DNA Structure & Replication Quiz

DNA Structure & Replication

• Nucleotide: Composed of a sugar (deoxyribose), a phosphate group, and a nitrogenous base (A, T, C, G).
• Chargaff's Rule: A = T and C = G (complementary base pairing).
• Antiparallel: The two DNA strands run in opposite directions (5' to 3' vs 3' to 5').
• Watson and Crick: Discovered the double-helix structure.
• Rosalind Franklin: Contributed to the structure via X-ray diffraction images.
• Erwin Chargaff: Discovered base pairing rules (A = T, C = G).
• Helicase: Unwinds the DNA helix.
• DNA Polymerase: Adds complementary nucleotides to the growing strand.
• Ligase: Seals the gaps between Okazaki fragments.
• Primase: Creates RNA primers to start replication.
• Leading Strand: Synthesized continuously in the 5' to 3' direction.
• Lagging Strand: Synthesized discontinuously in fragments (Okazaki fragments).
• Okazaki Fragments: Short segments of DNA synthesized on the lagging strand.

Protein Synthesis

Transcription

• Location: Occurs in the nucleus (eukaryotes).
• Process:
  • RNA Polymerase binds to DNA at the promoter region.
  • RNA polymerase creates an mRNA strand using the DNA template.
  • mRNA synthesis occurs from 5' to 3'.
  • In eukaryotes, mRNA is processed (splicing, capping, and tailing).

Translation

• Location: Occurs in the ribosome (cytoplasm).
• Process:
  • mRNA is read in sets of three bases (codons).
  • tRNA brings the corresponding amino acids to the ribosome.
  • Ribosome forms peptide bonds to create a polypeptide chain.
  • Codon Chart/Wheel: Used to match mRNA codons to amino acids.
  • START Codon: AUG, signals the beginning of translation.
  • STOP Codons: UAA, UAG, UGA, signal the end of translation.

Gene Expression

• Importance: Regulates which proteins are made, when, and in what amounts.
• Transcription Factors:
  • Positive: Activate/enhance gene expression.
  • Negative: Repress gene expression.
  • Binding Sites: Bind to specific regions on the promoter of a gene.
• Interfering RNA (RNAi):
  • Types: miRNA and siRNA.
  • Function: Regulate gene expression by binding to mRNA, preventing translation, or degrading mRNA.
• Operons:
  • Definition: Genes regulated together.
  • Example: Lac Operon (bacteria).
• Epigenetics: Study of changes in gene expression without changing DNA sequence.
  • Examples: DNA Methylation (suppresses gene expression via methyl group addition to DNA) and Histone Modification (alters chromatin condensation, affecting gene accessibility).

Variation & Mutations

• Mutations: Changes in DNA sequences.
• Frameshift Mutations: Caused by insertions or deletions, shifting the reading frame of codons.
• Point Mutations: Changes in a single nucleotide.
  • Substitution: One base is replaced by another.
    • Silent Mutation: No change in the protein sequence.
    • Missense Mutation: Changes one amino acid.
    • Nonsense Mutation: Changes a codon to a stop codon, creating a truncated protein.
• Impact on Fitness: Mutations can be beneficial, harmful, or neutral for survival and reproduction.
• Chromosomal Mutations:
  • Deletions: Loss of a chromosome segment.
  • Duplications: Repetition of a chromosome segment.
  • Inversions: Reversal of a chromosome segment.
  • Translocations: Exchange of segments between non-homologous chromosomes.
• Mutations and Population Variation: Mutations contribute to genetic diversity. Natural selection can act upon these variations.