24. Nutrition, Metabolism, Energy Balance

Metabolic functions of the liver

Metabolism

The Liver - Functions

What does the liver do?

ATP and Food 

Before amino acids can be oxidized for energy, they must be deaminated. A by-product of deamination is ammonia (NH3), which is toxic to cells. Fortunately, the process of deamination occurs in the liver, and the liver is able to convert the toxic intermediate&mdash;ammonia&mdash;into urea. Urea is then removed from the blood by the kidneys.

 As proteins are broken down for energy, __________ is generated; the liver then converts this potentially toxic intermediate into __________. 

Fed State

Overview of metabolism: Anabolism and catabolism

Oxidation and reduction in metabolism | Biomolecules

Metabolism & Nutrition

Function of the Liver

Cellular Respiration: The Electron Transport Chain and Oxidative Phosphorylation

ATP & Respiration

Ketone Body Synthesis | Ketogenesis | Formation Pathway and Regulation

Cellular Respiration: Glycolysis

Redox reactions are coupled oxidation-reduction reactions essential to the chemical and physiological processes that sustain life. In oxidation, electrons are lost; in reduction, electrons are gained. One useful mnemonic to help you remember this is OIL RIG (Oxidation Is Loss, Reduction Is Gain). Redox reactions are prevalent in cellular respiration, and they tend to be catalyzed by enzymes.

 A substance that is reduced has lost an electron. 

 Rising blood glucose levels after a carbohydrate-containing meal act as a humoral stimulus that prods the beta cells of the pancreatic islets to secrete more insulin. 

 The hormone that controls essentially all events of the absorptive state is __________. 

Liver Functions

Cholesterol Metabolism, LDL, HDL and other Lipoproteins

LDL and HDL Cholesterol | Good and Bad Cholesterol

Cholesterol plays an important structural and functional role in human physiology. About 15% of cholesterol in the body (in the blood, primarily) comes from the diet; the rest is made by the liver. Because cholesterol is not water soluble, it is transported through the blood as lipoproteins. There are several classes of lipoproteins: very low-density lipoproteins (VLDLs), low-density lipoproteins (LDLs), and high-density lipoproteins (HDLs). The main role of HDLs is to collect cholesterol from peripheral tissues and deliver it to the liver for removal from the body. For this reason, HDLs are considered a "good" type of cholesterol. LDLs deposit cholesterol in blood vessels; high LDL levels are associated with an increased risk of heart disease. It is recommended that blood levels of LDL be maintained at 100 mg/dl or less.

 __________ are considered "good" cholesterol; high blood levels of this cholesterol are thought to be beneficial. 

Oxidative Deamination of Amino Acids

Oxidation of Fatty Acids

Cellular Respiration, 3 Electron Carriers

Anabolic and Catabolic Reactions

Glycogenesis & Glycogenolysis

NAD+ and FAD+ Cofactors

Oxidative phosphorylation and the electron transport chain

 glycogen is broken down to release glucose 

 The absorptive state is the fed state; in this state, glucose is the primary fuel source. The metabolic activities that occur in the absorptive state are regulated by insulin. In the absorptive state, anabolism exceeds catabolism, which means that synthesis (anabolic) reactions are more prevalent than breakdown (catabolic) reactions. In the fed state, glycogen and triglycerides are converted into fat to store energy. 

 insulin serves as the main regulatory hormone 

Overview of Fatty Acid Oxidation

Glycogen Breakdown

Substrate-Level Phosphorylation

Substrate Level vs. Oxidative Phosphorylation

 Most of the ATP produced during cellular respiration is produced by oxidative phosphorylation during the chemiosmotic process. 

 oxidative phosphorylation during the chemiosmotic process 

 Most of the ATP produced during cellular respiration is produced by __________. 

Overview of Glycogenesis

Fasted State

 The inner membrane of the mitochondrion contains the integral proteins necessary for electron transport. 

 The site of electron transport is the __________. 

Cellular Respiration: The Citric Acid Cycle

Introduction to Gluconeogenesis

 The liver mobilizes glucose reserves quickly and efficiently to maintain blood sugar levels for about four hours during the postabsorptive state. 

 to store excess glucose by glycogenesis 

 to mobilize glucose reserves by glycogenolysis 

 A function of the liver during the postabsorptive state is __________. 

Substrate Level Phosphorylation and Oxidative Phosphorylation

Amino acid catabolism (Transamination | Deamination | Urea cycle)

Cellular Respiration

Metabolism refers to all of the metabolic processes in a cell. Metabolic processes are categorized as being either anabolic or catabolic. Anabolism refers to the building of macromolecules from smaller precursors (for example, building proteins from amino acids). Catabolism refers to the breakdown of large molecules into smaller components. Cellular respiration is a catabolic process in which food fuels (energy sources) are broken down to provide ATP, which fuels cellular work.

 absorbing nutrients into the blood from the intestines 

 Which of the following is an example of catabolism? 

The electron transport chain (ETC) is located in the mitochondria of cells. The ETC transports the electrons from the reduced coenzymes NADH and FADH2 to the final electron acceptor, oxygen (O2). As the electrons combine with oxygen, water is generated. Because oxygen is required as the final electron acceptor, the ETC is an aerobic pathway. As electrons are transported down the ETC, a proton (H+) gradient is established. The potential energy of the proton gradient is then harnessed (through a process called chemiosmosis) to produce ATP.

 The final electron acceptor in the electron transport chain is __________. 

 Fatty acids cannot be used to bolster blood glucose levels. During fasts lasting several weeks, blood glucose is maintained by gluconeogenesis by the kidney and liver. 

 During fasts lasting several weeks, there is no glucose to break down. Blood glucose is maintained by gluconeogenesis by the kidney and liver. 

 During fasts lasting several weeks, all the glycogen stores are depleted. Blood glucose is maintained by gluconeogenesis by the kidney and liver. 

 During fasts lasting several weeks, blood glucose is maintained by __________. 

 Amino acids are monomers of proteins. The greater the proportion of protein, the higher the density of the lipoprotein. 

 The higher the percentage of a lipid in a lipoprotein, the lower the density. 

 If the proportion of protein in a lipoprotein were high, its density would be higher. 

 A low-density lipoprotein contains __________. 

The citric acid cycle generates a rich supply of the reduced coenzymes, NADH and FADH2.

 The citric acid cycle occurs in the cytosol of the cell. 

The citric acid (Krebs) cycle is an aerobic pathway that occurs in the mitochondria of cells. Pyruvic acid is a charged molecule and must enter the mitochondria by active transport. In the mitochondria, pyruvic acid is converted to acetyl CoA, which then enters the citric acid cycle. Acetyl CoA combines with oxaloacetic acid to produce the first intermediate of the citric acid cycle, citric acid. As the steps of the cycle continue, CO2 is generated, along with a rich supply of NADH and FADH2. A small amount of ATP is also made in the citric acid cycle. The rich supply of the reduced coenzymes, NADH and FADH2, represents a great energy investment for the cell; these reduced coenzymes enter the electron transport chain and yield an abundance of ATP.

 The citric acid cycle is an anaerobic pathway. 

 Pyruvic acid directly enters the citric acid cycle. 

 Which of the following is a characteristic of the citric acid (Krebs) cycle? 

Ketogenesis

 In a “redox” reaction, oxidized substances lose energy. 

 The substance being reduced loses an electron. 

 In a “redox” reaction, the substance being reduced gains an electron. 

 In a “redox” reaction, oxidized substances either gain an oxygen or lose a hydrogen. 

 Which of the following statements about “redox” reactions in human metabolism is correct? 

 The role of high-density lipoproteins is to transport excessive cholesterol from peripheral tissue to the liver, where it is broken down and becomes part of bile. 

 Chylomicrons transport fat in the lymph. The role of high-density lipoproteins is to transport excessive cholesterol from peripheral tissue to the liver, where it is broken down and becomes part of bile. 

 The role of __________ is to transport excessive cholesterol from peripheral tissue to the liver, where it is broken down and becomes part of bile. 

 Which lipoprotein contains the most cholesterol? 

 Glucose must be activated by two ATP molecules forming fructose-1,6-bisphosphate. 

 During glycolysis, glucose must be activated by how many ATP molecules? 

What happens to your body after eating a meal?

 The production of glyceraldehyde 3-phosphate is the result of one of the middle steps in glycolysis and is not one of the final products of glycolysis. 

two molecules of pyruvic acid, two molecules of NAD+, and a net gain of two ATP

 two molecules of acetyl coenzyme A and two molecules of carbon dioxide 

 Acetyl coenzyme A and carbon dioxide are produced during the transitional phase before the Krebs cycle, not by glycolysis. 

 FAD molecules are reduced during the Krebs cycle and are not produced during glycolysis. 

 The final product of glycolysis is __________. 

 NAD is reduced to NADH in both glycolysis and the Krebs cycle. 

 Which coenzyme is reduced in both glycolysis and the Krebs cycle? 

Transamination of Amino Acids

Fasting - What does it do to your body?

 The main goal of the postabsorptive state is to maintain blood glucose levels within the homeostatic range. The postabsorptive state is regulated by the hormone glucagon. In this state, glycogen and fats are the primary fuels. Glucose is also formed by gluconeogenesis to help boost blood glucose levels. Catabolic processes such as glycogenolysis (the breakdown of glycogen to release glucose) and lipolysis are prevalent in the postabsorptive state. 

 In the postabsorptive state, __________. 

 Glycolysis produces a net gain of 2 ATP molecules per glucose molecule. 

Glycolysis, an anaerobic process, occurs in the cytosol. The term anaerobic means that the reactions of glycolysis occur whether or not oxygen is present. Glycolysis begins with glucose-6-phosphate and ends with the production of two molecules of pyruvic acid, a net gain of 2 ATP molecules, and 2 NADH.

 The final products of glycolysis include two molecules of pyruvic acid. 

 Glycolysis occurs in the cytosol of a cell. 

 Which of the following is NOT a characteristic of glycolysis? 

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