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  Section: General Biochemistry » Nucleic Acid Synthesis
 
 
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Repetitive Sequences: Selfish DNA

 
     
 
Content of Nucleic Acid Synthesis
» Nucleic Acids
» Structure and Function of Nucleic Acids
    » Basic Chemical Structure
    » Base Pairing in Nucleic Acids: Double Helical Structure of Dna
    » Size, Structure, Organization, and Complexity of Genomes
    » Information Storage, Processing, and Transfer
    » Chromosomal Dna Compaction and Its Implications in Replication and Transcription
    » DNA Sequence and Chromosome Organization
    » Repetitive Sequences: Selfish DNA
    » Chromatin Remodeling and Histone Acetylation
» Nucleic Acid Syntheses
    » Similarity of DNA and RNA Synthesis
    » DNA Replication Vs Transcription: Enzymatic Processes
    » Multiplicity of DNA and RNA Polymerases
» DNA Replication and Its Regulation
    » DNA Replication
    » Regulation of DNA Replication
    » Regulation of Bacterial DNA Replication at the Level of Initiation
    » DNA Chain Elongation and Termination in Prokaryotes
    » General Features of Eukaryotic DNA Replication
    » Licensing of Eukaryotic Genome Replication
    » Fidelity of DNA Replication
    » Replication of Telomeres—The End Game
    » Telomere Shortening: Linkage Between Telomere Length and Limited Life Span
» Maintenance of Genome Integrity
» DNA Manipulations and their Applications
» Transcriptional Processes
    » Recognition of Prokaryotic Promoters and Role of S-Factors
    » Regulation of Transcription in Bacteria
    » Eukaryotic Transcription
    » RNA Splicing in Metazoans
    » Regulation of Transcription in Eukaryotes
    » Fidelity of Transcription (RNA Editing)
» Chemical Synthesis of Nucleic Acids (Oligonucleotides)
» Bibliography of Nucleic Acid Synthesis
Even before the precise genome sequences are elucidated, one unique feature of the metazoan DNA sequence has been established from a number of studies. A large fraction (perhaps up to 90% or more) of the total genomic sequence in metazoan cells do not encode any information. Some of these sequences are present as noncoding intervening regions in genes, named “introns,” which do not code for proteins. However, the intron sequences are transcribed but are removed during processing (“splicing”) to generate mature mRNA, as discussed later. Many of the other genomic sequences are not even transcribed, and these may often be present as multimeric repeats of shorter units. These repetitive sequences have no known function in the cell, yet are maintained and replicated as an integrated part of the genome; such DNA is referred to as “selfish DNA.”

Metaphase chromosomes are organized in substructures distinguished by their staining with dyes. Euchromatin regions contain transcribed sequences, while heterochromatin regions contain large segments of repetitive sequences. Metaphase chromosomes are also characterized by specific stained sequences (named centromeres) in the middle of the elongated structure, in addition to telomeres at the termini, as discussed earlier. Both centromeres and telomeres have unique repetitive sequences, and in some cases similar sequences have been observed in other regions of chromosomes; these regions are highly condensed and not transcribed.
 
     
 
 
     



     
 
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