Energy in the Cell

A. All living organisms must be able to obtain energy from the environment in which they live.

B. Autotrophs - Plants and other green organisms are able to trap the light energy in sunlight and store it in the bonds of certain molecules for later use.

I. The Need for EnergyI. The Need for Energy

C. Heterotrophs cannot use sunlight directly, they eat plants or other heterotrophs that eat plants to obtain energy.

D. Cells require energy for various activities.

1. active transport

2. cell division

3. movement of flagella or cilia

4. production, transport, and storage of proteins.

E. ATP (adenosine triphosphate) is a molecule that provides quick source of energy for any organelle in the cell that needs it.

1. ATP is composed of an adenosine molecule with 3 phosphate groups attached.

2. As more phosphate groups are added, more energy is required to make the molecule.

3. When the phosphate bonds are broken, energy is released and is available to the cell.

4. When ATP is broken down the energy must be captured and used efficiently by cells.

5. Many proteins have a specific site where ATP can bind.

Adenosine

3 phosphate groups

2 phosphate groups

II. Trapping Energy from SunlightII. Trapping Energy from Sunlight

A. The process that uses the sun’s energy to make simple sugars is called photosynthesis.

B. The general equation for photosynthesis is written as 6CO2 + 6H2O + sunlight →C6H12O6 + 6O2

C. Chlorophyll, a green pigment found in chloroplasts and infolded membranes of photosynthetic bacteria, absorbs almost all wavelengths of light except green.

D. Photosynthesis happens in 2 phases.

1. The light-dependent reactions convert light energy into chemical energy.

a. sunlight excites the electrons in the chlorophyll.

b. The excited electrons can convert ADP to ATP.

c. Water molecules are broken into H+ ions and O2 gas

2. ATP produced in the light-dependent reactions is used to fuel the light-independent reactions that produce simple sugars.

a. In the Calvin Cycle, CO2 is converted into 3-carbon chains.

b. 3-carbon chains are converted into sugar and other carbohydrates.

III. Converting Food into EnergyIII. Converting Food into Energy

A. Cellular respiration is the process by which cells break down food molecules to produce ATP. C6H12O6 + 6O2 6CO2 + 6 H2O + energy

B. There are 3 stages of cellular respiration.

1. Glycolysis – breaking down glucose

a. is anaerobic - no oxygen is required.

b. breaks glucose into 2 3-carbon molecules

c. produces only 2 ATP molecules

d. takes place in the cytoplasm

2. Citric Acid Cycle or Krebs cycle, is a series of chemical reactions that breaks down 3-carbon molecules into CO2.

a. at each turn of the cycle, 1 ATP and 2 CO2 are produced

b. occurs inside the inner membrane of mitochondria

3. Electron Transport Chain

a. molecules of NADH and FADH2 give up electrons that pass through a series of reactions.

b. occurs inside mitochondria

c. requires oxygen and produces 32 ATP molecules

Citric acid cycle

C. Fermentation – an anaerobic process that supplies energy when oxygen is not available.

1. Lactic acid fermentation – produces lactic acid in animals (build up of lactic acid causes the “burn” we feel in our muscles)

2. Alcoholic fermentation - used by yeast cells and some bacteria to produce CO2 and ethyl alcohol. (important to baking and production of wine and other alcoholic beverages)

Comparison of Photosynthesis and Cellular Respiration

Photosynthesis Cellular Respiration

Food synthesized Food broken down

Energy from sun stored in glucose

Energy of glucose released

Carbon dioxide taken in Carbon dioxide given off

Oxygen given off Oxygen taken in

Produces sugars Produces CO2 and H2O

Requires light Does not require light

Occurs only cells with chlorophyll

Occurs in all living cells

The End