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With its clear and conversational writing style, comprehensive coverage, and sophisticated presentation, Marine Biology: Function, Biodiversity, Ecology, Fifth Edition, is regarded by many as the most authoritative marine biology text. Over the course of five editions, Jeffrey Levinton has balanced his organismal and ecological focus by including the latest developments on molecular biology, global climate change, and ocean processes.
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BONUS CHAP TER
Molecular Tools for Marine Biology Introduction and Definitions ■ Molecular techniques use DNA, RNA, and related
molecules to understand a wide range of biological processes.
DNA is the fundamental molecule that determines the structure of life, and in recent years DNA technology has become a necessity in understanding natural systems including the biology of individuals, marine biological species, communities, and ecosystems. It is the purpose of this chapter to introduce you to the basics required to understand much of the new revolution that is sweeping through marine biology through the use of molecular techniques (DNA-based or DNA-related). We will discuss how molecular data is collected (e.g., through DNA sequencing) and how related observations, such as the expression of genes, can be important in the understanding of biological processes and performance in marine systems. We will also show how DNA-based data can be used to assess biological diversity. Here are some important terms that come up in molecular studies. DNA is the carrier of genetic information from one generation to the next. DNA is usually packaged in chromosomes found in the cell nucleus, which replicate during ordinary mitosis, or cell division, or during meiosis, in which gametes are produced to form the next generation. DNA is a double-stranded molecule held together by weak hydrogen bonds. The backbone of DNA is a repeated pattern of a sugar group, deoxyribose, alternating with a phosphate group. Each strand has a sequence of nucleotides, which serve as the monomers, which, when assembled are Courtesy of Wikimedia Commons, user Lilly_M.
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the crucial determinants of genetic identity on the DNA strand. There are four nucleotides: adenine (A), guanine (G), cytosine (C), and thymine (T). Each strand of the double helix has a sequence of nucleotides, but binding between strands occurs only between A and T, or G and C. If you have a sequence of nucleotides on one of the two DNA strands, the nucleotide sequence on the other strand is therefore a sequence of the complementary nucleotides that can bind with those in the first strand. Eventually, each amino acid in a protein will be determined by three sequential nucleotides, or a triplet. A table relating the specific triplets to specific amino acids is the genetic code. This is an oversimplification, but a gene is a stretch of nucleotides that eventually codes for a protein—a string of amino acids—synthesized through a series of steps. The DNA sequence of the entire gene is the template for transcription to produce a complementary strand of RNA, which is the eventual template for the process of translation, in which the synthesis of protein produces a defined polypeptide sequence of amino acids. The strand of amino acids is then folded into a three-dimensional structure that is crucial in the protein’s function, for example, in catalyzing a cellular reaction, such as an enzyme. I repeat: this is an oversimplification. For example, many genes (strings of nucleotides) are interrupted by noncoding sequences, usually called introns. For proper transcription to occur, the sequencing part of the DNA, known as exons, have to be read and connected to construct the entire gene sequence that will be transcribed to produce the complete transcribed sequence of RNA. The process of RNA spli