Name _______________________________________________________
Test Date _Tues, 11/30______
UNIT 7 – DNA
I. DNA (pp. 287-294)
_Deoxyribonucleic acid_______ contains the _genetic code____ and the _working instructions______ for a
cell. In a _eukaryotic___ cell, DNA is located in the _nucleus___. Although _prokaryotic____ cells do not
contain a nucleus, they do contain a _single__ molecule of DNA, or one _chromosome__________.
A. History of the Discovery of DNA
Scientists in the early 1900s realized that inheritance was dependent on DNA and that chromosomes
were composed of _DNA___ and _protein__.
1. Griffith - 1928
Worked with _bacteria that caused pneumonia__. Cultured non-living, _pathogenic______________
bacteria with living bacteria that did not cause disease. Discovered ability of bacteria to cause disease
could be passed from one bacteria to another. Griffith called this _transformation___________.
_Avery_____ later identified this “transforming substance” as _DNA______.
2. Hershey and Chase - 1952
Identified _DNA___ as the part of chromosomes that contain the genetic instructions. They used a
bacteriophage which is a _virus_____ that infects _bacteria___. Scientists knew viruses were made of
_DNA____ and _protein___. They also knew viruses injected their genetic material into a
_host___ cell so that the host cell would _make copies of the virus____. Hershey & Chase were able to
chemically prove that the injected genetic material was _DNA____, not _protein______.
3. Chargaff – 1950
Chemically proved the nitrogen base-pairing rules
4. Watson & Crick - 1953
First identified the _double helix______ structure of DNA. They accomplished this by building
molecular models and studying a copy of an x-ray of DNA taken by _Rosalind Franklin____.
They also confirmed “Chargaff’s Rules” structurally.
B. DNA Structure
DNA is a _nucleic acid____ composed of _monomers____ called _nucleotides____.
Each nucleotide of DNA consists of:
1. __5___ carbon sugar - _Deoxyribose_____
2. _Phosphate____ group
3. _Nitrogen___ base - there are 4 possibilities for the nitrogen base:
a. _adenine____________________
b. _thymine____________________
c. _guanine____________________
d. _cytosine___________________
It is the _number___ and _pattern_____ of nucleotides that makes each gene unique. There are
strong, stable _covalent___ bonds that hold the parts of each nucleotide together. Nucleotides form
strong _covalent___ bonds with other nucleotides, resulting in a long strand of nucleotides. The
DNA molecule is created when weak _hydrogen___ bonds form between the _nitrogen___ bases of two
nucleotide strands. The two strands form a twisted ladder-like structure, producing the
_double helix___ structure of DNA.
C. A Closer Look at Chargaff’s Rules
Chargaff’s chemical analysis of DNA showed that the % of adenine = % _thymine___ and the % of
guanine = the % _cytosine_____. Watson & Crick confirmed that base pairing can only occur between
two specific nitrogen bases:
___adenine ____________ and _thymine___________
OR
___guanine_____________ and _cytosine___________
II. DNA Replication
(pp. 295-299)
Prior to cell division, the DNA must _copy itself______. This is known as DNA _replication_____________.
During this process, DNA is in the form of fine strand wrapped in protein, known as
_chromatin____________. DNA can replicate itself exactly due to _Chargaff’s Rules______________.
Replication occurs in the _nucleus__________ of a eukaryotic cell and requires the participation of several
_enzymes_________. Replication may be summarized in two steps:
A. An _enzyme____ breaks the weaker _hydrogen____ bonds between the _nitrogen bases_____ and
DNA is _unzipped____. This “unzipping” occurs in _several places___ along the DNA molecule, like a
_broken zipper_____.
B. Free _nucleotides_____ located in the nucleus are added to each exposed _nitrogen bases___
by the enzyme _DNA Polymerase___, according to _Chargaff’s _____ rules. The result is two
_identical______ DNA molecules - each new DNA consists of one _original_______ strand and one
_new______ strand. These two identical DNA molecules are known as _sister chromatids_______ and
they remain “_glued___” together until the cell _divides_____ into two _identical_______ cells.