The membrane must be fluid and mobile, rather than rigid, to allow for optimal functioning and adaptation to the internal environment. All of the dietary macronutrients—carbohydrates, fats, and proteins—are found in the cell membrane.
Fat is needed for proper cell structure and function, and the most abundant form of fat found in the cell membrane is the phospholipids.
The phospholipids have a hydrophobic or water-fearing tail and a hydrophilic or water-loving head. This love-hate relationship with water is what gives the membrane its unique structure and stability. Cholesterol is another type of fat-related compound found in the cell membrane.
Cholesterol improves the mechanical stability of the membrane and helps to regulate the fluidity. If the diet is too low in cholesterol, cell membrane structure can be compromised. The second major nutrient found in the cell membrane is protein. Proteins play a small role in forming the structure of the membrane, but they mostly contribute to the membrane functions. Earlier thought in the nutrition field suggested that eating proteins only contributed to muscle function, quality, and size.
However, proteins direct proper operations within each individual cell and also the healthy functioning of your entire body. At the cellular level, proteins serve as pumps, gates, receptors, and catalysts for biochemical reactions. Cellular communication occurs at all times for various reasons. They communicate to take up nutrients from your bloodstream, to excrete waste products from the body, to signal chemical reactions, and more.
Proteins serve as channels by opening and closing when the cell receives a particular signal. They can also act as information transporters for what is going on outside the cell and within other adjacent cells.
Without this sophisticated communication network, the cells throughout your body will not work together, and bodily functions will start to fail. As soon as one message is not transmitted or received properly, the entire message is messed up.
Cells do not use the energy from oxidation reactions as soon as it is released. Instead, they convert it into small, energy-rich molecules such as ATP and nicotinamide adenine dinucleotide NADH , which can be used throughout the cell to power metabolism and construct new cellular components.
In addition, workhorse proteins called enzymes use this chemical energy to catalyze, or accelerate, chemical reactions within the cell that would otherwise proceed very slowly.
Enzymes do not force a reaction to proceed if it wouldn't do so without the catalyst; rather, they simply lower the energy barrier required for the reaction to begin Figure 4. Figure 4: Enzymes allow activation energies to be lowered. Enzymes lower the activation energy necessary to transform a reactant into a product.
On the left is a reaction that is not catalyzed by an enzyme red , and on the right is one that is green. In the enzyme-catalyzed reaction, an enzyme will bind to a reactant and facilitate its transformation into a product. Consequently, an enzyme-catalyzed reaction pathway has a smaller energy barrier activation energy to overcome before the reaction can proceed. The high-energy phosphate bond in this phosphate chain is the key to ATP's energy storage potential.
Figure Detail The particular energy pathway that a cell employs depends in large part on whether that cell is a eukaryote or a prokaryote. Eukaryotic cells use three major processes to transform the energy held in the chemical bonds of food molecules into more readily usable forms — often energy-rich carrier molecules. Adenosine 5'-triphosphate, or ATP, is the most abundant energy carrier molecule in cells.
This molecule is made of a nitrogen base adenine , a ribose sugar, and three phosphate groups. The word adenosine refers to the adenine plus the ribose sugar. The bond between the second and third phosphates is a high-energy bond Figure 5.
The first process in the eukaryotic energy pathway is glycolysis , which literally means "sugar splitting. Glycolysis is actually a series of ten chemical reactions that requires the input of two ATP molecules.
Two NADH molecules are also produced; these molecules serve as electron carriers for other biochemical reactions in the cell. 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. Animals use energy for metabolism, obtaining that energy from the breakdown of food through the process of cellular respiration. Animals need food to obtain energy and maintain homeostasis.
Homeostasis is the ability of a system to maintain a stable internal environment even in the face of external changes to the environment. Humans maintain this temperature even when the external temperature is hot or cold. The energy it takes to maintain this body temperature is obtained from food. Adenosine triphosphate, or ATP, is the primary energy currency in cells. ATP is produced by the oxidative reactions in the cytoplasm and mitochondrion of the cell, where carbohydrates, proteins, and fats undergo a series of metabolic reactions collectively called cellular respiration.
It is produced through various pathways during the cellular respiration process, with each making different amounts of energy. ATP is required for all cellular functions.
It is used to build the organic molecules that are required for cells and tissues. It also provides energy for muscle contraction and for the transmission of electrical signals in the nervous system. When blood sugar drops, the liver releases glucose from stores of glycogen. Skeletal muscle converts glycogen to glucose during intense exercise.
The process of converting glucose and excess ATP to glycogen and the storage of excess energy is an evolutionarily-important step in helping animals deal with mobility, food shortages, and famine. Privacy Policy. Skip to main content. Animal Nutrition and the Digestive System. Search for:. Nutrition and Energy Production.
Learning Objectives Describe the essential nutrients required for cellular function that cannot be synthesized by the animal body. Key Takeaways Key Points The animal diet needs to be well-balanced in order to ensure that all necessary vitamins and minerals are being obtained. Vitamins are important for maintaining bodily health, making bones strong, and seeing in the dark. Water-soluble vitamins are not stored by the body and need to be consumed more regularly than fat-soluble vitamins, which build up within body tissues.
Essential fatty acids need to be consumed through the diet and are important building blocks of cell membranes. Nine of the 20 amino acids cannot be synthesized by the body and need to be obtained from the diet. Key Terms nutrient : a source of nourishment, such as food, that can be metabolized by an organism to give energy and build tissue catabolism : destructive metabolism, usually including the release of energy and breakdown of materials vitamin : any of a specific group of organic compounds essential in small quantities for healthy human growth, metabolism, development, and body function.
Food Energy and ATP Animals use energy for metabolism, obtaining that energy from the breakdown of food through the process of cellular respiration. Learning Objectives Summarize the ways in which animals obtain, store, and use food energy. Key Takeaways Key Points Animals obtain energy from the food they consume, using that energy to maintain body temperature and perform other metabolic functions.
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