Chapter 11 BSC 1005 Mr. TidwellDNA: The Molecule of Heredity- In 1933, J. L. Alloway showed that transformation occurred readily in culture dishes.- In the 1940s, Oswald Avery, Collin MacLeod, and Maclyn McCarty isolated DNA from killed S-strain bacteria, mixed it with R-strain bacteria, and produced live S-strain bacteria.o This suggested that the transforming molecule from the S-strain was DNA.o To rule out the possibility that a protein contaminant was actually causing the transformation, Avery treated samples with protein-destroying enzymes and still induced transformation.o When DNA-destroying enzymes were added to the samples, transformation did not occur.- The secrets of DNA and heredity are found in the 3D structure of the DNA molecule.- In the 1940s, biochemist E. Chargraff determined that the amount of A in a DNA molecule equaled the amount of T, and the amount of C equaled the amount of G.o This finding is referred to as “Chargraff’s Rule”.- From x-ray patterns they determined DNA is long and thin, and has a uniform diameter of 2 nanometers.- The two strands in a DNA double helix are said to be antiparallel (oriented in opposite directions).- Adenine (A) bonds with thymine (T) and guanine (G) bonds with cytosine (C).o Bases that bond with each other are called complementary base pairs.- Adenine and guanine (Purines) are large molecules; thymine and cytosine (Pyrimidines) are relatively smaller.o Because base pairing always places a large molecule with a small one, the diameter of the double helix remains constant.- The key to the diverse amount of information DNA codes for lies in the sequence, not the number, of subunits.o Within DNA strand, the four types of bases can be arranged in any linear order, and this sequence is what encodes genetic information.o An organism has millions (bacteria) to billions (plants and animals) of nucleotide bases.Page 1 of