LECTURE 5: CHEM BASIS OF HEREDITY

• Chromosome


  Prokaryote & Eukaryote
• Components of chromosome


  • Lipids
  • Proteins
  • Nucleic acids
• Proteins in chromosome


  • NHCP
  • Histone
• Nucleic acids in chromosome


  • DNA
  • RNA
• Replication


  1. Initiation

  2. Elongation

  3. Termination
• Concept of the Gene


  • Mendelian concept (1865) - Mendelian Factor
  • R. A. Fisher (1930) - quantitative geneticist; 2 viewpoints about genes - Hypothetical entity, Chemical compound
• Chemical composition of the chromosome


  • Lipids
  • Proteins - Histones or protamines (basic proteins), Non-histone chromosomal protein (acidic proteins)
  • Nucleic acids - DNA and RNA
• Characteristics of a GENETIC MATERIAL (H.J. MULLER)


  • Can duplicate itself with extra fidelity
  • Stable molecular structure
  • Mutation is duplicated faithfully
  • Can carry all necessary biological information
  • Can transmit the information from generation to generation
  • Stored information must be decoded and translated into action
• Events leading to the discovery of DNA


  1. Proteins - most important molecule

  2. Friedrich Miescher (1860) - Isolated a molecule from the nucleus and called it "nuclein" (DNA in 1930s)

  3. Ernst Haeckel (1866) - Discovered that the most obvious cellular component of the cell is the NUCLEUS

  4. Edmund Wilson (1895) - Staining technique to study karyokinesis of ovium, Important nuclear element handed from cell to cell: DNA

  5. Frederick Griffith (US Medical Officer, 1928) - Transformation experiment using Streptococcus pneumoniae, Declared the presence of transforming principle

  6. Oswald Avery, Colin Macleod, Maclyn McCarty (1944) - Identified the transforming principle (TP) as DNA

  7. Alfred Hershey and Martha Chase (1952) - Proved that DNA is the genetic material of the bacterial viruses

  8. Norton Zinder, Joshua & Esther Lederberg (1952) - Performed transduction experiment in Salmonella typhimurium

  9. Elucidation of the structure of the DNA (1953) - Francis Crick, James D. Watson, Maurice Wilkins, Rosalind Franklin
• Nucleotide


  Building block of nucleic acids (basic unit) - Phosphate group, Nucleoside - 2-Deoxyribose, Nitrogen Base - Purine (Adenine Guanine), Pyrimidine (Thymine Cytosine)
• Features of the DNA ATCG


  • Composed of 2 polynucleotide strands
  • 2 strands are antiparallel
  • A = T (2 hydrogen bonds), C = G (3 hydrogen bonds)
  • Forms a helical coil
  • Sugar is 2-deoxy-D-ribose, Starts with 5' and ends with 3', 1 complete turn = 360 degrees with 10 base pairs, 3.4 nm apart from each other = 34 Angstrom, width = 20 A or 2 nm
• Evidence to show that the DNA is the genetic material


  • Relative constancy of DNA in all diploid tissues
  • Haploid cell has half the amount of DNA in diploid cell
  • Doubling of DNA at S phase
  • Cells with extra sets of chromosomes have a proportional increase in DNA content
  • Parallelism of UV absorption with mutation rates
  • Transformation and transduction in bacteria
  • Production of new viral particles in bacterial cells
  • RNA content of Tobacco Mosaic Virus caused infection not the protein coat
• RNA Structure


  Composed of one polynucleotide strand, Sugar is D-ribose, No Thymine but instead Uracil; Adenine Cytosine Guanine
• Steps in replication process (SEMI-CONSERVATIVE)


  1. Initiation - starts at the ori-site (origin), formation of single stranded DNA templates, Helicase - helix unwinding proteins DENATURATION/UNWINDING, SSBPs - single-strand binding proteins, DNA gyrase - relaxes tension at the fork

  2. Elongation - Leading strand - Primase - adds RNA primers, Lagging strand - Primase provides RNA primers, have several primers, DNA Pol III adds in the 5' to 3' direction, Okazaki fragments - Short sequences, synthesized discontinuously, DNA Pol I for excision of primers and filling in of gaps left by the primers, Ligase - joins the phosphodiester bonds

  3. Termination - two identical DNA molecules
• Replisome


  DNA Pol III with 2 catalytic cores, Primosome (helicase + primase)
• Significance of replication

  • Faithful copying of a DNA to produce two DNA molecules
  • DNA molecules are identical to each other and to the parent molecule
  • Transmission of biological information from a parent cell to its daughter cells; from generation to generation
• Mechanisms of high precision replication


  • Specificity of base pairing
  • Proof reading ability of DNA Polymerases
  • Excision repair mechanisms - repair of thymine dimer, N glycosidase activity - Hydrolyzes bond between damaged base and sugar
• Prokaryotic chromosome


  Escherichia coli with single chromosome - double stranded, approximately 11,000 μm long, 1.1 cm (1mm = 1000 μm), 4 x 10^6 bp (1 kb = 1000 bp); amount of DNA approximately 1,000x the length of E. coli
• Prokaryotic chromosome organization


  • Nucleoid, 10 independent domain, Each domain consists of loops, Each loop: 40,000 bp of supercoiled DNA, DNA binding protein Hu and H
• Eukaryotic Chromosome


  Eukaryotic cell with large amount of DNA, diploid human cell, length of DNA is 6 ft. long (end to end), 6 ft. X 12 in./ft. x 2.54 cm/inch =183 cm, 5.5 x 10^9 bp (or 5.5 billion bp), 5 x 10^-4 cm. (or 5 μm) diameter of nucleus
• chemical components of the chromosome


  nucleic acids (DNA and RNA)

  proteins

  lipids
• 2 types of proteins


  1 histones or protamines (basic)

  2 non-histone chromosomal proteins (acidic)
• 6 characteristics of DNA as genetic material


  1 can duplicate itself w/ extra fidelity (1/1 M copies)

  2 stable molecular structure (low mutation frequency)

  3 mutation is duplicated faithfully (inheritance of mutation/genetic source of variation)

  4 can carry all necessary biological information

  5 can transmit info from generation to generation

  6 stored information must be decoded and translated into action
• were thought to be the most important molecule


  proteins (proteios) "of first importance"
• - protein from pus cells

  - isolated a molecule from the nucleus and called it nuclein

  Friedrich Miescher
• most obvious cellular component of the cell is the nucleus

  Ernst Haeckel
• • staining technique to study karyokinesis of ovum

  •important nuclear element handed from cell to cell: DNA


  Edmund Wilson
• • transformation experiment using Streptococcus pneumoniae

  • avirulent (R) strain was transformed to virulent (S)

  • declared the presence of transforming principle


  Frederick Griffith
• • identified the transforming principle (TP) as DNA


  Oswald Avery, Colin MacLeod and Maclyn McCarty
• • proved that DNA is the genetic material of the bacterial viruses (phages)

  • DNA is labeled with P32

  • protein coat is labeled with 35S

  • famous blender experiment

  Alfred Hershey and Martha Chase
• • performed transduction experiment in Salmonella typhimurium


  Norton Zinder, Joshua and Esther Lederberg
• Elucidation of the structure of the DNA


  James Watson and Francis Crick
• ➢ helical DNA structure

  ➢ sugar and phosphate outside

  ➢ nucleotides inside

  Rosalind Franklin, Gosling and Maurice Wilkins
• - triple helix

  - phosphate in the center


  James Watson and Francis Crick
• - triple helix DNA

  Linus Pauling
• - nucleotides are flat, one on top of another

  - possibility of A=T, C=G pairing

  - Crick saw the importance of specific pairing

  in replication.

  John Griffith
• purine-pyrimidine ratio 1:1 (Chargaff's rule)

  Erwin Chargaff
• - H in the bases can change its position

  - possibility for H bonding


  Jerry Donohue
• component of nucleotide


  phosphate group and nucleoside
• component of nucleoside


  nitrogenous base and 2-deoxyribose