DNA and RNA

3 Key excerpts on "DNA and RNA"

• 

  eBook - ePub

  Molecular Biology

  Structure and Dynamics of Genomes and Proteomes

  • Jordanka Zlatanova(Author)
  • 2023(Publication Date)
  • Garland Science

    (Publisher)

  Nucleic Acids

  DOI: 10.1201/9781003132929-4

  Learning objectives

  Information storage and transmission involve two kinds of nucleic acids: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Nucleic acids are polymers built on a repetitive backbone of sugar moieties linked by phosphodiester bonds. In RNA the sugar is ribose; in DNA the sugar is 2′-deoxyribose. Attached to each sugar is a basic unit, either a purine or a pyrimidine. In DNA, the purines are adenine (A) and guanine (G), and the pyrimidines are cytosine (C) and thymine (T); in RNA uracil (U) substitutes for T. The sequence of bases along the polynucleotide chain provides the information for protein structure. Here, we present the Watson and Crick double-helical structure of the DNA, with base pairing of A with T and G with C in the complementary strands. This structure of DNA allows for copying and information transfer from one cell generation to the next.

  We also describe the possible structures of circular DNA molecules, introducing the concepts of supercoiling and linking number, Lk, the total number of times one strand crosses the other. We also introduce the classes of enzymes (topoisomerases) that can change the linking number of DNA molecules in the cell.

  RNA molecules are usually found in vivo as single-stranded molecules that have been copied (transcribed) from one strand of genomic DNA. RNAs are intermediaries in the transfer of genetic information from DNA to proteins. They can also perform many other functions, from regulation of transcription to the enzyme functions of ribozymes.

  4.1 Introduction

  Protein sequences are dictated by nucleic acids

  We have seen that proteins, in their enormous variety, can play a host of roles in the cell, both structural and functional. Each protein accomplishes this by having a unique amino acid sequence, which determines its secondary, tertiary, and quaternary structures. The information that dictates these sequences must somehow be stored in the cell, expressed in proteins, and transmitted through generations of cells and organisms. These vital functions are provided by biopolymers called nucleic acids, or polynucleotides, of which there are two kinds: ribonucleic acid (RNA) and deoxyribonucleic acid (DNA

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  eBook - ePub

  The Handy Biology Answer Book

  • Patricia Barnes-Svarney, Thomas E. Svarney(Authors)
  • 2014(Publication Date)
  • Visible Ink Press

    (Publisher)

  DNA, RNA, CHROMOSOMES, AND GENES

  HISTORY OF NUCLEIC ACIDS

  What are nucleic acids?

  DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are nucleic acids. They are molecules comprised of monomers (structural unit of a polymer) known as nucleotides. These molecules may be relatively small (as in the case of certain kinds of RNA) or quite large (a single DNA strand may have millions of monomer units). Individual nucleotides and their derivatives are important in living organisms. For example, ATP, the molecule that transfers energy in cells, is built from a nucleotide, as are a number of other molecules crucial to metabolism.

  Which came first—DNA or RNA?

  The first molecule had to be able to reproduce itself and carry out tasks similar to those done by proteins. However, proteins, even though bigger and more complicated than DNA, can’t make copies of themselves without the help of DNA and RNA. Therefore, RNA was the likely candidate as the first “information” molecule—mainly because scientists have found that RNA, unlike DNA, can replicate and then self-edit.

  What is the difference between DNA and RNA?

  DNA and RNA are both nucleic acids formed from a repetition of the simple building blocks called nucleotides. A nucleotide consists of a phosphate (PO4 ), sugar, and a nitrogen base, of which five types exist: adenine (A), thymine (T), guanine (G), cytosine (C), and uracil (U). In a DNA molecule, this basic unit is repeated in a double helix structure made from two chains of nucleotides linked between the bases; these links are either between A and T or between G and C. (The structure of the bases does not allow other kinds of links.)

  The structures of DNA (left) and RNA (right) are shown here. The arrangement of adenine, thymine, guanine, cytosine, and uracil nucleotydes are used to send instructions to cells to make proteins.

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  eBook - ePub

  Biomedical Science

  • Ian Lyons(Author)
  • 2011(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  2 Molecular biology and genetics

  The human genome contains all the information necessary to generate all the components of the human body; it is found in almost every cell in the body. This information is encoded through the four different nucleotide types in deoxyribonucleic acid (DNA). DNA contains functional units known as genes, which encode protein or nucleic acid molecules with a specific function.

  The process by which a gene is converted into its product is well established, as are the mechanisms that regulate the expression of a gene. Changes to a gene, or deletions of parts of the genome, can result in disease, through changes to the proteins produced.

  DNA and genes

  The basic unit of genetic information is the gene. Genes are stretches of DNA that encode protein or RNA molecules with a specific function (or group of functions). The DNA in a cell (in almost every case) is the same as the DNA found in the zygote and possesses all the genetic information for creating a complete organism; the ability to reliably copy DNA to ensure accurate transmission of the genome is aided by the structure of DNA and its method of replication.

  Structure of nucleic acids

  DNA and RNA are made up of chains of nucleotides that are linked together to form a long continuous molecule. Each nucleotide base has common elements (Fig. 2.1 ):

  • A phosphate group
  • A deoxyribose (in DNA) or a ribose (in RNA) sugar
  • A base group made up of carbon–nitrogen rings; there are two types of bases used in nucleic acids:
    – purine bases (adenine and guanine) are made up of two carbon–nitrogen rings. The bases differ in the side chains attached to the rings
    – pyrimidine bases (cytosine and thymine) are made up of a single carbon–nitrogen ring; the different pyrimidine bases also have different side chains.

  The bases are the only part of the nucleotides that vary, and this variation stores information in the genetic code.

  The precursors for DNA synthesis are the deoxynucleotide triphosphates

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