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.
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Carbohydrates
Chapter
Carbohydrate Metabolism
This chapter reviews the crucial roles carbohydrates play in the metabolic processes of living organisms as they serve as energy sources and structural elements in living cells. It looks at the role of carbohydrates in energy production, focusing on its synthesis, degradation, and storage as the monosaccharide glucose is a prominent energy source in almost all living cells. The term metabolism is used to describe the thousands of enzyme-catalysed biochemical reactions that sustain life in living organisms. The chapter analyses how biochemical reactions are spatially and temporally organised into complex, interconnected networks. It classifies all biochemical reaction pathways into three major categories: signal transduction pathways, genetic regulatory pathways, and core metabolic pathways.
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Carbohydrates and Carbohydrate Metabolism
Alex White and Helen Burrell
This chapter focuses on carbohydrates, which are molecules composed almost exclusively of carbon, hydrogen, and oxygen. Carbohydrate monomers are called monosaccharides and are found throughout nature. The chapter explains how carbohydrates are synthesized in plants during the process of photosynthesis, with their carbon atoms being obtained from atmospheric carbon dioxide. The chapter considers carbohydrates as the main fuel source in human bodies and they are divided into two groups: simple sugars and complex carbohydrates. Simple sugars like glucose are metabolized directly via glycolysis and the citric acid cycle, whereas complex carbohydrates like starch and glycogen are first broken down into simple sugars.
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Open chain and ring structure of monosaccharides
This chapter analyzes the empirical formula CH2O, which is the formula of a carbohydrate. This molecule has an oxygen atom attached to each carbon. The chapter states that aldose is the most common type of structure which consists of a linear carbon chain with an aldehyde CHO group at C-1. A varying number of carbon atoms are secondary alcohols CHOH, and there is a primary alcohol at the other end of the chain. The chapter also mentions glyceraldehyde as an example of aldose consisting of several carbons. The chapter explains the Fischer convention which is commonly used for structures that have several stereogenic centres. It highlights the carbon atoms of aldoses that are numbered so that the aldehyde terminus is labelled as C-1.
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Carbohydrate recognition in cell adhesion and signalling
This chapter describes carbohydrate recognition in cell adhesion and signalling. Some lectins that serve as receptors for specific glycans recognize foreign cell surfaces and mediate or modulate immune responses to pathogens while others bind to endogenous carbohydrates and mediate adhesion or signalling events at the cell surface. Indeed, cell adhesion and signalling are mediated by structurally diverse lectins that recognize diverse glycans. One common feature of these systems is that they often involve transient interactions between cells that are moving relative to each other. Mice lacking individual lectins of the types discussed in the chapter are viable, but suffer from developmental or immunological abnormalities. The phenotypes of these mice demonstrate the importance of lectin recognition events in the precise orchestration of cell–cell interactions in mammals.
Book
Trudy McKee and James R. McKee
Biochemistry begins with an introduction to the topic. Discussions covered include living cells, the importance of water to life, energy, and amino acids, peptides, and proteins. The book also contains chapters on carbohydrates, carbohydrate metabolism, aerobic metabolism, and lipids and membranes. The text goes on to examine photosynthesis, nitrogen metabolism, nucleic acids, and genes. Finally, it looks at protein synthesis.
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Biological molecules
This chapter reviews how molecules are built up by linking atoms together with covalent bonds and explores the way in which molecules interact with one another non-covalently in the aqueous environment of the cell. There are four major classes of biological molecules that play essential roles in all organisms: nucleotides, amino acids, carbohydrates, and lipids. Each of them can be found in cells both as individual small molecules or covalently linked to form larger molecules known as polymers or macromolecules. Nucleic acids are polymers of nucleotides that are responsible for carrying genetic information. Proteins, on the other hand, are polymers of amino acids that function as workhorses, carrying out most of the chemical reactions in the cell and giving cells their structure and shape. Many biological molecules can be covalently modified in ways that alter their chemical properties and allow their function to be regulated.
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Carbohydrates
Andrew Reynolds and Jim Mann
This chapter discusses carbohydrates, which are the most important source of food energy in the world. The major sources of dietary carbohydrate worldwide are cereal grains (primarily rice, wheat, and maize), with refined sugar, root crops (potatoes, cassava, yams, sweet potatoes, and taro), pulses, vegetables, fruit, and milk products contributing less to overall energy intake. Carbohydrate-containing foods, with the exception of sugar, contribute important amounts of protein, vitamins, minerals, phytochemicals, sterols, and antioxidants to diet. The chapter then looks at the measurement of dietary carbohydrates; the digestion and absorption of carbohydrates; and carbohydrate metabolism. It also considers the relationship between carbohydrates and postprandial glycaemia, gut disorders, and non-communicable disease. Finally, the chapter examines energy values and recommended intakes of carbohydrates.
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Molecules
This chapter discusses molecules, starting with an explanation of bonds. Living organisms are made of up of organic molecules consisting mainly, though not exclusively, of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S). These are held together by bonds which vary in strength and length. The chapter then looks at covalent bonds, ionic or electrostatic bonds, dipole–dipole interactions, hydrogen bonds, van der Waals forces, and the hydrophobic effect. It also considers proteins, lipids, and carbohydrates, before looking at DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). DNA is the genetic material of most living organisms and it exists as a very long filamentous double helix. Meanwhile, RNA s a single-stranded polymer of ribonucleotides linked by phosphodiester bonds.
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Food and nutrient structure
Yannan Jin and Louise Dunford
This chapter details the main structure of the macronutrients within foods. Due to the development of the understanding of food composition, classifying food components into macronutrients and micronutrients and understanding the features of carbohydrates, fats, and proteins became more convenient. The chapter then elaborates on the chemical structures, properties, and functions of a wide range of food components, which include macronutrients, phytoprotectants, and toxic substances. It also considers the effects of processing and storage on these components. Ultimately, food processing operations applied to foods aim to either improve their palatability or to extend their shelf-life, especially by the destruction of microorganisms.
Book
Richard Bowater, Laura Bowater, and Tom Husband
Biochemistry introduces this topic with an examination of carbohydrates, asking why we need them in our lives. It then looks at the building blocks of a cell, namely, lipids and proteins. Nucleotides and nucleic acids are the next topic to be covered. The text moves on to consider metabolism. It asks what it means and how energy is transformed. Other questions asked include: how is a metabolic balance maintained? How can we solve the problems of the future with natural products? Finally, the text looks at bioenergy and the environment.
Chapter
Carbohydrates: Why Life is Sweet
This chapter describes the chemistry that underpins biomolecules, before considering the variety and flexibility of carbohydrates and their roles in living organisms. All biological cells are made up of common building blocks, or biomolecules, which carry out similar types of biochemical reactions. There are four types of these fundamental biomolecules: carbohydrates, proteins, lipids, and nucleic acids. Carbohydrates are the most abundant biomolecules on Earth and are characterized by great chemical and structural diversity. They are classified by size as monosaccharides, disaccharides, oligosaccharides, or polysaccharides. Carbohydrates are found in plant cell walls, the connective tissues of animals, and exoskeletons, and they are essential to the function of some proteins and cell-to-cell communication. They are also important fuels and energy stores, underpinning energy-yielding pathways in non-photosynthetic organisms.
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Other Drug Targets
This chapter focuses on other biomolecules which act as drug targets such as lipids, carbohydrates, and proteins other than those dealt with in the previous chapters. The majority of drugs which target lipids do so by interfering with the lipid structure of cell membranes, either human or bacterial. They do so in a variety of ways, although all disrupt the cell membrane in some respect. Meanwhile, in addition to antibacterial and antiviral activity, drugs which target these carbohydrate molecules may also be of use in cancer and autoimmune diseases, which often show changes in cell surface recognition carbohydrates. The chapter then considers non-enzymatic proteins as drug targets.
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Chemistry of Biomolecules
This chapter addresses some of the major constituents of our body: carbohydrates, nucleic acids, proteins, and lipids, and related compounds. It emphasizes that although structures of many biomolecules may be complicated, their chemistry is not especially difficult. The chapter notes that their reactions are governed by the principles of the chemistry of simple organic compounds. The chapter also introduces the kinds of compounds which play major roles in living systems, and identifies the molecular features which allow them to function in their biological roles. Finally, the chapter looks at fats and oils, and phospholipids. It then considers the nature of terpenes, steroids, and eicosanoids.
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Plants in Human Nutrition, Diet, and Health
Maarten J. Chrispeels
This chapter looks at food not from a production standpoint, but from the point of view of human nutrition. It describes nutritional biochemistry in terms of some familiar molecules: carbohydrates, fats, proteins, and vitamins. In addition to being the ultimate source of all our food, plants also contain non-nutritive molecules that affect other organisms by defending the plants against herbivory or attracting pollinators. The chapter then considers the consequences of nutritional deficiencies, before exploring organically grown plants. Although humans are omnivores, millions of vegetarians and vegans attest to the fact that animal foods are not essential to our health. The chapter also studies how the intestinal microbiome significantly influences human health.
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Biological macromolecules: the infrastructure of life
This chapter studies some of the key biological macromolecules that make life happen: amino acids and proteins, nucleic acids, carbohydrates, and lipids. Amino acids join together to form polymers named polypeptides. The structure of proteins is built up over four levels of hierarchy: primary, secondary, tertiary, and quaternary. Protein structure is stabilized by both non-covalent interactions (including hydrogen bonds and hydrophobic interactions) and covalent bonding, including disulfide bonds. The chapter also describes the two key natural nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). Nucleic acids are polymers of nucleotides. The chapter then considers the three main classes of carbohydrate (sugar)—monosaccharides, disaccharides, and polysaccharides. It also looks at the three most important types of lipid: steroids, triacylglycerols, and the glycerophospholipids.
