Chapter 7 metabolism and energy

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings

Fundamentals of

Anatomy & PhysiologySIXTH EDITION

Frederic H

. MartiniChapter 7

Metabolism and Energetics


Learning Objectives

• Explain why cells need to synthesis new organic components

• Describe the basic steps in glycolysis, the TCA cycle, and the electron transport chain

• Summarize the energy yield of glycolysis and cellular respiration

• Describe the pathways involved in lipid, protein and nucleic acid metabolism


Learning Objectives

• Summarize the characteristics of the absorptive and postabsorptive metabolic states

• Explain what constitutes a balanced diet and why such a diet is important

• Define metabolic rate and discuss the factors involved in determining an individual’s BMR


SECTION 25-1 An Overview of Metabolism


• Metabolism is all the chemical reactions that occur in an organism

• Cellular metabolism

• Cells break down excess carbohydrates first, then lipids

• Cells conserve amino acids

• 40% of the energy released in catabolism is captured in ATP

• Rest is released as heat

Metabolism

Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings Figure 25.1

Figure 25.1 An Introduction to Cellular Metabolism


• Performance of structural maintenance and repairs

• Support of growth

• Production of secretions

• Building of nutrient reserves

Anabolism


Figure 25.2 Metabolic Turnover and Cellular ATP Production


• cells provide small organic molecules for their mitochondria

• Mitochondria produce ATP used to perform cellular functions

Cells and Mitochondria


Figure 25.3 Nutrient Use in Cellular Metabolism

Figure 25.3


SECTION 25-2 Carbohydrate Metabolism


• Glycolysis

• One molecule of glucose = two pyruvate ions, two ATP, two NADH

• Aerobic metabolism (cellular respiration)

• Two pyruvates = 34 ATP

• The chemical formula for this process is C6H12O6 + 6 O2 6 CO2 + 6 H2O

Most cells generate ATP through the breakdown of carbohydrates


• The breakdown of glucose to pyruvic acid

• This process requires:

• Glucose molecules

• Cytoplasmic enzymes

• ATP and ADP

• Inorganic phosphate

• NAD (nicotinamide adenine dinucleotide)

• The overall reaction is: Glucose + 2 NAD + 2 ADP + 2Pi 2 Pyruvic acid + 2 NADH + 2 ATP

Glycolysis


Figure 25.4 Glycolysis

Animation: Steps in GlycolysisPLAY

Figure 25.4


Figure 25.4 Glycolysis

Figure 25.4


• Pyruvic acid molecules enter mitochondria

• Broken down completely in TCA cycle

• Decarboxylation

• Hydrogen atoms passed to coenzymes

• Oxidative phosphorylation

Mitochondrial ATP Production (cellular respiration)


Figure 25.5 The TCA Cycle

Animation: TCA CyclePLAY

Figure 25.5



Figure 25.5a



Figure 25.5b


• Requires coenzymes and consumes oxygen

• Key reactions take place in the electron transport system (ETS)

• Cytochromes of the ETS pass electrons to oxygen, forming water

• The basic chemical reaction is: 2 H2 + O2 2 H2O

Oxidative phosphorylation and the ETS


Figure 25.6 Oxidative Phosphorylation

Figure 25.6

Animation: ChemiosmosisPLAY



Figure 25.6a



Figure 25.6b


• Per molecule of glucose entering these pathways

• Glycolysis – has a net yield of 2 ATP

• Electron transport system – yields approximately 28 molecules of ATP

• TCA cycle – yields 2 molecules of ATP

Energy yield of glycolysis and cellular respiration


Figure 25.7 A Summary of the Energy Yield of Aerobic Metabolism


• Gluconeogenesis

• Synthesis of glucose from noncarbohydrate precursors

• Lactic acid, glycerol, amino acids

• Liver cells synthesis glucose when carbohydrates are depleted

• Glycogenesis

• Formation of glycogen

• Glucose stored in liver and skeletal muscle as glycogen

• Important energy reserve

Synthesis of glucose and glycogen


Figure 25.8 Carbohydrate Breakdown and Synthesis


Fundamentals of


Frederic H

. MartiniChapter 25, part 2



SECTION 25-3 Lipid Metabolism


• Lipolysis

• Lipids broken down into pieces that can be converted into pyruvate

• Triglycerides are split into glycerol and fatty acids

• Glycerol enters glycolytic pathways

• Fatty acids enter the mitochondrion

Lipid catabolism


• Beta-oxidation

• Breakdown of fatty acid molecules into 2-carbon fragments

• Enter the TCA

• Irreversible

• Lipids and energy production

• Cannot provide large amounts in ATP in a short amount of time

• Used when glucose reserves are limited

Lipid catabolism


Figure 25.9 Beta Oxidation

Figure 25.9


• Almost any organic molecule can be used to form glycerol

• Essential fatty acids cannot be synthesized and must be included in diet

• Linoleic and linolenic acid

Lipid synthesis (lipogenesis)


Figure 25.10 Lipid Synthesis

Figure 25.10


• Transport assure by lipoproteins:

• 5 types of lipoprotein

• Lipid-protein complex that contains large glycerides and cholesterol

• Chylomicrons

• Largest lipoproteins composed primarily of triglycerides

• Very low-density lipoproteins (VLDLs)

• contain triglycerides, phospholipids and cholesterol

Lipid transport and distribution


• 5 types of lipoprotein (continued)

• Intermediate-density lipoproteins (IDLs)

• Contain smaller amounts of triglycerides

• Low-density lipoproteins (LDLs)

• Contain mostly cholesterol

• High-density lipoproteins (HDLs)

• Equal amounts of lipid and protein

Lipid transport and distribution


• Enzyme that breaks down complex lipids

• Found in capillary walls of liver, adipose tissue, skeletal and cardiac muscle

• Releases fatty acids and monglycerides

Lipoprotein lipase


Figure 25.11 Lipid Transport and Utilization

Figure 25.11a


Figure 25.11 Lipid Transport and Utilization

Figure 25.11b


SECTION 25-4 Protein Metabolism


• If other sources inadequate, mitochondria can break down amino acids

• TCA cycle

• removal of the amino group (-NH2)

• Transamination – attaches removed amino group to a keto acid

• Deamination – removes amino group generating NH4

+

• Proteins are an impractical source of ATP production

Amino acid catabolism


Figure 25.12 Amino Acid Catabolism

Figure 25.12



Figure 25.12a



Figure 25.12b



Figure 25.12c


• Essential amino acids

• Cannot be synthesized by the body in adequate supply

• Nonessential amino acids

• Can be synthesized by the body via amination

• Addition of the amino group to a carbon framework

Protein synthesis


Figure 25.13 Amination

Figure 25.13


Figure 25.14 A Summary of the Pathways of Catabolism and Anabolism


SECTION 25-5 Nucleic Acid Metabolism


• Nuclear DNA is never catabolized for energy

• RNA catabolism

• RNA molecules are routinely broken down and replaced

• Generally recycled as nucleic acids

• Can be catabolized to simple sugars and nitrogenous bases

• Do not contribute significantly to energy reserves

Nucleic acid metabolism


• Most cells synthesis RNA

• DNA synthesized only when preparing for division

Nucleic acid synthesis


Fundamentals of


Frederic H

. MartiniChapter 25, part 3



SECTION 25-6 Metabolic Interactions


• No one cell of the human body can perform all necessary homeostatic functions

• Metabolic activities must be coordinated

Homeostasis


• Liver

• The focal point for metabolic regulation and control

• Adipose tissue

• Stores lipids primarily as triglycerides

• Skeletal muscle

• Substantial glycogen reserves

Body has five metabolic components


• Neural tissue

• Must be supplied with a reliable supply of glucose

• Other peripheral tissues

• Able to metabolize substrates under endocrine control

Body has five metabolic components


• The period following a meal

• Nutrients enter the blood as intestinal absorption proceeds

• Liver closely regulates glucose content of blood

• Lipemia commonly marks the absorptive state

• Adipocytes remove fatty acids and glycerol from bloodstream

• Glucose molecule are catabolized and amino acids are used to build proteins

The absorptive state


Figure 25.15 The Absorptive State

Figure 25.15


• From the end of the absorptive state to the next meal

• Body relies on reserves for energy

• Liver cells break down glycogen, releasing glucose into blood

• Liver cells synthesize glucose

• Lipolysis increases and fatty acids released into blood stream

• Fatty acids undergo beta oxidation and enter TCA

The Postabsorptive state


• Amino acids either converted to pyruvate or acetyl-CoA

• Skeletal muscles metabolize ketone bodies and fatty acids

• Skeletal muscle glycogen reserves broken down to lactic acid

• Neural tissue continues to be supplied with glucose

The Postabsorptive state


Figure 25.16 Metabolic Reserves

Figure 25.16a


Figure 25.17 The Postabsorptive State

Figure 25.17


SECTION 25-7 Diet and Nutrition


• Nutrition

• Absorption of nutrients from food

• Balanced diet

• Contains all the ingredients necessary to maintain homeostasis

• Prevents malnutrition

Diet and Nutrition


• Food groups and food pyramids

• Used as guides to avoid malnutrition

Food


• Six basic food groups of a balance diet arranged in a food pyramid

• Milk, yogurt and cheese

• Meat, poultry, fish, dry beans, eggs, and nuts

• Vegetables

• Fruits

• Bread, cereal, rice and pasta

• Base of pyramid

• Fats, oils and sweets

• Top of pyramid

Food Groups


Figure 25.18 The Food Pyramid and Dietary Recommendations


• N compounds contain nitrogen

• Amino acids, purines, pyrimidines, creatine, porphyrins

• Body does not maintain large nitrogen reserves

• Dietary nitrogen is essential

• Nitrogen balance is an equalization of absorbed and excreted nitrogen

Nitrogen balance


• Act as co-factors in enzymatic reactions

• Contribute to osmotic concentrations of body fluids

• Play a role in transmembrane potentials, action potentials

• Aid in release of neurotransmitters and muscle contraction

• Assist in skeletal construction and maintenance

• Important in gas transport and buffer systems

• Aid in fluid absorption and waste removal

Minerals


• Are needed in very small amounts for a variety of vital body activities

• Fat soluble

• Vitamins A, D, E, K

• Taken in excess can lead to hypervitaminosis

• Water soluble

• Not stored in the body

• Lack of adequate dietary intake = avitaminosis

Vitamins


SECTION 25-8 Bioenergetics


• The study of acquisition and use of energy by organisms

• Energy content of food expressed in Calories per gram (C/g)

Bioenergetics


• Catabolism of lipids yields 9.46 C/g

• Catabolism of proteins and carbohydrates yields ~4.7 C/g

Food and energy


• Total of all anabolic and catabolic processes underway

• Basal metabolic rate (BMR) is the rate of energy used by a person at rest

Metabolic rate


• Homeostatic regulation of body temperature

• Heat exchange with the environment involves four processes:

• Radiation

• Conduction

• Convection

• Evaporation

Thermoregulation


Figure 25.19 Routes of Heat Gain and Loss

Figure 25.19


• Preoptic area of hypothalamus acts as thermostat

• Heat-loss center

• Heat-gain center

• Mechanisms for increasing heat loss include:

• Peripheral vasodilation

• Increase perspiration

• Increase respiration

• Behavioral modifications

Regulation of heat gain and loss


• Decreased blood flow to the dermis

• Countercurrent heat exchange

• Shivering thermogenesis and nonshivering thermogenesis

• Differs by individuals due to acclimatization

Mechanisms promoting heat gain


Figure 25.20 Countercurrent Heat Exchange

Figure 25.20


• Problems in infants

• Lose heat quickly due to their small size

• Do not shiver

• Use brown fat to accelerate lipolysis - energy escapes as heat

• Variations in adults

• Use subcutaneous fat as an insulator

• Different hypothalamic thermostatic settings

Thermoregulation


• Fever is body temperature greater than 37.2oC

• Can result from a variety of situations including:

• Heat exhaustion or heat stroke

• Congestive heart failure

• Impaired sweat gland activity

• Resetting of the hypothalamic thermostat by circulating pyrogens

Pyrexia is elevated body temperature


• Why cells need to synthesis new organic components

• The basic steps in glycolysis, the TCA cycle, and the electron transport chain

• The energy yield of glycolysis and cellular respiration

• The pathways involved in lipid, protein and nucleic acid metabolismBMR

You should now be familiar with:


• The characteristics of the absorptive and postabsorptive metabolic states

• What constitutes a balanced diet and why such a diet is important

• Metabolic rate and the factors involved in determining an individual’s BMR

You should now be familiar with:

Chapter 7 metabolism and energy

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