What we already know:
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The nucleus contains DNA
Eukaryotes have linear DNA
Prokaryotes have circular DNA
DNA is copied during Interphase of
the Cell Cycle
What we already know:
• Traits are distinguishing
features or
characteristics
• Traits are passed from
parent to offspring
• Traits are passed on
through genes
• Genes are specific
sections of DNA
• In sexual reproduction,
offspring get half of
their genes from each
parent
DNA is INFORMATION
• DNA= deoxyribose
nucleic acid
• A molecule that
stores information
• Contains the
instructions for
making proteins
• Like a cookbook
contains the
instructions for
making a cake
Proteins and
Amino Acids
• Proteins are large
molecules made up of
chains of amino acids
• There are 20 different
amino acids that
combine into thousands
of different proteins
• Folding of the string of
amino acids is critical for
protein function
Proteins and
Amino Acids
• Proteins can vary in size from
just 20 amino acids, like this
one found in Gila Monster
saliva…
To this protein
nicknamed
“Titan” with
34,350 amino
acids, found in
human muscle
tissue
Check for Understanding:
• What is the relationship between
proteins and amino acids?
• What is a trait?
• When is DNA copied?
• What is a gene?
Check for Understanding:
• What is the relationship between proteins and
amino acids?
• 20 amino acids come together in various
combinations to make proteins
• What is a trait?
• Distinguishing features or characteristics
• When is DNA copied?
• During Interphase of the Cell Cycle
• What is a gene?
• A specific section of DNA that contains the
code for a protein
DNA & The Genetic Code
• DNA molecule is shaped like
a twisted ladder
• The molecule is formed from
nucleotide subunits that
consist of:
• Phosphate
• Sugar (Deoxyribose)
• Nitrogen Base
DNA & The Genetic Code
• The side rails of the
ladder are formed by the
sugar-phophates
• The rungs of the ladder
are formed by two bases
coming together
• There are four different
bases in DNA
• Adenine
• Thymine
• Cytosine
• Guanine
All Tigers Can Growl
Some comic relief…
DNA Structure Video
DNA & The Genetic Code
• The sequence (order) of
bases in a strand of DNA
makes the code for building
proteins
• The genetic code is a
“triplet” code meaning that
every three bases codes
for one amino acid
• A gene is the entire
sequence of bases that
codes for a specific protein
• Like a recipe for a
specific dish
Replication of the DNA
• Replication is the
copying of DNA
1. Two strands
separate
2. Free-floating
nucleotides match
up with the
nucleotides on each
strand
3. Two identical
molecules of DNA
are made
Watch Replication in Action
• This movie shows a computer animation of how DNA is replicated
Another video on YouTube
Check for Understanding
• What three components make up the
nucleotide subunit?
• What are the four bases and what is the rule
about how they pair together?
• Describe what is meant by a “triplet code.”
• What are the steps of DNA replication?
Check for Understanding
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What three components make up the nucleotide
subunit?
• Phosphate, Sugar, Nitrogen Base
What are the four bases and what is the rule
about how they pair together?
• Adenine pairs with Thymine
• Cytosine pairs with Guanine
Describe what is meant by a “triplet code.”
• Three bases code for one amino acid
What are the steps of DNA replication?
1. Strands separate
2. Nucleotides pair up
3. Two identical strands are made
A HISTORY OF DNA
•(1928) Frederick Griffith
•Discovers that a “transforming factor”
changes harmless bacteria into deadly
bacteria
•(1952) Rosalind Franklin
•Takes x-ray photographs of DNA
•(1953) James Watson and Francis Crick
•Use Franklin’s images to describe the
structure of DNA
•(1962) Watson, Crick, and Wilkins win the Nobel
Prize, Franklin has already died from cancer
(1958) so she does not get recognition