Download The CENTRAL DOGMA in Biology

The CENTRAL DOGMA in Biology:
Introduction to Transcription
& Translation
Review:
One of the key discoveries in biology is that DNA is the genetic material that codes
for traits. But exactly HOW does it code for traits? The ‘central dogma in biology’
states that DNA provides a code for synthesizing proteins. Ultimately, it is the
proteins in our body that determine all of our traits! In other words:
Proteins are highly complex molecules comprised of chains of amino acids.
Amino acids are compounds containing carbon, hydrogen, oxygen, nitrogen and
occasionally sulphur. There are _____ different amino acids (the human body can
make some amino acids, others must be obtained from food). Amino acids link to
form polypeptide chains which make up the primary structure of a protein.
 A typical protein may contain ____________ or more amino acids.
 Each protein has its own unique _______________ & ________________of amino acids
which determine its particular ________________________ & ______________________.
THE ROLE OF DNA and RNA in making proteins
DNA is the genetic material that we inherit, but proteins are actually responsible
for determining our traits. DNA provides our cells with the information on what
proteins should be synthesized. DNA provides a code, in the language of base
pairs (
____
) that instructs the cells to make specific proteins.
DNA stores the ‘codes’ in the ________________ of a cell, but a messenger is needed to
take the information to the sites where proteins are actually assembled. The
information from nucleus is carried to the _____________________ in the form of RNA.
The messenger of this information is called mRNA or messenger-RNA (RNA
stands for RiboNucleic Acid). The process of reading a DNA strand and creating
RNA is called transcription. The process of using the code of RNA to assemble a
protein is called translation.
DNA
mRNA
Protein
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RNA:
RNA is made from the DNA and has a fairly similar structure to DNA, with a few
differences we can summarize below in a Venn Diagram:
TRANSCRIPTION: creating mRNA from DNA
 First, the 2 strands of DNA ‘unzip’ exposing the gene (section of DNA holding
the code for that particular protein)
 Using one strand of DNA as a template, a complimentary strand of RNA is
produced. Wherever a thymine (T) would have been used for DNA, uracil (U)
is used instead.
 Messenger RNA (mRNA) carries the message to a ribosome, where the protein
is then manufactured.
 Inside the nucleus, the 2 strands of DNA rejoin and recoil.
EXAMPLE:
Double stranded DNA molecule:
One strand of DNA is used as a template to
make the mRNA molecule:
…T A C C C T A G G A G C A T G…
…T A C C C T A G G A G C A T G …
…A T G G G A T C C T C G T A C…
mRNA: …A U G G G A U C C U C G U A C…
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Translation: Creating a Protein from RNA
Translation is the process that creates, or synthesizes, proteins from the genetic code, which is
now in mRNA form. The mRNA is read in triplet, _________ base pairs at a time. Each triplet,
called a ________________, codes for a specific amino acid that will be added to the protein.
For example: consider the following sequence of mRNA:
AUGGAUCCUCGU…
This sequence would be read, 3 bases at a time, as
-
-
-
The codons above represent the following different amino acids.
-
-
-
We use the following chart to determine which amino acids are coded for each of the ______
possible triplet combinations of A, U, C, and G.
Note that some triplet combinations code for the same amino acids!
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NOTE:
The ribosome begins adding amino acids when it finds a ‘start’ codon: _______
The protein is ‘complete’ when the ribosome reaches one of the 3 STOP codons: __________
____________ & ___________
This synthesis employs another set of RNA, known as transfer RNA, or tRNA. Each tRNA
has 2 ends: an _________________________________(which is complementary to a codon) and the
corresponding _________________________________________
The Steps of PROTEIN SYTHESIS
1. The ribosome starts at the start codon AUG. It attracts the tRNA with the correct anticodon & corresponding amino acid (in the case of the start codon, it would be methionine).
2. The tRNA binds its anticodon to the start codon.
3. The ribosome then reads the next codon, and attracts the corresponding tRNA, which binds
to the corresponding codon.
4. The two amino acids form a peptide bond – the beginning of a protein.
5. The ribosome releases the first tRNA, then reads next codon.
6. The ribosome continues this process, growing a chain of amino acids. The resulting chain of
amino acids is the primary structure of the protein.
7. The process ends once the ribosome reaches one of the 3 STOP codons – UGA, UAA or
UAG.
8. The protein folds to obtain its secondary, tertiary, and quaternary structure.
9. The protein is complete!
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Central Dogma Analysis Questions (also reference text chapter 12-3 (pages 300-306)
1. Summarize the ‘Central Dogma’ of biology.
2. Describe the structure of a protein (what are the sub-components of a protein? What makes
proteins different from each other? How is its final structure formed?)
3. Differentiate the places in a cell where DNA is stored in a cell and where proteins are
manufactured in a cell. What molecule delivers the ‘message’ between those 2 places?
4. Compare and contrast RNA and DNA (give both similarities and differences)
Use the following base sequence of ONE strand of a DNA molecule to answer 5-9:
…T A C A A T G C C A G T G G T T C G C A C …
5. Draw the complete DNA molecule – provide both the strand given above and its complementary
strand.
6. Give the base sequence of the strand of mRNA that will be read from the original DNA strand.
7. What sequence of amino acids (protein fragment) would this mRNA code for? Why do you think
I only had you do a fragment rather than a whole protein?
8. If the seventh nucleotide in the original DNA strand was replaced with a cytosine, what would the
resulting mRNA look like?
9. What would the resulting protein fragment (sequence of amino acids) look like?
10. What is the start codon? What then is always the first amino acid of any protein?
11. Which 3 codons cue the ribosome to stop adding more amino acids (stop codons)?
Central Dogma Analysis Questions (also reference text chapter 12-3 (pages 300-306)
1. Summarize the ‘Central Dogma’ of biology.
2. Describe the structure of a protein (what are the sub-components of a protein? What makes
proteins different from each other? How is its final structure formed?)
3. Differentiate the places in a cell where DNA is stored in a cell and where proteins are
manufactured in a cell. What molecule delivers the ‘message’ between those 2 places?
4. Compare and contrast RNA and DNA (give both similarities and differences)
Use the following base sequence of ONE strand of a DNA molecule to answer 5-9:
…T A C A A T G C C A G T G G T T C G C A C …
5. Draw the complete DNA molecule – provide both the strand given above and its complementary
strand.
6. Give the base sequence of the strand of mRNA that will be read from the original DNA strand.
7. What sequence of amino acids (protein fragment) would this mRNA code for? Why do you think
I only had you do a fragment rather than a whole protein?
8. If the seventh nucleotide in the original DNA strand was replaced with a cytosine, what would the
resulting mRNA look like?
9. What would the resulting protein fragment (sequence of amino acids) look like?
10. What is the start codon? What then is always the first amino acid of any protein?
11. Which 3 codons cue the ribosome to stop adding more amino acids (stop codons)?
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