Cell Energy and Cell Functions
Cells manage a wide range of functions in their tiny package — growing, moving, housekeeping, and so on and most of those functions require energy. But how do cells get this energy in the first place? And how do they use it in the most efficient manner possible.
Cells, like humans, cannot generate energy without locating a source in their environment. However, whereas humans search for substances like fossil fuels to power their homes and businesses, cells seek their energy in the form of food molecules or sunlight. In fact, the Sun is the ultimate source of energy for almost all cells, because photosynthetic prokaryotes, algae, and plant cells harness solar energy and use it to make the complex organic food molecules that other cells rely on for the energy required to sustain growth, metabolism, and reproduction.
Cellular nutrients come in many forms, including sugars and fats. In order to provide a cell with energy, these molecules have to pass across the cell membrane, which functions as a barrier — but not an impassable one. Like the exterior walls of a house, the plasma membrane is semi-permeable. In much the same way that doors and windows allow necessities to enter the house, various proteins that span the cell membrane permit specific molecules into the cell, although they may require some energy input to accomplish this task.
What are the nutrients used to build and repair cells?
Adults and developing children use food nutrition to fuel cellular growth, maintenance and repair. The process of metabolism transforms dietary protein, carbohydrates and fatty acids into usable energy, which enable the thousands of cellular functions that sustain human life. Damaged cells, such as wounded skin tissue, are repaired with the help of vitamin C. Because the lives of cells themselves are finite, with cells continually dying off and being replaced with new ones, you need a new supply of essential nutrients every day.
Protein
Your body uses the amino acids in dietary protein to form other proteins, build new body cells and generate energy for cellular functions. Protein in foods is known as complete, containing all the essential amino acids, or incomplete, lacking one or more of these elements. You get complete protein from animal-based foods such as fish, meats, eggs and milk. Eating a variety of different grains, fruits and vegetables, which contain incomplete protein, will supply all the amino acids. Adults should get between 46 and 56 grams of protein per day.
Carbohydrates
Of the three main types of carbohydrates, the body does not digest fiber for cellular use, but does convert sugar and starch into energy. You need these major sources of energy daily for every body process, including movement, thought, physical sensation, and respiration and other organ functions. Digestion breaks down dietary carbohydrates from foods such as bread, potatoes, beans, milk and apples to generate chemical energy.
Fats
Essential fatty acid classifications include saturated, monounsaturated and polyunsaturated fats, as designated by their molecular structures. Like carbohydrates, fats are present in different combinations in many foods. Animal-based meats and dairy products contain larger amounts of saturated fats than most plant-based foods. Nuts and seeds have greater monounsaturated fat, while vegetables and fruits may contain more polyunsaturated fat. Your body uses fatty acids for energy production. It draws on energy reserves from carbohydrates first during activity, and second from fats, during extended activity. You should limit your total fat intake to 20 to 35 percent of all dietary calories.
Vitamin C
Dietary vitamin C from foods such as oranges, potatoes, tomatoes, melons and peppers assists in forming proteins used in cellular growth and scar tissue used to heal wounds. This essential vitamin works harder at night while you sleep, during a phase that the body uses for cellular growth and repair. It also acts as an antioxidant to prevent environmental damage to your body, such as from smoke and radiation. Your body can’t store vitamin C, so you need between 75 and 90 milligrams from food daily.
Taking supplements
Talk to your doctor before you start taking supplements. While additional nutrients are essential for cell growth and repair, ingesting high doses can have a toxic effect. On the other hand, deficiencies in these nutrients can be detrimental to your health as well as inhibit your cells’ abilities to function properly. If you are concerned about your vitamin or mineral intake, discuss this with your health care provider.
How do cells turn nutrients into usable energy?
Complex organic food molecules such as sugars, fats, and proteins are rich sources of energy for cells because much of the energy used to form these molecules is literally stored within the chemical bonds that hold them together. Scientists can measure the amount of energy stored in foods using a device called a bomb calorimeter. With this technique, food is placed inside the calorimeter and heated until it burns. The excess heat released by the reaction is directly proportional to the amount of energy contained in the food.
Adenosine Triphosphate and Energy
Life’s Energy
Adenosine triphosphate ATP is a high energy molecule that cells use to power their various functions. One such function is muscle cell contraction. For this reason, ATP is sometimes referred to as the energy currency of life.
By using electrons from an array of materials, Earth’s organisms produce adenosine triphosphate (ATP), which powers biological reactions. In the case of mammals and most microbial organisms, (eukaryotes), sugars and other organic molecules are common electron sources, the oxidation of which drives ATP production. Bacteria and archaea can use a range of other chemicals, from sulfide to iron to ammonium.
Our cells take up these electron-rich molecules and capture their electrons, which jump down an electron transport chain in the mitochondrial or cell membrane. As electrons move along the membrane toward a final electron acceptor, protons are pumped from the cell’s interior to the exterior, setting up a chemical gradient.
Finally, protons stream back into the cell, releasing the chemical pressure and generating ATP. With each energy-requiring reaction, from flagella construction to cell division and growth, cells draw upon their ATP bank.
This elegant, multistep process is a universal feature of life as we know it, but energetic challenges are ever-present. If the electrical potentials of electron donor and acceptor are too closely aligned, for example, it won’t be possible to squeeze much energy from their coupling. The concentrations of the reactants and the speed at which enzymes can mobilize them are also key factors. These two components—the magnitude of energy available from a pairing and the rate of such reactions—determine how much energy a cell can produce.
Cataloging the biochemical parts list of a cell is one challenge. Individual biosynthetic pathways—the production of lipids from glycerol derivatives, for example—are relatively well characterized under “standard” conditions, but a cell’s ever-changing chemical environment can render baseline calculations inaccurate.
Scaled over millions of such reactions, the margin of error may be a substantial proportion of the available energy. And this is just considering the biosynthesis of new cellular material. In most environments, microbes must always be vigilant against biochemical breakdown resulting from environmental stresses, calling on energy reserves to restore old enzymes or patch holes in cell walls. Competition among residents may also demand additional energy expenditure, such as powering flagella to swim around in search of food or producing antibiotic molecules to keep predatory neighbors at bay.
If, we can estimate how much energy is required for survival, and compare that to how much energy is available to be extracted from the environment, we can begin to consider “extreme” organisms in a more objective fashion. Some of the most “exotic” environments offer luxurious energetic balances; it’s the microbes with low net energy availability that are the real extremophiles, whether they live an expensive existence in a high-energy environment, or an ascetic life in an energetic desert.
Cells make up every part of your body, and they require many nutrients to grow and repair properly. While all the vitamins and minerals you eat contribute to healthy cells, certain ones play a larger role in cell functions, such as vitamin A, phosphorus and zinc. In addition, the USDA is requiring clearer product labels so consumers will know whether products they purchase contain added solutions that might not be apparent. USDA also recently began requiring nutrition labels on single-ingredient raw meat and poultry products to provide more information to consumers.
References
- Vieille, G.J. Zeikus, “Hyperthermophilic enzymes: Sources, uses, and molecular mechanisms for thermostability,” Microbiol Mol Biol R, 65:1-43, 2001.
- M. McCollom, J.P. Amend, “A thermodynamic assessment of energy requirements for biomass synthesis by chemolithoautotrophic micro-organisms in oxic and anoxic environments,” Geobiology, 3:135-44, 2005.
- S. Rokem et al., “Systems biology of antibiotic production by microorganisms,” Nat Prod Rep, 24:1262-87, 2007.
- Boetius et al., “A marine microbial consortium apparently mediating anaerobic oxidation of methane,” Nature, 407:623-26, 2000.
- J. Marlow et al., “Microbial abundance and diversity patterns associated with sediments and carbonates from the methane seep environments of Hydrate Ridge, OR,” Front Mar Sci, doi:10.3389/fmars.2014.00044, 2014.
- J. Marlow et al., “Carbonate-hosted methanotroph represents an unrecognized methane sink in the deep sea,” Nat Comm, 5:5094, 2014.
- USDA