File Name: metabolism of carbohydrates lipids and proteins .zip
Lipid and carbohydrate metabolism are highly conserved processes that affect nearly all aspects of organismal biology.
You have learned about the catabolism of glucose, which provides energy to living cells. But living things consume more than glucose for food. How does a turkey sandwich end up as ATP in your cells? This happens because all of the catabolic pathways for carbohydrates, proteins, and lipids eventually connect into glycolysis and the citric acid cycle pathways see [link]. Metabolic pathways should be thought of as porous—that is, substances enter from other pathways, and intermediates leave for other pathways.
These pathways are not closed systems. Many of the substrates, intermediates, and products in a particular pathway are reactants in other pathways. Glycogen, a polymer of glucose, is an energy storage molecule in animals. When there is adequate ATP present, excess glucose is shunted into glycogen for storage. Glycogen is made and stored in both liver and muscle. The glycogen will be hydrolyzed into glucose monomers GP if blood sugar levels drop.
The presence of glycogen as a source of glucose allows ATP to be produced for a longer period of time during exercise. Glycogen is broken down into GP and converted into GP in both muscle and liver cells, and this product enters the glycolytic pathway.
Sucrose is a disaccharide with a molecule of glucose and a molecule of fructose bonded together with a glycosidic linkage. Fructose is one of the three dietary monosaccharides, along with glucose and galactose which is part of the milk sugar, the disaccharide lactose , which are absorbed directly into the bloodstream during digestion.
The catabolism of both fructose and galactose produces the same number of ATP molecules as glucose. Proteins are hydrolyzed by a variety of enzymes in cells. Most of the time, the amino acids are recycled into the synthesis of new proteins. If there are excess amino acids, however, or if the body is in a state of starvation, some amino acids will be shunted into the pathways of glucose catabolism [link]. Each amino acid must have its amino group removed prior to entry into these pathways.
The amino group is converted into ammonia. In mammals, the liver synthesizes urea from two ammonia molecules and a carbon dioxide molecule. Thus, urea is the principal waste product in mammals produced from the nitrogen originating in amino acids, and it leaves the body in urine.
Connections of Lipid and Glucose Metabolisms The lipids that are connected to the glucose pathways are cholesterol and triglycerides. Cholesterol is a lipid that contributes to cell membrane flexibility and is a precursor of steroid hormones. The synthesis of cholesterol starts with acetyl groups and proceeds in only one direction. The process cannot be reversed. Triglycerides are a form of long-term energy storage in animals.
Triglycerides are made of glycerol and three fatty acids. Animals can make most of the fatty acids they need. Triglycerides can be both made and broken down through parts of the glucose catabolism pathways.
Glycerol can be phosphorylated to glycerolphosphate, which continues through glycolysis. Fatty acids are catabolized in a process called beta-oxidation that takes place in the matrix of the mitochondria and converts their fatty acid chains into two carbon units of acetyl groups.
The acetyl groups are picked up by CoA to form acetyl CoA that proceeds into the citric acid cycle. Evolution Connection Pathways of Photosynthesis and Cellular Metabolism The processes of photosynthesis and cellular metabolism consist of several very complex pathways.
If these cells reproduced successfully and their numbers climbed steadily, it follows that the cells would begin to deplete the nutrients from the medium in which they lived as they shifted the nutrients into the components of their own bodies. This hypothetical situation would have resulted in natural selection favoring those organisms that could exist by using the nutrients that remained in their environment and by manipulating these nutrients into materials upon which they could survive.
Selection would favor those organisms that could extract maximal value from the nutrients to which they had access. Early photosynthesis did not produce free oxygen because it did not use water as the source of hydrogen ions; instead, it used materials like hydrogen sulfide and consequently produced sulfur. It is thought that glycolysis developed at this time and could take advantage of the simple sugars being produced, but these reactions were unable to fully extract the energy stored in the carbohydrates.
Living things adapted to exploit this new atmosphere that allowed aerobic respiration as we know it to evolve. When the full process of oxygenic photosynthesis developed and the atmosphere became oxygenated, cells were finally able to use the oxygen expelled by photosynthesis to extract considerably more energy from the sugar molecules using the citric acid cycle and oxidative phosphorylation.
The breakdown and synthesis of carbohydrates, proteins, and lipids connect with the pathways of glucose catabolism. The simple sugars are galactose, fructose, glycogen, and pentose. These are catabolized during glycolysis. The amino acids from proteins connect with glucose catabolism through pyruvate, acetyl CoA, and components of the citric acid cycle. Cholesterol synthesis starts with acetyl groups, and the components of triglycerides come from glycerolphosphate from glycolysis and acetyl groups produced in the mitochondria from pyruvate.
Would you describe metabolic pathways as inherently wasteful or inherently economical, and why? They are very economical. The substrates, intermediates, and products move between pathways and do so in response to finely tuned feedback inhibition loops that keep metabolism balanced overall.
Intermediates in one pathway may occur in another, and they can move from one pathway to another fluidly in response to the needs of the cell. Skip to content Cellular Respiration. Learning Objectives By the end of this section, you will be able to: Discuss the ways in which carbohydrate metabolic pathways, glycolysis, and the citric acid cycle interrelate with protein and lipid metabolic pathways Explain why metabolic pathways are not considered closed systems.
Connections of Other Sugars to Glucose Metabolism Glycogen, a polymer of glucose, is an energy storage molecule in animals. Connections of Proteins to Glucose Metabolism Proteins are hydrolyzed by a variety of enzymes in cells. The carbon skeletons of certain amino acids indicated in boxes derived from proteins can feed into the citric acid cycle.
Glycogen from the liver and muscles, hydrolyzed into glucosephosphate, together with fats and proteins, can feed into the catabolic pathways for carbohydrates. Evolution Connection. Section Summary The breakdown and synthesis of carbohydrates, proteins, and lipids connect with the pathways of glucose catabolism.
Free Response Would you describe metabolic pathways as inherently wasteful or inherently economical, and why? Previous: Metabolism without Oxygen. Next: Regulation of Cellular Respiration.
Metabolism and energetics
Metabolism basically refers to all the chemical reactions within the body used to produce energy. This involves a complex set of processes that convert fuels into specialised compounds loaded with energy. In the body, the primary final agent to produce energy is called adenosine triphosphate ATP. When ATP is broken down or used by cells huge amounts of energy is released. This energy is essential for cells to grow and divide, synthesise important compounds, for muscles to contract and numerous other important functions. Metabolism therefore produces energy to perform all the functions of different tissues within the body. Metabolism works by breaking down foods in the diet or compounds in the body into their smaller components.
may determine impaired carbohydrate, lipid, and. protein metabolism. In turn, altered macronutrient. metabolism may eventually lead to insulin.
Metabolic Functions of the Liver
The formation of polysaccharides and of phospholipids from their component building blocks not only requires the investment of the energy of nucleoside triphosphates but uses these molecules in a novel manner. The biosynthetic reactions described thus far have mainly been accompanied by the formation of energy-rich intermediates e. This unique process necessitates reactions by which ATP , or another nucleoside triphosphate, which can be readily derived from ATP via reactions of type [43a], combines with a phosphorylated reactant to form a nucleoside-diphosphate product.
The cellular energy metabolism includes all of the processes that generate cellular energy ATP following the demolition of sugar glycolysis , lipids, and small percentage of proteins. ATP production is essential for the proper performance of vital functions as cellular reactions and processes of the body that require energy are supplied from the conversion of ATP to ADP; among them there are, for example, the transmission of nerve impulses, muscle contraction, active transport through plasma membranes, protein synthesis and cell division. There are several vitamins and minerals that help the metabolic processes and for every need you can choose the supplementation which is most appropriate for remedying the problems.
Sugars, such as galactose, fructose, and glycogen, are catabolized into new products in order to enter the glycolytic pathway. You have learned about the catabolism of glucose, which provides energy to living cells.
How do we break them down? Liwayway Memije-Cruz 2. Several types of lipids can be microbially degraded. Figure 5.