Yes, the wrecking ball has energy because the wrecking ball has the potential to do work. This form of energy is called potential energy because it is possible for that object to do work in a given state.
Objects transfer their energy between potential and kinetic states. Once the ball is released, its kinetic energy increases as the ball picks up speed. At the same time, the ball loses potential energy as it nears the ground. Other examples of potential energy include the energy of water held behind a dam or a person about to skydive out of an airplane. Potential energy vs. Moving water, such as in a waterfall or a rapidly flowing river, has kinetic energy. Potential energy is not only associated with the location of matter, but also with the structure of matter.
A spring on the ground has potential energy if it is compressed, as does a rubber band that is pulled taut. The same principle applies to molecules. On a chemical level, the bonds that hold the atoms of molecules together have potential energy. This type of potential energy is called chemical energy, and like all potential energy, it can be used to do work. For example, chemical energy is contained in the gasoline molecules that are used to power cars.
When gas ignites in the engine, the bonds within its molecules are broken, and the energy released is used to drive the pistons. The potential energy stored within chemical bonds can be harnessed to perform work for biological processes. Different metabolic processes break down organic molecules to release the energy for an organism to grow and survive.
Chemical energy : The molecules in gasoline octane, the chemical formula shown contain chemical energy. This energy is transformed into kinetic energy that allows a car to race on a racetrack. An anabolic pathway requires energy and builds molecules while a catabolic pathway produces energy and breaks down molecules. The processes of making and breaking down carbohydrate molecules illustrate two types of metabolic pathways.
A metabolic pathway is a step-by-step series of interconnected biochemical reactions that convert a substrate molecule or molecules through a series of metabolic intermediates, eventually yielding a final product or products. For example, one metabolic pathway for carbohydrates breaks large molecules down into glucose.
Another metabolic pathway might build glucose into large carbohydrate molecules for storage. The first of these processes requires energy and is referred to as anabolic. The second process produces energy and is referred to as catabolic. Consequently, metabolism is composed of these two opposite pathways:. Anabolic and catabolic pathways : Anabolic pathways are those that require energy to synthesize larger molecules.
Catabolic pathways are those that generate energy by breaking down larger molecules. Anabolic pathways require an input of energy to synthesize complex molecules from simpler ones.
One example of an anabolic pathway is the synthesis of sugar from CO 2. Other examples include the synthesis of large proteins from amino acid building blocks and the synthesis of new DNA strands from nucleic acid building blocks.
Catabolic pathways involve the degradation of complex molecules into simpler ones, releasing the chemical energy stored in the bonds of those molecules. Some catabolic pathways can capture that energy to produce ATP, the molecule used to power all cellular processes. Other energy-storing molecules, such as lipids, are also broken down through similar catabolic reactions to release energy and make ATP.
Chemical reactions in metabolic pathways rarely take place spontaneously. Each reaction step is facilitated, or catalyzed, by a protein called an enzyme. Enzymes are important for catalyzing all types of biological reactions: those that require energy as well as those that release energy.
Organisms break down carbohydrates to produce energy for cellular processes, and photosynthetic plants produce carbohydrates. Carbohydrates are one of the major forms of energy for animals and plants. Plants build carbohydrates using light energy from the sun during the process of photosynthesis , while animals eat plants or other animals to obtain carbohydrates.
Plants store carbohydrates in long polysaccharides chains called starch, while animals store carbohydrates as the molecule glycogen. The energy required for cellular activities is provided directly by molecules of adenosine triphosphate ATP. ATP is made of one adenosine molecule and three phosphate groups, called Pi for short. Each molecule of ATP stores a small quantity of chemical energy. Glycolysis is an ancient, major ATP-producing pathway that occurs in almost all cells, eukaryotes and prokaryotes alike.
This process, which is also known as fermentation , takes place in the cytoplasm and does not require oxygen. However, the fate of the pyruvate produced during glycolysis depends upon whether oxygen is present. In the absence of oxygen, the pyruvate cannot be completely oxidized to carbon dioxide, so various intermediate products result. For example, when oxygen levels are low, skeletal muscle cells rely on glycolysis to meet their intense energy requirements.
This reliance on glycolysis results in the buildup of an intermediate known as lactic acid, which can cause a person's muscles to feel as if they are "on fire. In contrast, when oxygen is available, the pyruvates produced by glycolysis become the input for the next portion of the eukaryotic energy pathway.
During this stage, each pyruvate molecule in the cytoplasm enters the mitochondrion, where it is converted into acetyl CoA , a two-carbon energy carrier, and its third carbon combines with oxygen and is released as carbon dioxide. At the same time, an NADH carrier is also generated. Acetyl CoA then enters a pathway called the citric acid cycle , which is the second major energy process used by cells.
Figure 6: Metabolism in a eukaryotic cell: Glycolysis, the citric acid cycle, and oxidative phosphorylation Glycolysis takes place in the cytoplasm.
Within the mitochondrion, the citric acid cycle occurs in the mitochondrial matrix, and oxidative metabolism occurs at the internal folded mitochondrial membranes cristae. The third major process in the eukaryotic energy pathway involves an electron transport chain , catalyzed by several protein complexes located in the mitochondrional inner membrane. This process, called oxidative phosphorylation, transfers electrons from NADH and FADH 2 through the membrane protein complexes, and ultimately to oxygen, where they combine to form water.
As electrons travel through the protein complexes in the chain, a gradient of hydrogen ions, or protons, forms across the mitochondrial membrane. Cells harness the energy of this proton gradient to create three additional ATP molecules for every electron that travels along the chain. Overall, the combination of the citric acid cycle and oxidative phosphorylation yields much more energy than fermentation - 15 times as much energy per glucose molecule!
Together, these processes that occur inside the mitochondion, the citric acid cycle and oxidative phosphorylation, are referred to as respiration , a term used for processes that couple the uptake of oxygen and the production of carbon dioxide Figure 6. The electron transport chain in the mitochondrial membrane is not the only one that generates energy in living cells. In plant and other photosynthetic cells, chloroplasts also have an electron transport chain that harvests solar energy.
Even though they do not contain mithcondria or chloroplatss, prokaryotes have other kinds of energy-yielding electron transport chains within their plasma membranes that also generate energy. When energy is abundant, eukaryotic cells make larger, energy-rich molecules to store their excess energy.
The resulting sugars and fats — in other words, polysaccharides and lipids — are then held in reservoirs within the cells, some of which are large enough to be visible in electron micrographs. Animal cells can also synthesize branched polymers of glucose known as glycogen , which in turn aggregate into particles that are observable via electron microscopy.
A cell can rapidly mobilize these particles whenever it needs quick energy. Athletes who "carbo-load" by eating pasta the night before a competition are trying to increase their glycogen reserves. Under normal circumstances, though, humans store just enough glycogen to provide a day's worth of energy. Plant cells don't produce glycogen but instead make different glucose polymers known as starches , which they store in granules. In addition, both plant and animal cells store energy by shunting glucose into fat synthesis pathways.
One gram of fat contains nearly six times the energy of the same amount of glycogen, but the energy from fat is less readily available than that from glycogen. Still, each storage mechanism is important because cells need both quick and long-term energy depots. Fats are stored in droplets in the cytoplasm; adipose cells are specialized for this type of storage because they contain unusually large fat droplets. Humans generally store enough fat to supply their cells with several weeks' worth of energy Figure 7.
Figure 7: Examples of energy storage within cells. A In this cross section of a rat kidney cell, the cytoplasm is filled with glycogen granules, shown here labeled with a black dye, and spread throughout the cell G , surrounding the nucleus N. B In this cross-section of a plant cell, starch granules st are present inside a chloroplast, near the thylakoid membranes striped pattern. C In this amoeba, a single celled organism, there is both starch storage compartments S , lipid storage L inside the cell, near the nucleus N.
Qian H. Letcher P. A Bamri-Ezzine, S. All rights reserved. This page appears in the following eBook. Aa Aa Aa. Cell Energy and Cell Functions.
0コメント