Genetics-__Chapter_10_DNA_Structure_and_Analysis

Chapter 10: DNA Structure and Analysis

Learning Objectives

• 10.1 The Genetic Material Must Exhibit Four Characteristics

• 10.2 Until 1944, Observations Favored Protein as the Genetic Material

• 10.3 Evidence Favoring DNA as the Genetic Material Was First Obtained during the Study of Bacteria and Bacteriophages

• 10.4 Indirect and Direct Evidence Supports the Concept That DNA Is the Genetic Material in Eukaryotes

• 10.5 RNA Serves as the Genetic Material in Some Viruses

• 10.6 Knowledge of Nucleic Acid Chemistry Is Essential to the Understanding of DNA Structure

• 10.7 The Structure of DNA Holds the Key to Understanding Its Function

• 10.8 Alternative Forms of DNA Exist

• 10.9 The Structure of RNA Is Chemically Similar to DNA, but Single-Stranded

• 10.10 Many Analytical Techniques Have Been Useful during the Investigation of DNA and RNA

10.1 The Genetic Material Must Exhibit Four Characteristics

• Genetic Material: Information within genes passed to new generations, source of variability in organisms.

Criteria for Genetic Material

To function as genetic material, a molecule must be capable of:

• Replication: Must replicate accurately.

• Storage of Information: Must store genetic information.

• Expression of Information: Must express genetic information.

• Allow Variation by Mutation: Must allow for variations through possible mutations.

The Central Dogma

• Central Dogma of Molecular Genetics:

  • Transcription: DNA makes RNA.

  • Translation: RNA is translated to synthesize proteins.

10.2 Until 1944, Observations Favored Protein as the Genetic Material

• In the 1940s, geneticists favored proteins due to their diversity and abundance over nucleic acids.

• Tetranucleotide Hypothesis:

  • Proposed that DNA had equal amounts of four nucleotides, leading to insufficient chemical diversity to account for genetic material properties.

10.3 Evidence Favoring DNA as the Genetic Material

Avery, MacLeod, and McCarty

• 1944 Experiment: Demonstrated that DNA was the molecule responsible for heredity.

  • Utilized DNase to destroy the transforming activity, confirming DNA, not protein, carried genetic information.

10.5 RNA Serves as the Genetic Material in Some Viruses

• Some viruses utilize RNA rather than DNA for genetic material.

Tobacco Mosaic Virus (TMV)

• The 1956 study demonstrated RNA serves as genetic material.

Retroviruses

• Retroviruses use RNA to synthesize DNA through reverse transcriptase.

10.6 Chemistry of Nucleic Acids

Nucleotides

• Building Blocks of DNA and RNA:

  • Composed of:

    • Nitrogenous Base: Two types – Purines (Adenine, Guanine) and Pyrimidines (Cytosine, Thymine, Uracil).

    • Pentose Sugar: Deoxyribose in DNA; Ribose in RNA.

    • Phosphate Group: Connects nucleotides.

Ribose and Deoxyribose

• RNA contains ribose sugar; DNA contains deoxyribose (lacking an oxygen at the 2' position).

10.7 Structure and Function of DNA

Watson and Crick Model

• Proposed DNA as a double helix (1953) with two anti-parallel strands.

Base Pairing

• Complementarity: A-T pairs with double bond; G-C pairs with triple bond provides the chemical stability of the DNA helix.

Semiconservative Replication

• Genetic information storage is intrinsic in the base sequence with potential for mutations.

10.9 Structure of RNA

• Differences from DNA:

  • Contains ribose instead of deoxyribose.

  • Utilizes uracil instead of thymine.

  • Generally exists as single-stranded molecules, with exceptions in some viruses.

• Three Major Classes of RNA:

  • Messenger RNA (mRNA): Template for protein synthesis, carries genetic information.

  • Ribosomal RNA (rRNA): Structure of ribosomes.

  • Transfer RNA (tRNA): Transfers amino acids for protein synthesis.

10.10 Analytical Techniques in DNA and RNA Research

Useful Techniques

• Absorption of UV Light: Hyperchromic shift.

• Molecular Hybridization: Combining complementary DNA/RNA strands.

• Electrophoresis: Separating nucleic acid fragments by size; smaller pieces migrate faster through a gel.

Electrophoresis

• Agarose gel method utilized to visualize and separate different nucleic acid sizes.