what are chromosomes made of?. by mass, chromosomes are about half protein and about half dna if...

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

Proteins:

• 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 structure of 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, 1944stripped away protein without destroying the transforming principle