Biochemistry or biological chemistry is the branch of science dealing with the chemical compounds, reactions and other processes that occur in living organisms  It includes, but is not limited to, living matter. It is a branch of organic chemistry. Much of biochemistry deals with the structures, functions and interactions of cellular components such as proteins, carbohydrates, lipids, nucleic acids and other biomolecules.
- Main article: Carbohydrates
The carbohydrates or sugars are the most abundant biomolecules in nature, consisting mainly of carbon, hydrogen, and oxygen. Sorted by size, carbohydrates can be denominated monosaccharides, oligosaccharides or polysaccharides.
They comprise a class of large organic compounds, which are one of the main dietary requirements of organisms (often called carbs). Their function is to provide energy for the body, especially the brain and the nervous system. The liver breaks down carbohydrates into glucose (blood sugar), which is used to generate energy in a process called cellular respiration.
There are different types of carbohydrates, some of which are healthier than others. Sugars are found naturally in fruits, vegetables, milk, and milk products. Foods such as cakes and cookies have had sugars added. Starches are complex carbohydrates that are broken down in your into simple sugars. Starches are found in certain vegetables, such as potatoes, beans, peas, and corn. They are also found in breads, cereals, and grains. All of these sugars can be converted to glucose. In contrast, dietary fibers (cellulose) are carbohydrates that your body cannot digest. They pass through your body without being broken down into sugars. Even though your body does not get energy from fiber, you still need fiber to stay healthy.The fiber grain, fruit, and vegetables can reduce the body's absorption of fructose, even from fruit which is naturally high in the sugar. Fiber also helps get rid of excess fats in the intestine reducing the risk of heart disease, and helps push food through the intestines, which prevents constipation.
- Main article: Proteins
Proteins are molecular machines that perform the majority of the biochemical processes within cells. Proteins that speed up chemical reactions are called enzymes. They also serve as the building blocks for many structural components.
Proteins are assembled as part of a complex series of biochemical reactions known as gene expression. Genes are basically the instructions or blueprints that tell the cell how to make proteins. They are found on chromosomes, which are made of DNA. Genes are transcribed by RNA polymerases into messenger RNA (mRNA). Ribosomes then use the mRNA as instructions for linking amino acids together to form a long chain called a polypeptide. After further modification, the polypeptide becomes a protein.
Proteins are composed of twenty different types of amino acids. Amino acids have many structures, but the general formula is NH2-C-COOH. Each contains an amine group (NH2) and a carboxylic acid (COOH). The amino acid residues in a protein are linked together by peptide bonds.
Most proteins form globular structures, but others are chain-like. Proteins have two distinctive types of functions: structural and biological activity. However, some proteins serve both functions. Important structural proteins in animals include collagen, which is the component of the bones, muscles and skin, and keratin, which is the component of the hair, feather, and finger nail.
- Main article: Lipids
Lipids, otherwise known as fats, comprise one of the three groups of macronutrients (nutrients that the body needs in large quantities), along with proteins and carbohydrates. There are many different types of lipids, which generally fall under one of three categories: fats (typically triglycerides), phospholipids, and steroids. All lipids, however, share a few common characteristics. First, they all contain primarily carbon and hydrogen atoms. Also, they are hydrophobic (insoluble in water), but they do dissolve in alcohol and other nonpolar solvents. Nowadays, many people want to lose fat and try to do so by cutting fatty foods out of their diets. However, fat serves several vital roles in the body, and no one can survive without some fat. In addition, there are some fats called essential fatty acids that must be obtained from food because the body cannot manufacture them.
- Main article: Deoxyribonucleic acid
Deoxyribonucleic Acid (DNA) is the molecular substance used to encode heritable information in all living cells. DNA is made up of a chain of nucleotides, which contain a sugar, a phosphate group, and a nitrogenous base. Four bases are used: adenine, cytosine, guanine, and thymine. In eukaryotic cells, DNA is contained in a membrane-bounded region called the nucleus. It exists in long strands called chromosomes. The number and length of chromosomes differs among organisms. Prokaryotic cells have one circular chromosome, as well as smaller DNA pieces called "plasmids".
The information is divided into discrete units called genes, which when activated send out instructions specifying cellular machinery to assemble proteins. This process, called gene expression, is needed to build and maintain all biological systems. The instructions contained within genes consist of a code with rules of syntax comparable to those found in written language. In the DNA code, the gene is much like a sentence that contains "words" known as codons (triplets of nucleotides).
A typical human cell contains a total of 46 chromosomes and about 6 × 109 nucleotides. To understand the data compression involved in this form of information, the amount of DNA in cell could in theory be packed into a space about 1.9 cubic micron in size. By comparison, 6 x 109 letters in a book would occupy more than a million pages, thus requiring more than 1017 times as much space.
- Main article: Ribonucleic acid
Ribonucleic acid (RNA) is another nucleic acid that is similar to DNA. There are two important structural differences between DNA and RNA. The first is that the sugar is different. The second is that RNA uses the base uracil instead of thymine.
There are many forms of RNA, with different functions. Messenger RNA (mRNA) is a transcript of DNA that is read by ribosomes to synthesize proteins. Transfer RNA (tRNA) carries amino acids to ribosomes. Ribosomal RNA (rRNA) is a component of ribosomes.
- Smith, A. D.; Datta, S. P.; Smith, G. H.; Campbell, P. N.; Bentley, R.; McKenzie, H. A., ed. (2000). Oxford Dictionary of Biochemistry and Molecular Biology (revised ed.). Oxford: Oxford University Press. p. 70. ISBN 0-19-850673-2.
- Alberts, Bruce; Johnson, Alexander; Lewis, Julian; Raff, Martin; Roberts, Keith; Walter, Peter (2010) (in Portuguese). Biologia Molecular da Célula [Molecular Biology of the Cell] (5th ed.). Porto Alegre: Artmed. p. 55. ISBN 978-85-363-2066-3.
- Karp Gerald (2008). Cell and Molecular Biology:Concepts and Experiments (5th ed.). New Jersey: John Wiley & Sons. p. 42-47. ISBN 978-0-470-04217-5.
- Carbohydrates by Medline Plus
- Carbohydrates by the Office on Women's Health in the U.S. Department of Health and Human Services.
- Image Number K3839-3 by the U.S. Department of Agriculture
- The Human Body: Fearfully and Wonderfully Made! by Dr. Jay L. Wile and Marilyn M. Shannon, M.A. Apologia Educational Ministries, Inc. Indiana: 2001. pp. 47, 49, 381, 407, 454.
- Fats by Jeffrey Radecki and Susan Kim, faqs.org, Nutrition and Well-Being A to Z.
- Prokaryotic and Eukaryotic Cells. 9 September 2004. College of DuPage Center for Independent Learning.
- Molecular Biology of the Cell 3rd edition. 1994. by Bruce Alberts, et. al., Chapter 8 "The Cell Nucleus"
- Sally Robertson. What Are Ribozymes? News-Medical.