The Search For Genetic Material
1. Thomas Hunt Morgan
showed that genes are located on _______________________
1.
chromosomes are made up of ________ and ________ , thus it was thought that the genetic material was either
DNA or proteins.
2. Frederick Griffith
- worked with Streptococcus pneumoniae , which causes
pneumonia in mammals
he had 2 strains:
1.
S (smooth) strain = ______________________________
2.
R (rough) strain = _______________________________
discovered that DNA from the dead S cells had genetically transformed some of the living R bacteria into S bacteria, which he called ________________________________
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________________________ – a change in genotype and phenotype due to the incorporation of external DNA by a cell
3. Alfred Hershey and Martha Chase
- worked with ________________ = _______________________
viruses are made up of only ________ and ________________
they labeled the DNA and protein with different radioactive isotopes
discovered that the radioactive labeled DNA was injected into the host cell and _____________________________________
___________________________________________________
They now knew DNA was the genetic material but what was its structure?
It was already known that DNA was a polymer (repeated subunits) of
________________
Each nucleotide is made up of:
1. ________________
2. ________________
3. ________________
It was also known that the bases could be:
1. ________________ 3. ________________
2. ________________ 4. ________________

2 families of nitrogenous bases
2

 _____________ – 6-membered ring of carbon and nitrogen atoms

____________ – 6-membered ring fused to a five membered ring
4. Erwin Chargaff
- determined that the ________________ composition was different for each organism
- _____________________________________________________
________________________________________________________
~ the number of adenines = the number of ____________ A = T
~ the number of guanines = the number of ____________ G = C
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5. James Watson and Francis Crick
determined that DNA is a _________________________ shape
~ looks like a ladder that has been twisted: sides of the ladder = _________, __________ backbone rungs of the ladder = ___________________________
base pairing in DNA:

A-T

C-G
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1. Watson and Crick
- after Watson and Crick announced their double helix model
they also proposed an idea about ________________________
DNA replication
1.
before duplication the bonds between the
________________ break
2.
each half of the old double helix acts as a _______________ for the new strand
3.
________________ plug into the appropriate sites
4.
bonds reform between the nitrogen bases (now have 2 identical strands)
- each DNA molecule now has one “old” strand and one
“new” strand
This model ________________ by Watson and Crick is known as the
________________________________________________
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2. Matthew Meselson & Franklin Stahl
- ________________________________________________
________________________________________________
~ A human cell can copy all of its DNA in just a few _____________
~ There is only about 1 error per billion nucleotides (6 billion
nucleotides total)
Mechanisms of DNA Replication
________________________________ –sites where DNA replication begins
- in eukaryotes each chromosome has ________________ of
replication origins
- at each replication origin a
“_______________________” forms and DNA replication occurs in __________________ away from the replication origin
______________________________
– a Y-shaped point on a replicating DNA molecule where new strands are growing
6

________________________________ – enzymes that speed up the elongation of new DNA at a replication fork by adding nucleotides to the strand
adds complementary nucleotides to the growing end of the new
DNA strand
The Problem of Antiparallel DNA Strands
The sugar phosphate backbones of DNA run in opposite directions
there is a 5’ end
and a 3’ end
THE PROBLEM
- DNA polymerase can only add nucleotides to the 3’ end
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If replication occurs in the ____ to ____ direction away from the replication origin it is not a problem. The nucleotides get added as the replication fork opens up. This is called the ____________________
____________________ - the new _______________ complementary
DNA strand made in the 5’ to 3’ direction
To add nucleotides to the other strand, DNA polymerase must work
__________ from the replication fork. The DNA synthesized in this direction is called the ____________________
____________________
–
___________________ synthesized DNA strand that elongates in the direction away from the replication fork
in this way DNA is replicated in short segments instead of 1 continuous strand
The short segments of replicated DNA are called
____________________
Then, the enzyme ____________________ joins the Okazaki fragments to make one continuous strand
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Other Proteins That Aid in DNA Replication
___________________________ – an enzyme that untwists the double helix at the replication fork, separating the two old strands
___________________________
– hold the DNA strands apart while they serve as templates for synthesis of the new DNA strand
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