DNA
Deoxyribonucleic
Acid
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THE master molecule of
life!
DNA
• DNA is often called
the blueprint of life.
• Why would we refer
to this molecules as a
blueprint?
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DNA Contains instructions for building an
organism like these are instructions for
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building the batmobile.
It shows all needed parts and how they fit
together.
The DNA in the nucleus gives instructions
on how to build proteins. Proteins are
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how traits (such as eye, skin, and hair
color) are expressed.
Individual Components of DNA/RNA
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DNA
• Nucleotides
– Phosphates
– Deoxyriboses
– Nitrogenous Bases:A,T,G,C
• Histones
• Hydrogen Bonds
• Make up Genes
RNA
• Nucelotides
– Phosphates
– Riboses
– Nitrogenous Bases:A,U,G,C
• Is DNA’s message
To get lots of DNA into a small space…
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• We wrap up the DNA• Allow DNA to coil around
histones so that the coils are
even and safe from breaking!
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Click on picture to watch video. Stop after histones (1:40).
Organization of the DNA
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Hydrogen
Phosphates
Sugars
Nucleotides
DNA
Genes
Histones
Chromosomes
From smallest to largest
sized structures
?
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Review monomers versus polymers – what
do those words mean?
Which of the previous items are monomers
and which are polymers?
Checkpoint
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What is the monomer for DNA?
What are the 3 components of that
monomer?
Checkpoint
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What is the monomer for DNA?
What are the 3 components of that
monomer?
• Genes are a series of nucleotides or a
segment/section
Free
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• There are many genes on a chromosome.
• Humans have 23 homologous
chromosomes. (22 pairs are autosomal, 1
pair is sex)
• Chromosomes are in the nucleus of 2 types
of cells:
– Somatic cells are non-sex cells and are diploid.
(Example skin cells)
– Gametic cells are sex cells and are haploid.
(Example sperm or egg)
THINK – PAIR - SHARE
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Using root words to figure this out,
what do haploid and diploid
mean?
More review…Look at the picture showing DNA and answer
the following:
What organelle is the DNA coming from?
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What other organelles have DNA in eukaryotic cells?
What is an example of a gene shown?
What makes up genes?
Is DNA a polymer or monomer?
The Shape of the Molecule
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• DNA is a very long
polymer.
• What type of organic
compound is this?
• What functional group
would you find on
nucleic acids like DNA
or RNA?
• The basic shape is like
a twisted ladder or
zipper.
• This is called a double
helix.
The Double Helix Molecule
• The DNA double
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helix has two
strands twisted
together.
• The nucleotides on
each strand are
held together with
covalent bonds
• The strands are
held together by
hydrogen bonds
Label your DNA coloring
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Complementary Bases
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• Review the possible
DNA base pairs and
how they bind
together in the
DNA.
• Also, review the
actual names of the
4 nitrogenous base
pairs found in DNA.
Compare DNA and RNA by
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creating
a venn diagram. Include
all of the following traits:
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Both nucleic acids
Both have phosphate in their back bone
DNA has a deoxyribose sugar in the backbone
RNA has a ribose sugar in the backbone
Uses the bases A,T,C,G and U
Single stranded
Double stranded
Can be found outside the nucleus
Both are polymers
Think about this:
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• When would you need to make a copy
of DNA?
• Would the copy of DNA need to be
identical or slightly different from the
original?
• In what organelles would you find DNA
or RNA?
• How will enzymes be involved in
copying DNA? In making RNA?
Stop here for now! You’ll be told when
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to continue on to DNA replication!
Thanks!
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DNA Replication
Check for understanding
before DNA replication
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What does “to replicate” mean?
When would a cell want to replicate its DNA?
What does it mean if something ends in –ase?
What are the two types of bonds in DNA and
which is the easier to break?
• What is meant by the term complementary?
• What does it mean that DNA is a “double
helix”?
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Goal……
Predict some things about the process
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of replication…..
• When will do this process?
• What has to happen to DNA in order to copy?
• What should we end with after replication?
Think about the product of the replication.
Some basics about the chemistry of
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DNA
• The ends of each strand of DNA’s sugar-phosphate
backbone, is polar.(What does that mean?)
• The sugar side is slightly positive (OH) (aka 3’)
• The phosphate side is slightly negative (P) (aka 5’)
• Enzymes all build new strands in a 5 (-) to 3’ (+)
direction when they work!
• That means they move along the original strand from
3’ to 5’
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Possible ways to get from original
(parental
DNA) to a newly synthesized
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molecule of DNA…..
Conservative
Dispersive
Semiconservative
DNA replication Determined by
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Meselson and Stahl
Steps to make more DNA (an exact copy)
1. Unwind double helix and break the H bonds
(helicase)
2. Stabilize open strands (use the spooling
proteins called histones)
3. Copy DNA by adding complementary
nucleotides (DNA polymerase)
4. Check for errors (ligase and polymerase)
5. Connect fragments on the lagging strand
(ligase)
Semi-conservative replication
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• Each DNA molecule will consist of an old and a new
strand of DNA.
• This means each parental or original strand of DNA
can act as a template to copy.
• However, based on those back bone charges and
the mandatory direction of DNA polymerase, we
have a leading and lagging strand during
replication.
Charges and Copy Issues
• Charges
on DNA strands and charges on the
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enzymes copying the DNA cause a “leading” and
“lagging” strand during replication. These terms are
used to describe the template strand (one being
copied) of DNA.
• Replication enzymes move along the template
(original DNA) from 3’ – 5’. While building the new
strand from the 5’ – 3’
• So the parental strand (template/original) of DNA
that starts with the 3’ side is called the “leading
strand”.
• The one that starts with a 5’ is called the “lagging
strand”.
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Click on pictures for links to video