Download What are chromosomes made of?

What are chromosomes made of?
•  By mass, chromosomes are about half
protein and about half DNA
•  If genes are on chromosomes, are they
protein or DNA or perhaps a mix?
Basic chemistry of DNA and protein
•  What are the subunits of protein?
•  How many different types of subunit are
there?
General structure of an amino acid
DNA
•  DNA was discovered in 1869 by Friedrich
Miescher, a German Chemist. Extracted
from the nucleus.
•  DNA has subunits.
•  How many different subunits are there?
The basic structureof DNA and RNA
determined by Levene in the 1920’s
General structure of a nucleotide
Levene’s tetranucleotide theory
•  Logic behind the theory—
–  Genetic information needs to be complex
–  More complexity possible in proteins than
in DNA—he suggests DNA plays a role as
‘scaffolding’, a repeating sequence of 4
bases
–  The evidence? Approximately equal
amounts of each of the 4 bases found in
DNA
Avery, MacLeod and McCarty, 1944
•  Assumption: Protein is the genetic material
•  Plan: if ‘transforming principle’ treated
chemically to remove protein, it should lose its
power – removed all but 0.02%
•  Problem: It didn’t
Avery, MacLeod and McCarty, cont.
•  After chemically removing protein,
‘transforming principle’ still able to convert
rough bacteria to smooth bacteria
•  After treatment with proteinase, ditto
•  After treatment with RNAase, ditto
•  After treatment with DNAase –’transforming
principle’ activity destroyed
•  FIRST PAPER SUPPORTING DNA AS
GENETIC MATERIAL
Tetra nucleotide theory accepted for
nearly 30 years
•  What finally shifted thought away from
protein as the genetic material to DNA as
the genetic material?
•  The ‘transforming principle’ of Griffith,
using ‘Rough’ and ‘Smooth’ bacteria in
1928
•  Avery, MacLeod and McCarty, 1944
stripped away protein without destroying
the transforming principle