CHAPTER 5Harvesting Chemical

Energy

Chemical Energy and Food

• All organisms require energy to carry out their life functions.

• Evolution has produced a number of biochemical processes that organisms use to obtain energy stored in food.

• Food provides: – Energy for living things and their cells to function

• How much energy is in food?– Calorie: amount of energy needed to raise the

temperature of one gram of water one degree Celsius

– Food labels are kilocalories (1,000 calories)

Metabolism

• Metabolism – all chemical reactions in an organism

• Composed of 2 parts:1) Synthesis

a) Reactions that require energyb) Use carbon skeletons and energy for cell

growth and maintenancec) Example:Photosynthesis!

Metabolism, continued

• Composed of 2 parts:2) Decomposition

a. Release energy from foodb. Produce carbon skeletonsc. Example:

6O2 + C6H12O6 6CO2 + 6H2O + Energy

Which of the above makes ATP/ energy? Which of the above uses ATP/ energy?

Overview of Cellular Respiration

• Main Points:–Decomposition reaction– Provides cells with energy they need

to function– Each step catalyzed by an enzyme– Releases energy by oxidizing sugars

and other organic substances

Two Types of Respiration1) Aerobic Respiration (which is typically referred

to as Cellular Respiration)a. Requires oxygenb. Electrons flow to oxygenc. Raw materials are fats, proteins, and carbohydratesd. Energy is releasede. Overall Equation:

2) Anaerobic Respirationa. Occurs without oxygenb. Electrons flow to another acceptor, such as nitrogen

or sulfur in bacteria and yeast

6O2 + C6H12O6 6CO2 + 6H2O + ATPEnzymes

The Stages of Aerobic Respiration

Glycolysis Krebs Cycle Electron Transport

Location

What goes in?

What comes out?

ATP formed

Cytoplasm Mitochondrial Matrix

MitochondrialMembranes

Glucose

H2O

Pyruvate/ Acetyl CoA

O2, NADH and FADH2

22 Net 34

Pyruvate &NADH

CO2, NADH, & FADH2

Glycolysis• The first stage for both aerobic and

anaerobic respiration.

• Definition:– The anaerobic (does not require O2) process

of breaking down glucose into 2 molecules of pyruvic acid

– Each step is catalyzed by different enzymes

• Location in the Cell:– Cytoplasm of the cell

Steps of Glycolysis

1. Glucose is converted into glucose-6-phosphate– Requires the use of 2 ATP, which releases its

phosphates

2. Glucose-6-phosphate is rearranged and eventually splits into two 3-C sugar-phosphates

3. Partial oxidation of these 3-C molecules results in …– the formation of pyruvic acid (pyruvate) – the production of ATP– NAD+ is reduced to form NADH, which will be

sent to the ETS

Glycolysis Totals

• Total Energy Made:– To start glycolysis 2 ATP needed– During glycolysis 4 ATP made

Net gain: 2 ATP

• Electron carrier:– 2 NAD+ 2 NADH

accepts e-

– NAD+ accepts 4 high energy electrons and forms NADH. NADH holds them until they are passed to other molecules.

The FATE of PYRUVATE

• The PRESENCE or ABSENCE of OXYGEN in the cell determines the FATE of PYRUVATE.

Aerobic(oxygen)

LACTATE Enters MITOCHONDRI

A

Anaerobic(no oxygen)

PYRUVATE

Lactic Acid Fermentation

• Convert NADH and pyruvate into NAD+ and lactate• NAD+ cycles back to glycolysis • Small amounts of ATP are made.

Other types of fermentation:• Alcoholic fermentation…

– Produces ethyl alcohol and CO2.

– EX: yeast used to make bread

• Acetic Acid fermentation…– Produces vinegar– EX: bacteria used to make yogurt, cheese, and sour

cream

Fermentation cont.

• Total Energy Output of Fermentation=No new ATP made!

(only 2 ATP from glycolysis)

This is why we can’t exercise rapidly for long periods of time!

Cellular Respiration (Aerobic!)

The FATE of PYRUVATE

• The PRESENCE or ABSENCE of OXYGEN in the cell determines the FATE of PYRUVATE.

Aerobic(oxygen)

LACTATE Enters MITOCHONDRI

A

Anaerobic(no oxygen)

PYRUVATE

Glycolysis Review

• At the end of glycolysis, there is still a lot of unused energy stored in the 2 molecules of pyruvic acid

• To access this energy, cells need O2.

• Therefore, the final steps in cellular respiration are aerobic because they require O2

Pyruvate enters the Mitochondria…

• Produces acetate (acetic acid)• Produces NADH from NAD+• CoEnzyme A picks up acetate and

forms Acetyl CoA• CoA delivers acetate to the Krebs

Cycle• Also known as the Citric Acid Cycle

The Mitochondria– Cite of ATP synthesis– Compartments in which the Krebs cycle and

electron transport chain occurs– Number in cells vary from 10 to 1000s

based on activity– Made of 2 membranes:

1. Inner – contains many enzymes, made of more protein than lipids, forms cristae (folds) which increase surface area.

2. Outer – regulates movement of molecules in and out of the mitochondria

Steps of the Kreb’s Cycle• An enzyme combines the 2C acetyl group of

acetyl CoA with a 4C acid (oxaloacetate), forming a 6 C acid (citric acid) and releasing CoA.

• Enzymes rearrange the 6C acid and convert it into a 5 C acid (Ketogluterate). These reactions release CO2 into the atmosphere and harvest electrons to form NADH from NAD+.

• Enzymes rearrange the 4 C acid two times, forming one molecule of ATP (2) and FADH2

• Finally, enzymes convert the rearranged 4 C acid into oxaloacetate and form a third molecule of NADH. The cycle continues as oxaloacetate enters the beginning.

Pyruvic acid or

Pyruvate

Acetyl- CoA

CO2

atmosphereCitric acidor Citrate

Other molecules

electrons

CO2

Captured by NAD+ and FAD

To E.T.C

H+

2 ATP

Remember…

• The CO2 released is the source of the CO2 in your breath when you exhale

• ATP produced directly in the Kreb’s cycle can be used in cellular activities

• When O2 is present, the high energy electrons can be used to generate huge amounts of ATP

Steps of the Electron Transport System

1. H atoms are carried by NAD and FAD to the ETS2. Each system consists of a series of electron

carriers, enzymes, and other proteins known as cytochromes which are embedded in the cristae of the mitochondria.

3. H atoms are accepted by the system and separated into electrons and protons.

4. The electron carriers transfer the electrons step by step through the system to a cytochrome.

5. The cytochrome combines the electrons with protons and O2 forming H2O (this step requires oxygen!)

Steps of the Electron Transport System

6. At each step the electrons release free energy, some is used by proton pumps to actively transport protons from the matrix across the cristae to the intermembrane space.

7. A high concentration of protons accumulate causing it to be unstable

8. Protons diffuse back to the matrix of the mitochondria, they pass through the ATP synthase (where ATP is made.)

9. ATP can be transferred out of the mitochondria and used by the cell.

e-e-

e-e-

ATP

e-

ATP

ATP

ATP

NADH NAD+ + e- + H+

FADH2 FAD + e- + H+

O2 H+

H2O

Exhaled as waste

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