DNA
Structure and Function
The Role of DNA
• Molecule of Heredity
– Stores information for various
genetic traits
– Controls development and
growth of each cell as well as
the entire organism
– Copies itself : before a cell
divides, genetic information
must be copied
– Transmits information from one
generation to the next
http://www.youtube.com/
watch?v=l0TC9Lt7IGU&
safe=active
• What is the
structure of DNA
and how was it
discovered?
•
•
The Chemical Structure of DNA
I:
http://www.youtube.com/watch?v=
nExcd_wTcHg&safe=active
• Discovery of DNA
Structure
– Watson-Crick: worked
together on DNA structure
and came up with “double
helix” model
– Won Nobel Prize in 1962
– Helped by X-ray
crystalography images by
Rosalind Franklin
•
•
The Chemical Structure of DNA II:
http://www.youtube.com/watch?v=oZiAwqo77GM&s
afe=active
• Chargaff’s Ratios:
– Helped scientist understand how the bases
paired up
•
http://www.hhmi.org/biointeractive/media/DNAi_chargaff_ratio-lg.mov
The Chemical Structure of DNA
• DNA:
(Deoxyribose Nucleic
Acid)
Hydrogen bonds
(weak)
• Large Polymer Molecule
• Two long chains of
nucleotide subunits
• Nucleotides from each
chain pair up and bond
together with hydrogen
bonds
Strand 1
Strand 2
Nucleotide Structure
– 3 components of nucleotide:
• 5 carbon deoxyribose sugar
• Phosphate group
• Nitrogenous Bases
– Adenine, thymine, cytosine, guanine
4 bases possible (A, T, C, G)
http://www.hhmi.org/biointeractive/media/DNAi_
building_blocks-lg.mov
• Nitrogenous Base Pairs
– Adenine - Thymine
– Cytosine - Guanine
• Nucleotides join together
into two long chains
• Phosphate of one
nucleotide is joined to sugar
of next nucleotide by a
covalent bond
• The two chains are joined
together by hydrogen
bonds (weak bonds)
between the nitrogenous
bases.
• Base pairs always A-T, C-G
Double Helix Structure
• Base pairs are rungs on a
ladder
• Sides of ladder are
phosphate and sugar
• Whole ladder is twisted into
a “double helix” structure
•
•
Video: Chemical Structure of DNA III
http://www.youtube.com/watch?v=54n8DLr
eEe4&safe=active
•
http://www.hhmi.org/biointeractive/media/DNAi_paired_s
trands-lg.mov
Nucleotide Base Sequence
• Order of A, T, C, G
nitrogenous bases
eventually codes for
different proteins.
• The order of nucleotides
is unique for different
organisms
• The more closely related
two organisms are the
more similar the DNA
sequences
– Way to determine
evolutionary relationships
• Build a DNA Molecule
• http://learn.genetics.utah.edu/content/begi
n/dna/builddna/
DNA Replication
• DNA duplicates itself
prior to cell division
• Each strand serves as
a pattern or “template”
to make a new DNA
molecule
• Enzymes:
– Break open (unzip) weak
H-bonds between bases
pairs
– Bind free nucleotides to
complimentary bases of
unzipped single strand
• (DNA polymerase)
• Produces 2 identical
DNA double helix
strands (called
complimentary
strands)
• Each new strand
made of one of the
original strands plus
one new synthesized
strand.
•
•
http://www.youtube.com/watch?v=z685FFq
mrpo&safe=active
http://www.youtube.com/watch?v=zdDkiRw
1PdU&safe=active
Focus Question
• Why is accuracy so important in replication
of DNA?