Module 19: Metabolism and Nutrition

Lesson 4: Protein Metabolism

Chuyển Hóa Protein

Nội dung bài học:
Mỗi bài học (lesson) bao gồm 4 phần chính: Thuật ngữ, Luyện Đọc, Luyện Nghe, và Bàn Luận.
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Dưới đây là danh sách những thuật ngữ Y khoa của module Metabolism and Nutrition.
Khái quát được số lượng thuật ngữ sẽ xuất hiện trong bài đọc và nghe sẽ giúp bạn thoải mái tiêu thụ nội dung hơn. Sau khi hoàn thành nội dung đọc và nghe, bạn hãy quay lại đây và luyện tập (practice) để quen dần các thuật ngữ này. Đừng ép bản thân phải nhớ các thuật ngữ này vội vì bạn sẽ gặp và ôn lại danh sách này trong những bài học (lesson) khác của cùng một module.

Medical Terminology: Metabolism and Nutrition

absorptive state
also called the fed state; the metabolic state occurring during the first few hours after ingesting food in which the body is digesting food and absorbing the nutrients
acetyl coenzyme A (acetyl CoA)
starting molecule of the Krebs cycle
anabolic hormones
hormones that stimulate the synthesis of new, larger molecules
anabolic reactions
reactions that build smaller molecules into larger molecules
ATP synthase
protein pore complex that creates ATP
basal metabolic rate (BMR)
amount of energy expended by the body at rest
beta (β)-hydroxybutyrate
primary ketone body produced in the body
beta (β)-oxidation
fatty acid oxidation
bile salts
salts that are released from the liver in response to lipid ingestion and surround the insoluble triglycerides to aid in their conversion to monoglycerides and free fatty acids
biosynthesis reactions
reactions that create new molecules, also called anabolic reactions
body mass index (BMI)
relative amount of body weight compared to the overall height; a BMI ranging from 18–24.9 is considered normal weight, 25–29.9 is considered overweight, and greater than 30 is considered obese
amount of heat it takes to raise 1 kg (1000 g) of water by 1 °C
catabolic hormones
hormones that stimulate the breakdown of larger molecules
catabolic reactions
reactions that break down larger molecules into their constituent parts
cellular respiration
production of ATP from glucose oxidation via glycolysis, the Krebs cycle, and oxidative phosphorylation
cholecystokinin (CCK)
hormone that stimulates the release of pancreatic lipase and the contraction of the gallbladder to release bile salts
vesicles containing cholesterol and triglycerides that transport lipids out of the intestinal cells and into the lymphatic and circulatory systems
pancreatic enzyme that digests protein
proenzyme that is activated by trypsin into chymotrypsin
citric acid cycle
also called the Krebs cycle or the tricarboxylic acid cycle; converts pyruvate into CO2 and high-energy FADH2, NADH, and ATP molecules
transfer of heat through physical contact
transfer of heat between the skin and air or water
pancreatic enzyme that digests protein
electron transport chain (ETC)
ATP production pathway in which electrons are passed through a series of oxidation-reduction reactions that forms water and produces a proton gradient
energy-consuming phase
first phase of glycolysis, in which two molecules of ATP are necessary to start the reaction
energy-yielding phase
second phase of glycolysis, during which energy is produced
enzyme located in the wall of the small intestine that activates trypsin
transfer of heat that occurs when water changes from a liquid to a gas
high-energy molecule needed for glycolysis
fatty acid oxidation
breakdown of fatty acids into smaller chain fatty acids and acetyl CoA
flavin adenine dinucleotide (FAD)
coenzyme used to produce FADH2
cellular enzyme, found in the liver, which converts glucose into glucose-6-phosphate upon uptake into the cell
process of glucose synthesis from pyruvate or other molecules
phosphorylated glucose produced in the first step of glycolysis
form that glucose assumes when it is stored
series of metabolic reactions that breaks down glucose into pyruvate and produces ATP
cellular enzyme, found in most tissues, that converts glucose into glucose-6-phosphate upon uptake into the cell
hydroxymethylglutaryl CoA (HMG CoA)
molecule created in the first step of the creation of ketone bodies from acetyl CoA
inactive proenzymes
forms in which proteases are stored and released to prevent the inappropriate digestion of the native proteins of the stomach, pancreas, and small intestine
hormone secreted by the pancreas that stimulates the uptake of glucose into the cells
ketone bodies
alternative source of energy when glucose is limited, created when too much acetyl CoA is created during fatty acid oxidation
Krebs cycle
also called the citric acid cycle or the tricarboxylic acid cycle, converts pyruvate into CO2 and high-energy FADH2, NADH, and ATP molecules
synthesis of lipids that occurs in the liver or adipose tissues
breakdown of triglycerides into glycerol and fatty acids
metabolic rate
amount of energy consumed minus the amount of energy expended by the body
sum of all catabolic and anabolic reactions that take place in the body
inorganic compounds required by the body to ensure proper function of the body
monoglyceride molecules
lipid consisting of a single fatty acid chain attached to a glycerol backbone
smallest, monomeric sugar molecule
high-energy molecule needed for glycolysis
nicotinamide adenine dinucleotide (NAD)
coenzyme used to produce NADH
loss of an electron
oxidation-reduction reaction
(also, redox reaction) pair of reactions in which an electron is passed from one molecule to another, oxidizing one and reducing the other
oxidative phosphorylation
process that converts high-energy NADH and FADH2 into ATP
pancreatic lipases
enzymes released from the pancreas that digest lipids in the diet
enzyme that begins to break down proteins in the stomach
complex carbohydrates made up of many monosaccharides
postabsorptive state
also called the fasting state; the metabolic state occurring after digestion when food is no longer the body’s source of energy and it must rely on stored glycogen
process of breaking proteins into smaller peptides
three-carbon end product of glycolysis and starting material that is converted into acetyl CoA that enters the Krebs cycle
transfer of heat via infrared waves
gaining of an electron
salivary amylase
digestive enzyme that is found in the saliva and begins the digestion of carbohydrates in the mouth
hormone released in the small intestine to aid in digestion
sodium bicarbonate
anion released into the small intestine to neutralize the pH of the food from the stomach
terminal electron acceptor
oxygen, the recipient of the free hydrogen at the end of the electron transport chain
external temperature at which the body does not expend any energy for thermoregulation, about 84 °F
process of regulating the temperature of the body
transfer of an amine group from one molecule to another as a way to turn nitrogen waste into ammonia so that it can enter the urea cycle
tricarboxylic acid cycle (TCA)
also called the Krebs cycle or the citric acid cycle; converts pyruvate into CO2 and high-energy FADH2, NADH, and ATP molecules
lipids, or fats, consisting of three fatty acid chains attached to a glycerol backbone
pancreatic enzyme that activates chymotrypsin and digests protein
proenzyme form of trypsin
urea cycle
process that converts potentially toxic nitrogen waste into urea that can be eliminated through the kidneys
organic compounds required by the body to perform biochemical reactions like metabolism and bone, cell, and tissue growth
Nội dung này đang được cập nhật.
Dưới đây là các bài văn nằm ở bên trái. Ở bên phải là các bài luyện tập (practice) để đánh giá khả năng đọc hiểu của bạn. Sẽ khó khăn trong thời gian đầu nếu vốn từ vựng của bạn còn hạn chế, đặc biệt là từ vựng Y khoa. Hãy kiên nhẫn và đọc nhiều nhất có kể, lượng kiến thức tích tụ dần sẽ giúp bạn đọc thoải mái hơn.
Much of the body is made of protein, and these proteins take on a myriad of forms. They represent cell signaling receptors, signaling molecules, structural members, enzymes, intracellular trafficking components, extracellular matrix scaffolds, ion pumps, ion channels, oxygen and CO2 transporters (hemoglobin). That is not even the complete list! There is protein in bones (collagen), muscles, and tendons; the hemoglobin that transports oxygen; and enzymes that catalyze all biochemical reactions. Protein is also used for growth and repair. Amid all these necessary functions, proteins also hold the potential to serve as a metabolic fuel source. Proteins are not stored for later use, so excess proteins must be converted into glucose or triglycerides, and used to supply energy or build energy reserves. Although the body can synthesize proteins from amino acids, food is an important source of those amino acids, especially because humans cannot synthesize all of the 20 amino acids used to build proteins.

The digestion of proteins begins in the stomach. When protein-rich foods enter the stomach, they are greeted by a mixture of the enzyme pepsin and hydrochloric acid (HCl; 0.5 percent). The latter produces an environmental pH of 1.5–3.5 that denatures proteins within food. Pepsin cuts proteins into smaller polypeptides and their constituent amino acids. When the food-gastric juice mixture (chyme) enters the small intestine, the pancreas releases sodium bicarbonate to neutralize the HCl. This helps to protect the lining of the intestine. The small intestine also releases digestive hormones, including secretin and CCK, which stimulate digestive processes to break down the proteins further. Secretin also stimulates the pancreas to release sodium bicarbonate. The pancreas releases most of the digestive enzymes, including the proteases trypsin, chymotrypsin, and elastase, which aid protein digestion. Together, all of these enzymes break complex proteins into smaller individual amino acids (Figure 1), which are then transported across the intestinal mucosa to be used to create new proteins, or to be converted into fats or acetyl CoA and used in the Krebs cycle.

In order to avoid breaking down the proteins that make up the pancreas and small intestine, pancreatic enzymes are released as inactive proenzymes that are only activated in the small intestine. In the pancreas, vesicles store trypsin and chymotrypsin as trypsinogen and chymotrypsinogen. Once released into the small intestine, an enzyme found in the wall of the small intestine, called enterokinase, binds to trypsinogen and converts it into its active form, trypsin. Trypsin then binds to chymotrypsinogen to convert it into the active chymotrypsin. Trypsin and chymotrypsin break down large proteins into smaller peptides, a process called proteolysis. These smaller peptides are catabolized into their constituent amino acids, which are transported across the apical surface of the intestinal mucosa in a process that is mediated by sodium-amino acid transporters. These transporters bind sodium and then bind the amino acid to transport it across the membrane. At the basal surface of the mucosal cells, the sodium and amino acid are released. The sodium can be reused in the transporter, whereas the amino acids are transferred into the bloodstream to be transported to the liver and cells throughout the body for protein synthesis.

Freely available amino acids are used to create proteins. If amino acids exist in excess, the body has no capacity or mechanism for their storage; thus, they are converted into glucose or ketones, or they are decomposed. Amino acid decomposition results in hydrocarbons and nitrogenous waste. However, high concentrations of nitrogenous byproducts are toxic. The urea cycle processes nitrogen and facilitates its excretion from the body.
The urea cycle is a set of biochemical reactions that produces urea from ammonium ions in order to prevent a toxic level of ammonium in the body. It occurs primarily in the liver and, to a lesser extent, in the kidney. Prior to the urea cycle, ammonium ions are produced from the breakdown of amino acids. In these reactions, an amine group, or ammonium ion, from the amino acid is exchanged with a keto group on another molecule. This transamination event creates a molecule that is necessary for the Krebs cycle and an ammonium ion that enters into the urea cycle to be eliminated.

In the urea cycle, ammonium is combined with CO2, resulting in urea and water. The urea is eliminated through the kidneys in the urine (Figure 2).

Amino acids can also be used as a source of energy, especially in times of starvation. Because the processing of amino acids results in the creation of metabolic intermediates, including pyruvate, acetyl CoA, acetoacyl CoA, oxaloacetate, and α-ketoglutarate, amino acids can serve as a source of energy production through the Krebs cycle (Figure 3). Figure 4 summarizes the pathways of catabolism and anabolism for carbohydrates, lipids, and proteins.

OpenStax. (2022). Anatomy and Physiology 2e. Rice University. Retrieved June 15, 2023. ISBN-13: 978-1-711494-06-7 (Hardcover) ISBN-13: 978-1-711494-05-0 (Paperback) ISBN-13: 978-1-951693-42-8 (Digital). License: Attribution 4.0 International (CC BY 4.0). Access for free at

Enzymes in the stomach and small intestine break down proteins into amino acids. HCl in the stomach aids in proteolysis, and hormones secreted by intestinal cells direct the digestive processes.

Nitrogen is transaminated, creating ammonia and intermediates of the Krebs cycle. Ammonia is processed in the urea cycle to produce urea that is eliminated through the kidneys.

Amino acids can be broken down into precursors for glycolysis or the Krebs cycle. Amino acids (in bold) can enter the cycle through more than one pathway.

Nutrients follow a complex pathway from ingestion through anabolism and catabolism to energy production.

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Dưới đây là video và các luyện tập (practice) của bài này. Nghe là một kĩ năng khó, đặc biệt là khi chúng ta chưa quen nội dung và chưa có nhạy cảm ngôn ngữ. Nhưng cứ đi thật chậm và đừng bỏ cuộc.
Xem video và cảm nhận nội dung bài. Bạn có thể thả trôi, cảm nhận dòng chảy ngôn ngữ và không nhất thiết phải hiểu toàn bộ bài. Bên dưới là script để bạn khái quát nội dụng và tra từ mới.
  1. Digestion of proteins begins in the stomach, where hydrochloric acid and pepsin begin the process of breaking down proteins into their constituent amino acids.
  2. As the chyme enters the small intestine, it mixes with bicarbonate and digestive enzymes.
  3. The bicarbonate neutralizes the hydrochloric acid, and the digestive enzymes break down the proteins into smaller peptides and amino acids.
  4. Digestive hormones secretin and cholecystokinin are released from the small intestine to aid in digestive processes.
  5. Also, digestive proenzymes are released from the pancreas, which are trypsinogen and chymotrypsinogen.
  6. Enterokinase, an enzyme located in the wall of the small intestine, activates trypsin, which in turn activates chymotrypsin.
  7. These enzymes liberate the individual amino acids that are then transported via sodium-amino acid transporters across the intestinal wall into the cell.
  8. The amino acids are then transported into the bloodstream for dispersal to the liver and cells throughout the body to be used to create new proteins.
  9. When in excess, the amino acids are processed and stored as glucose or ketones.
  10. The nitrogen waste that is liberated in this process is converted to urea in the urea acid cycle and eliminated in the urine.
  11. In times of starvation, amino acids can be used as an energy source and processed through the Krebs cycle.
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