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Chapter 10 General Biology: DNA, RNA, and Protein Synthesis

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  • What are DNA and RNA composed of?
    DNA and RNA are polymers of nucleotides, which are their monomers.
  • What are the four nitrogenous bases in DNA?
    Adenine (A), Cytosine (C), Guanine (G), and Thymine (T).
  • How does RNA differ from DNA in sugar and bases?
    RNA contains ribose sugar (with an ―OH group) and uracil (U) instead of thymine (T). DNA contains deoxyribose sugar and thymine.
  • Describe the structure of DNA.
    DNA is a double helix with two polynucleotide strands; sugar-phosphate backbones are on the outside, and nitrogenous bases pair inside.
  • What base pairing rules maintain DNA's uniform diameter?
    Adenine (purine) pairs with Thymine (pyrimidine), and Guanine (purine) pairs with Cytosine (pyrimidine).
  • How many hydrogen bonds form between C-G and A-T base pairs?
    C-G pairs form three hydrogen bonds; A-T pairs form two hydrogen bonds.
  • What is the semiconservative model of DNA replication?
    Each daughter DNA molecule contains one old (parental) strand and one newly synthesized strand.
  • Where does DNA replication begin in eukaryotic chromosomes?
    At specific sites called origins of replication.
  • In which direction do DNA polymerases add nucleotides during replication?
    DNA polymerases add nucleotides to the 3' end, synthesizing DNA in the 5' → 3' direction.
  • What are Okazaki fragments?
    Short DNA fragments synthesized discontinuously on the lagging strand during DNA replication.
  • What enzyme joins Okazaki fragments into a continuous strand?
    DNA ligase.
  • What is the flow of genetic information in cells?
    DNA → RNA → Protein.
  • What are the two main stages of gene expression?
    Transcription (DNA to RNA) and Translation (RNA to protein).
  • What is the one gene–one enzyme hypothesis?
    Each gene dictates the production of a specific enzyme (later expanded to proteins).
  • What is a codon?
    A triplet of nucleotide bases in DNA or RNA that specifies an amino acid.
  • What is the start codon and what amino acid does it code for?
    AUG, which codes for methionine (Met) and signals the start of translation.
  • Name the three stop codons in RNA.
    UAA, UAG, and UGA; they signal termination of translation.
  • What is the role of RNA polymerase in transcription?
    RNA polymerase synthesizes RNA by following base-pairing rules using one DNA strand as a template.
  • What modifications occur to eukaryotic mRNA before it leaves the nucleus?
    Addition of a 5' cap, a 3' poly-A tail, and removal of introns by RNA splicing.
  • What is the function of transfer RNA (tRNA)?
    tRNA transfers specific amino acids to the ribosome and matches them to mRNA codons via its anticodon.
  • Describe the structure of tRNA.
    Single-stranded RNA with a cloverleaf shape, containing an anticodon and an amino acid attachment site.
  • What are ribosomes composed of and what is their function?
    Ribosomes consist of two subunits made of proteins and rRNA; they coordinate mRNA and tRNA to synthesize polypeptides.
  • What happens during the initiation phase of translation?
    mRNA binds the small ribosomal subunit; initiator tRNA pairs with the start codon; the large subunit joins to form a functional ribosome.
  • Outline the three steps of elongation in translation.
    1) tRNA anticodon pairs with mRNA codon in A site; 2) peptide bond forms between amino acids; 3) ribosome moves, releasing empty tRNA.
  • What signals termination of translation?
    A stop codon (UAA, UAG, or UGA) in the A site causes release of the polypeptide and ribosome disassembly.
  • What is a polyribosome?
    Multiple ribosomes simultaneously translating a single mRNA molecule.
  • How does the genetic code demonstrate redundancy and universality?
    Multiple codons can specify the same amino acid (redundancy), and the code is nearly universal across all organisms.
  • What is the significance of complementary base pairing in DNA replication?
    It ensures accurate copying of genetic information by matching bases on the template strand with complementary free nucleotides.