If the DNA of one cell is stretched out, it makes a 7 ft. long string
There are about 5 trillion cells in the human body
If you connected all the DNA together, it would be long enough that
it would take light over 10 hours to travel its length
(ruptured bacteria)
This is a whole lot of information
The Basics of
DNA
DNA and Heredity…
Rosalind Franklin’s
research was used in the
discovery of DNA
structure
Francis Crick & James
Watson developed the
first model of DNA
Watson & Crick
concluded that all living
cells contain DNA
• Prokaryotes
Genetic material is a single loop
of DNA
Located in the cytoplasm
• Eukaryotes
Genetic material in the form of a
chromosome
Located in the nucleus
Review the Cell…
• Cells contain the nucleus
• The nucleus is the “brains”
of the cell
Chromatin – DNA tightly
wrapped around proteins
(histones)
Chromatin supercoils to form
chromosome
Chromosome visible during
mitosis
Review the Cell…
• Chromosomes are found
•
•
inside the nucleus
Chromosomes contain genes
Genes are made up of DNA
What is DNA?
• The genetic material
determines how an
organism develops.
• How? The sequence of
nucleotides (nitrogen
bases)determine the
traits of an organism.
The main functions of
DNA are to:
1.) Store and maintain
genetic information
2.) Provides
instructions for making
organisms
What does DNA Stand for?
• DNA is a Double Helix - like a twisted
rubber ladder made from three main
components (like legos)
• Sides of the ladder are composed of
alternating sugar and phosphate pieces
• Each “rung” of the ladder is made up of
two complementary nitrogenous bases
– A complements T
– C complements G
• DNA is put together in chunks called
NUCLEOTIDES
– Each nucleotide has a sugar, PO43- and base
• A nucleotide is held together
with strong molecular bonds
• Oxygens provide the “hooks”
necessary to bind to other
NTP’s
• We identify where these
Oxygens are by labeling the
carbons of the deoxyribose
sugar
5’
1’
4’
3’
2’
(see, no oxygen at 2’…)
• Each of the components of the
nucleotide binds to another
nucleotide to form a single
DNA strand
– Since Oxygen easily forms two
strong bonds, the phosphate and
sugars both bind most strongly
– The Hydrogens on the base bind
less strongly with an Oxygen or
Nitrogen from another base to
bind one strand to another
• Finally we have the characteristics of
double stranded DNA
• STRONG bonds between the
deoxyribose sugars and phosphates
• WEAK bonds between the Hydrogen
and Oxygen or Nitrogen (weaker
between A and T than C and G)
• Twisting of the two anti-parallel
strands to form a double helix
• Heat it up, which bonds break first?...
• We start with some double stranded
DNA
• Replication= The copying of DNA
prior to the cell undergoing division
• It occurs at multiple sites along the
DNA strand simultaneously
• DNA strands are complementary- that is
each strand can be used to make the other
strand.
• DNA Helicase comes on the scene
binds and
• UNWINDS the DNA upstream
• Then UNZIPS the hydrogen bonds
between the base pairs This site is
known as the replication bubble
• DNA single-stranded binding proteins
stabilize the single strand structure.
– The sites on DNA where separation and
replication occur are called replication
forks.
– Replication takes place in both directions
until each chromosomes is completely
copied. In a 5’→ 3’ direction.
– There are two replicating strands the
leading strand and the lagging strand.
The leading strand moves in a forward
motion. The lagging strand move in a
backwards motion.
• Extra: The lagging strand is made up of
Okazaki fragments which replicate short
pieces of DNA at a time.
• DNA polymerase joins individual nucleotides to
produce a DNA molecule, which is a polymer.
• Complementary Bases begin adding into both sides
of the ds DNA
• A binds with T, C binds with G (no other possibility
because of the shape of the bases!)
• The final job of the Polymerase is to Proofread the
sequence of nucleotides after they are added (back
on the 5’ end) and to clip out any that are incorrectly
paired nucleotides.
• Extra Primase is an enzyme that
helps start DNA replication in
an Okazaki fragment.
• Extra DNA ligase removes the
gaps that are in place due
mainly to the use of primase in
the lagging strand.
• Finally you have 2 identical copies
of double stranded DNA
–The original strand serves as a
template for the new strand
–The resulting DNA molecules
are made up of one parent
(original) strand and one daughter
(new) strand
YouTube - DNA Replication 45 seconds
http://youtu.be/qoERVSWKmGk
YouTube - BioRap (DNA Replication and Protein
Synthesis with a Beat)
Review
Questions
Which of the following
determines the traits of an
organism?
A cell nucleus
B chromosomes
C DNA
D eggs
Which of the following
determines the traits of an
organism?
A is incorrect because the
nucleus does not determine
traits but contains information
that does.
B is also incorrect because
chromosomes do not
determine traits but contain
information that does.
Which of the following
determines the traits of an
organism?
C is correct because DNA is the
genetic information, found in
the nucleus, that determines
the traits of an organism.
D is incorrect because eggs are
a cell that contain genetic
material that will be used to
determine traits, but does not
determine an organism's
traits itself.
DNA molecules separate into
single strands, which are then
used to construct two identical
strands of DNA. This process
ensures that the —
A cytoplasm is in equilibrium
B mitochondria are genetically
identical to the chloroplasts
C parent cells use little ATP
D daughter cells are genetically
identical to the parent cells
DNA molecules separate into single
strands, which are then used to
construct two identical strands of DNA.
This process ensures that the —
A is incorrect because cytoplasm
is not part of DNA molecules;
rather, cytoplasm is the fluid-like
substance that fills a cell.
B is incorrect because
mitochondria are not identical
to chloroplasts; further,
animal cells do not have
chloroplasts, but do replicate
DNA.
DNA molecules separate into single
strands, which are then used to
construct two identical strands of DNA.
This process ensures that the —
C is incorrect because ATP is a
high energy molecule needed to
provide energy for normal
cellular function and is not part
of DNA.
D is correct because by producing
identical strands of DNA, it
ensures that the daughter cells
are genetically identical to the
parent cell.
The nucleus is
the part of the
cell that 
A provides structure and
support.
B supplies energy to the other
organelles.
C changes sunlight into
carbohydrates.
D contains genetic information
about the organism.
The nucleus is the
part of the cell
that 
A is incorrect because structure
and support is provided by cell
membranes and cell walls.
B is incorrect because
mitochondria are the parts of
the cell that provide energy.
The nucleus is the
part of the cell
that 
C is incorrect because
chloroplasts are the organelles
that carry on photosynthesis.
D is correct because the nucleus
contains chromosomes that are
made up of genes that contain
DNA which is the genetic
information about an organism.
Which of the following is not a
part of DNA?
A adenine
B citric acid
C deoxyribose
D phosphate
Which of the following is not a part of
DNA?
A is incorrect because adenine is one
of the bases that make up DNA.
B is correct because citric acid is not
part of DNA.
C is incorrect because deoxyribose is
sugar which is part of DNA
D is incorrect because phosphate is a
part of DNA.