Energyinacell


 * __ Energy In A Cell __**

// What You’ll Learn: // v You will recognize why organisms need a constant supply of energy and where that energy comes from. v You will identify how cells store and release energy as ATP. v You will describe the pathways by which cells obtain energy. v You will compare ATP production in mitochondria and in chloroplasts.

//__ Section 1 __// //__ The Need For Energy __//

** Cell Energy ** Energy is essential for all life. Living organisms obtain energy from their environment. Plants receive their energy by trapping the light energy of the sun, but animals must get their energy from eating other organisms that have stored energy. All activities require energy, whether you are participating in the Iron Man or you are writing a paper for school. After you finish any activity, especially a rigorous exercise, your body needs a quick source of energy, so you may drink Gatorade or eat some snacks. For a cell, a quick source of energy comes from the molecule **ATP**, or **adenosine triphosphate**. This energy molecule provides energy to any organelle that needs it. ATP is made of an adenosine molecule with three phosphate groups attached.

Only a little bit of energy is needed and the chemical bond doesn’t store much energy when only one phosphate group bonds to form AMP, or adenosine monophosphate. More energy is needed and the chemical bond stores more energy when two phosphate groups bond to form **ADP**, or **adenosine diphosphate**. Lots of energy is needed to bond the three phosphate groups to form ATP, and the chemical bond stores a lot more energy. When these chemical bonds are broken, energy is released. Once a bond breaks, the energy released becomes available to the cell and an ADP molecule remains. This molecule then bonds with another phosphate group to form ATP again. This process makes it so the cell doesn’t have to store all of the ATP it needs. ATP can be formed as long as phosphate groups are available. This process also makes it so that ADP can be used as a source of energy. Many cell functions need more energy than others and so they have to use the energy stored in ATP. However, the cell functions that don’t need that much energy can use ADP as a source of energy. Cells must be able to obtain and use the energy from ATP efficiently or it is wasted. In the cell, many proteins have sites where ATP can bind itself to the protein. If the ATP molecule is attached to protein, once the chemical bond in ATP is broken, the cell can use that energy for various tasks like making other proteins. After the bond is broken, the resulting ADP is unattached to the protein and another ATP molecule may bind to the protein.
 * Forming and Breaking Down ATP **

Energy is used by cells in many ways. One way that cells use energy is to create molecules such as enzymes. Another way that cells use energy is to build up the plasma membrane and to build new organelles. Cells also use energy for very unique things such as to create light through the process of bioluminescence. Other cells use energy to move and transport various particles.
 * Uses of Cell Energy **

//__ Section 2 __// //__ Photosynthesis: Trapping the Sun’s Energy __//

** Trapping Energy From Sunlight ** In order to use the energy of sunlight, plants must store the energy where it can be easily accessed for use. One such place is in the chemical bonds of ATP. **Photosynthesis** is the process that uses the sun’s energy to make simple sugars, which are later converted to complex carbohydrates that store energy. The first step of this process is a **light-dependent reaction** and it turns light energy from the sun into chemical energy. The second step of photosynthesis is a **light-independent reaction** in which simple sugars are produced. The chloroplast is the organelle in which photosynthesis takes place. More specifically, it takes place within the membranes of the thylakoid discs within the chloroplast. **Pigments,** molecules that absorb certain wavelengths of sunlight, are located in these membranes and they collect the energy of the sunlight. Pigments are organized in different clusters within the thylakoid membranes known as photosystems. The most common pigment in photosystems is chlorophyll. Chlorophyll is a pigment that absorbs many wavelengths of light, but not green. As a result, the leaves of the trees appear green. In autumn, trees cease to produce chlorophyll and other pigments show up, causing the leaves to change into red, yellow, and other colors. Do the Mini-Lab at the end of this section to study more about pigments by separating the various pigments in a leaf.

Since the first step in photosynthesis is a light-dependent reaction, it requires sunlight. When sunlight hits chlorophyll in various photosystems within thylakoid membranes, the energy of the light is moved to electrons. These electrons, which are highly energized, are sent through a series of proteins embedded in the thylakoid membrane, also known as an **electron transport chain.** Electrons are passed from protein to protein, losing energy each time they are passed. The energy electrons lose is used to move hydrogen ions into the thylakoid disc or to form ADP or ATP, which is important in light-independent reactions. Once the electrons are through the first chain, they are energized again and are sent through another chain. In order to conserve the energy left after the electrons have passed through both chains, electrons are moved into the stroma of the chloroplast. An electron carrier molecule known as **NADP+**, or nicotinamide adenine dinucleotide phosphate, is used to accomplish this task. Two highly energized electrons and a hydrogen ion (H+) may combine with NADP+ to form NADPH. NADPH stores the energy from the electrons until it can be moved to the stroma. NADPH also has a major role in the light-independent reactions of photosynthesis. In the beginning of photosynthesis, electrons leave the chlorophyll molecules. These must be replaced or light will not be absorbed and ATP production as well as light-dependent reactions will stop. **Photolysis,** the splitting of water molecules in the first photosystem, is used to replace the electrons. Two hydrogen ions, one half molecule of oxygen and two electrons are the results of splitting one molecule in photolysis. Hydrogen ions diffuse out of the thylakoid because of the concentration gradient across the membrane created by the high concentration of hydrogen ions in the thylakoid. The oxygen is released into the air for animals to breathe. The two electrons are transferred back to the chlorophyll.
 * Light-Dependent Reactions **

Since the second step in photosynthesis is a light-independent reaction, it doesn’t require sunlight. This step happens within the stroma of the chloroplast. It is a series of reactions that use carbon dioxide to form sugars, called the **Calvin cycle.** It is called the Calvin cycle because the man who worked out the details of the reactions was named Melvin Calvin. This step is called a cycle because one of the molecules needed in the first chemical reaction is a product of one of the last chemical reactions. The complicated process of turning a molecule of CO2 into a complex carbohydrate is converted by the light-independent reactions into many small steps. The first step of this cycle, called carbon fixation, occurs when a six-carbon sugar is created by one molecule of carbon dioxide combining with a molecule of RuBP. After going more reactions take place, the sugar is broken down and is made into two three-carbon sugars called phosphoglyceraldehyde, or PGAL. After this cycle is completed three times, six molecules of PGAL have been created. Five of these are manipulated to create three molecules of RuBP, which can then be used to start the cycle again. The remaining molecule of PGAL can then be used to form sugars, complex carbohydrates, and other organic compounds. PGAL also has a significant role in cellular respiration.
 * Light-Independent Reactions **

MINI LAB Experiment: Separating Pigments – Chromatography is an important diagnostic tool. In this experiment, you will use paper chromatography to separate different pigments from plant leaves. Procedure: 1. Obtain a pre-made plant solution from your teacher. 2. Place a few drops 2 cm high on a 5 cm X 14 cm strip of filter paper. Let it dry. Make sure a small colored spot is visible. 3. Pour rubbing alcohol in a 100 mL beaker to a depth of 1 cm. 4. Place the filter paper into the beaker. The filter paper should touch the alcohol, but the dot should not. Hold it in place 15 minutes and observe what happens. Analysis: 1. Explain – What did you observe as the solvent moved up the filter paper? 2. Infer – Why did you see different colors at different locations on the filter paper?

//__ Section 3 __// //__ Getting Energy to Make ATP __//

** Cellular Respiration ** **Cellular respiration** is the process in which mitochondria break down food molecules to produce ATP. The first step of cellular respiration is called glycolysis and it is **anaerobic**, so it requires no oxygen. The second step, the citric acid cycle, and the third step, the electron transport chain, are **aerobic** and need oxygen. The first step of cellular respiration occurs when a series of chemical reactions within the cytoplasm breaks down a six-carbon compound called glucose into two three-carbon compounds known as pyruvic acid, is called **glycolysis.** However glycolysis isn’t very effective because only two molecules of ATP are created for each molecule of glucose that is broken down. Glycolysis also involves an electron carrier, known as NAD+, or nicotinamide adenine dinucleotide, which turns into NADH when it combines with two energized electrons. Two molecules of PGAL are formed as part of glycolysis. PGAL made during photosynthesis can also enter this process and help with the formation of organic molecules and ATP. After glycolysis is completed, molecules of pyruvic acid move into the mitochondria where they go through a series of chemical reactions. One molecule of pyruvic acid gives off a molecule of CO2 and combines with a molecule known as coenzyme A. This forms acetyl-CoA, and a molecule of NADH and H+ is also created. The second step of cellular respiration is another series of chemical reactions in which the first molecule used is one of the last products of the cycle. This step is known as the **citric acid cycle** or the Krebs cycle. One molecule of ATP and two molecules of carbon dioxide are produced for every time the cycle is completed. Three NADH, three H+, and one FADH2 are also produced. NAD+ and FAD, or flavin adenine dinucleotide, are two electron carriers used in this cycle. Each carrier gives two energized electrons to the electron transport chain within the inner membrane of the mitochondria. This electron transport chain is similar to that in the thylakoid membrane of the chloroplast during photosynthesis. NADH and FADH2 pass energized electrons to the beginning of the chain. Electrons are sent down the chain, losing energy as they go. Part of this energy is directly used to make ATP while other parts of the energy is used to move H+ ions into the middle of the mitochondria. The positively charged hydrogen ions in the center of the mitochondria create a concentration gradient across the inner membrane, providing the energy needed to create ATP. Oxygen is the last electron acceptor in this chain. It reacts with four positively charged hydrogen ions and four electrons to produce two molecules of water. Without the oxygen at the end of the electron transport chain, ATP production would cease, and that is why oxygen is so vital to the function of our bodies. The electron transport chain produces 32 ATP molecules that are combined with the four already created to make a grand total of 36. The aerobic steps in cellular respiration are much more effective than the anaerobic steps.

Oxygen is not always going to be available. During these short periods of time when oxygen isn’t accessible, such as during heavy exercise, after glycolysis takes place an anaerobic process called fermentation occurs in order to create ATP until oxygen is accessible once again. The first type of fermentation is called lactic acid fermentation. When NADH and FADH2 get held up because they cannot get rid of their energized electrons, the supply of NAD+ and FAD needed for glycolysis and the citric acid cycle dwindles because the cell doesn’t have a method to replace FAD. However, lactic acid fermentation can replace NAD+. In the process of **lactic acid fermentation,** which is one of the processes which supplies the cell with energy when oxygen is absent, the series of reactions that produced pyruvic acid are reversed. NADH is combined with two molecules of pyruvic acid to create two molecules of lactic acid. NAD+ is released and used in glycolysis to create two molecules of ATP to provide energy. Lactic acid is produced in muscles during exercise, where it is moved to the liver and turned back into pyruvic acid. Muscle fatigue is what happens when too much lactic acid is built up in muscle cells. The second type of fermentation is called **alcoholic fermentation.** This is used by some bacteria and yeast to create ethyl alcohol and CO2. One example of this is yeast in bread. Yeast produces CO2 that creates bubbles within the dough. Then bread is put in the oven, the immense heat kills the yeast and the CO2 remains to lighten the bread.
 * Fermentation **


 * ** Comparing Fermentation and Cellular Respiration ** ||
 * ** Step ** || ** Lactic Acid Fermentation ** || ** Alcoholic Fermentation ** || ** Cellular Respiration ** ||
 * 1 || Glucose || Glucose || Glucose ||
 * 2 || Glycolysis (Pyruvic Acid) || Glycolysis (Pyruvic Acid) || Glycolysis (Pyruvic Acid) ||
 * 3 || Lactic Acid + 2 ATP || CO2 + Alcohol + 2 ATP || CO2 +H2O + 36 ATP ||

** Comparing Photosynthesis and Cellular Respiration ** Both producing and breaking down food molecules have unique process that are similar in certain ways. Both processes use a cycle in order to create ATP and they both use electron carriers. Both processes use electron transport chains to directly produce ATP and indirectly create ATP by forming a concentration gradient across the membrane with positively charged hydrogen ions. These two processes also have their differences. Photosynthesis produces oxygen and makes complex carbohydrates from the energy of the sun while cellular respiration uses oxygen to break down food molecules in order to produce ATP molecules and other compounds that are sources of energy for the cell. Another major difference is that CO2 is one of the starting products for photosynthesis while it is one of the final products of cellular respiration.

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 * ** Comparing Photosynthesis and Cellular Respiration ** ||
 * ** Photosynthesis ** || ** Cellular Respiration ** ||
 * Food made || Food broken down ||
 * Sun’s energy stored in glucose || Energy stored in glucose released ||
 * Carbon dioxide collected || Carbon dioxide produced ||
 * Oxygen produced || Oxygen used ||
 * Makes simple sugars from PGAL || Produces CO2 and H2­O ||
 * Needs light || Doesn’t need light ||
 * Occurs in organisms with chlorophyll || Occurs in all organisms ||