but, there is a problem…
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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!
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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
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The Scoop On RNA:
• Examine the following pictures…how is RNA different from DNA?
One nucleotide of RNA
RNA vs. DNA
Name:
Structure:
Building Block:
Base Pairing Rules:
Ribonucleic Acid
Single-Stranded
Nucleotide sugar (ribose), phosphate, nitrogen base
Cytosine with Guanine, Adenine with Uracil
NO T’S IN RNA!!!
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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.
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Each type of RNA is composed of nucleotide chains. They are just different
in structure.
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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.
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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
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Transcription
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Practice, Practice, Practice!
• DNA: • AGGCTATAC• mRNA:• UCCGAUAUG• CODONS?• UCC, GAU, AUG
Codon = Each combination of 3
mRNA nucleotides
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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
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Once the mRNA is made in the nucleus, where does it go?
• To RIBOSOMES in the cytoplasm to be TRANSLATED!
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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!
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Codon
Anti -Codon
Amino
Acid
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How does the right amino acid get there?
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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