BIO181 Lecture 7 - DNA Stucture

Page 1: Title

  • DNA Structure

  • BIO 181: General Biology I Fall 2024

  • Dr. Hart 10/3/24

Page 2: Outline

  • Early DNA experiments

  • Structure of DNA

  • Chromosome Structure

Page 3: Properties of Genetic Material

  • What is the genetic material?

  • Four criteria for genetic material:

    • Information

    • Replication

    • Transmission

    • Variation

  • Late 1800s: Biochemical basis of heredity postulated.

  • Chromosomes are the bearers of genetic information; proteins expected to be the genetic material.

Page 4: Friedrich Miecher's Discovery

  • 1869: Miecher discovers "nuclein" while isolating proteins.

  • Isolated from white blood cells in discarded bandages.

  • Pure DNA from salmon sperm found only in cell nuclei.

Page 5: Chargaff’s Analysis

  • Erwin Chargaff analyzed DNA base composition across species.

  • Findings:

    • Adenine (A) = Thymine (T)

    • Cytosine (C) = Guanine (G)

  • Example percentages from various organisms.

Page 6: Griffith’s Bacterial Transformation

  • Late 1920s: Frederick Griffith works with S. pneumoniae bacteria.

  • Two strains: Smooth (S) - fatal, Rough (R) - non-fatal.

  • Smooth strains have protective capsules; heat-killed S are non-fatal.

  • Live R mixed with heat-killed S result in fatalities (transformation).

Page 7: Griffith’s Results

  • Question: How did R obtain the S strain's traits?

  • Genetic material transferred from heat-killed S to living R.

Page 8: Avery, MacLeod, and McCarty's Work

  • 1940s: Investigating the biochemical basis of transformation.

  • Conclusion: Only purified DNA from type S could transform type R.

  • Tested DNase, RNase, and proteases to confirm DNA as the genetic material.

Page 9: Replicating Avery's Findings

  • Further experimentation using DNase, RNase, proteases.

  • Absence of transformation by DNase confirms DNA as genetic material.

Page 10: Double-Helix Structure

  • 1953: Watson and Crick propose DNA's double helix structure using models.

  • Rosalind Franklin's X-ray diffraction provides crucial evidence.

Page 12: Nobel Prize Recognition

  • Watson, Crick, and Wilkins receive Nobel Prize in 1962.

  • Franklin’s contributions recognized posthumously.

Page 13: Levels of DNA Structure

  • Levels include:

    • Nucleotides

    • Strand

    • Double helix

    • Chromosomes

    • Genome

Page 14: Nucleotide Composition

  • Nucleotides made of:

    • Phosphate group

    • Pentose sugar (Deoxyribose for DNA)

    • Nitrogenous bases (A, G, C, T)

  • RNA has ribose and uses uracil (U).

Page 15: Nucleotide Numbering System

  • Sugar carbons numbered 1′ to 5′:

    • Base on 1′ carbon, phosphate on 5′ carbon.

Page 16: Phosphodiester Bonds

  • Nucleotides covalently bonded via phosphodiester bonds.

  • Backbone made of phosphates and sugars, bases project, written 5′ to 3′.

Page 17: Features of DNA

  • Characteristics:

    • Double-stranded, antiparallel strands, right-handed helix.

    • Sugar-phosphate backbone with bases on the inside.

Page 18: Grooves of the DNA Strand

  • Major groove: Proteins bind affecting gene expression.

  • Minor groove: Narrower, less accessible.

Page 19: RNA Characteristics

  • Usually single-stranded; sugar is ribose.

  • Uses uracil instead of thymine; multiple forms (mRNA, rRNA, tRNA).

Page 21: Eukaryotic Chromosomes

  • Eukaryotic chromosomes can be hundreds of millions of base pairs long.

  • Composed of chromatin (DNA-protein complex).

Page 22: Levels of DNA Compaction

  • Levels are:

    • DNA wrapping around histones (nucleosomes).

    • 30-nm fiber (3D zigzag of nucleosomes).

    • Radial loop domains formed by SMC proteins.

Page 23: Degrees of Compaction

  • Not uniform across chromosomes:

    • Heterochromatin (very compact).

    • Euchromatin (less compact); chromosomes highly compacted in metaphase.