1. Chapter 6 How Cells Harvest Chemical Energy
Overview:
Cellular Respiration
Reactions involved in cellular respiration
Glycolysis
Krebs Cycle
Electron Transport
Fermentation
Food used to produce ATP
ATP used to produce food

2. INTRODUCTION TO CELLULAR RESPIRATION
Photosynthesis and cellular respiration
provide energy for life
Nearly all the cells in our body break down sugars for ATP production
Cellular respiration occurs in mitochondria
Cellular respiration is a chemical process that harvests energy from organic molecules
Cellular respiration yields CO2, H2O, and a large amount of ATP

3. The ingredients for photosynthesis are carbon dioxide and water
CO2 is obtained from the air by a plant’s leaves
H2O is obtained from the damp soil by a plant’s roots
Chloroplasts rearrange the atoms of these ingredients to produce sugars (glucose) and other organic molecules
Oxygen gas is a by-product of photosynthesis

4. The Relationship Between Cellular Respiration and Breathing
Cellular respiration and breathing are closely related
Cellular respiration requires a cell to exchange gases with its surroundings
Breathing exchanges these gases between the blood and outside air

5. Cellular respiration banks (stores) energy in ATP molecules
Cellular respiration breaks down glucose molecules and banks their energy in ATP
The process uses O2 and releases CO2 and H2O
Glucose
Oxygen gas
Carbon dioxide
Water
Energy

6. Connection: The human body uses energy from ATP for all its activities
ATP powers almost all cell and body activities
A calorie is the amount of energy that raises the temperature of 1 gram of water by 1 degree Celsius

7. Cells tap energy from electrons transferred from organic fuels to oxygen
Glucose gives up energy as it is oxidized
Loss of hydrogen atoms
Energy
Glucose
Gain of hydrogen atoms

8. Redox Reactions
Chemical reactions that transfer electrons from one substance to another are called oxidation-reduction reactions
Redox reactions for short
The loss of electrons during a redox reaction is called oxidation
The acceptance of electrons during a redox reaction is called reduction

9. [Glucose loses electrons (and hydrogens)]
Oxidation
[Glucose loses electrons (and hydrogens)]
Glucose
Oxygen
Carbon
dioxide
Water
Reduction
[Oxygen gains electrons (and hydrogens)]

10. Why does electron transfer to oxygen release energy?
When electrons move from glucose to oxygen, it is as though they were falling
This “fall” of electrons releases energy during cellular respiration

11. NADH and Electron Transport Chains
The path that electrons take on their way down from glucose to oxygen involves many stops
An enzyme called dehydrogenase and a coenzyme called NAD+ (nicotinamide adenine dinucleotide) play important role in oxidizing glucose.

12. The first stop is an electron acceptor called NAD+
The transfer of electrons from organic fuel to NAD+ reduces it to NADH
The rest of the path consists of an electron transport chain
This chain involves a series of redox reactions
These lead ultimately to the production of large amounts of ATP

13. All of the reactions involved in cellular respiration can be grouped into three main stages
Glycolysis
The Krebs cycle
Electron transport

14. Stage 1: Glycolysis
A molecule of glucose is split into two molecules of pyruvic acid
Glycolysis breaks a six-carbon glucose into two three-carbon molecules
These molecules then donate high energy electrons to NAD+, forming NADH
Glycolysis occurs in the cytoplasm

15. Glycolysis makes some ATP directly when enzymes transfer phosphate groups from fuel molecules to ADP (This process is called substrate-level phosphorylation)
Enzyme

16. Stage 2: The Krebs Cycle
The Krebs cycle completes the breakdown of sugar
In the Krebs cycle, pyruvic acid from glycolysis is first “prepped” into a usable form, Acetyl-CoA

17. 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
The Krebs cycle and the electron transport chain occur in the mitochondria

18. 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

19. 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

20. The electrons from NADH and FADH2 travel down the electron transport chain to oxygen
Energy released by the electrons is used to pump H+ into the space between the mitochondrial membranes
In chemiosmosis, the H+ ions diffuse back through the inner membrane through ATP synthase complexes, which capture the energy to make ATP

21. Cyanide, carbon monoxide
Connection: Certain poisons interrupt critical events in cellular respiration
Rotenone
Cyanide, carbon monoxide
Oligomycin

22. Fermentation is an anaerobic alternative to aerobic respiration
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
Under anaerobic conditions, many kinds of cells can use glycolysis alone to produce small amounts of ATP

23. Aerobic metabolism Anaerobic metabolism Anaerobic metabolism
When enough oxygen reaches cells to support energy needs
Anaerobic metabolism
When the demand for oxygen outstrips the body’s ability to deliver it
Anaerobic metabolism
Without enough oxygen, muscle cells break down glucose to produce lactic acid
Lactic acid is associated with the “burn” associated with heavy exercise
If too much lactic acid builds up, your muscles give out

24. Fermentation in Human Muscle Cells
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

25. 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
The food industry uses yeast to produce various food products

26. In alcoholic fermentation, pyruvic acid is converted to CO2 and ethanol
This recycles NAD+ to keep glycolysis working

27. In lactic acid fermentation, pyruvic acid is converted to lactic acid
As in alcoholic fermentation, NAD+ is recycled
Lactic acid fermentation is used to make cheese and yogurt

28. INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS
Cells use many kinds of organic molecules as fuel for cellular respiration
Polysaccharides can be hydrolyzed to monosaccharides and then converted to glucose for glycolysis
Proteins can be digested to amino acids, which are chemically altered and then used in the Krebs cycle
Fats are broken up and fed into glycolysis and the Krebs cycle

29. Food molecules provide raw materials for biosynthesis
In addition to energy, cells need raw materials for growth and repair
Some are obtained directly from food
Others are made from intermediates in glycolysis and the Krebs cycle
Biosynthesis consumes ATP

30. Biosynthesis of macromolecules from intermediates in cellular respiration

31. The fuel for respiration ultimately comes from photosynthesis
All organisms have the ability to harvest energy from organic molecules
Plants, but not animals, can also make these molecules from inorganic sources by the process of photosynthesis