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Chapter

Cover Essentials of Human Nutrition

Energy  

Andrew M. Prentice

This chapter focuses on energy, which is the primary currency of nutrition. In humans, dietary energy is derived from four major food types—carbohydrate, fat, protein, and alcohol. These are termed macronutrients and each can be composed of numerous subtypes that have slightly different energy contents. Generation of energy from the various macronutrients requires different chemical processes, and for each there are optional pathways that can be used in different metabolic circumstances. The chapter then outlines the energy value of foods and how they may be calculated, and summarizes human energy needs and how these can be measured. It also looks at the mechanisms by which energy balance is regulated.

Chapter

Cover Essentials of Human Nutrition

Protein-Energy Malnutrition  

A. Stewart Truswell

This chapter focuses on malnutrition. People, young or old, who eat less food than they usually eat and need, lose body weight. The deficit of energy (or calories) in the diet is made up by drawing on the body's energy reserves: first fat, later muscle. Undernutrition can be mild or severe, beneficial (in someone who was obese) or dangerous. The loss of weight is a manifestation of energy depletion. Essential nutrients, protein, and micronutrients are likely to be depleted at the same time, but some micronutrients have large stores in the body, and requirements of some others are lower when energy intake is reduced. In children, who have higher protein requirements than adults, important depletion of protein is likely to accompany serious undernutrition. The chapter then looks at protein-energy malnutrition and famine.

Chapter

Cover Physical Chemistry

Fundamentals  

This chapter focuses on the units which are fundamental to the understanding and application of physical chemistry. It describes the Système International d'Unités (SI) system of units. This has been in use since 1970 and consists of seven base units, of which six are commonly used in chemistry. These measure mass, length, time, electrical current, temperature, and amount of substance. There is a seventh unit, namely luminous intensity, but this is only rarely relevant in chemistry. The chapter includes activities that determine the derived units for kinetic energy. These activities show that the unit for potential energy is equivalent to that of kinetic energy.

Chapter

Cover Elements of Physical Chemistry

The origin of thermodynamic properties  

This chapter shows how the molecular partition function is used to calculate and give insight into important thermodynamic functions: internal energy, heat capacity, entropy, and Gibbs energy. It talks about the final step into the calculations of chemically significant expressions when the Gibbs energy is available that shows how equilibrium constants can be calculated from structural and spectroscopic data. It also provides a molecular interpretation of thermodynamic properties that acts as a bridge between spectroscopy and thermodynamics. The chapter reviews how a partition function is used to calculate and interpret thermodynamic properties of systems as small as atoms and as large as biopolymers. It highlights the equilibrium constant, which is related to the distribution of molecules over the available states of a system composed of reactants and products.

Chapter

Cover Biochemistry

Carbohydrates  

This chapter discusses carbohydrates, which are an important source of rapid energy production for living cells,the structural building blocks of cells, and the components of numerous metabolic pathways. The chapter refers to sugar polymers linked to proteins and lipids which, it states, are now recognized as a high-density coding system. Their vast structural diversity is exploited by living organisms to produce the immense informational capacity required for living processes. The chapter describes the structures and chemistry of typical carbohydrate molecules found in living organisms. Carbohydrates are the most abundant biomolecules in nature and are a direct link between solar energy and the chemical bond energy of living organisms.

Chapter

Cover Statistical Thermodynamics

Applications of the molecular partition function  

This chapter explores how to use the molecular partition function to calculate internal energy and entropy. It highlights the link between the molecular partition function and thermodynamics. Additionally, the chapter notes the relation of β to temperature. It explains the link between the statistical weight of the predominant configuration and thermodynamic entropy. The chapter uses equation diagrams to explain modifications on molecular and internal energies. As the chapter shows, the spacing between successive energy states does not change on heating and stays at a constant volume, which is a defining condition for the internal energy. Thus, an infinitesimal reversible change in a system linked to an infinitesimal flow of heat produces a change in entropy.

Chapter

Cover Foundations of Chemical Biology

Metabolism and the biochemistry of glucose  

This chapter describes the nature of chemical energy within cells and looks at how this energy is harnessed from enzyme-catalysed reactions. It deals with the relation of cellular energy to the ability to facilitate dehydration chemistry in aqueous solution and the primary source of dehydrating power in cells. It also analyses the establishment of the nature of biochemical energy and explains how the biochemistry of glucose is used as an example of the manipulation of chemicals in cells. The chapter mentions mechanical, electrical, and chemical energies, which are the forms of energy cells use. It also discusses constructed polymers, which are characteristic of life. The polymers common to all living systems correspond to the joining of monomer units with concomitant loss of water.

Chapter

Cover Food and Sustainability

Energy  

Paul Behrens

This chapter focuses on the energy system, to investigate the ways in which energy is currently used in the food system and how this use may develop in the future. It outlines the physical nature of energy and power and describes the different sources of energy. The discussion highlights that food production uses around 15–20% of the total energy produced for human needs. The discussion covers two critical issues in energy use: the improved availability of energy in poorer countries and the implementation of low-carbon technologies in all countries. Furthermore, it explains the zero-carbon energy system. The chapter also explores how food systems can be decarbonized. Finally, it looks at the role agricultural systems could play in the energy transition itself.

Chapter

Cover Computational Chemistry

Molecular Mechanics Methods  

This chapter evaluates molecular mechanics methods. In this approach, a known chemical bonding pattern is assumed and used to define preferred bond lengths and angles, and thereby an energy expression that takes into account distortions away from these ideal values. For a given bonding environment, the type of energy terms needed, and the numerical parameters within the energy expression, are transferable from one system to another. Hence, general forcefields can be constructed with quite general applicability. The chapter describes how the energy terms and parameters are chosen, based on input from experiment and quantum chemistry. Molecular mechanics can be applied to large systems due to its efficiency, allowing calculations on liquids, solutions, and solids. This frequently makes use of periodically repeating models and the chapter looks at special measures needed to treat such models. Finally, it discusses the type of software used for molecular mechanics.

Chapter

Cover Chemistry for the Biosciences

Energy: what makes reactions go?  

This chapter explores the nature of energy, looking at how energy transfer drives the biochemical processes on which organisms depend for life. Energy is the capacity something has to do work, and is transferred between a system and its surroundings in the form of work and heat. The chapter introduces the concepts of enthalpy and entropy, and explains how the energy change associated with a chemical reaction is called the enthalpy change of reaction. Meanwhile, entropy is a measure of the energetic disorder of a system. The chapter also considers spontaneous reactions and what determines their spontaneity, and introduces the concept of Gibbs free energy.

Chapter

Cover Statistical Thermodynamics

Thermodynamic functions: towards a statistical toolkit  

This chapter explores thermodynamic functions as a statistical toolkit. It refers to state functions as major thermodynamic variables. The two thermodynamic functions most usually chosen as the basis for variables are the energy E—leading to the internal energy U—and entropy S. The chapter highlights that the Massieu bridge will form the basis of all of the other thermodynamic functions needed. It notes that the pressure is related to the Helmholtz free energy through the first derivative in relation to volume at a constant temperature. The chapter considers the relation between internal energy, heat capacity, entropy, enthalpy, and Gibbs free energy, which is linked with Helmholtz free energy. The chapter shares the full set of toolkit equations which can be used in the field of thermodynamics.

Chapter

Cover Essentials of Inorganic Chemistry 1

Gibbs energy  

This chapter addresses Gibbs energy, which is sometimes referred to as free energy, or as Gibbs free energy. Changes in Gibbs energy are more useful in chemistry because they determine whether reactions are energetically favourable. The second law of thermodynamics states that, in a spontaneous process, the change in entropy is equal to or greater than zero for the system and its surroundings. In the discussion of entropy, it was noted that it is important to distinguish in a chemical reaction that energy which is tied up in chemical bonds and that which is distributed amongst the translational, rotational, and vibrational degrees of freedom. For a spontaneous chemical process which leads to an enthalpy change, the corresponding change in the enthalpy of the surroundings is –∆H.

Chapter

Cover Atkins’ Physical Chemistry

Concentrating on the system  

This chapter highlights the Helmholtz and Gibbs energies to develop the Clausius inequality. The Clausius inequality implies a number of criteria for spontaneous change under a variety of conditions which may be expressed in terms of the properties of the system alone. A spontaneous process at constant temperature and volume is accompanied by a decrease in the Helmholtz energy. The change in the Helmholtz energy is equal to the maximum work obtainable from a system at constant temperature. Meanwhile, a spontaneous process at constant temperature and pressure is accompanied by a decrease in the Gibbs energy. The change in the Gibbs energy is equal to the maximum non-expansion work obtainable from a system at constant temperature and pressure. The chapter then looks at the standard Gibbs energies of formation and the Born equation.

Chapter

Cover Computational Chemistry

Molecular mechanics  

This chapter examines molecular mechanics. By bringing together features from both the Central Force Field and Valence Force Field methods, it proved possible to derive energy functions which were at once chemically intuitive while still retaining the concept of through space attractions and repulsions. The theoretical basis of the molecular mechanics method can be derived by taking an alternative approach to the Born–Oppenheimer approximation to that considered in molecular orbital methods. The chapter then looks at energy calculation, energy minimization, force field parameterization, and conformational analysis. Force field methods are finding increasing application in many areas of structural chemistry. Minimization of structures is usually required to remove strain from poorly defined geometries. Meanwhile, conformational search procedures often utilize molecular mechanics calculations, but one must be careful that the methods used do not introduce bias into the calculation.

Chapter

Cover Ecology

Production  

This chapter explores how energy enters ecosystems, how it is measured, and what controls rates of energy flow through ecosystems. The generation of chemical energy by autotrophs, known as primary production, is derived from the uptake of carbon during photosynthesis and chemosynthesis. Carbon not used in respiration is available for growth and reproduction, storage, and defence against herbivory. The carbon available for these functions is determined by the balance between gross primary production (GPP) and autotrophic respiration, and is called net primary production (NPP). The chapter then looks at the environmental controls on and global patterns of NPP. Energy that is derived from the consumption of organic compounds produced by other organisms is known as secondary production. Organisms that obtain their energy in this manner are known as heterotrophs.

Chapter

Cover Human Physiology

Nutrition and the regulation of food intake  

This chapter talks about diet, which is the selection of foods eaten by an individual. It explains what a nutrient is, which is any substance that is absorbed into the bloodstream from the diet and utilized to promote the various functions of the body. Nutrients include carbohydrates, proteins, fats, vitamins, mineral salts, and water. These are essential to health and a balanced diet contains appropriate amounts of each nutrient. The chapter notes a key function of diet, which is to provide the source of energy for cell metabolism. The chapter finally looks at the nutritional requirements of the body as a whole.

Chapter

Cover Human Physiology

Energy balance and the control of metabolic rate  

This chapter looks at energy balance and metabolic rate and the various factors that influence them. The scale of the chemical reactions of the body can be gauged by considering the fact that an average human being uses about 360 litres of oxygen each day to burn several hundred grams of carbohydrates and fats and generate about 7500 kJ of heat. The chapter details the chemical processes of the body which are responsible for generating the heat which make up the metabolism of the body. This may be divided into two categories: anabolic and catabolic. The chapter then discusses anabolic metabolism, which involves the synthesis of complex molecules from simpler ones. Catabolic metabolism involves the breaking down of large, complex molecules to smaller, simpler ones.

Chapter

Cover Physical Chemistry for the Life Sciences

Water in transition  

This chapter examines water in transition. It explains that water (like any other substance) tends to make a transition to the phase with lowest molar Gibbs energy. As the chapter reveals, the freezing, melting, evaporating, and condensing of water are phase changes that have a profound effect on the environments in which life is found. The thermodynamic analysis of these phase changes opens up a route to understanding many other properties and some of the roles of water in cells. To that end, the chapter begins by examining the variation of Gibbs energy with pressure. Afterward, the variation of Gibbs energy with temperature is discussed.

Chapter

Cover Statistical Thermodynamics

The Boltzmann law  

This chapter looks at the Boltzmann law with respect to the concept of classical thermodynamics. It stresses that thermodynamics is based on three laws of experience. The chapter discusses the Boltzmann factor wherein the unit, energy per unit of temperature, is needed to make the exponent dimensionless. It explores the average basis of matter behaviour. Additionally, certain aspects of the laws of probability are used to establish assumptions and understand the Boltzmann law. The chapter briefly discusses these aspects, including distinct and independent particles, configurations of sharing energy, statistical weights, equal probability of configurations, conservation of number and energy, and maximization subject to constraints.

Chapter

Cover Physical Chemistry for the Life Sciences

Internal energy and enthalpy  

This chapter discusses internal energy and enthalpy. The ‘internal energy’ is a property that keeps track of energy transactions and is central to the formulation of the First Law of thermodynamics. The property known as the ‘enthalpy’ plays a special role when processes occur at constant pressure, as in many biological systems. As this chapter shows, the most fundamental way to monitor the energy involved in a biological process is in terms of the internal energy. The internal energy of an isolated system is constant; the heat released by a system at constant pressure is equal to the enthalpy change of the system. This is because the enthalpy is a state function; a change in enthalpy between two states of a system is independent of the path between them.