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An Introduction to Molecular Biotechnology. Группа авторовЧитать онлайн книгу.

An Introduction to Molecular Biotechnology - Группа авторов


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Elements of biomembranes Deoxynucleotide DNA Storage, replication, and safe transfer of genetic information; recombination Nucleotide RNA rRNA: structural molecules for the construction of ribosomes ribozymes and siRNA: catalytic and regulatory processes tRNA: mediators in translation mRNA: messengers and mediators between genes and proteins snRNA: splicing of mRNA snoRNA: chemically modify rRNA siRNA: can influence gene expression by directing degradation of selective mRNAs and the establishment of compact chromatin structures miRNA: can control gene activity,development, and differentiation by specifically blocking translation of particular mRNA piRNA: bind to piwi proteins and protect germline from transposable elements lncRNA: apparently play a role in regulating gene transcription

      Inorganic ions, sugars, amino acids, fatty acids, organic acids, nucleotides, and various metabolites are counted among the low‐molecular‐weight components and building blocks of the cell. The qualitative composition of cells is similar in prokaryotes and eukaryotes (Table 1.1), even though eukaryote cells generally have a higher protein content and bacterial cells a higher RNA content. Animal cells have a volume that is 103 times larger than that of bacterial cells.

      Owing to their shared evolution, the structure and function of the important cellular molecules is very similar in all organisms, often even identical. Apparently, reliable and functional biomolecules were developed and, if useful for the producer, were selected early in evolution (Table 2.2) and are therefore still used today.

Image described by caption.

      Many important nitrogen‐containing derivatives of these monosaccharides (Figure 2.1c) use galactose and glucose as a base. Examples include glucosamine, N‐acetylglucosamine, and glucuronic acid. These derivatives can be present either as glycosides or as part of a polysaccharide.

      Condensation reactions between sugar molecules result in the formation of glycosidic bonds with the elimination of a water molecule. As hydroxyl groups can be present in either the α or β position, the stereochemistry of sugar molecules is of great importance. The condensation of two sugar molecules results in the formation of a disaccharide (Figure 2.1d); that of three sugar molecules, correspondingly, is a trisaccharide. Oligosaccharides are built from a few sugar monomers, and polysaccharides (e.g. starch, glycogen, cellulose, chitin, etc.) are made up of many sugar monomers.

      Sugar molecules can be easily activated through esterification with an acid, one important example being esterification with phosphoric acid. Sugar phosphates are important in glycolysis.

      The most important polysaccharide in animal cells is glycogen, which is stored as an energy source in liver and muscle. Glycogen can be quickly converted into glucose‐1‐phosphate and then channeled into glycolysis. Glycogen is a branched polysaccharide formed from glucose molecules linked by α‐(1→4)‐glycosidic bonds or α‐(1→6)‐glycosidic bonds (Figure 2.1d). This results in many free ends on which the enzyme glycogen phosphorylase can begin degradation simultaneously.

      Starch or amylose (Figure 2.1d) consists of glucose residues linked by α‐(1→4)‐glycosidic bonds. In amylopectin, additional glucose residues linked by α‐(1→6)‐glycosidic bonds are built in. Amylopectin, therefore, has a similar structure to glycogen but is less strongly branched. Starch is formed by photosynthesis in plant cells, where it is stored in amyloplasts. Starch can be broken down easily by animals and is therefore an important part of human nutrition.

      Further important polysaccharides are found in animals. Hyaluronic acid is made up of many disaccharide building blocks, which themselves consist of glucuronic acid and N‐acetylglucosamine. Hyaluronic acid has a very high viscosity and is therefore found in synovial fluid in the joints and in the vitreous humor in the eye. Furthermore, polysaccharides made from disaccharides consisting of sulfated glucuronic acid and N‐acetylglucosamine or N‐acetylgalactosamine units, respectively, are found in the connective tissues. Examples include chondroitin‐4‐sulfate, chondroitin‐6‐sulfate,


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