Molecular Biology: Gene Expression and Protein Synthesis
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Questions and Answers

What is the primary function of genes in an organism?

  • To replicate the genetic code
  • To regulate the expression of traits
  • To dictate the synthesis of proteins (correct)
  • To transmit information from protein to nucleic acid

    • What is the term for the process by which DNA directs protein synthesis?

  • Central dogma
  • Protein synthesis
  • Gene expression (correct)
  • Translation

    • What is the flow of information from gene to protein based on?

  • A double helix structure
  • A universal code
  • A triplet code (correct)
  • A degenerate code

    • What is the minimum number of nucleotides required to code for an amino acid?

    <p>3</p> Signup and view all the answers

    What is the term for the three-nucleotide code of mRNA that is translated into an amino acid?

    <p>Codon</p> Signup and view all the answers

    How many possible codons are there in the genetic code?

    <p>64</p> Signup and view all the answers

    What is the term for the phenomenon where multiple codons can code for the same amino acid?

    <p>Degeneracy</p> Signup and view all the answers

    Why is it essential to read codons in the correct reading frame?

    <p>To ensure the synthesis of the correct protein</p> Signup and view all the answers

    What is the significance of the universality of the genetic code?

    <p>It allows genes to be transplanted between species</p> Signup and view all the answers

    Who is credited with the discovery of the double helix structure of DNA?

    <p>Watson and Crick</p> Signup and view all the answers

    What is the characteristic of DNA replication that is described as semiconservative?

    <p>Each new DNA molecule is composed of one old strand and one new strand</p> Signup and view all the answers

    What is the function of the primer in DNA replication?

    <p>To initiate the synthesis of a new DNA strand</p> Signup and view all the answers

    What is the name of the process by which RNA molecules are synthesized from a DNA template?

    <p>Transcription</p> Signup and view all the answers

    What is the function of the anticodon on a tRNA molecule?

    <p>To base-pair with a codon on mRNA</p> Signup and view all the answers

    What is the name of the enzyme that ensures a correct match between a tRNA and an amino acid?

    <p>Aminoacyl-tRNA synthetase</p> Signup and view all the answers

    What is the result of a mutation that confers new or enhanced activity to a protein?

    <p>Gain of function</p> Signup and view all the answers

    What is the term for the process of removing introns and joining exons to create a mature mRNA molecule?

    <p>RNA splicing</p> Signup and view all the answers

    What is the name of the site on the ribosome where the tRNA that carries the growing polypeptide chain is held?

    <p>P site</p> Signup and view all the answers

    What is the characteristic of DNA that allows it to serve as a template for the synthesis of a new strand?

    <p>Its double helix structure</p> Signup and view all the answers

    What is the term for the process of synthesizing a new DNA strand in short, discontinuous segments?

    <p>Lagging strand synthesis</p> Signup and view all the answers

    What is the main role of proteins in the relationship between genotype and phenotype?

    <p>To act as a link between genotype and phenotype</p> Signup and view all the answers

    What is the consequence of not reading codons in the correct reading frame?

    <p>A polypeptide with a completely different sequence of amino acids is produced</p> Signup and view all the answers

    What is the primary reason why purine cannot pair with another purine in the DNA molecule?

    <p>The width of the DNA molecule would be too wide</p> Signup and view all the answers

    What is the significance of the degeneracy of the genetic code?

    <p>That it allows for multiple codons to code for the same amino acid</p> Signup and view all the answers

    What is the role of the RNA polymerase in transcription?

    <p>To attach to the promoter region</p> Signup and view all the answers

    What is the result of a mutation that causes a loss of protein function?

    <p>Loss of function</p> Signup and view all the answers

    What is the difference between the central dogma and the genetic code?

    <p>The central dogma is the flow of information from gene to protein, while the genetic code is the sequence of nucleotides in DNA</p> Signup and view all the answers

    What is the result of a mutation that changes the reading frame of a codon?

    <p>A polypeptide with a completely different sequence of amino acids is produced</p> Signup and view all the answers

    What is the purpose of the Okazaki fragments in DNA replication?

    <p>To synthesize the lagging strand</p> Signup and view all the answers

    What is the function of the aminoacyl-tRNA synthetase enzyme?

    <p>To ensure a correct match between a tRNA and an amino acid</p> Signup and view all the answers

    What is the minimum number of nucleotides required to code for a single amino acid?

    <p>3</p> Signup and view all the answers

    What is the characteristic of RNA that allows it to function in translation?

    <p>Its ability to form a three-dimensional structure</p> Signup and view all the answers

    What is the significance of the universality of the genetic code?

    <p>That it allows for the synthesis of proteins in all organisms</p> Signup and view all the answers

    What is the main difference between transcription and translation?

    <p>Transcription is the synthesis of mRNA, while translation is the synthesis of protein</p> Signup and view all the answers

    What is the term for the process of synthesizing a protein from a mRNA sequence?

    <p>Translation</p> Signup and view all the answers

    What is the role of DNA in the synthesis of proteins?

    <p>It provides the template for protein synthesis</p> Signup and view all the answers

    What is the role of the ribosomes in protein synthesis?

    <p>To couple tRNA anticodons with mRNA codons</p> Signup and view all the answers

    What is the relationship between the sequence of nucleotides in DNA and the sequence of amino acids in a protein?

    <p>The sequence of nucleotides in DNA determines the sequence of amino acids in a protein</p> Signup and view all the answers

    What is the result of a gain-of-function mutation?

    <p>Gain of new or enhanced protein function</p> Signup and view all the answers

    What is the purpose of the primer in DNA replication?

    <p>To provide a starting point for DNA synthesis</p> Signup and view all the answers

    Study Notes

    Gene Expression and the Central Dogma

    • The information content of genes is in the specific sequences of nucleotides.
    • DNA inherited by an organism leads to specific traits by dictating the synthesis of proteins.
    • Proteins are the links between genotype and phenotype.
    • Gene expression, the process by which DNA directs protein synthesis, includes two stages: transcription and translation.
    • Central dogma: information cannot be transferred from protein to protein or protein to nucleic acid, but can be transferred between nucleic acids and from nucleic acid to protein.

    The Genetic Code

    • The flow of information from gene to protein is based on a triplet code: a series of three nucleotides.
    • The code of a gene is transcribed into a complementary three-nucleotide code of mRNA called a codon.
    • 64 possible codons: 3 stop codons, 61 sense codons.
    • The genetic code is 'degenerate' but not ambiguous.
    • Codons must be read in the correct reading frame in order for the specified polypeptide to be produced.
    • The genetic code is nearly universal, shared by the simplest bacteria to the most complex animals.

    DNA Structure and Replication

    • Watson: DNA was a double helix.
    • Watson and Crick: built models of a double helix to conform to the X-rays and chemistry of DNA.
    • Franklin: two outer sugar-phosphate backbones, with the nitrogenous bases paired in the molecule's interior.
    • Watson: built a model in which the backbones were anti-parallel.
    • Watson and Crick reasoned that the pairing was specific, dictated by the base structures.
    • Purine + purine = too wide.
    • Pyrimidine + pyrimidine = too narrow.
    • Purine + pyrimidine = width consistent with X-ray data.
    • Parental molecule: separation of parental strands into templates, formation of new strands complementary to template strands.
    • Semiconservative replication: DNA replication accomplished by separation of the strands of a parental duplex, each strand then acting as a template for synthesis of a complementary strand.

    Transcription

    • The stretch of DNA that is transcribed is called a transcription unit: it includes a promoter, an RNA-coding region, and a terminator.
    • The DNA sequence where RNA polymerase attaches is called the promoter.
    • The three stages of transcription: initiation, elongation, and termination.
    • Both strands of DNA can encode genes, but the coding sequence of one gene will always be on one strand.
    • RNA splicing removes introns and joins exons, creating an mRNA molecule with continuous coding sequence.
    • Some introns contain sequences that may regulate gene expression.
    • Some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during splicing.

    Translation

    • Genetic information flows from mRNA to protein through the process of translation.
    • Three properties of RNA enable it to function in this role: it can form a three-dimensional structure because of its ability to base-pair with itself, some bases in RNA contain functional groups that may participate in catalysis, RNA may hydrogen-bond with other nucleic acid molecules.
    • tRNA molecules are not identical: each carries a specific amino acid on one end and has an anticodon on the other end.
    • The anticodon base-pairs with a complementary codon on mRNA.
    • Translation is a complex biochemical and mechanical process.
    • Accurate translation requires two steps: a correct match between a tRNA and an amino acid, done by the enzyme aminoacyl-tRNA synthetase, a correct match between tRNA anticodon and an mRNA codon.
    • Ribosomes facilitate specific coupling of tRNA anticodons with mRNA codons in protein synthesis.
    • The two ribosomal subunits are made of proteins and ribosomal RNA.
    • P site: holds the tRNA that carries the growing polypeptide chain.
    • E site: discharged tRNA leaves.
    • A site: holds the tRNA that carries the next amino acid.

    Mutations

    • Mutations are sustainers of life and can cause problems.
    • Source of all genetic variation, which further provides the raw material for evolution, source of many diseases and disorders, useful for probing fundamental biological processes.
    • Main types of mutations: base substitutions, insertions, and deletions.
    • Loss of function mutations: a mutation that results in reduced/abolished protein function.
    • Gain-of-function mutations: a mutation that confers new/enhanced activity to a protein.
    • Conditional mutation: a mutant allele causes a mutant phenotype in only a certain environment, but causes a wild-type phenotype in some different environment.

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    Test your understanding of how genetic information is used to create proteins. Learn about the central dogma, transcription, and translation in this quiz.

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