Metabolism includes material metabolism and energy metabolism.Metabolism is composed of assimilation and alienation, two opposite and simultaneous processes.Assimilation and dissimilation are obviously different and closely related.If there is no assimilation, the organism cannot produce new protoplasm, nor can it store energy, and alienation cannot proceed;On the contrary, if there is no alienation, there can be no energy release, and the material synthesis in the organism can not be carried out.It can be seen that assimilation and alienation are both opposite and unified, and jointly determine the existence and continuity of organisms.[1]
Chinese name
the new supersedes the old
Foreign name
metabolism
Biological interpretation
The process of constantly replacing old substances with new ones
In the long-term evolution process, organisms constantly interact with their environment, and gradually form different types of metabolism.According to the different processes of assimilation and dissimilation in nature, the basic types of metabolism can be divided into assimilation and dissimilation.On the one hand, biological organisms transform the substances ingested from the environment into their own substances through a series of chemical reactions.This process is called assimilation, that is, substances from the outside to the inside, from small molecules to large molecules.Therefore, assimilation is a process of absorbing energy. For example, green plants use photosynthesis to transfer water andcarbon dioxideAnd other substances into starch, cellulose and other substances.The opposite is alienation, that is, from the body to the external environment, the process of transforming substances from macromolecules to small molecules, which is a process of releasing energy and expelling substances that are not needed or can not be used by organisms.[2]
Assimilation and alienation are two aspects of contradiction, which are both opposite and unified. They restrict, connect and rely on each other, and both of them take their opposites as conditions for existence.Alienation provides energy for assimilation, and assimilation provides material basis for alienation.For example, the metabolism of the human body is different at different ages.In childhood and adolescence, more nutrients are needed to promote the growth of the body. Assimilation plays a dominant role in this stage, and metabolism is strong. On the contrary, in the old age, human function gradually declines, and metabolism is gradually slow. At this time, the primary and secondary relationship between alienation and assimilation also changes.[2]
assimilation
According to the different ways of assimilation, organisms can be divided into autotrophic and heterotrophic types.People call the living organism that ingests the ready-made organic matter heterotrophic organism;The organisms that can absorb simple inorganic substances from the environment and assimilate them into complex organic substances are called autotrophic organisms.According to the different energy and carbon sources needed, organisms can be divided into four types.[3]
1. Photoautotrophic
Light as energy, COtwoOr carbonate as the main carbon source is called photoautotrophic organism.Such organisms usually have photosynthetic pigments. They use light as energy for photosynthesis, and use water or other inorganic substances as hydrogen donors to reduce COtwo, synthesis of cellular substances.For example, higher plants, algae and some bacteria with photosynthetic pigments belong to this type.Such organisms assimilate COtwoCan be summarized in a general formula.In the general formula, A is oxygen in higher plants and algae, and sulfur or other inorganic sulfide in fine bacteria.In the process of photosynthesis, higher plants absorb light energy, assimilate carbon dioxide and water, produce organic substances, and release oxygen.[3]
COtwo+2HtwoA→(CHtwoO)+2A+Htwozero[3]
The mechanism of photosynthesis is complex, including a series of optical steps and material transformation.It can be expressed by the following simple formula:[3]
6COtwo+6Htwo0→CsixHtwelveOsix+6Otwo[3]
2. Photoheterotrophic
Organisms that use light as energy and organic matter as the main carbon source are called photoheterotrophic hosts.Some bacteria have photosynthetic pigments and can carry out photosynthesis.They use organic substances as hydrogen donors, assimilate organic substances to form their own substances, which is a kind of photosynthesis that does not produce oxygen.[3]
3. Chemical energy autotrophic type
The energy source of chemoautotrophic main substance is chemical energy, and the main carbon source is COtwoThis kind of main substance can oxidize some inorganic substances, such as NHthreeAnd HtwoS% Obtain chemical energy to reduce COtwo, synthetic organic substances.for exampleNitrite bacteriaIt can oxidize ammonia to nitrous acid to obtain energy.Ammonia oxidation and COtwoThe reduction of TNF is coupled in the cells of bacteria.[3]
4. Chemical energy heterotrophic type
This kind of biological energy comes from the chemical energy generated by the oxidation of organic substances, and the carbon source is also mainly from organic substances, such as sugars, organic acids, etc. Therefore, organic carbides are both carbon sources and energy sources.Animals, fungi and most bacteria belong to this type.[3]
Alienation
According to the way of biological dissimilation (i.e. respiratory type), it can be divided into aerobic organisms and anaerobic organisms.[3]
1. Aerobic organisms
Most living things have to live in an oxygen rich environment. They can obtain free oxygen from the atmosphere to decompose organic matter in the body and obtain energy.[3]
2. Anaerobic organisms
Such organisms cannot absorb free oxygen from the atmosphere and oxidize it in the body to obtain energy.Aerobic respiration is carried out by aerobic organisms to make organic matter release energy through a series of reactions, and finally form COtwoAnd HtwoO, etc.Anaerobic organisms breathe without oxygen. Because the organic matter is not completely decomposed and the energy in it is not completely released, the energy released by anaerobic organisms is much less than that by aerobic organisms, and the efficiency is also low.[3]
However, the distinction between aerobic and anaerobic organisms is not absolute.Aerobic organisms can also carry out anaerobic respiration under certain conditions.For example, if the oxygen supply of human muscles is insufficient during strenuous exercise, anaerobic respiration can be used to supply energy.For another example, yeast and some intestinal bacteria can grow under aerobic or anoxic conditions, but obtain energy in different ways of oxidation.In the absence of oxygen, yeast performs ethanol fermentation and accumulates ethanol and COtwoWhen there is oxygen, carry out aerobic respiration to completely oxidize organic matter into COtwoAnd HtwoO, etc.[3]
function
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① Get nutrients, materials and energy from the external environment;[2]
② Transforming the substances obtained from external ingestion into its own components;[2]
③ Assembling structural elements into their own macromolecules such as proteins, nucleic acids and lipids;[2]
④ Decomposition of organic nutrients;[2]
⑤ Provide all energy for biological life activities.[2]
Material metabolism and energy metabolism
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Metabolism includes material metabolism and energy metabolism.Material metabolism refers to the exchange of substances between organisms and the external environment and the transformation process of substances in organisms. Energy metabolism refers to the exchange of energy between organisms and the external environment and the transformation process of energy in organisms. The two are interrelated and coupled.For example, fat synthesis increases when energy intake is excessive after eating;When hungry, fat is mobilized to release energy for the body to use.[2]
(1) Material metabolism
The decomposition of old substances and the synthesis of new substances in the organism are carried out at the same time. The metabolic changes of all substances in the organism are collectively referred to as material metabolism, which includes anabolism and catabolism.Anabolism refers to the synthesis of all substances in the organism, which belongs to the category of assimilation, such asAmino acid synthesisProtein and nucleotide synthesis of nucleic acid;Catabolism refers to the decomposition of all substances in the organism, which belongs to the category of alienation. For example, sugars are completely decomposed into carbon dioxide and water through the tricarboxylic acid cycle.[2]
(2) Energy metabolism
① Changes in energy metabolism
Energy metabolism refers to the simultaneous exchange of energy in the process of material exchange.The body absorbs nutrients from the outside environment for anabolism and energy from the outside, which mainly comes from the chemical energy contained in nutrients.When these nutrients are catabolized in the body, they release chemical energy for life activities.Chemical energy is not only used to synthesize other components in the body, but also used for various life activities.However, if the chemical energy can not be completely converted into the energy that can do work, some of it will inevitably be released in the form of heat, which will become exothermic (q).The energy used for doing work is called free energy (∆ F), and the total energy of transformation is called reaction heat (∆ H).according toconservation of energy, the reaction heat is equal to the sum of the free energy of transformation and the dissipated heat, that is, ∆ H=∆ F+q[2]
② Basal metabolism
Basic metabolism refers to the minimum energy required by all human organs to maintain life.It refers to the minimum energy metabolism required to maintain basic life activities such as heartbeat and respiration when the human body is awake and extremely quiet, and is not affected by factors such as muscle activity, environmental temperature, food and mental tension.In order to compare the energy metabolism level of different individuals, the amount of heat emitted by the body per square meter per hour [kJ/(h · mtwo）], i.eBasal metabolic rateTo represent.The BMR varies with different physiological conditions such as sex and age. The BMR of men is higher than that of women on average;The basal metabolic rate of infants was higher than that of adults on average;The older the age, the lower the basal metabolic rate.The basic metabolism of normal people is about 5900~7500kJ per day.[2]
③ Respiratory quotient and card price of food
a. Respiratory quotient
When nutrients are oxidized and decomposed in the body, they need to consume oxygen and release carbon dioxide. The ratio of the two is called respiratory quotient.Respiratory quotient is an important metabolic concept.Due to different structure and composition of various nutrients, the proportion of carbon, hydrogen and oxygen content is different, so the respiratory quotient is different.The respiratory quotient of sugar, protein and fat is 1.0, 0.8 and 0.7 respectively, and the average respiratory quotient of mixed diet of normal people is 0.85. The determination of respiratory quotient can predict the energy consumption under different physiological and pathological conditions.[2]
b. Card price of food
The energy needed by the human body comes from the three energy producing nutrients of carbohydrate, lipid and protein in animal and plant foods.The energy value generated by the oxidation of each gram of energy producing nutrients in the body is called "heat price of food" or "calorie price of food", also called "energy coefficient".In metabolic research, people often use the calorie value of food to measure the energy supply of food.The card prices of sugar, fat and protein per gram are 4kcal, 9kcal and 4kcal respectively. If converted into the current international common unit of calorie calculation, joule (J), the card prices of sugar, fat and protein per gram are 17kJ, 38kJ and 17kJ respectively.[2]
Research methods of substance metabolism
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There are more than one metabolic pathway in vivo, and the chemical reactions in the pathway are more complex, even many metabolic processes are carried out simultaneously in micro cells, so appropriate research methods are needed to track the metabolic process.[2]
1. Isotope tracer method
Isotopes refer to the same kind of elements with the same atomic number but different atomic weights.When the atom in the compound molecule is replaced by the isotope of the same element, but the molecular property after replacement has not changed, it is called“Isotope labeling”。Isotope labeling is a common method to study the metabolic level in vivo. The method to introduce isotope labeled compounds into the metabolic system to observe their metabolic process and results is the isotope tracer method.Isotopes include stable isotopes andradio isotopeBoth of them can be used as tracer atoms in metabolism research, but radioisotopes are more convenient and widely used than stable isotopes.For example, to study the decarboxylation of amino acidsfourteenThe C mark is on the carboxyl group, and only the amino acid with this location mark can be produced after decarboxylationfourteenCOtwo。TritiatedThymidine(threeH ‐ TdR) andUridine(threeH-UR) is two commonly used tracers. The former can effectively bind to DNA, while the latter can be incorporated into RNA. Their radiation decomposition rate increases with the increase of radioactivity and storage time, and their stability in different temperatures and solutions is also different.[2]
2. Enzyme inhibitor method and antagonist method
This method is often used in the study of metabolism in vitro.Basically, all metabolic reactions are enzymatic reactions, so you can use an enzyme inhibitor or antimetabolite to block a certain link of intermediate metabolism, and infer the metabolism of a substance in the body according to the results of inhibition of the reaction.For example, in the process of glycolysis, iodoacetic acid specifically inhibits the activity of triose phosphate dehydrogenase, leading to a large accumulation of triose phosphate in muscles, indicating that the metabolism of triose phosphate is inhibited by iodoacetic acid.[2]
3. Metabolic research at organ level
The metabolic function of an animal can be inferred from the observation of its metabolic changes after the removal of its organs and the administration of certain substances.For example, when studying the urea synthesis site of urinating animals, it was found that the amino acid level and blood ammonia in the blood of animals were increased on average after liver resection, while the urea content in the urine was decreased, and the survival period of animals was very short, but this phenomenon was not found in the kidneys of the excised animals, indicating that the liver was related to urea synthesis.[2]
4. Use of subcellular ingredients
Supercentrifugation, differential centrifugation or density gradient centrifugation are used to separate various organelles in the cell, such as nucleus, ribosome, microsome, mitochondria, etc., and then other methods are used to study the metabolic characteristics of subcellular components and the locations where various metabolic processes are carried out in the cell.For example, using this method, we know that lipid catabolism is carried out in mitochondria, fatty acid synthesis is carried out in cytoplasm, and ribosome isSynthetic proteinMain places of.[2]
5. Methods of using normal body
Infusion, feeding or injection of a large amount of certain metabolites into animals, and then analysis of intermediates or end products in blood, tissue or excreta can help us to obtain information about substance metabolism in vivo.For example, after giving fatty acids with different carbon atom numbers to experimental animals, the composition of their excreta was analyzed, and it was found that the fatty acids with odd carbon were different from the fatty acid metabolites with even carbon, which was also the basis for the proposal of fatty acid β - oxidation.[2]
Ways to accelerate metabolism
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(1) Drink water.Water is an essential substance for human body to burn heat. Without water, the metabolism level of human body will be reduced.Drinking 1.5L of water every day can burn nearly 50cal (1cal=4.186J) more calories.[2]
(2) Breakfast.Early rising is just the time when metabolism changes.People who often eat breakfast are usually energetic and do not easily grow fat.[2]
(3) Exercise.Life lies in exercise. We can appropriately change the way and type of exercise, avoid the boring feeling of a single way, burn more fat in the most happy way, and accelerate metabolism.[2]
