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Chapter

Cover Biochemistry

Nitrogen Metabolism I: Synthesis  

This chapter talks about nitrogen, which is found in a vast array of biomolecules, such as amino acids and the nitrogenous bases which are used in the synthesis of proteins and the nucleic acids. Other essential nitrogen-containing biomolecules include the porphyrins, certain membrane lipids, and a diverse group of metabolically important biomolecules that are synthesized in smaller amounts. The chapter traces nitrogen from nitrogen fixation, the process that converts inert N2 to biologically useful ammonia through the synthesis of the major nitrogen-containing biomolecules. It describes the nitrogen cycle as the biogeochemical cycle in which nitrogen atoms flow through the biosphere. Several biochemical processes convert nitrogen from one form to another.

Chapter

Cover Biochemistry and Molecular Biology

Nitrogen metabolism: amino acid metabolism  

This chapter refers to amino acids which are supplied in the diet from protein hydrolysis in the gut. This includes proteins in the body that are constantly degraded and resynthesized. The chapter clarifies how the body can synthesize about ten of the amino acids. The rest must be obtained from the diet, but all 20 are needed for protein synthesis. Amino acids are also used to synthesize a wide variety of other molecules. The chapter discusses amino acids in excess of immediate requirements and shows that these are deaminated as the amino nitrogen is mainly converted into urea in mammals and excreted. The carbon-hydrogen skeletons are oxidized to release energy or converted into fat or glycogen according to the metabolic controls operating at the time and the particular amino acid.

Chapter

Cover Biochemistry

Amino Acids, Peptides, and Proteins  

This chapter discusses proteins as molecular tools. These perform an astonishing variety of functions. In addition to serving as structural materials in all living organisms, proteins are involved in diverse functions as catalysis, metabolic regulation, transport, and defence. Proteins are composed of one or more polypeptides, unbranched polymers of 20 different amino acids. The chapter looks at the genomes of organisms which specify the amino acid sequences of thousands or tens of thousands of proteins. It describes proteins as a diverse group of macromolecules that are directly related to the combinatorial possibilities of the 20 amino acid monomers. Amino acids can be theoretically linked to form protein molecules in any imaginable size or sequence.

Chapter

Cover Biochemistry

Lipids and Proteins: The Building Blocks of a Cell  

This chapter discusses lipids and proteins, which are two of the key components of cellular life in every environment. Lipids are essential components of cell membranes. They can be used to store energy, they are able to provide a waterproof coating to animals, and they are the basic building blocks of essential molecules that include hormones, vitamins, and pigments. They are classified in different ways and they include fatty acids, phospholipids, and triglycerides. Proteins are essential to all cells since almost all tasks that cells perform at some point involve proteins. The versatility of proteins is due to the great variety of shapes that they can adopt. Overall structures are dictated by their primary structure and the sequence of amino acids, but these take on different secondary structural conformations, patterns, and shapes. These come together to form three-dimensional conformations, or tertiary structures, that are unique to each protein.

Book

Cover Biochemistry
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.

Chapter

Cover Chemistry for the Biosciences

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.

Chapter

Cover Biochemistry and Molecular Biology

Food digestion, absorption, and distribution to the tissues  

This chapter looks at digestion, wherein the polysaccharides and proteins of food are hydrolysed into their monomer subunits or simple sugars and amino acids in order to be absorbed by the intestinal epithelial cells in the bloodstream. The chapter looks at triacylglycerols or fats (TAGs) which are hydrolysed into fatty acids and monoacylglycerol, the process which is aided by bile salts that emulsify the fats to give a large surface area for the enzyme lipase to attack. The storage of fat is primarily in the adipocytes or fat cells of adipose tissue, where it occurs in large amounts as TAG. The chapter describes insulin, which is released in response to high glucose levels and stimulates fat and glycogen storage. Glucagon, released from the pancreas when blood glucose is low, stimulates release of glucose from the liver and of fatty acids from fat cells.

Chapter

Cover Biochemistry and Molecular Biology

Protein synthesis and controlled protein breakdown  

This chapter defines protein synthesis as the joining together of amino acids in the correct sequence to form a polypeptide chain. This involves three phases: initiation, chain elongation, and termination. The chapter analyzes messenger RNA (mRNA) and shows that it encodes the amino acid sequence of the protein in the form of triplets of bases known as codons. Of the 64 codons, AUG is the initiator or start codon, encoding methionine, and three codons are stop codons and the genetic code is degenerate as most amino acids are encoded by more than one codon. The chapter outlines the sequence of codons in an mRNA molecule. This is translated by cytosolic ribosomes. Ribosomes have a large and a small subunit, each containing RNA and many proteins.

Chapter

Cover Biochemistry and Molecular Biology

The structure of proteins  

This chapter focuses on proteins, which are made up of one or more polypeptide chains constructed from 20 species of amino acids. The length and sequence of each polypeptide is specified by its gene. The chapter describes 20 different amino acids which are of differing sizes and degrees of hydrophobicity, hydrophilicity, and electrical charge. These present the possibility of a vast variety of different proteins. The primary structure is the linear amino acid sequence, while the secondary structure involves folding of the polypeptide backbone. The chapter explains that the main secondary structure motifs are the α helix and the β-pleated sheet, which are stabilized by hydrogen bonding. The tertiary structure involves the further folding of the secondary structure motifs into the three-dimensional form of the protein.

Chapter

Cover Biochemistry and Molecular Biology

General principles of nutrition  

This chapter shows that nutrition is the science of food and the substances contained in it. The chapter notes that the main components of diet are macronutrients, which provide the bulk of the diet, and micronutrients, which include essential vitamins and minerals. The chapter explains that protein is needed to supply essential amino acids and fat is needed to supply essential fatty acids and provide sufficient energy in the diet. Most diets provide 10-15% of the energy in the form of protein and the remainder is made up of carbohydrate and fat. The chapter talks about the consumption of saturated fat, which is one of the risk factors for cardiovascular disease and some cancers, whereas consumption of polyunsaturated fat is considered healthy. A high consumption of sucrose can lead to dental caries.

Chapter

Cover Chemistry for the Biosciences

Functional groups: adding function to the framework of life  

This chapter discusses functional groups, which enhance the physical and chemical properties of organic compounds. Members of the same family of organic compound possess the same functional groups, and exhibit similar physical and chemical properties. Functional groups may increase the water solubility of the molecules to which they are attached and the extent of molecular interactions they experience. The chapter notes how alkyl groups above a certain size override the effect of an attached functional group, causing a relative decrease in solubility and melting and boiling points. The chapter then looks at organic compounds with oxygen-based functional groups, including the hydroxyl group, alkoxy group, carbonyl group, carboxyl group, and ester group. It also considers organic compounds with nitrogen-based functional groups, including the amino group and the amide group. Finally, the chapter studies the sulfur-based functional group known as the thiol group.