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Unit 3: DNA Structure & Function (Ch. 9 & 22)
Name: _______________________
I. DNA Function & Structure
DNA Functions
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___________________________________________________________________________
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____________________________________________________________________________
II. DNA History
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Fredrick Meischner (1869) ______________________________________________________________
___________________________________________________________________________________
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Phoebus Levene (1909) _________________________________________________________________
___________________________________________________________________________________
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What information led people to
hypothesize that protein was the
hereditary material?
____________________________
____________________________
____________________________
____________________________
____________________________
____________________________
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Explain how Griffith’s mouse
experiment provided evidence that
DNA is the hereditary material
rather than protein. ___________________
___________________________________
___________________________________
___________________________________
___________________________________
___________________________________
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Alexander Todd ______________________________________________________________________.
 Erwin Chargaff (1947) __________________________________________________________________
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Alfred Hershey & Martha Chase’s experiment in 1953 also confirmed that DNA is the genetic material.
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Maurice Wilkins and Rosalind Franklin used X-ray crystallography to determine the helical structure of DNA.
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If all the above scientists performed the experiments regarding DNA structure, why are James Watson and
Francis Crick the only ones given credit? ____________________________________________________
___________________________________________________________________________________
___________________________________________________________________________________
III. Structure of Nucleic Acids
Nucleotides (monomers of nucleic acids)
1) 5 Carbon Sugar (Ribose or deoxyribose)
2) Phosphate Group
3) Nitrogenous base
Characteristics of DNA:
1) Deoxyribose sugar
2) Phosphate Group
3) Four Bases (A, C, G, T)
4) Double Stranded
5) Helical shape
DNA Facts:
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The human genome is made up of more than 6 billion nucleotides, 3.3 billion base pairs.
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Mistakes in base pairing occur in only one per billion, but ____________________________________
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Every 10 nucleotide pairs = 360o turn within the “right- handed”, spiraling DNA molecule
IV. Characteristics of DNA
1) Consists of two parallel helical or twisted chains, each made up of subunits called ___________________.
2) The deoxyribose and phosphate portions of the nucleotides are on the outside of the molecule forming the
_________________ and the nitrogen bases are on the inside forming the _______________________.
3) Each nucleotide is connected to the other nucleotides in the same chain by ___________________ bonds,
which are strong chemical bonds between sugars and phosphates.
4) Each nucleotide is bound to a nucleotide on the other chain by weak chemical bonds called ______________,
which are between specific pairs of bases (A-T & C-G). The two chains are complementary in structure, so the
sequences of bases on one strand determine the sequence of bases on the other strand.
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A – A – G – G – C – C – T – T – G – A – C – T
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5) Adenine and Guanine are composed of double rings of C and N and are
called _____________________.
Cytosine and Thymine are composed of single rings of C and N and are
called ______________________.
Why does a pyrimidine always bond with a purine?
______________________________________________________
______________________________________________________
______________________________________________________
6) The sugar-phosphate backbone is ____________________. When
carbons of the sugar are assigned numbers to indicate the position of the
molecule, one can see the reverse orientation.
7)
When DNA replicates, the two chains come apart and each serves as a
__________________ (mold) of the formation of new chains.
8) The sequence of bases in each chain constitutes the ____________
_________, which provides information to construct specific proteins.
9) A gene is a segment of a DNA molecule that specifies the sequence of amino acids in a particular protein.
_____________ are determined by the activity of the protein.
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VI. DNA Replication
A. The process
1) The enzyme ________________ attaches to the DNA
molecule at an initiation site, breaking the weak H-bonds
between bases, thus “unzipping” the double helix. It also
holds the helix open. There are many origins (forks) of
replication on a single DNA molecule. Replication occurs
simultaneously at several points.
2) Binding proteins prevent the single strands from
rejoining.
3) An enzyme called a ____________________________
attracts complementary RNA nucleotides to build an RNA
primer at the start of a segment to be replicated. DNA
cannot initiate replication on its own; it must attach
nucleotides to an existing strand.
4) The RNA primer attracts the enzyme
______________________, which brings complementary
DNA nucleotides floating in the nucleus to the exposed
bases on the DNA molecule. Replication always occurs in a
__________________________ because DNA
polymerases must attach to the free 3’ end of the chain.
5) The new DNA strand grows as A bonds with T and C
bonds with G. The nucleotides are linked by
_______________bonds to the deoxyribose.
6) DNA polymerase also _____________________ to
ensure precise matching
7) When finished, the enzyme ___________________
removes the RNA primer and replaces it with DNA
compliments.
8) Lastly, enzymes called ___________________ connect
the sugar and phosphate backbone of the new strand.
B. Directionality - Because the DNA strands run in opposite
directions, the simultaneous synthesis of both strands in a
5’ – 3’ direction presents a problem. This problem is solved
by ___________________________.
a) The _______________ strand is the original 5’ – 3’ direction strand.
b) The _______________ strand, which runs in the 3’ – 5’ direction, is made as a series of short segments,
each formed in the 5’ – 3’ direction as the DNA molecule unzips.
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c) The segments are known as Okazaki fragments (100- 300 nucleotides long). Each Okazaki fragment needs
an RNA primer, which will start lagging strand replication; the primer is later replaced with DNA.
d) Finally, __________________ joins the 3’ end of each new fragment to the 5’ end of the growing chain.
DNA structure is said to be “__________________________” (half- saved) because each of the two new DNA
molecules have one ‘original strand’ and one ‘new strand’.
VII. DNA Technologies used to make a DNA Fingerprint
 Sir Alec Jefferys from Great Britain discovered the process in the 1980’s
 Since a 3-billion-base sequence of the 4 DNA nucleotides can produce more varied combinations than there
are humans, each of us should have a unique DNA sequence.
 The fingerprinting technique focuses on sequences of DNA that vary greatly from individual to individual,
such as
___________________________________________________________________________________
A. The Process – PCR, Digestion with Restriction Enzymes, then Gel Electrophoresis
1. PCR (Polymerase Chain Reaction) - Borrowing DNA’s Replication Abilities
Template DNA is placed in a tube along with:
A) Primers
B) DNA Polymerase
C) DNA Nucleotides
What does PCR do?
________________________________________________________________________________
________________________________________________________________________________
Why is a thermophilic bacteria’s DNA polymerase used for the process? _______________________
________________________________________________________________________________
A. Steps of PCR – template DNA (the DNA sample) is placed in a tube along with:
1. Denaturation: At high temperatures, the H-bonds holding the 2 DNA strands together break, so DNA (the
template DNA and Primers) becomes single stranded.
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2. Annealing:
_____________________________________
_____________________________________
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_____________________________________
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3. Extension:
_____________________________________
_____________________________________
_____________________________________
_____________________________________
Instead of copying the whole template DNA, only
targeted portions get copied (by the millions!)
How do you control which DNA sequence(s) get copied
by PCR? _________________________________
___________________________________________
___________________________________________
2. Restriction enzymes are ________________________________
_____________________________________________________
___________________________________________________
 Cutting double-stranded DNA makes single-stranded ends that
“stick” to each other through complementary base pairing.
 The natural function of restriction enzymes is to _____________
___________________________________________________
 Geneticists use restriction enzymes from bacteria to cut DNA at
specific base sequences.
 A restriction enzyme that recognizes a long sequence will cut the DNA
into a smaller number of larger fragments.
 These restriction fragment length
polymorphisms (RFLPs) are the basis of several
biotechnologies.
 Explain why cutting with the same restriction
enzyme(s) will produce different size
fragments for different individuals.
___________________________________
___________________________________
___________________________________
___________________________________
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3. Gel electrophoresis
An electrical field is used to separate molecules by size as they move through a gel.
For a DNA fingerprint, ________________________________________________________________
__________________________________________________________________________________
1) A gel is prepared which will act as a support for separation of the fragments of DNA. The gel is a jellolike material, usually agarose for DNA, a substance derived from seaweed. Holes (called wells) are created in
the gel. These will serve as a reservoir to hold the DNA solution.
2) DNA solutions (mixtures of different sizes of DNA fragments) are loaded in a well in the gel.
3) The gel matrix acts as a sieve for DNA molecules. Large molecules have difficulty getting through the
holes in the matrix. Small molecules move easily through the holes. Because of this, large fragments will
lag behind small fragments as DNAs migrate through the gel.

DNA ladders are often electrophoresed alongside the DNA samples. They are usually a mixture of
RFLPs with known lengths and are used to estimate the sizes of RFLPs in your DNA sample.
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A positive electrode is applied to one end of the gel & a negative electrode is applied to the other.
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The DNA pieces, carrying a negative charge because of the phosphate group, ________________
_____________________________________________________________________________
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The pieces migrate by size,______________________________________________________
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The pattern that forms from the different sized fragments, with the shorter pieces closer to the
positive pole and the longer fragments closer to the wells, is a DNA fingerprint.
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Today, many DNA Fingerprinting analyses use sequences of DNA called short tandem repeats (or
STRs). STRs consist of a 2-, 3-, 4-, or 5- base sequence in tandem.
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General genome statistics
Organism
Genome Size
# Known Genes
# Novel Genes
# Pseudogenes
E. coli
4.6 million bp
Yeast
12 million bp
6,530
167
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Worm
100 million bp
20,049
20
1150
Fruit Fly
133 million bp
4,751
9,288
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Human
3.3 billion bp
21,667
1,013
1,040
Mouse
3.4 billion bp
22,723
1,395
1350
Red Viscacha rat
8.2 billion bp
Mountain grasshopper
16.5 billion bp
Human Genetics Unit 3 Test Review
Fredrick Meischner
Phoebus Levene
Fredrick Griffith
Avery, MacLeod, and McCarty
Erwin Chargaff
Watson and Crick
Rosalind Franklin
Purines and Pyrimidines
Nucleotides
Bases
Phosphate Groups
Deoxyribose
Phosphodiester bond
Glycosidic bond
Hydrogen bond
Anti-parallel
DNA Polymerase
Primase
RNA Primer
Ligase
Leading Strand
Lagging Strand
Okazaki fragments
Frequency of mistakes
Genome
Primer
RFLP
Complementary
Direction of replication
Restriction enzymes
Gene
Helicase
Define and know steps of
 Semi-conservative DNA replication
 Gel Electrophoresis
 DNA fingerprinting
 Digestion with Restriction Enzymes
 PCR
 Recognize and be able to label the molecules and enzymes for DNA replication, including direction, leading
and lagging strands, Okazaki fragments, bases and enzymes.

Using a restriction map of a plasmid, describe the gene products that are produced when digested by a
restriction enzyme.
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Label parts of a DNA strand
Short Answer:
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Explain how a DNA fingerprint is made (each step in detail: PCR, Restriction Enzyme Digest, Gel
Electrophoresis) and identify ways that it can be used.
Explain the usefulness of deciphering the human genome.
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