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Kenneth Kang

Thursday, November 02, 1995


Chapter 10

Cellular Energy


Defined as the ability to do work, energy, is required to combat entropy. Entropy is a physical phenomenon where all materials and energy tend to expand. Energy can be expended to keep this from occuring. The big picuture is that cell need energy to stay together.

The energy is created by complex reaction. Presented below are photosynthesis and respiration.

Definitions of animal energy patterns include autotrophs, and living thing that can make its own food, and heterotroph, an animal that depend on other animals for food.

Biological Energy Chain

If considered as one system, one can see all the energy that passes between organisms to keep them all fuctioning.

ATP: Energy in a Molecule

Cell Energy

ATP is adenosine triphosphate and provides a constant supply of predictable energy. It goes through a cycle from ADP + Pi + Energy ATP. This is the "small change" that the cell uses as energy.

Forming ang Breaking Down ATP

The molecule consists of a adenine and ribose sugar with a branch that has either two or three phosphate groups. By breaking and forming the bond between the last phosphate, the cell can use or put in energy.

The Uses of Energy

The cells can use enegy to make proteins or to pump in or out materials.

Review Questions

  1. Why do cells use ATP and not just glucose?
  2. Why does ATP and ADP form a cycle?

Photosynthesis: Trapping Energy

CO2 + H2O C6H12O6 + O2

The diagrams on pages 224-246 in the text help more than the text.

The sun's energy is turned to ATP by photosynthesis. This energy is then stored in large molecules. The molecules are carbohydrates specifically the monosaccharide glucose. The general reaction equation is 6CO2 + 6H2O C6H12O6 + 6O22. This requires two reactions: a light reaction that requires light and a dark reaction, the CALVIN CYCLE, that does not require light.

Digression: The Leaf

This is the organ of a plant that does the photosynthesis. (X-Ref Text P. 649) The parts and their function are:

Inside the mesophyll cells the chloroplast organelles have the wonderful photosynthesis reaction.


The structure of the chloroplast consists of stacks of green disks called the granum. Each disk is a thylakoid. Within these disks that are shaped like dimes with holes in them are particles in the ring. These particles will be named in this document as photosystems

Two types of photosystems exists. They are photosystem I and photosystem II. They absorb different wavelenghts of light. Each contains a molecule that absorbs light energy and an electron transport chain.

Review Questions

  1. How does the leaf prevent water loss?
  2. Name the place of photosynthesis generalizing from the living kingdoms to the specific sub-sub-sub-structure of the cell.

Autotrophs and Sunlight

Using PHOTOSYNTHESIS a cell, an autotrophe, can make energy by gathering light other than green. Using carbon dioxide and water with cholorophyll and light, a cell can make simple sugars.

Photosynthesis is composed of a LIGHT REACTION and the CALVIN CYCLE. The Calvin cycle synthesizes the final product. The light reation does the photo part. This all takes place in the chloroplasts.

Light Reaction

(ADP+Pi) + NADP + H2O ATP + (NADPH+H+) + O2

In the thylakoids, the light releases an electron from the chlorophyll molecule. This electron passes down an ELECTRON TRANSPORT CHAIN which makes ATP. But, the chlorophyll molecule doesn't have an electron. So a water molecule breaks up and gives the cholorophyll an electron. The process where water is broken is called PHOTOLYSIS.

As the free O and 2H+ the H+ join with NADP+ (nicotinamide dinucleotide phosphate) to form NADPH + H+. NADP is a coenzyme.

For the test, the major things to know are that the light reaction creates NADPH + H+ and ATP.

Calvin Cycle

C5mol + H2O + ATP + (NADPH+H+) + CO2 C6H12O6 + (ADP+Pi) + NADP


NET: CO2 + H2O C6H12O6 + O2

So far the photo part has only made NADPH + H+ and ATP. Now using CO2 and the other stuff we can make a sugar. The reaction will take place in the stroma.

Using an enzyme, CO2 is added to a 5-C molecule. This results in the formation of an unstable six carbon molecule. Looking at the diagram, the reaction adds water changing the carbon to two PGAs (phosphoglyceric acid). Then using ATP and NADPH + H+, the carbon is turned to PGALs (phosphoglyceraldyhyde). This chunks into a sugar or back to the five carbon molecule (using further ATP).

Life Without Light

Using CHEMOSYNTHESIS an organism can use stuff like CO2 and H to form methane (CH4).

Review Questions

  1. What role does ATP and NADPH + H+ play between light reation and the Calvin cycle?
  2. What does the Calvin cycle do? What role does cholorophyll play in photosynthesis?

Getting Energy to Make ATP

Glucose breakdown can be classified as aerobic or anaerobic. It consists of three parts: glycolysis - glucose breakdown; Krebs (or citric acid) cycle; and the electron transport chain.


They have a double membrane structure. The inner folded memebrane is similar to a chloroplast inner memebrane without the photosystems. Instead, it contains electron transport molecules.

First Steps to Respiration

The extraction of energy is mainly from 6-carbon sugars (i.e. glucose C6H12O6) although other molecules can be digested as well. This extraction of energy from molecules is called RESPIRATION. This further can be broken into two types ANAEROBIC, meaning without O2, and AEROBIC, meaning with O2.

C6H12O6 + 2ATP 2ADP + 2PGAL (this is the same as the plant stuff, nature need not reinvent everything.)

THEN: PGAL + 4ADP+4Pi + NAD+ Pyruvic Acid + NADH+H+ +4ATP

NET: C6H12O6 + NAD+ +2ADP 2ATP + Pyruvic Acid + NADH+H+

This occurs outside the mitochondria membrane. First you must use the anaerobic process of GLYCOLYSIS. This process splits up a glucose into two pyruvic acids. (X-Ref Text p.250) This requires two ATPs but produces 4ATP and NAD+ (nicotinamide dinucleotide; also a coenzyme like NADP) NADH + H+.

Releasing Energy with Oxygen

PREREACTIONS: Pyruvic Acid Acetic Acid + CO2

NAD + Acetic Acid Acetyl-coA + NADH+H+

This occurs in two steps after glycolysis in the mitochondria. (X-Ref Text 252) First, the pyruvic acid is broken down to acetic acid group with a CO2. This is added with coenzyme A to form actyl-CoA and an NADH + H+.

CYCLIC REACTIONS: Acetyl-coA + (4C)oxloacetic acid (6C)citric acid

(6C)citric acid + NAD NADH+H+ + CO2 + (5C)ketoglutaric acid

(5C)ketoglutaric acid + ADP + NAD CO2 + NADH + ATP + (4C)succinic acid + NAD + FAD NADH + FADH + (4C)oxloacetic acid

In the next step, the CITRIC ACID CYCLE a.k.a. Kreb's Cycle, the acetyle-CoA is bonded to a oxaloacetic acid (a 4 carbon molecule) to form citric acid (a 6 carbon molecule). Then CO2 is release and also forms another NADH + H+. This leaves a five carbon molecule, ketoglutaric acid. Another CO2 is release while forming ATP and one more NADH + H+. This leaves succinic acid a four carbon molecule. Then FAD turn to FADH (flavin adenine dinucleotide, similar to NAD+) and another NADH + H+ is formed while changing to the four carbon oxaloacetic acid.


PYRUVIC ACID NET: Pyruvic acid + 4NAD + FAD + ADP 4NADH + FADH + ATP + 3CO2


After this, some ATP has been produced, but the NADH + H+ and FADH2 go into an electron chain thing to produce more ATP. This chain is aerobic. This chain, like the plant electron thing, requires the components of water so that the last electron can leave. This reaction occurs in the inner membrane proteins in the mitochondria. Each NADH = 3ATP each FADH = 2ATP. Glucose breakdown releases 38ATP. Finally the precious oxygen and the hydrogens from the FADH and NADH molecules are joined by an enzyme with the last remaining electron. If the oxygen disappears, the whole thing is backed up and can't move at all.

Releasing Energy Without Oxygen

No additional ATP is formed, but NADH + H+ is reverted to NAD+ so that glycolysis can be done. Both of these will only happen when oxygen is not present, otherwise aerobic respiration occurs.

LACTIC ACID FERMENTATION is what happens to your fatigued muscles. This takes the two pyruvic acids and makes two lacitic acids. This creates an oxygen debt, the amount of oxygen needed to get rid of lactic acid.

ACLOHOLIC FERMENTATION is carried out in yeast. This changes the glycolysis products to two ethanols and two CO2s.

Comparing Photosynthesis and Aerobic Respiration

They both complement each other's products and reactants. (X-Ref Text 256)

Review Questions

  1. What are the possible outcomes of a decomposed glucose molecule? Make sure to account for all atoms.
  2. Compare the amout of ATP energy released from respiration and compare to the energy in photosynthesis.
  3. Why don't plants just use the ATP from their light reations?

Year in Review