Let’s Review!
• What is a macromolecule?
- A large organic molecule (made of carbon!)
• What are the four kinds of organic
molecules?
- Carbohydrates, lipids, proteins and nucleic acids
• What are nucleic acids made of?
- Phosphate group, 5-carbon sugar, nitrogenous base
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What other molecule is made up of
phosphates and 5-carbon sugar? (hint:
it releases energy!)
• ATP!
Adenine
Ribose
3 Phosphate groups
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• Nucleic Acids are the chemical link
between generations dating back to the
beginning of life on earth.
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• A nucleic acid is a
complex
macromolecule that
stores information in
cells in the form of a
code.
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• Nucleic acids are made of long chains
of nucleotides.
• Nucleotides are made
components:
1. sugar
2. phosphate group
3. nitrogen base
of
three
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• Examples of nucleic acids are :
1. DNA
2. RNA
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DNA = deoxyribonucleic acid
its components are:
1. deoxyribose (sugar)
2. phosphate group
3. nitrogen base
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The Components and Structure of DNA
There are four
kinds of bases
in in DNA:
1. adenine
2. guanine
3. cytosine
4. thymine
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• James Watson and Francis Crick
proposed that DNA has a specific pairing
between nitrogen bases:
Adenine (A) – Thymine (T)
Guanine (G) – Cytosine (C)
A and G are purines (AGgies eat Purina)
C and T are pyrimidines
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• Watson and Crick
also said the paired
nitrogen bases
formed two long
strands of
nucleotides that
compliment each
other.
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• Nitrogen Bases are connected
between sugars and phosphates
• They declared, “This structure is
a “double helix”.
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DNA Double Helix
The Components and Structure of DNA
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• DNA forms chromosomes, units of
genetic information which pass from
parent to offspring.
DNA is wound into
structures called
chromosomes
during cell
division
(prophase)
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• If you unraveled all your chromosomes
from all of your cells and laid out the
DNA end to end, the strands would
stretch from the Earth to the Moon
about 6,000 times.
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• RNA has a different sugar than DNA
• RNA = ribonucleic acid
• It’s components are :
1. ribose (sugar)
2. phosphate group
3. nitrogen base
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• It also has different bases than DNA
adenine --- uracil
cytosine --- guanine
• RNA is also single stranded, not double
stranded like DNA.
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DNA
RNA
- Double stranded
- Single stranded
- Sugar =
deoxyribose
- Adenine pairs with
Thymine
- Sugar = ribose
- Adenine pairs with
Uracil
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I. Why Must DNA Replicate?
• Every time a cell divides, it must first
make a copy of it’s chromosomes.
• Therefore, each cell
can have a complete set
of chromosomes.
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• Without replication, species could not
survive and individuals could not
successfully grow and reproduce.
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II. How DNA Replicates
• DNA is a molecule composed of TWO
strands, each consisting of a sequence of
nucleotides.
• The order of the nitrogen bases on one
strand mandates the sequence of bases
on the complementary strand.
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If you know the bases on one strand, you can predict which bases
will occur on the complementary strand.
A
G
T
C
C
C
T
-----------------------------
T
C
A
G
G
G
A
This is as
easy as
break
dancing!
During Replication each strand serves as a template to create a
new strand.
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III. Steps In
Replication
1) Enzymes break
down the hydrogen
bonds between the
two DNA strands,
unzipping the
molecule
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2) As the DNA unzips,
free nucleotides
(from surroundings
in the nucleus)
bond to the single
strands by base
pairing (A-T, G-C)
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3) Another Enzyme bonds the new
nucleotides into a chain
** The result of this process is the
formation of TWO DNA molecules, each
identical to the original molecule.
Replication! Rah,Rah, Rah!
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New Strand
Original strand
DNA Replication
Nitrogen Bases
Growth
Growth
Replication Fork
Replication Fork
DNA Polymerase
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1. What are the two types of nucleic acids?
2. What are the three components of a
nucleotide?
3. What are the similarities between DNA and
RNA? What are the differences?
4. Describe the process of DNA replication.
5. Why does a DNA molecule undergo
replication?
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