REPORT FOR ANALYTICAL CHEMISTS
v Quantitative spectral scanning of TLC and other solid or liquid media to 3 O.D. units has become a reality with the SCHOEFFEL SPECTRO DENSITOMETER SD 3000
The unit includes a quartz prism MONOCHROMATOR 200-700 mu (190-1500 mu optional) and a Xe or XeHg ILLUMINATION UNIT as well as automatic PLATE TRANSPORT. (20cm plates scan in 2 min.)
Figure 10.
Purine-pyrimidine base pairing and hydrogen bonding in DNA
Figure 1 1 . Transcription of the genetic code (left) showing complementarity of the messenger RNA with one strand of the DNA. Translation at one ribosome (right) is occurring with the polypeptide chain growing from left to right
ented to allow formation of the carboxamide bond of the protein (Figure 11). An integral component in the sys tem is a class of smaller RNA mol ecules, referred to as soluble or transfer RNA (tRNA). These are 77 nucleotides long (molecular weight approximately 25,000), and serve as adaptors positioning the amino acid on the mRNA template (Figure 11). Probably one tRNA molecule corresponds to each code word. One end of the tRNA mol ecule terminates in the nucleotide sequence CCA (cytidylic acid, cytidylic acid, adenylic acid). The appropriate amino acid is bound to the last of these. The tRNA is charged with its specific amino acid by a series of enzymatically cata lyzed steps. The amino acid is first
activated to form an amino acid adenylate: AA + ATP
amino acyl = ί synthetase AA~AMP +
The INTEGRATION UNIT and DENSITY COMPUTER permit rapid data junction with the base line errors • 0.1"·'. and 0.5% plates.
acquisition in con SD 3000. Average are better than with normal TLC
P~P
The amino acyl intermediate then becomes attached to thje tRNA while still bound to the same ac tivating enzyme. A A ~ A M P + tRNA
amino acyl t
synthetase A A ~ t R N A + AMP Somewhere on the tRNA molecule there must be a triplet sequence which is complementary to the mRNA codon and which gives the molecule in part its specificity. I t is the tRNA which binds with the
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SCHOEFFEL INSTRUMENT-CORP Westwood, N. J. 07675 (201) 664-7263 See ACS Laboratory Guide for All Products/Sales Office Circle No. 146 on Readers' Service Card
VOL. 40, NO. 1, JANUARY 1968
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