Download Nucleic Acids and DNA Replication

Lab Biology- Chapter 10
Honors Biology- Chapter 9
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Found on chromosomes
Segment of DNA
Codes for a trait
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Characteristic due to a single gene or
multiple genes
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Eye color
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Hair color
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Blood type
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Deoxyribose sugar
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Phosphate group
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Nitrogen containing base
◦ Four possible bases
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2 rings of carbon and
nitrogen
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Adenine
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Guanine
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1 ring of carbon and
nitrogen atoms
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Thymine
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Cytosine
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DNA is composed of
2 nucleotide chains
Nucleotides
connected through
covalent bonds
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Each strand has a 5’
and a 3’ end
Each strand runs in an
opposite (antiparallel)
direction
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Nucleotide linkage
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Covalent bonds
5’
between sugar
and phosphate
molecules
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Forms a sugar-
phosphate
backbone
3’
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Covalent bond
Chemical bonding through sharing of
electron pairs
Purine
Pyrimidine
A
T – 2 Hydrogen bonds
C
G – 3 Hydrogen bonds
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Hydrogen bonding between base pairs
Hydrogen atom - electronegative atom
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Hydrogen bonds?
Covalent bonds?
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Chargaff’s rule
The DNA of any given species contains
◦ adenine = thymine
◦ guanine = cytosine
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Wilkins and Franklin
Used X-ray diffraction
◦ A picture of how X-rays bounced off a DNA
molecule
X-ray
diffraction
Wilkins
Franklin
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X-Ray diffraction
Used to determine arrangement of atoms
within a crystal structure
Distance between dark spots- distance
between turns of the helix
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Performed no physical experiments on DNA
Spent a lot of time thinking about DNA
Focused on creating a model that fit with the
data
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Wilkins, Watson, and Crick received the Nobel
Prize in 1962
Franklin died in 1958 and was not recognized
Nobel Prize cannot be awarded posthumously
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Write a two paragraph reflection on Rosalind
Franklin.
◦ One paragraph should detail her contribution to the
discovery of the structure of DNA.
◦ Second paragraph should state your answer to the
questions:
 Do you think Franklin deserved the Nobel Prize?
 Why do you think she did not receive more
recognition?
◦ Evidence must be provided to support your
opinions.
◦ Complete this assignment on loose leaf paper.
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Occurs in all living organism
Takes place in the nucleus
One double stranded molecule
two identical copies
Original
strand
New
strand
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Helicase (enzyme) holds the two strands apart
◦ Break hydrogen bonds between bases
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Replicates simultaneously
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DNA polymerase synthesizes DNA by adding
nucleotides in a 5’
3’ direction
Leading strand- continuous
◦ Moves in the direction of unwinding
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Lagging strand- discontinuous
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Lagging Strand
Discontinuous
Forms in the opposite direction of replication fork
Creates Okazaki fragments
Must wait for a new primer to be placed
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DNA Primase- lays down short segments of
RNA primer
DNA Polymerase III- adds new nucleotides
DNA ligase- bonds Okazaki fragments
together
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Semiconservative
model
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What happens when DNA Polymerase makes a
mistake?
Mutation- Change in nucleotide sequence
Can be repaired through DNA repair
mechanisms
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One nucleotide is substituted for another
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Sickle Cell Anemia
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A nucleotide is deleted
Cystic fibrosis
◦ Deletion of "AT" from the
sequence "ATAT" in
the CFTR gene
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Causes a frameshift
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A nucleotide is added
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Huntington’s disease
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Causes a frameshift
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DNA segment is
broken and flipped
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No frameshift
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No loss of genetic
information
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Different order
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Hemophilia
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Part of the gene is moved
◦ Either moved on the same chromosome or moved
to a different chromosome
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A form of Down syndrome
Part of Chromosome 21 is moved to
Chromosome 14
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DNA Replication Game
http://www.nobelprize.org/educational/medi
cine/dna_double_helix/dnahelix.html
Honors: DNA Replication
http://www.wiley.com/college/pratt/047139
3878/student/animations/dna_replication/in
dex.html
DNA Replication:
http://www.mcb.harvard.edu/losick/images/t
rombonefinald.swf