Protein Synthesis: THE BIG PICTURE
We continually say that DNA is our “genetic
code” or “instruction manual” for life. If
that’s true, then how does DNA determine
our hair color, body type, or eye color?
Well, all of those things—hair, eyes, muscle—
are made of proteins. So, the instructions
contained in DNA are used to make
different kinds of proteins!
But, there is a problem…
• Where is the genetic code, or instructions
for making proteins found?
• DNA (in the nucleus)
• Where are proteins made & assembled?
• Ribosome (in the cytoplasm)
• Can DNA leave the nucleus?
• NO! Its too valuable
• How do the instructions get from the
nucleus to the ribosome?
• RNA
The Scoop On RNA:
• Examine the following pictures…how is RNA
different from DNA?
RNA vs. DNA
One nucleotide of RNA
Name: Ribonucleic Acid
Structure: Single-Stranded
Building Block: Nucleotide  sugar (ribose), phosphate, nitrogen base
Base Pairing Rules: Cytosine with Guanine, Adenine with Uracil
NO T’S IN RNA!!!
3 Types of RNA:
• mRNA  Messenger:
Carries DNA’s information
to the ribosome.
• tRNA  Transfer: Changes
the language of the
information, from RNA to
amino acids.
• rRNA  Ribosomal: Makes
up ribosomes.
Each type of RNA is composed of nucleotide
chains. They are just different in structure.
Protein Synthesis: An Overview
1.
Transcription
• Process by which genetic
information is copied from DNA
to mRNA, occurs in the nucleus
2.
Translation
• Process of assembling proteins,
occurs at the ribosome.
Order of nucleotides in mRNA
converted into an order of
amino acids.
Transcription
• Purpose:
To get instructions from DNA inside
the nucleus out to the ribosomes in
the cytoplasm.
• What Happens?
– In the nucleus, a portion of DNA
(gene) unwinds and unzips,
revealing it’s code.
– DNA is transcribed into mRNA
according to base pairing rules.
– Ex: G becomes C, C becomes G
A becomes U, T becomes A
Transcription
Practice, Practice, Practice!
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DNA:
AGGCTATAC
mRNA:
UCCGAUAUG
CODONS?
UCC, GAU, AUG
Codon = Each combination of 3
mRNA nucleotides
Practice: If this is the sequence of
DNA, what mRNA strand would be
transcribed?
G-A-T-T-C-C-G-A-G
C-U-A-A-G-G-C-U-C
Once the mRNA is made in the nucleus,
where does it go?
• To RIBOSOMES in the
cytoplasm to be TRANSLATED!
Translation
• Purpose:
To translate mRNA into a protein. Like
switching languages (nucleotides to amino
acids)
• What Happens?
– mRNA attaches to a ribosome. The
ribosome moves along the mRNA,
“reading” codons.
– Each codon is paired with the opposite
tRNA anticodon according to base
pairing.
– Each tRNA anticodon carries an amino
acid. The chain of amino acids
attaches with peptide bonds and
becomes a protein!
Codon
Anti Codon
Amino
Acid
How does the right amino acid get there?
Practice Makes Perfect!
• DNA:
• CGTGCCCAAATT
• mRNA:
• GCACGGGUUUAA
• Codons? GCA, CGG, GUU, UAA
• tRNA:
• CGUGCCCAAAUU
• Anti-Codons? CGU, GCC, CAA, AUU
• Amino Acids:
• Ala, Arg, Val, STOP