Lecture 2
tRNA: Structure & Function
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Major players in protein synthesis:
mRNA, tRNA and the ribosome
|
|
mRNA
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Messenger RNA, a copy of DNA blueprint
of the gene to be expressed. |
Information
|
|
tRNA
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Aminoacyl transfer RNA, also called anticodon
or adaptor molecule. One or more tRNAs for each amino
acid. |
Supply
|
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Ribosome
|
A very large complex of several rRNAs (ribosomal RNA)
and many protein molecules. Total molecular weight over 2 million dalton. |
Factory
|
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Protein
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Polypeptide chain with sequence dictated by the mRNA
sequence. Also called the gene product. |
Product
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Protein Synthesis
Electronmicrograph of a so-called polysome: one mRNA strand (faint
horizontal line) with many individual ribosomes attached (dark blobs).
The newly synthesized polypeptide chains (proteins) can be
seen as irregularly shaped extensions from the ribosomes:
The bottom panel shows a schematic representation of the process in the
upper panel.
Now let's magnify a ribosome to the size of a "Big Mac" (factor 10,000,000).
At this magnification an E. coli bacterium would be about 10 meters
(or 30 feet) in diameter. You would be about 10,000 miles tall:
| Ribosome |
20 nm or
200 Å
|
Big Mac
20 cm
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8 inches
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| tRNA |
5 nm or
50 Å
|
5 cm
|
2 inches
|
| mRNA (900 bases) |
450 nm or
4,500 Å
|
450 cm
|
15 feet
|
Extended (unfolded) protein
(300 amino acids) |
90 nm or
900 Å
|
90 cm
|
3 feet
|
Globular (folded) protein
(300 amino acids) |
5 nm or
50 Å
|
5 cm
|
2 inches
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1 nm (nanometer) is 10-9
meters.
1 Å (angstrom) is 10-10
meters or 0.1 nm.
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