Which stratum should contain the greatest proportion of extinct organisms?

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#Question id: 159

#XL - T Zoology

The chirality of an amino acid results from the fact that its alpha carbon:

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#Question id: 160

#XL - T Zoology

Of the 20 standard amino acids, only ___________ is not optically active.  The reason is that its side chain ___________.

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#Question id: 161

#XL - T Zoology

Two amino acids of the standard 20 contain sulfur atoms.  They are:

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#Question id: 162

#XL - T Zoology

All of the amino acids that are found in proteins, except for proline, contain a(n):

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#Question id: 163

#XL - T Zoology

Which of the following statements about cystine is correct?

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#Question id: 164

#XL - T Zoology

The uncommon amino acid selenocysteine has an R group with the structure —CH2—SeH (pKa = 5).  In an aqueous solution, pH = 7.0, selenocysteine would: