5 Key excerpts on "Central Dogma"

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  eBook - ePub

  Biophysics for Beginners

  A Journey through the Cell Nucleus

  • Helmut Schiessel(Author)
  • 2021(Publication Date)
  • Jenny Stanford Publishing

    (Publisher)

  Chapter 1

  Molecular Biology of the Cell

  1.1 The Central Dogma of Molecular Biology

  An introduction to the fundamentals of the molecular biology of the cell would easily fill this book. Instead, I shall focus on one set of problems in molecular biology that Francis Crick, one of the discoverers of the DNA double helix, has termed the Central Dogma of molecular biology. This Central Dogma states that there are three types of crucial biological macromolecules, DNA, RNA and proteins, that “communicate” in such a way that genetic information flows in the single direction from DNA to RNA to proteins. Figure 1.1 specifies the different steps of that information flow, which we will discuss below.

  Figure 1.1 The Central Dogma of molecular biology: information flows from DNA to RNA to proteins. The DNA molecules contain the complete genetic information of the cell in the form of genes which are often separated by pieces of “junk” DNA. Each gene is a building plan of a protein. Whenever a cell needs a certain protein, a transcript of its gene is made in the form of an RNA copy. This copy is then used as blueprint to assemble the protein. Also shown are enlarged portions of the three types of macromolecules: DNA and RNA are chemically very similar, except DNA is double stranded whereas RNA is single stranded. Proteins are chemically very different and are made from a sequence of amino acids (aa's). The physical properties of these aa’s cause the protein to fold in a unique three-dimensional shape.

  The whole genetic information about a cell, its genome, is written down in one or several DNA molecules (DNA stands for DeoxyriboNucleic Acid). When a cell divides, the information must be passed on to its two daughter cells, and therefore the DNA needs to be replicated before the division can take place. To understand how elegant nature’s solution to replication works, we first need to discuss the structure of the DNA chain itself. The genetic text on the DNA chain is made from four letters, the nucleotides: adenine (A), guanine (G), cytosine (C) and thymine (T). These letters are chemically linked into a one-dimensional chain producing a text like AAGCTTAG, but much, much longer. A DNA molecule in a cell carries this information not only once, but effectively twice, since it occurs in a double-stranded form. The two DNA strands are linked via hydrogen bonds through base pairing such that an A is always paired with a T and a G with a C. So our AAGCTTAG strand will be paired with a TTCGAATC strand (more precisely CTAAGCTT, since each strand has a chemically built-in direction and the two strands run anti-parallel). Therefore, the two strands are not identical, but they carry exactly the same genetic information. To duplicate the DNA, the double stranded chain just needs to be unzipped and each strand used as a template to convert it back to a double stranded molecule using the base pairing rules, see Fig. 1.2

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  eBook - ePub

  Molecular Biology

  • David P. Clark(Author)
  • 2009(Publication Date)
  • Academic Cell

    (Publisher)

  Fig. 3.17 ).

  Figure 3.17 The Central Dogma (Simple Version) The information flow in cells begins with DNA, which may either be replicated, giving a duplicate molecule of DNA, or be transcribed to give RNA. The RNA is read (translated) as a protein is built.

  The genetic information stored as DNA is not used directly to make protein. During cell growth and metabolism, temporary, working copies of the genes known as messenger RNA (mRNA) are used. These are RNA copies of genetic information stored by the DNA and are made by a process called transcription . The messenger RNA molecules carry information from the genome to the cytoplasm, where the information is used by the ribosomes to synthesize proteins . In eukaryotes, mRNA is not made directly. Instead, transcription yields precursor RNA molecules (pre-mRNA) that must be processed, to produce the actual mRNA as detailed in Ch. 12 .

  Under normal circumstances, genetic information flows from DNA to RNA to protein. As a result, proteins are often referred to as “gene products”. Some RNA molecules are also “gene products” as they act without being translated into protein.

  Central Dogma	Basic plan of genetic information flow in living cells which relates genes (DNA), message (RNA) and proteins
  chromosome banding technique	Visualization of chromosome bands by using specific stains that emphasize regions lacking genes
  karyotype	The complete set of chromosomes found in the cells of a particular individual
  messenger RNA (mRNA)	The molecule that carries genetic information from the genes to the rest of the cell
  replication	Duplication of DNA prior to cell division

  The DNA that carries the primary copy of the genes is present as gigantic molecules, each carrying hundreds or thousands of genes. In contrast, any individual messenger RNA molecule carries only one or a few genes’ worth of information. Thus, in practice, multiple short segments of DNA are transcribed simultaneously to give many different messenger RNA molecules. In eukaryotes, each mRNA normally carries only a single gene, whereas in prokaryotes, anywhere from one to a dozen genes may be transcribed as a block to give an mRNA molecule carrying several genes, usually with related functions (Fig. 3.18

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  eBook - ePub

  Genetics 101

  From Chromosomes and the Double Helix to Cloning and DNA Tests, Everything You Need to Know about Genes

  • Beth Skwarecki(Author)
  • 2018(Publication Date)
  • Adams Media

    (Publisher)

  translation) . That works too.

  The Central Dogma

  In 1957, Francis Crick, already famous for his role in discovering the structure of DNA, gave a lecture in which he explained a hypothesis he had: that “the main function of the genetic material is to control . . . the synthesis of proteins.” He argued that the information in a nucleic acid like RNA can be used to make proteins, but not vice versa, and called this idea the “Central Dogma” of molecular biology. A variation on this, the rule of thumb that DNA is transcribed into RNA, and that RNA is translated into protein, is part of every genetics student’s education today.

  The only problem is that it’s not really a dogma. Dogma is a religious term for a set of principles that some authority declares to be true and everybody must believe it. That’s not how science works! An idea only sticks around for as long as it is backed up by evidence. Crick later admitted that he misunderstood the word—but it was too late. The name stuck.

  WHAT IS RNA?

  RNA is ribonucleic acid. Compare that to DNA’s full name, deoxyribonucleic acid. These two molecules are very close relatives.

  Like DNA, RNA is made of nucleotides that in turn are each made of a phosphate, a sugar, and a nitrogenous base. In DNA, the sugar portion is a type of sugar called deoxyribose. In RNA, it’s ribose. The difference, as you might guess from the name, is that ribose has an extra oxygen atom that deoxyribose does not.

  This chemical difference has consequences. RNA breaks down more easily, while DNA is more stable. (Be glad that your genome is stored on DNA!) RNA is also more flexible than stiff and stuffy DNA, so you’ll find RNA in all kinds of shapes, not just a long double helix. Thanks to this folding, RNA can also base-pair with itself, so it doesn’t need another strand to act as its partner. In some of the sections to come, we’ll see some of the ways RNA takes advantage of these features.

  Finally, RNA and DNA also differ in their nucleotide code. You’ll recall that in DNA, adenine matches up with thymine, and guanine matches up with cytosine. But RNA doesn’t use thymine, so adenine binds with uracil instead. (Guanine and cytosine still work the usual way.)

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  Inquiry-Based Science Activities in Grades 6-12

  Meeting the NGSS

  • Patrick Brown, James Concannon(Authors)
  • 2018(Publication Date)
  • Routledge

    (Publisher)

  10 Model Lesson 8: Students Conceptualizing Transcription and Translation from a Cellular Perspective

  James Concannon and Maegan Buzzetta

  About This Lesson

  It is difficult for students to conceptualize biochemical processes that are portrayed as two-dimensional figures in a textbook. Instead of relying on overheads, PowerPoint, or textbook figures, the authors have students imagine themselves actually being inside a cell. Students have a specific role in the cell: helping with the transcription and translation process.

  One of the most difficult tasks for science teachers is to explain concepts that cannot be seen with the naked eye or even with a standard classroom microscope. Students develop some sort of personal and often incorrect conception of these processes. Good science teachers use models to explain the invisible. This allows the teacher to assess and guide students’ ideas. For example, a teacher may have students use pipe cleaners and beads to create models of different types of macromolecules. In this lesson, students use simple models of various macromolecules. This lesson takes three full 50-minute class periods.

  Purpose

  On completion of the lesson, students should be able to describe the location and properties of DNA, the process of transcription and translation, and the role enzymes play in protein synthesis. This activity addresses the following National Science Education Standard:

  Life Science Content Standard C: As a result of their activities in grades 9–12, all students should develop understanding of the molecular basis of heredity. In all organisms, the instructions for specifying the characteristics of the organism are carried in DNA, a large polymer formed from subunits of four kinds (A, G, C, and T). The chemical and structural properties of DNA explain how the genetic information that underlies heredity is both encoded in genes and replicated. Each DNA molecule in a cell forms a single chromosome.

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  eBook - ePub

  Cell Biology E-Book

  • Thomas D. Pollard, William C. Earnshaw, Jennifer Lippincott-Schwartz, Graham Johnson(Authors)
  • 2016(Publication Date)
  • Elsevier

    (Publisher)

  chromosomes store the information required for cellular growth, multiplication, and function. Each DNA molecule is composed of two strands of four different nucleotides (adenine [A], cytosine [C], guanine [G], and thymine [T]) covalently linked in linear polymers. The two strands pair, forming a double helix held together by interactions between complementary pairs of nucleotide bases with one on each strand: A pairs with T and C pairs with G. The two strands separate during enzymatic replication of DNA, each serving as a template for the synthesis of a new complementary strand, thereby producing two identical copies of the DNA. Precise segregation of one newly duplicated double helix to each daughter cell then guarantees the transmission of intact genetic information to the next generation.

  FIGURE 1.3 DNA STRUCTURE AND REPLICATION. Genes stored as the sequence of bases in DNA are replicated enzymatically, forming two identical copies from one double-stranded original.

  2. Linear chemical sequences stored in DNA code for both the linear sequences and three-dimensional structures of RNAs and proteins ( Fig. 1.4 ). Enzymes called RNA polymerases copy (transcribe) the information stored in genes into linear sequences of nucleotides of RNA molecules. Many RNAs have structural roles, regulatory functions, or enzymatic activity; for example, ribosomal RNA is by far the most abundant class of RNA in cells. Other genes produce messenger RNA (mRNA) molecules that act as templates for protein synthesis, specifying the sequence of amino acids during the synthesis of polypeptides by ribosomes. The amino acid sequence of most proteins contains sufficient information to specify how the polypeptide folds into a unique three-dimensional structure with biological activity. Two broad mechanisms control the production and processing of RNA and protein from tens of thousands of genes. Genetically encoded control circuits consisting of proteins and RNAs respond to environmental stimuli through signaling pathways. Epigenetic

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