Download History and Shape of DNA

History and Shape of
DNA
Notes for in-class objectives &
chapter 11
History
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For hundreds of years scientists have
searched for a molecule that transmits
inherited traits from one generation to
another

1944- Avery found that DNA stored
information
History

1950s-Rosalind Franklin discovered the
twisted shape of the molecule
History

1953- Watson and Crick find the molecule
has a double helix shape
What is DNA?
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DNA stands for Deoxyribonucleic Acid
DNA is the genetic content of a living cell; the
instruction manual for a living organism.
DNA contains directions for assembling
amino acids into proteins
The molecule is subdivided into thousands of
genes that each code for a trait
Important definitions

Proteins: carry out all structures and
functions of a cell. Ex: gene for eye color,
nose shape or cystic fibrosis
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Heredity: The transmission of
characteristics from parent to offspring.

Genes: A sequence of DNA that codes for a
protein and determines a trait
Central Dogma of Molecular
Biology
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DNA
RNA
Protein
Forms of DNA:
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Chromatin-the DNA is one long continuous
strand of information
Chromosomes- the DNA is broken up into
tightly wound X-shaped structures and moves
around while the cell divides.
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Each Chromosome can hold thousands of
genes
Each person has 46 chromosomes and about
23,000 genes total
Structure of DNA
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The molecule has a double twist- called a
double helix
Subunits of DNA
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A DNA molecule consists of billions of
nucleotides bonded together
Nucleotide
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Made of 3 parts:
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Sugar
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Nitrogen Base
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DNA: Deoxyribose
RNA: Ribose
Purines- Adenine and Guanine
Pyrimidines- Thymine and Cytosine
Phosphate
DNA is a twisted ladder
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Outside- a sugarphosphate backbone
Inside- nitrogen
containing bases
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The N-bases are held
together by hydrogen
bonds (2 nucleotides =
base pair)
Chargaff’s Rule
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Adenine always bonds to Thymine, Cytosine
always bonds to Guanine

Number of A = Number of T
Number of C = Number of G
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Function of DNA
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Control of cellular activities: DNA carries
the code for assembling enzymes and the
other proteins that function in the cell’s
metabolism.
Replication: DNA replicates itself so that its
genetic information is passed on. The
genetic information lies in the sequence of
the base pairs.
Steps of Replication
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Unwind
Unzip
Insert
Proofread
DNA Replication
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DNA replication: the DNA strand “unzips” the
weak hydrogen bond comes undone and the
base pairs separate.
Insert

After the DNA molecule opens up, new
nucleotides are brought in and match up to
their complimentary base. (A-T, C-G)

http://highered.mcgrawhill.com/sites/0072437316/student_view0/cha
pter15/animations.html
Proofreading
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The nucleus has enzymes that “read”
through the molecule looking for mistakes.
If one is found, the molecule cuts out the
incorrect nucleotide and replaces it.
Even with this molecule, sometimes a
mistake is made, causing a change.
Something old something new

The process is semi-conservative; each new
molecule has one of the old strands and one
of the new strands.
Modern DNA Research
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Dolly the sheep and cloning.
britannica.com
Modern DNA Research
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Can we clone a T-rex?
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www.pbs.org/wgbh/nova/nature/t-rexblood.html
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