Test 3: Intro to Nucleic Acids

Introduction to Genetics and Viruses

  • Emphasizes the importance of genetics in understanding viruses.

    • Viruses consist of DNA or RNA. Understanding nucleic acids is crucial for comprehending viral structures..

Overview of Nucleic Acids

Definition of Nucleic Acids

  • Nucleic acids are polymers of nucleotides.

  • Nucleotides consist of:

    • A five-carbon sugar (pentose)

    • A phosphate group

    • A nitrogen-containing base

Structure of a Nucleotide

  • The five-carbon sugar's carbons are numbered from 1' to 5'.

    • 5' end: has a free phosphate.

    • 3' end: has a hydroxyl group (−OH) that is crucial for replication.

Comparison of RNA and DNA

DNA vs RNA

  1. Type of Nucleotide:

    • DNA: Polymer of deoxyribonucleotides

    • RNA: Polymer of ribonucleotides

  2. Strand Structure:

    • DNA: Double-stranded

    • RNA: Single-stranded

  3. Sugar Composition:

    • DNA: Deoxyribose

    • RNA: Ribose (difference lies at the 2' carbon where ribose has an O and deoxyribose does not)

  4. Nitrogen Bases:

    • Purines in DNA: Adenine (A), Guanine (G)

    • Pyrimidines in DNA: Cytosine (C), Thymine (T)

    • Purines in RNA: Adenine (A), Guanine (G)

    • Pyrimidines in RNA: Cytosine (C), Uracil (U)

    • Important Note: DNA contains thymine (T) not uracil (U).

Bonding in DNA

  • Purines have a double cyclic structure, whereas pyrimidines have a single cyclic structure.

  • Hydrogen bond strengths:

    • A-T pair: 2 hydrogen bonds

    • G-C pair: 3 hydrogen bonds (stronger bond due to more hydrogen bonds).

Discovery of DNA Structure

  • The structure of DNA was discovered by Watson and Crick in 1953, credited to their foundational understanding of the double helix.

Double-helix Structure of DNA

  • Composed of two backbones made of sugar and phosphate.

  • Regions rich in G-C pairings are harder to separate than A-T pairings due to hydrogen bond differences.

  • Understanding the 5' and 3' ends is crucial in DNA structure.

Genes and Genetic Information

Definition of a Gene

  • Defined as the entire DNA sequence necessary for producing a functional RNA or protein.

    • Example types of functional RNA:

    • Ribosomal RNA (rRNA)

    • Transfer RNA (tRNA)

Comparison of Prokaryotic and Eukaryotic DNA

  1. Chromosome Count:

    • Prokaryotes: Single chromosome

    • Eukaryotes: Multiple chromosomes (46 in humans)

  2. Chromosome Structure:

    • Prokaryotic chromosomes are circular.

    • Eukaryotic chromosomes are linear

  3. Haploid vs Diploid:

    • Prokaryotes: Generally haploid (one copy of each gene)

    • Eukaryotes: Can be both haploid (gametes) and diploid (somatic cells).

  4. Introns:

    • Prokaryotes generally lack introns, while eukaryotes contain both introns and exons.

Definition of Introns and Exons

  • Introns: Intervening non-coding sequences that are removed during RNA processing.

  • Exons: Sequences that are expressed and retained in the final RNA product.

  • More introns than exons in eukaryotic DNA.

RNA Processing Differences

Eukaryotes vs Prokaryotes

  • Eukaryotes undergo RNA processing:

    • Addition of a 5' cap and 3' poly-A tail for stability and transport.

  • Prokaryotes do not undergo such modifications.

Collinearity in Gene Expression

  • Collinearity: The relationship between DNA sequence and its corresponding protein product. Eukaryotes break this due to introns, while prokaryotes maintain it due to a lack of introns.

Semi-Conservative DNA Replication

Basic Principles

  • Each strand of the double helix serves as a template.

  • The process requires specific starting points (ori site) and a primer to initiate replication (in prokaryotes, RNA serves as the primer).

Key Rules for DNA Replication

  1. A template strand is necessary.

  2. An RNA primer is required for initiation.

  3. Replication occurs in the 5' to 3' direction.

Summary of DNA Replication Mechanism

  • Semi-conservative replication involves the unwinding of the double helix, followed by each original strand acting as a template for a new strand.

  • Essential enzymes participate in the replication process, though specifics are not covered here due to time constraints.