate(4-carbon)

• Forms a 6 carbon acid “citrate”• Where it gets its nickname “citric acid cycle”

C CCoA C C C C

oxaloacetateAcetyl/CoA complex

Kreb’s Cycle: Step 1

• Acetate Group of Acetyl/CoA combines with oxaloacetate(4-carbon)

• Forms a 6 carbon acid “citrate”• Where it gets its nickname “citric acid cycle”

C C C C C C

citrate

Kreb’s Cycle: Step 2

• Two carbon atoms are oxidized to form 2 more CO2

• NAD converted to NADH

• Produces a 4 carbon acid

C C C C C C

citrate

NAD+

Kreb’s Cycle: Step 2

• Two carbon atoms are oxidized to form 2 more CO2

• NAD converted to NADH

• Produces a 4 carbon acid

C CC C C C

4-carbon acid

NAD+

NADH

2 carbon dioxide

Kreb’s Cycle: Step 3

• 4 carbon acid is rearranged and oxidized to form original oxaloacetate• Produce 3 NADH• Produce 1 FADH2• Produce 1 ATP• Produce 2 CO2

• NOTE: One glucose molecule makes two pyruvate, so two Kreb’s cycles run from one glucose molecule

C C C C

4-carbon acid

Kreb’s Cycle: Step 3

• 4 carbon acid is rearranged and oxidized to form original oxaloacetate• Produce 3 NADH• Produce 1 FADH2• Produce 1 ATP• Produce 2 CO2

• NOTE: One glucose molecule makes two pyruvate, so two Kreb’s cycles run from one glucose molecule

C C C C

oxaloacetate

1 NADH

1 FADH2

1 ATP