Download DNA Kit Instructions

DNA KIT
DNA REPLICATION
Remember that in Interphase of mitosis, the chromosomes replicate a clone of themselves before
the cell divides. This is how that is done: A double stand of DNA unwinds from its helix
structure. Then the DNA strands break apart while it’s still in the nucleus, and a new nucleotide
comes in at each open spot in the DNA strand and takes its place. For every unpaired A, a T
comes in and binds there. For every unpaired T an A comes and binds there. For every unpaired
G a C comes in and binds there, and for every unpaired C a G comes in and binds there. Now we
have two double-stranded DNA molecules, and the cell can continue on to prophase, metaphase,
anaphase, and telophase.
PROTEIN SYNTHESIS
A double stand of DNA unwinds from its helix structure. Then the DNA strands break apart
while it’s still in the nucleus. It only unwinds at a certain sequence of nucleotides (called a gene).
A new nucleotide comes in at each open spot in the DNA strand and takes its place. Again, for
every unpaired A, a T comes in and binds there. For every unpaired T an A comes and binds
there. For every unpaired G a C comes in and binds there, and for every unpaired C a G comes in
and binds there. This new strand detaches, and the original DNA strands pair up again and the
helix shape reforms. The newly formed detached strand is called mRNA. It is an exact opposite
of the original DNA strand that was copied. The mRNA strand leaves the nucleus and enters the
cytoplasm, and finds a ribosome. In the ribosome, the nucleotides are paired up again with freefloating nucleotides, creating a strand of the DNA that is an exact copy of the original.
But we are not done yet: Every three nucleotides form a code (called a codon) that tells one
particular amino acid to come to the ribosome. For instance, GCG forms the amino acid
“Alanine”, and GGG forms the amino acid “Glycine”, etc. These amino acids are strung together
in the sequence, according to the nucleotide triplet code. This code should form a protein that
makes sense and functions properly. That is how a gene on DNA becomes a new protein.
There’s only one problem: messenger RNA doesn’t have any Thymine (T). It has Uracil (U)
instead. So when a DNA codon says TGA, the messenger RNA writes down UGA. However,
the ribosome knows how to translate this so the protein is made properly. When the message is
over, there is a stop codon inserted to indicate the protein is finished.
On your handout, you will see a word written on each amino acid. If you have done the exercise
properly, the words should form a sentence that makes sense.
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I know you’re confused now, so let’s go to page G-4 in your handout and I’ll show you how to
fill in the first table. In the first row of the table, you are already given the sequence of
nucleotides from the given DNA strand. Use your DNA kit to make this series of nucleotides.
The color codes for the nucleotides are white (A), grey (G), green (C), black (T).
Make this sequence:
AGAGAGACAGGCAGAAGTTAG.
Then use your kit to make the other DNA strand that it pairs up with. Your sequence should now
be TCTCTCTGTCCGTCTTCAATC.
Write that nucleotide sequence on the second row of the table on p. G-4. Now use your kit to
link the 2 stands together to form your double-stranded DNA. This represents the segment of a
chromosome that is a gene for a particular protein. Now we will begin the process of making a
protein from this gene.
First, break apart the double strand of DNA into two strands. This represents the gene unzipping
so it can be used to make a protein. The original strand is called the primary strand (line 1 of
the table), and the second strand is called the secondary strand (line 2 of the table).
We will now make the messenger RNA (mRNA) for the protein that we are going to make. If we
use the primary strand to make the mRNA, it will code for one protein, but if we use the
secondary strand, it will code for a different protein. That means that the same segment in the
DNA can code for 2 different proteins, depending on which protein we want.
We will use the secondary strand to make this particular protein, so set the primary strand aside.
Using the secondary strand, you want to pair each G (grey) with a C (green), and A (white)
normally pairs with a T (black), but mRNA does not have any letter “T’s”, so it pairs with U
(purple) instead. This nucleotide sequence goes on the third row of your table. Use the DNA kit
to make this new strand of mRNA. Your sequence should be
AGAGAGACAGGCAGAAGUUAG. The process of creating the mRNA is called
transcription.
Now you can detach the mRNA and set it aside to be used for the next step. The mRNA has to
leave the nucleus and go to the cytoplasm. Now attach the original primary strand back to the
secondary strand. That represents the DNA zipping back together. These two original strands
stay in the nucleus as part of the chromosome.
Now we have to perform the step called translation. This is the step where the actual protein is
made, and it occurs in the cytoplasm. Put away your original double-stranded DNA; we are done
with that. Use your mRNA for the next step.
Skip the fourth row of the table and go to the fifth row of the table. The first three nucleotides
are AGA. Go to page G-6 and find out what that codes for. It codes for the word “THE”. Write
that in the bottom box on page G-4. Look up the rest of the words now, and it should form a
sentence that makes sense. Whenever a codon codes for the word “STOP”, that means you have
reached the end of the protein. This sentence says “The puppies ran to see the students STOP”.
Do just one of the other tables yourself and skip the rest.
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TYPES OF MUTATIONS
Nucleotide SUBSTITUTION: for instance, instead of T there is A, C, or G
Nucleotide INSERTION: an extra T, A, C, or G is inserted.
Nucleotide DELETION: a nucleotide is missing.
RESULTS OF MUTATIONS
MISSENSE: one amino acid changes to another amino acid, such as AGA becomes TGA.
NONSENSE: causes a “stop” codon to appear too early, forming a protein that’s too short.
FRAMESHIFT: due to insertion or deletion of a number of nucleotides not divisible by 3. For
instance, 1, 2, 4, 5, 7, 8, 10, 11, or 13 nucleotides are inserted or deleted.
On page G-7 there is one more activity. Choose one of the DNA sequences you did earlier. Write
the DNA sequence number of the one you choose, and write down the sentence it translates into.
Then on the first line of the first table write the original DNA sequence, except replace the first
“A” with a “T”.
For instance, for DNA sequence #1, the given strand started with AGA, so we’re going to write
down TGA. The rest of the sequence is the same. On the second line, the other DNA strand
would be ACT, and the rest is the same. That makes the messenger RNA codon UGA, and the
rest is the same. What word does UGA code for? It’s a stop codon! That means that the single
nucleotide substitution resulted in the protein being stopped before it even began! Now look at
the last line; what mutation effect is it? Since a stop codon was inserted too early, it is a nonsense
mutation, but it was caused by one amino acid AGA being changed into another amino acid
TGA, so it is also a missense mutation.
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