Medical Terminology: Metabolism and Nutrition
absorptive state
acetyl coenzyme A (acetyl CoA)
anabolic hormones
anabolic reactions
ATP synthase
basal metabolic rate (BMR)
beta (β)-hydroxybutyrate
beta (β)-oxidation
bile salts
biosynthesis reactions
body mass index (BMI)
calorie
catabolic hormones
catabolic reactions
cellular respiration
cholecystokinin (CCK)
chylomicrons
chymotrypsin
chymotrypsinogen
citric acid cycle
conduction
convection
elastase
electron transport chain (ETC)
energy-consuming phase
energy-yielding phase
enterokinase
evaporation
FADH2
fatty acid oxidation
flavin adenine dinucleotide (FAD)
glucokinase
gluconeogenesis
glucose-6-phosphate
glycogen
glycolysis
hexokinase
hydroxymethylglutaryl CoA (HMG CoA)
inactive proenzymes
insulin
ketone bodies
Krebs cycle
lipogenesis
lipolysis
metabolic rate
metabolism
minerals
monoglyceride molecules
monosaccharide
NADH
nicotinamide adenine dinucleotide (NAD)
oxidation
oxidation-reduction reaction
oxidative phosphorylation
pancreatic lipases
pepsin
polysaccharides
postabsorptive state
proteolysis
pyruvate
radiation
reduction
salivary amylase
secretin
sodium bicarbonate
terminal electron acceptor
thermoneutral
thermoregulation
transamination
tricarboxylic acid cycle (TCA)
triglycerides
trypsin
trypsinogen
urea cycle
vitamins
Glucose + 2ATP + 2NAD+ + 4ADP + 2Pi → 2 Pyruvate + 4ATP + 2NADH + 2H+
This equation states that glucose, in combination with ATP (the energy source), NAD+ (a coenzyme that serves as an electron acceptor), and inorganic phosphate, breaks down into two pyruvate molecules, generating four ATP molecules—for a net yield of two ATP—and two energy-containing NADH coenzymes.Cách hiểu:Hiện chưa có bản dịch The NADH that is produced in this process will be used later to produce ATP in the mitochondria.Cách hiểu:Hiện chưa có bản dịch Importantly, by the end of this process, one glucose molecule generates two pyruvate molecules, two high-energy ATP molecules, and two electron-carrying NADH molecules.Cách hiểu:Hiện chưa có bản dịch The following discussions of glycolysis include the enzymes responsible for the reactions.Cách hiểu:Hiện chưa có bản dịch When glucose enters a cell, the enzyme hexokinase (or glucokinase, in the liver) rapidly adds a phosphate to convert it into glucose-6-phosphate.Cách hiểu:Hiện chưa có bản dịch A kinase is a type of enzyme that adds a phosphate molecule to a substrate (in this case, glucose, but it can be true of other molecules also).Cách hiểu:Hiện chưa có bản dịch This conversion step requires one ATP and essentially traps the glucose in the cell, preventing it from passing back through the plasma membrane, thus allowing glycolysis to proceed.Cách hiểu:Hiện chưa có bản dịch It also functions to maintain a concentration gradient with higher glucose levels in the blood than in the tissues.Cách hiểu:Hiện chưa có bản dịch By establishing this concentration gradient, the glucose in the blood will be able to flow from an area of high concentration (the blood) into an area of low concentration (the tissues) to be either used or stored.Cách hiểu:Hiện chưa có bản dịch Hexokinase is found in nearly every tissue in the body.Cách hiểu:Hiện chưa có bản dịch Glucokinase, on the other hand, is expressed in tissues that are active when blood glucose levels are high, such as the liver.Cách hiểu:Hiện chưa có bản dịch Hexokinase has a higher affinity for glucose than glucokinase and therefore is able to convert glucose at a faster rate than glucokinase.Cách hiểu:Hiện chưa có bản dịch This is important when levels of glucose are very low in the body, as it allows glucose to travel preferentially to those tissues that require it more.Cách hiểu:Hiện chưa có bản dịch In the next step of the first phase of glycolysis, the enzyme glucose-6-phosphate isomerase converts glucose-6-phosphate into fructose-6-phosphate.Cách hiểu:Hiện chưa có bản dịch Like glucose, fructose is also a six carbon-containing sugar.Cách hiểu:Hiện chưa có bản dịch The enzyme phosphofructokinase-1 then adds one more phosphate to convert fructose-6-phosphate into fructose-1-6-bisphosphate, another six-carbon sugar, using another ATP molecule.Cách hiểu:Hiện chưa có bản dịch Aldolase then breaks down this fructose-1-6-bisphosphate into two three-carbon molecules, glyceraldehyde-3-phosphate and dihydroxyacetone phosphate.Cách hiểu:Hiện chưa có bản dịch The triosephosphate isomerase enzyme then converts dihydroxyacetone phosphate into a second glyceraldehyde-3-phosphate molecule.Cách hiểu:Hiện chưa có bản dịch Therefore, by the end of this chemical-priming or energy-consuming phase, one glucose molecule is broken down into two glyceraldehyde-3-phosphate molecules.Cách hiểu:Hiện chưa có bản dịch The second phase of glycolysis, the energy-yielding phase, creates the energy that is the product of glycolysis.Cách hiểu:Hiện chưa có bản dịch Glyceraldehyde-3-phosphate dehydrogenase converts each three-carbon glyceraldehyde-3-phosphate produced during the energy-consuming phase into 1,3-bisphosphoglycerate.Cách hiểu:Hiện chưa có bản dịch This reaction releases an electron that is then picked up by NAD+ to create an NADH molecule.Cách hiểu:Hiện chưa có bản dịch NADH is a high-energy molecule, like ATP, but unlike ATP, it is not used as energy currency by the cell.Cách hiểu:Hiện chưa có bản dịch Because there are two glyceraldehyde-3-phosphate molecules, two NADH molecules are synthesized during this step.Cách hiểu:Hiện chưa có bản dịch Each 1,3-bisphosphoglycerate is subsequently dephosphorylated (i.e., a phosphate is removed) by phosphoglycerate kinase into 3-phosphoglycerate.Cách hiểu:Hiện chưa có bản dịch Each phosphate released in this reaction can convert one molecule of ADP into one high-energy ATP molecule, resulting in a gain of two ATP molecules.Cách hiểu:Hiện chưa có bản dịch The enzyme phosphoglycerate mutase then converts the 3-phosphoglycerate molecules into 2-phosphoglycerate.Cách hiểu:Hiện chưa có bản dịch The enolase enzyme then acts upon the 2-phosphoglycerate molecules to convert them into phosphoenolpyruvate molecules.Cách hiểu:Hiện chưa có bản dịch The last step of glycolysis involves the dephosphorylation of the two phosphoenolpyruvate molecules by pyruvate kinase to create two pyruvate molecules and two ATP molecules.Cách hiểu:Hiện chưa có bản dịch In summary, one glucose molecule breaks down into two pyruvate molecules, and creates two net ATP molecules and two NADH molecules by glycolysis.Cách hiểu:Hiện chưa có bản dịch Therefore, glycolysis generates energy for the cell and creates pyruvate molecules that can be processed further through the aerobic Krebs cycle (also called the citric acid cycle or tricarboxylic acid cycle); converted into lactic acid or alcohol (in yeast) by fermentation; or used later for the synthesis of glucose through gluconeogenesis.Cách hiểu:Hiện chưa có bản dịch A. Anaerobic RespirationCách hiểu:Hiện chưa có bản dịch When oxygen is limited or absent, pyruvate enters an anaerobic pathway called fermentation.Cách hiểu:Hiện chưa có bản dịch In these reactions, pyruvate can be converted into lactic acid.Cách hiểu:Hiện chưa có bản dịch In addition to generating an additional ATP, this pathway serves to keep the pyruvate concentration low so glycolysis continues, and it oxidizes NADH into the NAD+ needed by glycolysis.Cách hiểu:Hiện chưa có bản dịch In this reaction, lactic acid replaces oxygen as the final electron acceptor.Cách hiểu:Hiện chưa có bản dịch Anaerobic respiration occurs in most cells of the body when oxygen is limited or mitochondria are absent or nonfunctional.Cách hiểu:Hiện chưa có bản dịch For example, because erythrocytes (red blood cells) lack mitochondria, they must produce their ATP from anaerobic respiration.Cách hiểu:Hiện chưa có bản dịch This is an effective pathway of ATP production for short periods of time, ranging from seconds to a few minutes.Cách hiểu:Hiện chưa có bản dịch The lactic acid produced diffuses into the plasma and is carried to the liver, where it is converted back into pyruvate or glucose via the Cori cycle.Cách hiểu:Hiện chưa có bản dịch Similarly, when a person exercises, muscles use ATP faster than oxygen can be delivered to them.Cách hiểu:Hiện chưa có bản dịch They depend on glycolysis and lactic acid production for rapid ATP production.Cách hiểu:Hiện chưa có bản dịch B. Aerobic RespirationCách hiểu:Hiện chưa có bản dịch In the presence of oxygen, pyruvate can enter the Krebs cycle where additional energy is extracted as electrons are transferred from the pyruvate to the receptors NAD+, GDP, and FAD, with carbon dioxide being a “waste product” (Figure 3).Cách hiểu:Hiện chưa có bản dịch The NADH and FADH2 pass electrons on to the electron transport chain, which uses the transferred energy to produce ATP.Cách hiểu:Hiện chưa có bản dịch As the terminal step in the electron transport chain, oxygen is the terminal electron acceptor and creates water inside the mitochondria.Cách hiểu:Hiện chưa có bản dịch- A net of two ATP are produced through glycolysis (four produced and two consumed during the energy-consuming stage).Cách hiểu:Hiện chưa có bản dịch However, these two ATP are used for transporting the NADH produced during glycolysis from the cytoplasm into the mitochondria.Cách hiểu:Hiện chưa có bản dịch Therefore, the net production of ATP during glycolysis is zero.Cách hiểu:Hiện chưa có bản dịch
- In all phases after glycolysis, the number of ATP, NADH, and FADH2 produced must be multiplied by two to reflect how each glucose molecule produces two pyruvate molecules.Cách hiểu:Hiện chưa có bản dịch
- In the ETC, about three ATP are produced for every oxidized NADH.Cách hiểu:Hiện chưa có bản dịch However, only about two ATP are produced for every oxidized FADH2.Cách hiểu:Hiện chưa có bản dịch The electrons from FADH2 produce less ATP, because they start at a lower point in the ETC (Complex II) compared to the electrons from NADH (Complex I) (see Figure 5).Cách hiểu:Hiện chưa có bản dịch
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 openstax.org.
Cellular respiration oxidizes glucose molecules through glycolysis, the Krebs cycle, and oxidative phosphorylation to produce ATP.
During the energy-consuming phase of glycolysis, two ATPs are consumed, transferring two phosphates to the glucose molecule. The glucose molecule then splits into two three-carbon compounds, each containing a phosphate. During the second phase, an additional phosphate is added to each of the three-carbon compounds. The energy for this endergonic reaction is provided by the removal (oxidation) of two electrons from each three-carbon compound. During the energy-releasing phase, the phosphates are removed from both three-carbon compounds and used to produce four ATP molecules.
The process of anaerobic respiration converts glucose into two lactate molecules in the absence of oxygen or within erythrocytes that lack mitochondria. During aerobic respiration, glucose is oxidized into two pyruvate molecules.
During the Krebs cycle, each pyruvate that is generated by glycolysis is converted into a two-carbon acetyl CoA molecule. The acetyl CoA is systematically processed through the cycle and produces high-energy NADH, FADH2, and ATP molecules.
The electron transport chain is a series of electron carriers and ion pumps that are used to pump H+ ions out of the inner mitochondrial matrix.
Carbohydrate metabolism involves glycolysis, the Krebs cycle, and the electron transport chain.
Gluconeogenesis is the synthesis of glucose from pyruvate, lactate, glycerol, alanine, or glutamate.
Script:
- Metabolic enzymes catalyze catabolic reactions that break down carbohydrates contained in food.
- The energy released is used to power the cells and systems that make up your body.
- Excess or unutilized energy is stored as fat or glycogen for later use.
- Carbohydrate metabolism begins in the mouth, where the enzyme salivary amylase begins to break down complex sugars into monosaccharides.
- These can then be transported across the intestinal membrane into the bloodstream and then to body tissues.
- In the cells, glucose, a six-carbon sugar, is processed through a sequence of reactions into smaller sugars, and the energy stored inside the molecule is released.
- The first step of carbohydrate catabolism is glycolysis, which produces pyruvate, nicotinamide adenine dinucleotide, and ATP.
- Under anaerobic conditions, the pyruvate can be converted into lactate to keep glycolysis working.
- Under aerobic conditions, pyruvate enters the Krebs cycle, also called the citric acid cycle or tricarboxylic acid cycle.
- In addition to ATP, the Krebs cycle produces high-energy molecules, flavin adenine dinucleotide or FADH2 and nicotinamide adenine dinucleotide or NADH.
- They provide electrons to the oxidative phosphorylation process that generates more high-energy ATP molecules.
- For each molecule of glucose that is processed in glycolysis, a net of 36 ATPs can be created by aerobic respiration.
- Under anaerobic conditions, ATP production is limited to those generated by glycolysis.
- While a total of four ATPs are produced by glycolysis, two are needed to begin glycolysis, so there is a net yield of two ATP molecules.
- In conditions of low glucose, such as fasting, starvation, or low carbohydrate diets, glucose can be synthesized from lactate, pyruvate, glycerol, alanine, or glutamate.
- This process, called gluconeogenesis, is almost the reverse of glycolysis and serves to create glucose molecules for glucose-dependent organs, such as the brain, when glucose levels fall below normal.
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