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DNA’s Function
DNA
• DNA
deoxyribonucleic
acid.
http://ed.ted.com/lessons/
the-twisting-tale-of-dnajudith-hauck
DNA
• DNA carries the
genetic
information in the
cell
– the instructions for
making all the
structures and
materials the body
needs to function.
DNA
• DNA is capable of
making a copy of
itself through a
process called,
replication.
Location of DNA
• Most of the DNA occurs in the cell
nucleus; however, each
mitochondrion contains 37 genes –
this is referred to as mitochondrial
DNA.
The structure of DNA
• The shape of the
molecule is
described as a
“double helix”.
• The building
blocks of DNA are
nucleotides.
The ladder model
• The structure of DNA
can be understood more
easily by untwisting the
double helix and
displaying the molecule
as if it were a ladder.
The ladder model
• The side rails of the
ladder (the “backbone”)
are alternating
phosphate and sugar
molecules.
The rungs are paired
nitrogen base
molecules held together
by a hydrogen bond.
The base pairing rule
• Each “rung” of the
DNA ladder is
formed from two
nitrogen bases.
The base pairing rule
• There are four bases – adenine (A), thymine
(T), cytosine (C), and guanine (G).
• The base adenine always bonds with thymine
(A-T), and cytosine always bonds with
guanine (C-G).
The base pairing rule
• Chargaff’s Rule –
The amount of
adenine is the same
as the amount of
thymine, and the
amount of cytosine is
the amount of
guanine.
The structure of DNA
• A nucleotide
consists of one
phosphate
molecule, a fivesided sugar
molecule
(deoxyribose
sugar), and one
nitrogen base.
The base pairs
The binding of two
nucleotides forms a
base pair. In DNA,
cytosine and guanine
are bound together by 3
hydrogen bonds,
whereas adenine and
thymine are bound by 2
hydrogen bonds.
NIH - National Human Genome Research Institute
The function of DNA
Genes
• A chromosome consists of segments of
DNA known as genes.
The function of DNA
Genes
• Genes contain the instructions for the
construction of a particular protein, or
RNA.
The genetic code
• The sequence of
bases in a gene is
a code instructing
the cell how to
construct a
particular
protein.
The genetic code
• Proteins are responsible for different
functions throughout the body.
– Hormones, hemoglobin, insulin, etc.
• Proteins are involved in the expression
of traits.
– Curly hair, eye color, skin tone, etc.
The function of DNA
Genes
• It is estimated that there
are about 20,000–
25,000 genes in the
human genome (i.e.
about 3 billion base
pairs).
Introns and exons
• Genes consist of introns and exons
• Exons are sections of coding DNA – i.e. they
contain instructions for making proteins.
• Introns are sections of non-coding DNA
(once called "junk DNA") – i.e. they do not
contain instructions for making proteins but
are now believed to serve other important
functions.
DNA Packaging
• DNA is very thin and very fragile.
• Around 6 feet of DNA must fit inside
each cell’s nucleus.
• How is this possible?
DNA
Packaging
• First: DNA is wrapped around proteins
called Histones, this new structure is
called a Nucleosome.
DNA Packaging
• Second: The Nucleosomes tighten up
and form loops.
DNA Packaging
• Third: The loops tighten together to form
supercoils, known as chromatin.
DNA Packaging
• Finally: the chromatin condenses,
during prophase, to form chromosomes.
DNA Packaging
Fight or Flight response
in the body
• http://learn.genetics.utah.edu/content/be
gin/cells/cellcom/