Week 9: Informational Molecules; Carbohydrates, Protein and Nucleic acid

Proteins are the key working molecules and building blocks in all cells. They are produced in a similar two-step process in all organisms – DNA is first transcribed into RNA, then RNA is translated into protein.

Proteins are the major ‘working molecules’ within every organism. Among their many jobs, proteins catalyse reactions, transport oxygen and defend organisms from infection. They’re also crucial building blocks of organisms. They are the major components of wool, cartilage and milk, they package up the DNA in chromosomes and they insulate the cells of the nervous system. In short, proteins are hugely important. 

Important nucleic acids in nature include deoxyribonucleic acid, or DNA, and ribonucleic acid, or RNA. They are called acids because they are proton (i.e., hydrogen atom) donors, and therefore they carry a negative charge.

Chemically, DNA and RNA are polymers, meaning that they consist of repeating units, often a very large number of them. These units are called nucleotides. All nucleotides in turn include three distinct chemical portions: a pentose sugar, a phosphate group and a nitrogenous base.

DNA differs from RNA in three primary ways. One is that it the sugar that makes up the structural "backbone" of the nucleic acid molecule is deoxyribose, whereas in RNA it is ribose.The second difference is that while one of the four nitrogenous bases found in DNA is thymine, the corresponding base in RNA is uracil. The nitrogenous bases of nucleic acids are what dictate the ultimate characteristics of these molecules, because the phosphate and sugar portions do not vary within or between molecules of the same type.

Finally, DNA is double-stranded, meaning that it consists of two long chains of nucleotides chemically bound by two nitrogenous bases. The DNA is wound into a "double helix" shape, like a flexible ladder twisted in opposite directions at both ends.

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