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.