DNA Structure and Replication Quiz

DNA Structure

• Watson and Crick discovered the double-helix shape of DNA in 1953.
• This structure helps explain how genetic information is passed from one generation to the next.
• DNA is made up of two strands of nucleotides.
• Nucleotides have three components:
  • a sugar (deoxyribose)
  • a phosphate group
  • a nitrogenous base
• There are five kinds of nitrogenous bases:
  • Adenine (A) - a purine found in both DNA & RNA.
  • Guanine (G) - a purine found in both DNA & RNA.
  • Cytosine (C) - a pyrimidine found in both DNA & RNA.
  • Thymine (T) - a pyrimidine found only in DNA.
  • Uracil (U) - a pyrimidine found only in RNA.

DNA Replication

• DNA replication occurs when a new strand of DNA is created from an original strand.
• It occurs semi-conservatively: One original strand serves as a template to create a new strand.
• When a DNA molecule is copied, one half of the original molecule is in each copy.
• DNA replication proceeds in two directions at many sites simultaneously.
• It begins at origins of replication.
• A codon is a sequence of 3 nucleotides.
• Each codon specifies a particular amino acid.

Protein Synthesis

• Protein synthesis is when information encoded in DNA is used to create proteins.
• It includes two main steps:
  • Transcription: DNA is used to create messenger RNA (mRNA).
  • Translation: mRNA interacts with ribosomes to make proteins.
• During translation, tRNA reads the mRNA codons and links corresponding amino acids together.
• The process starts when mRNA leaves the nucleus and goes to the ribosome.
• tRNA brings in amino acids that match the codons on the mRNA.
• Amino acids link together to form a growing protein chain.
• Once the protein is complete, the tRNA detaches and the mRNA can be used again.