Molecular Genetics

DNA Composition and Location

• DNA is composed of nucleotides.
• DNA can be found in the nucleus and cytoplasm of the cell.
• DNA can also be found in the mitochondria.

DNA Structure

• The structure of DNA is a double helix.
• The sugar in DNA is deoxyribose.
• Nucleotides consist of a phosphate group, a sugar (deoxyribose), and a nitrogen base.
• A nucleotide consists of nitrogenous bases & sugar-phosphate backbone.

Base Pairing Rules

• The base pairing rules for DNA are:
  • Adenine (A) pairs with Thymine (T).
  • Cytosine (C) pairs with Guanine (G).
• Example DNA sequence: ATCGGCTAGCCG

DNA Replication

• DNA replication involves:
  • DNA helicase to unwind the DNA.
  • DNA polymerase to add nucleotides.
  • A proofreading DNA polymerase to correct errors.
• Strict base pairing rules ensure each DNA strand is complementary to the other.
• DNA replication occurs in the nucleus.
• Enzymes involved:
  • DNA Helicase: unwinds the DNA.
  • DNA Polymerase: attaches to the DNA and adds nucleotides at the replication forks, while another DNA Polymerase proofreads for errors.
• The result is two semi-conservative strands, each with one new and one old helix.
• DNA Polymerase is the enzyme responsible for checking errors during DNA replication.
• Briefly explain how DNA is copied: DNA Helicase unwinds the DNA, and DNA Polymerase attaches to the DNA and adds nucleotides at the replication forks, while another DNA Polymerase proofreads for errors. The result is two semi-conservative strands, each with one new and one old helix.

DNA vs. RNA

• DNA contains deoxyribose, while RNA has ribose sugar.
• DNA is a double-stranded helix, while RNA is single-stranded.
• DNA uses Thymine (T), while RNA replaces thymine with uracil (U).

Transcription

• Transcription is the process where RNA polymerase copies DNA's genetic code into messenger RNA (mRNA).
• Transcription takes place in the nucleus of the cell.
• The enzyme involved in transcription is RNA polymerase.
• Briefly explain how to make a strand of RNA: RNA Polymerase unwinds the DNA strand and introduces new nucleotides to create an RNA strand.

RNA Base Pairing Rules

• RNA uses uracil (U) instead of thymine (T).
• Base pairing rules:
  • A \rightarrow U
  • C \rightarrow G
  • G \rightarrow C
  • U \rightarrow A

Codons

• A codon is a series of 3 nucleotides.
• mRNA (messenger RNA) carries genetic info from DNA to make proteins and is used to search for codons.

Translation

• Translation takes place in the cytoplasm by the ribosomes or Rough ER.
• Genetic code is used to translate genetic info into proteins.
• Example:
  • DNA: TACCGCATG
  • RNA: AUG GCG UAC
  • Amino Acids: met-Ala-Tyr
• Anticodons are found on tRNA (transfer RNA) molecules.
• Proteins are made in ribosomes or rough ER (cytoplasm).

Introns vs. Exons

• Introns are between exons and do not code for protein (removed during RNA processing).
• Exons code for proteins and are outside of introns (they remain and are translated into proteins).

Mutations

• A mutation is a change in DNA sequence.
• Point mutation: when a codon letter is slightly altered or different.
• Translocation: occurs when a codon goes to a different location.
• Inversion mutation: happens when a segment is flipped.