Download Part I: To Transcribe! In previous lessons, you`ve learned the

B.6CDE: Transcription and Translation
Mechanisms of Genetics
•  What is the purpose of transcription of DNA?
Part I: To Transcribe!
In previous lessons, you’ve learned the importance of DNA in living things. You may recall that
DNA contains all of the genetic information for an organism. Most of the information in DNA is
stored in segments called genes. A gene is a specific sequence of nucleotides in a strand of DNA
that codes for a specific sequence of amino acids. The amino acids form chains that make a
certain protein depending on the order of the nitrogen bases. Just like 26 letters of the alphabet
make words, 20 amino acids can be joined together in various order and lengths to make
different proteins. Now let’s discuss how that genetic information gets processed into the
molecules needed to make proteins.
Proteins are some of the most valuable molecules for life. Proteins are essential to build muscle.
They’re found in cell membranes to help with transport. Hormones and enzymes are also made
of proteins. Without these vital biomolecules, life would not exist!
DNA is basically an informational molecule; it stores the information needed to produce the
proteins. You may remember that the DNA molecule is made of repeating nucleotides composed
of a sugar, a phosphate, and a nitrogen base (adenine, thymine, cytosine or guanine). DNA has
the “plan” to make all of the proteins. However, DNA is a large molecule and it can’t fit through
the nuclear pores. It has to remain inside the nucleus. So, how does the information get to the
ribosomes for the production of proteins? That’s where a molecule called RNA comes in!
RNA is known as ribonucleic acid. RNA is different from DNA in a few ways.
1. 
2. 
3. 
4. 
5. 
The sugar in RNA is ribose.
RNA is single-stranded.
RNA is smaller than DNA, but can be 500-1000 nucleotides long
RNA can leave the nucleus
RNA has the nitrogen base “Uracil” instead of Thymine. (Uracil binds with Adenine)
There are three main types of RNA : mRNA, rRNA and tRNA. These RNA molecules have different
structures and therefore have different jobs in the protein-making process- Protein Synthesis.
Protein Synthesis:
This process of making proteins consists of two major stages: transcription and translation.
Continue on to the next page.
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B.6CDE: Transcription and Translation
Mechanisms of Genetics
•  What is the purpose of transcription of DNA?
Part I: To Transcribe, continued: The Steps of Transcription
1. An enzyme, RNA polymerase, separates the DNA section that
codes for a particular protein.
2. A complementary mRNA strand is formed by base-paring to
the original DNA strand.
3. Once the sequence of the DNA is copied into mRNA,
the DNA zips back up.
4. mRNA now contains the DNA ‘message’ and leaves
the nucleus.
The mRNA molecule now has the genetic code to make the protein. The mRNA strand
will be read three letters at a time. These three letter sections are called codons. These
codons will specify a single amino acid that will be added to a string of amino acids
which will eventually make a protein.
Example:
DNA: T A C G G A T C G A T T G C G A T T
mRNA
A: A U G C C U A G C U A A C G C U A A
Codon
Codon
Complete Part I in your Student Journal.
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B.6CDE: Transcription and Translation
Mechanisms of Genetics
•  How are genetic combinations predicted?
Part II: Translation
Now that the mRNA has left the nucleus, it is on its way to the ribosome. The ribosome is
made of rRNA where it will bind to the mRNA and help assemble the amino acids into a
protein. Before the protein can be made, the mRNA codons have to be translated at the
ribosome.
Here are the steps of translation:
1. Translation begins with the ‘Start’ codon: AUG.
This codon moves into the ribosome.
2. For every mRNA codon, there is a tRNA anticodon
that binds to the bases of mRNA. Each tRNA molecule
can only carry one specific amino acid. The tRNA brings
the correct amino acid to the ribosome.
3. The next codon is read. tRNA binds to the codon,
then brings the correct amino acid to the ribosome.
4. The ribosome joins the two amino acids. Another
tRNA molecule comes in and reads the next codon.
This process repeats and the protein will continue growing until a “Stop” codon signals
that the end for making that particular protein.
Complete Part II in your Student Journal.
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B.6CDE: Transcription and Translation
Mechanisms of Genetics
•  How do changes in DNA affect production of amino acids?
Part III: Mutations
As you can see, protein synthesis is a very detailed process! Sometimes during this process, a cell
will make a mistake in copying the DNA. Occasionally, an extra base is inserted, or a base may
be left out. Any change in the DNA or genetic material is called a mutation. There are two major
kinds of mutations: gene mutations and chromosomal mutations.
A gene mutation happens in a single gene. There are different types of gene mutations.
Point Mutations: these occur at a particular point in the gene. It involves changing one or
sometimes just a few nitrogen bases in the nucleotides.
Examples include:
Frameshift Mutations:
Insertion: a base is inserted into the DNA sequence.
Insertions and deletions are
considered frameshift mutations
because if a base is added or
deleted, the sequence moves
over and now may read an
incorrect template for a codon.
Deletion: A base is deleted from the DNA sequence
Sample of Deletion Mutation:
Cystic Fibrosis
Substitution: One base is substituted for another.
Example of Substitution Mutation:
Sickle Cell Anemia
Continue on to the next page.
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B.6CDE: Transcription and Translation
Mechanisms of Genetics
•  How do changes in DNA affect production of amino acids?
Part III: Mutations, continued
Chromosomal Mutations:
Chromosomal mutations happen when changes occur in the number or the structure of a
chromosome. The examples of chromosomal mutations include:
Inversion:
Deletion:
Duplication:
Translocation:
Complete Part III in your Student Journal.
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B.6CDE: Transcription and Translation
Mechanisms of Genetics
•  How do changes in DNA affect production of amino acids?
•  Why is it important that gene expression is regulated?
Part IV: To Transcribe or To Translate? That is the Question…
Your Mission: Recognize that gene expression is a regulated process.
The segments of DNA that code for traits are called “genes.” The genes contain
information that can be translated to mRNA and then transcribed into a protein. In other
words, the genes found on DNA strands code for proteins. However, it is very important
to note that not all of the genes in an organism's DNA are expressed all of the time. For
example, the DNA in a heart cell does not, and cannot, express the same genes that an
eyeball cell does. Both of those cells contain the exact same version, or copy, of the
organism's DNA, with both types of genes included, but each gene is not expressed.
Gene expression has to be regulated. The details of regulation depend on environmental
factors and heredity. Gene expression is regulated in a way similar to the use of a light
switch. Look closely at the two light switch examples below.
Both the heart cell gene and the eyeball cell gene are found on each strand of DNA
within the organism. However, even though both of these genes are located in all of the
organism's DNA, only the heart cell genes will be turned on if the DNA strand is located
within the organism's heart.
In the organism's heart ...
HEART CELL GENE
Heart cell
proteins will
be created if
the DNA
strand is
transcribed
in the heart.
EYEBALL CELL GENE
ON
on
off
OFF
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Eyeball cell
proteins will
NOT be
created if the
DNA strand is
transcribed in
the heart.
B.6CDE: Transcription and Translation
Mechanisms of Genetics
•  How do changes in DNA affect production of amino acids?
•  Why is it important that gene expression is regulated?
Part IV: To Transcribe or To Translate? That is the Question…, continued
Your Mission: Recognize that gene expression is a regulated process.
To better understand how these gene switches work, you will explore the gene that
controls the production of digestive enzymes (proteins). For each scenario described
below, in Part III of your Student Journal, circle whether the gene will be turned On or Off
and explain your reasoning. Then, finish this part of your exploration by answering the
remaining questions.
Scenario 1
You are in the stomach of a person who has just eaten a large meal, which stretches the
walls of the stomach, signaling the body that the stomach is full. Will the gene be turned
on or off?
Scenario 2
You are in the mouth of a person who is not hungry and has no desire to eat. They do not
put any food in their mouth. Will the gene be turned on or off?
Scenario 3
The liver produces a product called bile that aids in the digestive process. When the
person is digesting, bile is secreted into the small intestine. When a person is not
digesting, the bile is stored in the gall bladder. You are in an empty small intestine. Will
the gene be turned on or off?
Scenario 4
You are in the veins that transport the nutrients from the digestive organs to the rest of the
body. In those veins, will the gene be turned on or off?
Complete Part IV in your Student Journal.
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