Chapter 8: Cellular Energy

Energy follows rules…

• The study of the flow and transformation of energy in the universe is called thermodynamics

• Entropy is the measure of disorder, or unusable energy, in a system.

Conservation of Energy• Energy is not lost or created. It is

conserved. According to the law of conservation of mechanical energy, all the energy in the universe remains the same. It merely changes from one form to another.

• For example, chemical energy is converted into mechanical energy when a muscle contracts.

Endergonic and Exergonic

• Exergonic is a reaction that releases energy. It is sometimes called a spontaneous reaction.• Endergonic is a reaction whereby

energy is absorbed. It is not spontaneous and energy is put into the system from the surroundings.

•

Reaction ATP produced ATP Used

Glycolysis 4 2

Production of Acetyl Co-A

0 2

Krebs Cycle 2 0

Electron Transport Chain

34 0

Photosynthesis

• 6CO2 + 6H2O --> C6H12O6 + 6O2

The role of Photosynthesis…

• Plants obtain and make their own energy using sunlight. They are not really “making” their own energy, so much as converting into a form that can be used by them—and eventually even us!

Photosynthesis…• During the light-dependent reactions of

photosynthesis, light energy is used to split water molecules generating protons and oxygen molecules.

• Light energy is trapped and converted into chemical energy during photosynthesis.

• It is an anabolic process.• Anabolic?• It means the synthesis of more complex materials

in living organisms from simpler substances.

Light-Dependent Reactions?

• When light strikes chlorophyll molecules, they lose electrons, which are ultimately replaced by splitting water into 2H+ and O2– .

There are several steps…

• Glycolysis• Kreb’s Cycle (also known as the Citric

Acid Cycle)• Electron Transport Chain• Each of these results in the formation

of a molecule or molecules needed for the continuation of the process.

Glycolysis

• The first stage of cellular respiration, glycolysis, is an anaerobic process.

• Glycolysis generates two ATP and two pyruvate.

• Most of the energy from the glucose is contained in the pyruvate.

Krebs Cycle (Citric Acid Cycle)

• Breaking down a single glucose molecule requires two turns of the Krebs cycle.

Chemiosmosis

• Hydrogen atoms diffuse down their concentration gradient out of the thylakoid into the stroma through ion channels in the membrane.

•

Reaction ATP produced ATP Used

Glycolysis 4 2

Production of Acetyl Co-A

0 2

Krebs Cycle 2 0

Electron Transport Chain

34 0

The Calvin Cycle

• In the second step of the Calvin cycle, chemical energy from ATP and NADPH is transferred to 3-PGA molecules to form the high-energy molecules G3P.

• The reactions of the Calvin cycle are not directly dependent on light, but they usually do not occur at night

• The Calvin Cycle depends on the products of the light-dependent reactions.

Without Oxygen?

• Alcohol fermentation is similar to lactic-acid fermentation in that NADH donates electrons during this reaction and NAD+ is regenerated.• Fermentation takes place in yeast

and some bacteria.

How?

•ATP is the energy of the cell. •How do we get it? Let’s

watch and see…

So, how do we get this energy?

• Our genes determine where our energy needs to be exerted through metabolic pathways.• A metabolic pathway is defined as a process

where the product of one reaction is used as the substrate for the next reaction.• ATP releases energy when the bond between

the second and third phosphate groups is formed.

Life…and its Limits

All of our every day functions require energy. Hence, our limits depend upon the energy that is made available to us.

And what ultimately determines this energy?

The Sun?

•Do plants experience limits regarding the sun? •How do they cope?

• Plants acquire carbon dioxide for photosynthesis through stomata in their leaves. They need the carbon dioxide during the day when photosynthesis is consuming it and so they generally have to have their stomata open during the day. The day is also when it is warmest and this leads to evaporation of water. Thus plants can make food only with their stomata open, but to do so they risk drying out.

How do they cope?• Some plant groups have adapted to

dry climates by modifying their photosynthesis so that the stomata can be open at night taking in carbon dioxide (and losing less water) that is stored and then used during the day. The stomata are closed during the day to prevent water loss. These are the CAM and C4 plants.

CAM plants

• Crassulacean Acid Metabolism• CO2 enters the plants at night and is

converted into organic acids. These organic acids then release CO2 during the day when the stomata is closed.• Examples of CAM plants include

cactii and orchids.

C4 plants

• CO2 is first fixed into a 4 carbon compound before entering the Calvin cycle.• On hot days, C4 plants keep their

stomata closed to minimize evaporation.• Examples: Sugarcane, sorghum