CHAPTER 16: Molecular Basis of Inheritance

Griffith’s experiment: worked with 2 strains of bacteria.

Mixed living non-pathogenic bacterial strain with a dead pathogenic strain and determined that the living non-pathogenic became virulent and deadly…he called this TRANSFORMATION

S and R strains; S-deadly R- non-pathogenic.

Transformation-is the genetic alteration of a cell resulting from the direct uptake, incorporation and expression of exogenous genetic material (exogenous DNA) from its surroundings and taken up through the cell membrane(s)

AVERY: expands upon Griffith’s experiment to determine what the “transforming factor” was. Was it DNA? RNA? Or protein? They determined that DNA was the transforming agent in the bacteria.

Hershey and Chase:

Determined that it was indeed DNA that transmitted the genetic material by tracing radioactively labeled P(phosphorus) through a bacteriophage (is any one of a number of viruses that infect bacteria)

DNA: and the structure: WATSON & CRICK took credit for this model

ROSALIND FRANKLIN really came up with this structure

DOUBLE HELIX – BACKBONE MADE OF DEOXYRIBOSE SUGAR and PHOSPHATE GROUPS; RIGHT HANDED in configuration

RNA AND DNA MOLECULAR STRUCTURE:

NUCLEOTIDE

1. DEOXYRIBOSE SUGAR

2. NITROGENOUS BASE

  • ADENINE - A
  • GUANINE- G
  • THYMINE- T
  • CYTOSINE- C

CHARGAFF’S RULES:A-T G-C

PURINES – GUANINE & ADENINE (2 organic rings)

PYRIMIDINES- CYTOSINE & THYMINE (1 organic ring)

  1. PHOSPHATE GROUP

EACH FULL TURN OF HELIX IS 3.4 nm

10 bases per turn at .34nm per base

DNA REPLICATION

DNA replication is SEMI CONSERVATIVE meaning there is an old strand and a new strand.

Enzymes used in DNA replication:

  1. Helicase
  2. Single Strand Binding Protein ( SSBP)
  3. DNA Polymerase 3
  4. RNA Polymerase/PRIMASE
  5. DNA Polymerase 1
  6. DNA Ligase

REPLICATION STEP BY STEP:

  1. Begins at the Origin of Replication creates a REPLICATION FORK!
  2. Helicase and Single Strand Binding Protein unwind the strand and keep it open while the replication proceeds.
  3. DNA polymerase 3 adds nucleotides to the growing complementary strand; 1 nucleotide at a time.
  4. All replication occurs in the 5’ 3’ direction.
  5. On the LEADING strand this happens continuously TOWARDS the replication fork!
  6. On the LAGGING strand, DNA polymerase works AWAY from the replication fork!
  7. On LAGGING strand, PRIMASE begins synthesis of an RNA primer for the Okazaki fragment
  8. DNA polymerase 1 removes the primer from the 5’ end and continues to add nucleotides to complete the fragment
  9. DNA ligase bonds the 3’ end of one fragment to the 5’ end of the following fragment