Composition of Cells

Topics: DNA, Protein, Biochemistry Pages: 5 (1650 words) Published: March 1, 2012
Chemical Composition of Cells

Living organisms are complex creatures that are largely made up of di-hydrogen mono-oxide (H2O) which is the most abundant substance found in living tissue. Along with water molecules – macromolecules are the second largest group of substances found in tissue, and then there is a small amount ions and molecules. Macromolecules are comprised primarily of proteins, nucleic acids, carbohydrates, and lipids – which when has gone through a condensation reaction (it is the process by which water is removed from the formation of bonds) will form the macromolecules.

Proteins are made of C, H, O, N and S; and have many levels of structure. Their primary level of structure is the sequence of amino acids linked together in a peptide chain. There are only 20 amino acids, each with a hydrogen, an amino group (NH2 -), a carboxyl group (COO -), and an R group. This R group is known as a side chain and is composed of varying molecules. It is the only distinction between the 20 amino acids. The secondary level of structure in proteins is the bending of this peptide chain into either an alpha helix (coil) or a beta sheet (plaited sheet) as a result of hydrogen bonding. The tertiary structure is based on the folding of the secondary structure caused by interactions between amino acid side chains. These include ionic and covalent bonds, disulphide bonds, and hydrophobic interactions. A protein's quaternary structure is based on the interaction between many peptide chains.

Proteins are the most versatile macromolecules in living systems and serve crucial functions in essentially all biological processes. They function as catalysts, they transport and store other molecules such as oxygen, they provide mechanical support and immune protection, they generate movement, they transmit nerve impulses, and they control growth and differentiation. Indeed, much of this text will focus on understanding what proteins do and how they perform these functions.

Nucleic acids include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Each is composed of a nitrogenous base, a five-carbon sugar (a pentose), and a phosphate group. There are five nitrogenous bases: adenine, guanine, thymine, uracil, and cytosine. It is important to remember that cytosine will only bond with guanine and that adenine will only bond with thymine. Also, uracil is only found in RNA and thymine is only found in DNA. The pentose in RNA is ribose and deoxyribose in DNA. A phosphate group is linked to the sugar via a phosphodiester bond and the three nucleotides have become a nucleic acid. Nucleic acids allow organisms to transfer genetic information from one generation to the next. There are two types of nucleic acids: deoxyribonucleic acid, better known as DNA and ribonucleic acid, better known as RNA. When a cell divides, its DNA is copied and passed from one cell generation to the next generation. DNA contains the "programmatic instructions" for cellular activities. When organisms produce offspring, these instructions, in the form of DNA, are passed down. RNA is involved in the synthesis of proteins. "Information" is typically passed from DNA to RNA to the resulting proteins. Carbohydrates are made up of sugars and their polymers. Simple sugars (monosaccharides) are hydrocarbon chains of varying length that possess a hydroxyl (OH) group on each carbon. The most common monosaccharide is glucose, a valuable sugar for all living things. Monosaccharides bond together, via glycosidic linkage, to form polysaccharides, the polymers of carbohydrates.

Carbohydrates are essential for both energy storage and structure. Starch is the chief energy source for plants and glycogen is the main energy source for animals. Cellulose in plants and chitin in invertebrate animals help to provide structure and support. Lipids fall into three main categories: fats, steroids, and phospholipids. A fat is composed of a glycerol molecule (a short...
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