The Utilization of Free Energy in Biological Sysytems

2.A.1- 2.A.3

All living systems require a constant input of free energy as well as matter to grow, reproduce and maintain order.

The concept of thermodynamics that represents the amount of free energy available is Delta G.

Thermodynamics is the law that says energy is transferred from the sun to something that converts it into energy available to be transferred to more energy users.

The First Law of Thermodynamics states that energy can neither be created nor destroyed, but it can be transferred and transformed.

 The Second Law of Thermodynamics states that spontaneous changes that do not require outside energy increase the entropy, or disorder, of the universe. This law is represented by Delta S. Living organisms can not violate this law, as entropy always increases over time.

Biological processes or entropy increase order. An example is photosynthesis.

Metabolism is the totality of the organisms’ chemical reactions (cellular respiration, photosynthesis etc.)

A metabolic pathway is started by a specific molecule, each step thereafter being catalyzed by a specific enzyme.

Catabolic pathways break down complex molecules into simpler compounds (polysaccharide, for example, into a monosaccharide). They are spontaneous and release energy. Delta G < 0 represents catabolic reactions, which are exergonic.

Anabolic pathways are the opposite of catabolic in which they build more complex compounds from simple ones and energy. There are endergonic, and therefore NOT spontaneous. This type of reaction is represented by Delta G > 0.

As order is maintained by a constant supply of free energy, when that energy supply is cut off, the organism dies, as it can no longer maintain cell processes that keep it “alive.”

The energy that an organism takes in must also exceed what is let out, as energy is lost as heat in cellular processes such as metabolism, any movement and homeostasis (which is the maintaining of inner and external boundaries.) But when an organism obtains excess free energy then it is either stored s far or used in growth. Insufficient energy causes the loss of mass and if prolonged, the death of the organism. Endergonic and exergonic reactions must go hand-in-hand to maintain entropy, which keeps organism alive.

The chloroplasts absorb most light waves, reflecting primarily green light waves, making the photosynthetic areas of autotrophs appear to be what we perceive as “green,” depending on the kind of chlorophyll contained within the leaf.

Photosynthesis is the process that occurs in the chloroplasts of a plant. It uses sunlight, water (6H2O) and carbon dioxide (CO2) to make glucose (C6H12O6) and oxygen (6O2). It is a two-step process of the Light Reaction and then the Calvin Cycle.

In the light reaction phase, light enters the chloroplast and travels to the thylakoid where it hits Photoreceptor II, exciting electrons within it that are then sent along the Electron Transport Chain. Water is split up into hydrogen and oxygen ions (a by-product that leaves the cell) by the moving electrons. The H+ ions go into the thylakoid’s lumen.. As more water is split, the accumulated H+ protons form a proton gradient. New electrons then replace electrons lost to the electron transport chain.

The protons diffuse through ATP synthase, which uses the energy of the proton gradient to phosphorylate ADP back into ATP.  This is known as photophosphorylation.

Another photon of light hits Photoreceptor I, exciting another electron. This electron reduces NADP+ to form NADPH, which is the final electron receptor in photosynthesis, where it leaves the thylakoid membrane.

The second step of photosynthesis is known as the Calvin cycle, which occurs in the stroma of the chloroplast. This cycle uses the energy produces in the Light Reaction to power the synthesis of carbohydrates. Rubisco is the prime enzyme for this process. It takes carbon dioxide out of the air and combines it with the products of the light process, making it useable to organisms. In order to work, it must go through the Calvin cycle twice. This step is called carbon fixation and creates CH2O.

All organisms stay alive by metabolizing energy through cellular respiration. Photoautotrophs consist of plants, algae, bacteria and some protist & prokaryotes, break down and use the energy/glucose they create through a process called photosynthesis. Heterotrophs metabolize the energy they take from plants and other heterotrophs through cellular respiration.

Photoautotrophs are the only organisms that capture, use and store free energy from the sun.

Other, non photosynthetic autotrophs use chemosynthesis to capture free energy from their environment.

Cellular respiration is how organisms use the free energy available in glucose to phosphorylate and create ATP. It is a catabolic reaction pathway that yields energy by oxidizing organic fuels. Exergonic reactions break down the sugars and release energy needed for cellular respiration.

Cellular respiration has several steps. The first step is Glycolysis, which occurs in the cytoplasm of the cell, outside the mitochondria. Glycolysis breaks down glucose to create 2 pyruvate molecules. It is an anabolic process that does not require oxygen.

Then is the transition reaction where the pyruvate enters the mitochondrion where it releases CO2, picks up Coenzyme A and turns into AcetylcoA.

The next step is known as the Kreb's cycle. The Kreb's cycle occurs in the inner matrix of the Mitochondria. It turns AcetylcoA into 2CO2 + 6NADPH + 2FADH2 + 4 CO2

After the Kreb's cycle is the Electron Transport Chain. It occurs in the inner cell membrane of mitochondria. In order to convert the stuff right, it must go through it twice. 

Then the remaining products go through Oxidative phosphorylation and through that energy and CO2 are released. 

Environmental changes cause cells to develop in certain ways to survive. 

Nutrient cycling is the cycling of matter through reservoirs. There are several cycles: The Carbon cycle, the nitrogen cycle, the water cycle and the phosphorous cycle. 


In order for an ecosystem to survive, nutrients have to circle through it in just the right proportions, or else the ecosystem will die. 

Sometimes a cell must increase its volume to surface area ratio. A larger surface area allows the cell to absorb more nutrients and also expel them.

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http://upload.wikimedia.org/wikipedia/commons/thumb/1/11/Chloroplast-new.jpg/400px-Chloroplast-new.jpghttp://upload.wikimedia.org/wikipedia/commons/1/18/Thylakoid_membrane.png 

http://s3.amazonaws.com/rapgenius/1376071616_photosynthesis-overview.gif 

http://longpointbiosphere.com/Publications/Grasses/Pics/figure2.1pg11.jpg
http://berryberryeasy.com/wp-content/uploads/2011/06/Photoautotrophs.jpg
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