DNA Explained
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
RNA is needed to make proteins:
•
RNA is ribonucleic acid and
is very similar to DNA
except:
1. RNA has ribose sugar
instead of deoxyribose
sugar
2. RNA has Uracil instead
of Thymine
3. RNA is a single strand
RNA is needed to make proteins:
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EUKARYOTES: RNA copies the information from the
DNA inside the nucleus then travels outside to the
cytoplasm
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PROKARYOTES: RNA and proteins are made in the
cytoplasm
RNA is needed to make proteins:
• Three different types of RNA are
involved in making protein:
• messanger RNA (mRNA)
• ribosomal RNA (rRNA)
• transfer RNA (tRNA)
• mRNA carries the message or code
outside the nucleus
• rRNA makes up part of the ribosome
• tRNA brings the correct amino acids
to the ribosome for protein
construction
Check for Understanding
• How is RNA different from
DNA?
• What are the three types of
RNA involved in making
proteins?
Check for Understanding
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How is RNA different from DNA?
1. RNA has ribose sugar instead of
deoxyribose sugar
2. RNA has Uracil instead of Thymine
3. RNA is a single strand
What are the three types of RNA involved in
making proteins?
1. messanger RNA (mRNA)
2. ribosomal RNA (rRNA)
3. transfer RNA (tRNA)
Transcription
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Transcription produces a
single-stranded molecule of
RNA
One strand of DNA is the
template or pattern
The steps of transcription
are:
1. The DNA molecule
opens up along a gene
2. RNA nucleotides
(A,U,C,G) match up and
join the open DNA
strand
3. The complete RNA
strand is released and
moves to the cytoplasm
Transcription
•
Transcription is different than
replication:
1. Only one strand of
DNA is transcribed so
only one strand of
mRNA is produced
2. The mRNA is
released, it does not
stay attached to the
DNA
3. Many copies of mRNA
can be made from a
single gene in a short
period of time
•
Transcription on YouTube
Check for understanding
• What are the steps of transcription?
• How is transcription different than
replication?
Check for understanding
•
What are the steps of transcription?
1. The DNA molecule opens up along a gene
2. RNA nucleotides (A,U,C,G) match up and join
the open DNA strand
3. The complete RNA strand is released and
moves to the cytoplasm
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How is transcription different than replication?
1. Only one strand of DNA is transcribed so only
one strand of mRNA is produced
2. The mRNA is released, it does not stay
attached to the DNA
3. Many copies of mRNA can be made from a
single gene in a short period of time
Translation
• Translation is how cells
TRANSLATE the language
or code of nucleotide bases
into the language of amino
acids
• Translation occurs in the
cytoplasm at the ribosome
• If DNA is the cookbook, and
mRNA is the recipe, then
the ribosome is the kitchen
and tRNA is the chef!
Translation
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rRNA is part of the
ribosome that attaches to
the mRNA
tRNA has a triplet of bases
on one end and can attach
to a single amino acid on
the other end
tRNA does the translation
of bases to amino acids
when it matches up with
mRNA
Brain Break!
• Link to Translation
Video
• Another video that
reviews Translation
and Transcription
Translation
1. Translation begins when a ribosome attaches to the
beginning of an mRNA molecule
2. A tRNA molecule carrying an amino acid matches up to a
complementary triplet on mRNA on the ribosome
3. The ribosome attaches one amino acid to another as it
moves along the mRNA molecule
4. The tRNA molecules are released after the amino acids they
carry are attached to the growing chain of amino acids
5. The ribosome completes the translation when it reaches the
end of the mRNA strand and the newly made protein
molecule is released
The Central Dogma
• The process of making
proteins is the same in all
cells
• This is the foundation of
molecular biology,
biochemistry, and genetics
Translation
Transcription
DNA
Another YouTube video!
RNA
Protein
Check for understanding
• Where does translation occur?
• Which RNA makes up the ribosome?
• Which RNA is the “recipe?”
• Which RNA does the actual translation of
bases into amino acids?
• What is the “central dogma” of molecular
biology?
Check for understanding
• Where does translation occur?
• In the cytoplasm
• Which RNA makes up the ribosome?
• rRNA
• Which RNA is the “recipe?”
• mRNA
• Which RNA does the actual translation of bases
into amino acids?
• tRNA
• What is the “central dogma” of molecular biology?
Transcription
DNA
Translation
RNA
Protein
Replication, Transcription,
Translation Challenge!
• Copy this DNA sequence:
• A-T-G-A-C-G
• Write the base pairs of the complimentary
strand of DNA (replication)
• Write the complimentary mRNA strand to
your new strand (transcription)
• Use the chart to find the correct amino
acids that the tRNA would attach to the
protein (translation)
The Universal Genetic Code
The Universal Genetic Code
Check your answers:
• Replication:
• T-A-C-T-G-C
• Transcription
• A-U-G-A-C-G
• Translation
• Met (Methionine) and Thr (Threonine)
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