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Cellular Respiration: Harvesting Chemical Energy

Cellular Respiration: Harvesting Chemical Energy

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Cellular Respiration: Harvesting Chemical Energy. The Metabolic Pathway of Cellular Respiration. Cellular respiration is an example of a metabolic pathway. A series of chemical reactions in cells All of the reactions involved in cellular respiration can be grouped into three main stages - PowerPoint PPT Presentation

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Page 1: Cellular Respiration:  Harvesting Chemical Energy

Cellular Respiration: Harvesting Chemical Energy

Page 2: Cellular Respiration:  Harvesting Chemical Energy

• Cellular respiration is an example of a metabolic pathway

– A series of chemical reactions in cells

• All of the reactions involved in cellular respiration can be grouped into three main stages

– Glycolysis

– The Krebs cycle

– Electron transport

The Metabolic Pathway of Cellular Respiration

Page 3: Cellular Respiration:  Harvesting Chemical Energy

A Road Map for Cellular Respiration

Cytosol

Mitochondrion

High-energyelectronscarriedby NADH

High-energyelectrons carriedmainly byNADH

Glycolysis

Glucose2

Pyruvicacid

KrebsCycle

ElectronTransport

Figure 6.7

Page 4: Cellular Respiration:  Harvesting Chemical Energy

Stage 1: Glycolysis

• A molecule of glucose is split into two molecules of pyruvic acid

– These molecules then donate high energy electrons to NAD+, forming NADH

– Glycolysis makes some ATP directly when enzymes transfer phosphate groups from fuel molecules to ADP

– Glycolysis occurs in the cytosol of the cell.

Page 5: Cellular Respiration:  Harvesting Chemical Energy

Figure 6.8

Glucose

2 Pyruvic acid

PGAL

Page 6: Cellular Respiration:  Harvesting Chemical Energy

If oxygen is available, pyruvic acid enters the pathways of aerobic respiration (respiration with oxygen)

Page 7: Cellular Respiration:  Harvesting Chemical Energy

Stage 2: The Krebs Cycle

• The Krebs cycle completes the breakdown of sugar

• Occurs inside of the mitochondria (mitochondrial matrix)

• In the Krebs cycle, pyruvic acid from glycolysis is first “prepped” into a usable form, Acetyl-CoA

2

Pyruvicacid

Aceticacid

Coenzyme A

Acetyl-CoA(acetyl-coenzyme A)

CO2

Page 8: Cellular Respiration:  Harvesting Chemical Energy

Mitochondria

Page 9: Cellular Respiration:  Harvesting Chemical Energy

• The Krebs cycle extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO2

– The cycle uses some of this energy to make ATP

– The cycle also forms NADH and FADH2

Hans Krebs

Page 10: Cellular Respiration:  Harvesting Chemical Energy

2

3

4

6

Page 11: Cellular Respiration:  Harvesting Chemical Energy

One glucose molecule causes two turns of the Krebs cycle

The two turns produce 6 NADH, 2 FADH2, 2 ATP, and 4 CO2.

So now there have been 4 molecules of ATP created up to this point (remember the 2 created during glycolysis)

Things to Remember

Page 12: Cellular Respiration:  Harvesting Chemical Energy

Stage 3: Electron Transport

• Electron transport releases the energy your cells need to make the most of their ATP

• The molecules of electron transport chains are built into the inner membranes of mitochondria

– The chain functions as a chemical machine that uses energy released by the “fall” of electrons to pump hydrogen ions across the inner mitochondrial membrane

– These ions store potential energy

Page 13: Cellular Respiration:  Harvesting Chemical Energy

• When the hydrogen ions flow back through the membrane, they release energy

– The ions flow through ATP synthase

– ATP synthase takes the energy from this flow and synthesizes ATP (Chemiosmosis)

Page 14: Cellular Respiration:  Harvesting Chemical Energy

Figure 6.12

Proteincomplex

Electroncarrier

Innermitochondrialmembrane

Electronflow

Electron transport chain ATP synthase

Page 15: Cellular Respiration:  Harvesting Chemical Energy

The Versatility of Cellular Respiration

• Cellular respiration can “burn” other kinds of molecules besides glucose

– Diverse types of carbohydrates

– Fats

– Proteins

Page 16: Cellular Respiration:  Harvesting Chemical Energy

Figure 6.13

Food

Polysaccharides Fats Proteins

Sugars Glycerol Fatty acids Amino acids

Amino groups

Glycolysis Acetyl-CoA

KrebsCycle Electron

Transport

Page 17: Cellular Respiration:  Harvesting Chemical Energy

Adding Up the ATP from Cellular Respiration

Figure 6.14

Cytosol

Mitochondrion

Glycolysis

Glucose2

Pyruvicacid

2Acetyl-

CoA

KrebsCycle Electron

Transport

bydirectsynthesis

by directsynthesis

byATPsynthase

Maximumper

glucose:

Page 18: Cellular Respiration:  Harvesting Chemical Energy

FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY

• Some of your cells can actually work for short periods without oxygen

– For example, muscle cells can produce ATP under anaerobic conditions

• Fermentation

– The anaerobic harvest of food energy

Page 19: Cellular Respiration:  Harvesting Chemical Energy

• Human muscle cells can make ATP with and without oxygen

– They have enough ATP to support activities such as quick sprinting for about 5 seconds

– A secondary supply of energy (creatine phosphate) can keep muscle cells going for another 10 seconds

– To keep running, your muscles must generate ATP by the anaerobic process of fermentation

Fermentation in Human Muscle Cells

Page 20: Cellular Respiration:  Harvesting Chemical Energy

• Glycolysis is the metabolic pathway that provides ATP during fermentation

– Pyruvic acid is reduced by NADH, producing NAD+, which keeps glycolysis going

– In human muscle cells, lactic acid is a by-product

Page 21: Cellular Respiration:  Harvesting Chemical Energy

Figure 6.15a

2 ADP+ 2

Glycolysis

Glucose

2 NAD

2 Pyruvicacid

+ 2 H

2 NAD

2 Lacticacid

(a) Lactic acid fermentation

Page 22: Cellular Respiration:  Harvesting Chemical Energy

Fermentation in Microorganisms

• Various types of microorganisms perform fermentation

– Yeast cells carry out a slightly different type of fermentation pathway

– This pathway produces CO2 and ethyl alcohol

Page 23: Cellular Respiration:  Harvesting Chemical Energy

• The food industry uses yeast to produce various food products

Figure 6.16

Page 24: Cellular Respiration:  Harvesting Chemical Energy

Two Types of Fermentation