Name _________________________________________________________________________________Test Date _______________
UNIT VI – DNA
I. DNA - THE DISCOVERY OF THE MOLECULE OF INHERITANCE
DNA contains the ______________________ and the __________________________ for a cell. Scientists in the early 1900s realized
that inheritance was dependent on _______________ found on _______________________ and that chromosomes were composed of
______________________ and ___________________________. It wasn’t until the 1940s that scientists established __________ as
the molecule of inheritance, and still another 15 years passed before the structure of DNA was discovered.
A. Griffith (1928)
 Discovered that bacteria can take up genetic material from environment in a process known as _______________________.
 Performed experiments with _________________________ and bacteria known as ________________________________.
o Mixed harmless living bacteria with dead ______________________________ bacteria and injected them into mice.
o Mice died.
B. Oswald Avery et. Al (1944)
 Set up experiments to identify “transforming substance” discovered by Griffith
 Used enzymes that destroyed carbohydrates, lipids, proteins, and RNA . . . transformation still occurred. Used an enzyme that
destroyed DNA, _____________________________________________________________________________.
 Concluded that ____________ stores and transmits the genetic information from one generation of an organism to the next.
 Scientific community did not completely accept their conclusion.
C. Alfred Hershey & Martha Chase (1952)
 Used a virus known as a __________________________________ which infects __________________________________.
 Viruses are composed of ______________and ____________________; require a ______________ cell in order to replicate.
 Hershey & Chase recognized that virus must inject its genetic material into the bacterial cell for replication to take place.
 Used labeled ____________________________________ to determine whether DNA or protein was injected into bacterium.
 Hershey & Chase concluded that the genetic material of the bacteriophage was _____________________________.
D. Watson & Crick (1953)
 Used molecular models to solve the 3-dimensional structure of DNA
 “Borrowed” an x-ray of DNA taken by ________________________________________ to solve the puzzle
 Proposed a _______________________________ structure with a backbone of alternating _______________________ and
_________________________________________ with _____________________________________ paired in the middle.
II. STRUCTURE OF DNA
DNA is a _________________________, a biomolecule composed of ___________________ called __________________________.
A. Each nucleotide of DNA consists of:
1. ____________ carbon sugar - _________________________________
2. ________________________ group (PO4)
3. ________________________ base
 Strong, stable __________________________ bonds hold the parts of each nucleotide together.
 In addition, nucleotides form strong _______________ bonds with other nucleotides, resulting in a long strand of nucleotides.
 Double helix created by weak ________________________ bonds between the _________________________ bases.
 The diameter of DNA is uniform due to specific pairing of nitrogen bases
o Purines – double-ringed nitrogen bases
 ________________________________
 ________________________________
o Pyrimidines - single-ringed nitrogen bases
 ________________________________
 ________________________________
o _____________________________ always base pairs with a ________________________________, specifically …
 _______________________________ base pairs with ___________________________
 _______________________________ base pairs with ___________________________
o _______________ and _______________ determined this structurally because the ______________ of DNA is
uniform.
_____________________ determined this chemically. His chemical analysis of DNA from many different organisms
always showed that the % of adenine = % _______________ and the % of guanine = the % ____________________.
These findings are known as ____________________________________________.
The two strands of nucleotides are _________________________________; that is, they run opposite to each other.
It is the _______________________ and ________________________ of nucleotides that makes each gene unique.
o
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DEOXYRIBONUCLEIC ACID
adenine
covalent bond
cytosine
deoxyribose
guanine
hydrogen bond
nitrogen bases
nucleotide
phosphate group
purines
pyrimidines
thymine
5’ end
3’ end
III. DNA REPLICATION
Prior to cell division, the DNA must ___________________________. This occurs in ________ of _________________________.
During this part of the cell cycle, DNA is in the form of ____________________________. DNA can replicate itself exactly due to
______________________________________. Replication occurs in the ________________________ of the cell and requires the
participation of several ___________________________.
Replication may be summarized in the following steps:
 DNA is “unzipped” by the enzyme, ___________________. Helicase breaks the ______________________ bonds between
the _________________________. The point where the unzipping begins is known as the
______________________________. The continuation of the unzipping is called the ________________________________.
This occurs in several places in each ______________________________, much like a ______________________________.
 __________________________________________ hold the separated DNA strands apart.
 Another enzyme, ______________________________________________ moves ahead of the ________________________
to relieve tension in the double helix as it is being unzipped.
 The enzyme, ________________________________________ adds nucleotides to both sides of the DNA molecule according
to __________________________ rules; however, DNA polymerase has two restrictions:
1) It can only add nucleotides in a _____________________ direction.
2) It can only add nucleotides to an existing strand.

Before DNA polymerase begins moving in nucleotides, a __________________________ must be put in place. Eventually this
primer is removed and replaced with DNA nucleotides.
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The two sides of the DNA molecule are replicated differently because nucleotides can only be added in a ___________
direction:
o One side of the DNA molecule is being replicated in the same direction as the ___________________________. This is
known as the ____________________ strand. Nucleotides are moved in by ___________________________________
in a _____________________________ direction as the DNA is unzipped.
o On the other side of the DNA molecule, nucleotides are added ________________ from the replication fork. This is known
as the _______________________________ strand. Short segments of nucleotides are synthesized, each with a new
_______________________________________, as the DNA is unzipped. These short segments are known as
____________________________________. Eventually, another enzyme known as _______________________ “glues”
together the _______________________________ fragments to create a continuous strand of nucleotides.
Another type of __________________________________________ proofreads the replicated DNA to minimize the chance of
___________________________.
The result is two ________________________ DNA molecules, each new DNA consists of one _____________________
strand and one ____________________ strand. This is known as the __________________________________________
model of replication.
These two identical DNA molecules are the ___________________________________________ that proceed through
_____________________________.
Once replication has been completed, the cell moves into __________ and then, ______________________________ of
_____________________________.
IV. A DETAILED VIEW OF DNA REPLICATION