Cellular Respiration:Harvesting Energy from Glucose

Cellular respiration: Purpose

Exergonic and endergonic reactions of metabolism…

Exergonic:

C6H12O6 + 6O2 6CO2 + 6H2O G = -686 kcal/mole Cellular respiration!

Endergonic:

6CO2 + 6H2O C6H12O6 + 6O2 G = +686 kcal/mole

Photosynthesis!

Provides the energy to run cell processes

Allows plants to make energy rich sugars from energy poor molecules

Summary of Cellular RespirationThe 3 stages of cellular respiration…

1. Glycolysis:

• occurs in the cytoplasm of the cell

• results in the partial breakdown of glucose

•anaerobic – no oxygen is used during glycolysis

Summary of Cellular Respiration

2. Krebs Cycle

• occurs in the mitochondrial matrix

• aerobic – although O2 is not used directly in this pathway, it will not occur unless enough is present in the cell.

• main catabolic pathway of C.R.

Summary of Cellular Respiration3. Electron Transport Chain• occurs along the inner mitochondrial membrane (IMM)

• aerobic – O2 is used during this pathway.• the main ATP producing pathway!

What happens during cellular respiration?

The Big Picture!

1.The oxidation of food molecules (i.e. glucose)

Stripping of high energy electrons (and H+ ions) from food molecules.

• food is broken down via oxidation-reduction reactions (Redox reactions).

Oxidation: Reduction:

Whenever a molecule is oxidized, another molecule picks up the electrons and becomes reduced.

Just remember…

LEO says GER!!!!

lose electrons

oxidation gai

nelectrons reduction

2. Electrons stripped from food molecules are accepted by electron carrier molecules (called NADH and FADH2).

The Big Picture (cont.)

• Food molecules are being oxidized, and the electron carriers are being reduced.

• Electrons stripped from food molecules have high potential energy.

They are in a high energy shell!

Electron Carriers (The Big Picture cont.)

2 H+ + 2 high energy electrons

Electron carriers (The Big Picture cont.)

3. Electron carriers take these high energy electrons to the Electron Transport Chain.

The Big Picture (cont.)

Electrons are run down an “electron slide”…The energy released from this “slide” is used to make ATP…

At the end of the slide, the electrons and H+ are accepted by oxygen…

…and become WATER!

C6H12O6 + 6O2 6CO2 + 6H2O

Oxidized!

Reduced!e- and

H+

Glycolysis

The energy investment phase

carbons

ATP/NADH Ledger

- 2 ATP

Energy coupling

ATP ADP + P: exergonic

Glu Glu-6-P :endergonic

Glycolysis

The energy payoff phase

ATP/NADH Ledger-2ATP

+2ATP

+2 NADH

Redox reactions

Energy coupling

Glycolysis

More energy coupling

ATP/NADH Ledger-2ATP+2ATP+2ATP

+2 NADH

End-products of glycolysis are 2 pyruvate molecules

Summary of Glycolysis

Glucose activation: Energy Input= 2 ATP

Energy Harvest= 4 ATP + 2NADH

Final Ledger-2ATP+2ATP+2ATP

+2ATP

+2 NADH

What you need to know• Final ledger for glycolysis• Starting materials – one 6

carbon glucose molecule• End products – two 3 carbon

pyruvate molecules• Don’t worry about all the

intermediate molecules they are just there to illustrate what’s going on.

• Each pyruvic acid molecule is broken down to form CO2 and a two-carbon acetate molecule that binds to coenzyme A. This forms acetyl CoA, which enters the Krebs cycle. 1 NADH is produced here.

Pyruvic acid must be chemically groomed to enter the Krebs cycle

Figure 6.10

Pyruvicacid

CO2

Acetyl CoA(acetate and coenzyme A)

• The Krebs cycle is a series of reactions in which enzymes strip away electrons and H+ from each acetyl CoA molecule

The Krebs cycle completes the oxidation of glucose, creating many NADH and FADH2

molecules

Figure 6.11A

Acetyl CoA

KREBSCYCLE

2CO2

Figure 6.11B

Oxaloaceticacid

Step Acetyl CoA stokesthe furnace

1

2 carbons enter cycle

Citric acid

Steps and NADH, ATP, , and CO2 are generated during redox reactions.

2 3

CO2 leaves cycle

Alpha-ketoglutaric acid

CO2 leaves cycle

Succinicacid

KREBSCYCLE

Steps and Redox reactions generate FADH2

and NADH.

4 5

Malicacid

1

2

3

4

5

What you must know about the Krebs Cycle

• Each turn requires one molecule of acetyl CoA.• Don’t forget there are 2 turns per glucose molecule• Each turn generates:

– 3 NADH molecules– 1 ATP

– 1 FADH2 molecule

– Almost all of the energy removed from pyruvate molecules are carried by electron carrier molecules NADH and FADH2

– Reaction intermediates (citric acid, oxaloacetate, etc.) are required to keep the cycle going.

Electron Transport Chain Electron carriers (NADH and FADH2) take these high energy electrons to the Electron Transport Chain.Electrons are run down an “electron slide”…The energy released from this “slide” is used to make ATP…

At the end of the slide, the electrons and H+ are accepted by oxygen…

…and become WATER!

Electron Transport results in H+ ions being

concentrated in the intermembrane space • Proton (H+)

gradient is built up as a result of NADH (produced by Krebs cycle reactions) feeding electrons into electron transport system.

ATP Synthase enzymes use a proton (H+) gradient to put ADP and P together

forming 32 ATP

Energy yield from Aerobic Cellular Respiration