1. Chapter 9: Energy in a Cell

2. 9.1 ATP in a Molecule

3. Cell Energy Energy is essential to life
All living organisms must be able to produce energy from the environment in which they live, store energy for future use, and use energy in a controlled manner

4. Work and need for energy
Several cell processes require energy
There is a molecule in your cells that is a quick source of energy for any organelle in the cell that needs it.
this energy is stored in the chemical bonds of the molecule
called adenosine triphosphate (ATP)
composed of an adenosine molecule with three phosphate groups attached
adenosine is made up of adenine bonded to a ribose

5. Forming and Breaking Down ATP
Phosphate groups are positively charged
Bonding phosphate groups to adenosine requires considerable energy
When only one phosphate group is attached…
A small amount of energy required
Stores a small amount of energy
Called adenosine monophosphate

6. When two phosphate groups are attached…
More energy required to force two phosphate groups together
Stores more energy
Called adenosine diphosphate (ADP)
When the third phosphate group is attached…
A tremendous amount of energy is required
Wants to break away from the other positively charged phosphate groups
When this bond is broken a great amount of energy is released

7. How cells tap into the energy stored in ATP
The energy of ATP becomes available when the molecule is broken down into ADP which can then bond with another phosphate group and form another ATP molecule.
How cells tap into the energy stored in ATP
When ATP is broken down and the energy is released, cells must have a way to capture that energy
Cellular proteins have a specific site where ATP can bind

8. Uses of Cell Energy
Making new molecules is one way that cells use energy
Cells use energy to maintain homeostasis

9. 9.2 Photosynthesis: Trapping the Sun’s Energy

10. Trapping Energy from Sunlight
Plant cells must trap light energy and store it in a form that is readily usable by cell organelles – that form is ATP
Photosynthesis = the process plants use to trap the sun’s energy and build carbohydrates, called glucose, that store energy

11. General equation = 6CO2 + 6H2O  C6H12O6 +6O2
Happens in two phases
Light-dependent reactions convert light energy into chemical energy
The molecules of ATP produced in the light-dependent reactions are then used to fuel the light-independent reactions that produce glucose.
General equation = 6CO2 + 6H2O  C6H12O6 +6O2

12. The chloroplast and pigments
Chloroplast is the organelle where photosynthesis occurs
Light-dependent reactions take place in the thylakoid discs
Contain molecules that absorb specific wavelengths of sunlight called pigments
Chlorophyll is the most common pigment
Appears green because that is the only wavelength that chlorophyll does not absorb, the green light is reflected

13. Light-Dependent Reactions
As sunlight strikes the chlorophyll the energy in the light is transferred to electrons which become highly energized
Excited electrons are passed from chlorophyll to an electron transport chain: a series of proteins embedded in the thylakoid membrane

14. At each step along the transport chain, the electron loses energy
Passed down the first electron transport chain, then a second chain, and then passed to the stroma
NADP+ is the electron carrier molecule that transports the electron to the stroma
Combines with a hydrogen to become NADPH
Transfers the energy to another series of reactions in the stroma

15. Restoring electrons to chlorophyll
Many electrons leave with the NADPH
To replace the lost electrons, molecules of water are split and each molecule produces two electrons
This reaction is called photolysis

16. Light-Independent Reactions
The Calvin cycle is a series of reactions in the stroma that use carbon dioxide to form carbohydrates
One of the last molecules formed is also one of the molecules needed for the first reaction of the cycle.
It takes six cycles to form one sugar molecule (6 carbon molecules) because only one CO2 molecule is added to each cycle

17. 9.3 Getting Energy to Make ATP

18. Cellular Respiration
The process by which mitochondria break down food molecules to produce ATP is called cellular respiration
Anaerobic = no oxygen required
Aerobic = oxygen required

19. Glycolysis Anaerobic process
A series of chemical reactions in the cytoplasm of a cell that break down glucose (6 carbon compound) into two molecules of pyruvic acid (3 carbon compound)
Two molecules of ATP used to start the reactions
Four ATP molecules are produced
Uses an electron carrier called NAD+ which forms NADH when carrying an electron

20. The citric acid cycle
Pyruvic acid molecules move into the mitochondria where they are exposed to oxygen
The citric acid cycle is a series of chemical reactions that breaks down glucose
One molecule of ATP is produced for every turn of the cycle
Two different electron carriers are used
NAD+
FAD
Electron carriers pass the energized electrons along to the electron transport chain in the inner membrane of the mitochondria

21. The electron transport chain
The electron transport chain in the inner membrane of the mitochondria is very similar to the electron transport chain of the thylakoid membrane
NADH and FADH2 pass energized electrons from protein to protein in the membrane
Slowly releasing small amounts of energy

22. The final acceptor in the chain is oxygen
Results in a high concentration of H+ in the inner membrane creating in both a chemical and electrical gradient
The inner membrane forms ATP from this gradient
The final acceptor in the chain is oxygen
Reacts with four hydrogen ions to form two water molecules
Without oxygen the transport chain would become blocked
Produces a total of 32 ATP molecules: very effective

23. Fermentation
When cells are without oxygen for a short period of time the anaerobic process of fermentation follows glycolysis and provides ATP until oxygen is available again.

24. Two types Lactic acid fermentation Alcoholic fermentation
Two molecules of pyruvic acid use NADH to form two molecules of lactic acid
Releases NAD+ to be used in glycolysis
Two ATP molecules formed for each glucose molecule
The liver changes lactic acid back into pyruvic acid
Alcoholic fermentation
Used by yeast cells to produce CO2 and ethyl alcohol

25. Comparing Photosynthesis an Cellular Respiration
Both photosynthesis and cellular respiration use electron carriers and a cycle of chemical reactions to form ATP
Photosynthesis produces high energy carbohydrates and oxygen from the sun’s energy, whereas cellular respiration uses oxygen to break down carbohydrates to form ATP and compounds of lower energy.
CO2 is produced by cellular respiration, but the beginning products for photosynthesis.
Table 9.2 in Figure 9.14