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DNA Biology Vocabulary

RNA Structure and Function

  • Ribonucleic acid (RNA) contains ribose sugar and uses uracil instead of thymine.
  • RNA is single-stranded.
  • Three types of RNA:
    • Messenger RNA (mRNA): Carries genetic message to ribosomes.
    • Transfer RNA (tRNA): Transfers amino acids to ribosomes.
    • Ribosomal RNA (rRNA): Forms ribosomes.

DNA vs. RNA

  • Similarities: Both are nucleic acids, composed of nucleotides, have a sugar-phosphate backbone, and four types of bases.
  • Differences:
    • DNA: Found in the nucleus, genetic material, deoxyribose sugar, bases are A, T, C, G, double-stranded.
    • RNA: Found in the nucleus and cytoplasm, helper to DNA, ribose sugar, bases are A, U, C, G, single-stranded.
    • DNA is transcribed into mRNA, tRNA, and rRNA. mRNA is translated to give proteins.

Gene Expression

  • DNA provides a blueprint for protein synthesis.
  • Genetic information flows from DNA to RNA to protein.
  • Gene expression involves transcription and translation.

Steps of Gene Expression

  • Transcription: DNA serves as a template to make mRNA; involves complementary base pairing.
  • Translation: mRNA directs the sequence of amino acids in a protein; rRNA and tRNA assist.

The Genetic Code

  • Triplet: 3-nucleotide sequence in DNA.
  • Codon: 3-nucleotide sequence in mRNA; encodes a single amino acid.
  • One start codon and three stop codons.

Transcription Process

  • Complementary RNA is made from a DNA template.
  • RNA polymerase attaches, causing DNA to unwind and unzip.
  • Bases join in the order dictated by the template DNA strand.

mRNA Processing

  • Pre-mRNA is processed in the nucleus.
    • Capping and addition of a poly-A tail provide stability.
    • Introns (non-coding regions) are removed, leaving only exons (coding regions).
    • Alternative splicing can produce different mRNA versions.
    • Mature mRNA leaves the nucleus and associates with ribosomes.

Translation

  • tRNA brings amino acids to mRNA in the cytoplasm.
  • Anticodon: tRNA group of 3 bases complementary to mRNA codon.
  • A protein contains the amino acid sequence specified in the DNA.

Ribosomes

  • Composed of proteins and ribosomal RNA (rRNA).
  • Site of translation/protein synthesis.
  • Two subunits (large and small) bind mRNA and two tRNA molecules
    • P-site: tRNA with amino acid attached.
    • A-site: Newly arrived tRNA with an amino acid
    • E-site: tRNA exits the ribosome.

Translation/Protein Synthesis Phases

  • Three phases: Initiation, Elongation, Termination.
    • Initiation: mRNA binds to small subunit ribosome, then the large subunit joins, forming the functional ribosome unit.
    • Elongation: Peptide chain lengthens one amino acid at a time; amino acids are joined by a peptide bond.
    • Termination: A stop codon binds to the ribosome; a release factor is added, causing ribosomal subunits and mRNA to dissociate, releasing the polypeptide.