Cellular genetic information process

In the nuclei of all eukaryotic cells, DNA is tightly wrapped around an octamer of histone proteins and is compacted into a dense structure known as chromatin. In order to access the genetic information which is required in numerous essential cellular processes including DNA replication, gene expression and DNA repair, chromatin needs to be partially unwound. One important mechanism to regulate chromatin structure and thus to control the access of the genomic DNA is through histone modifications [1-6]. The histone octamer is composed of two copies of H2A, H2B, H3 and H4 core histone proteins. Their tails, that protrude out of the surface of the... 

DNA stores the genetic information for a cell, but it is RNA that participates in the processes by which this information is used. RNA molecules are classihed according to their function or cellular location. Three major forms are found in prokaryotic cells ... 

Proteins are the most abundant of cellular components. They include enzymes, antibodies, hormones, transport molecules, and even components for the cytoskeleton of the cell itself. Proteins are also informational macromolecules, the ultimate heirs of the genetic information encoded in the sequence of nucleotide bases within the chromosomes. Structurally and functionally, they are the most diverse and dynamic of molecules and play key roles in nearly every biological process. Proteins are complex macromolecules with exquisite specificity each is a specialized player in the orchestrated activity of the cell. Together they tear down... 

In prokaryotes DNA, RNA, and protein synthesis all take place in the same cellular compartment. In eukaryotes the DNA is compartmentalized in the cell nucleus, and it became clear long before the biochemistry of these three processes was understood that DNA synthesis takes place in the nucleus, whereas the bulk of protein synthesis takes place in the cytoplasm. From these observations on eukaryotes it was self-evident that DNA cannot be directly involved in the synthesis of protein but must somehow transmit its genetic information for protein synthesis to the cytoplasm. Careful experiments with radioactive labels were used to demonstrate that RNA synthesis takes place in the nucleus much of this RNA is degraded rather quickly, but the portion that survives is mostly transferred to the cytoplasm (fig. 28.1). From observations of this kind it became clear that RNA was the prime candidate for the carrier of genetic information for the synthesis of proteins. 

Translation is the process by which an mRNA is read by tRNAs, ribosomes (complex structures consisting of rRNAs and ribosomal proteins), and numerous other enzymes. Each type of cell is programmed to synthesize only those proteins necessary for its particular cellular functions (Chapter 26). The difference between a neuron and a liver cell is the kind of proteins that are synthesized even though both cells contain exactly the same genetic information. Cellular differentiation is due to differential gene expression a tumor cell invariably is a cell that has lost the ability to regulate and express its genetic information... 

The mechanism by which genetic information is decoded and used to direct cellular processes begins with the synthesis of another type of nucleic acid, ribonucleic acid (RNA). RNA synthesis occurs by complementary pairing of ribonucleotide bases with the bases in a DNA molecule. 

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