β Sheets in proteins contain 2 to as many as 22 polypeptide strands, with an average of 6 strands. 

Each strand may contain up to 15 residues, the average being 6 residues.

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#Id: 7842

#Unit 1. Molecules and their Interaction Relevant to Biology

Two sugars that differ in configuration at only one chiral center are described as epimers.

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#Id: 7492

#Unit 4. Cell Communication and Cell Signaling

Exonuclease trimming sometimes occurs at the VDJ and VJ junctions, causing loss of nucleotides.

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#Id: 2493

#Unit 13. Methods in Biology

The band-sharpening effect relies on the fact that negatively charged glycinate ions (in the electrophoresis buffer) have a lower electrophoretic mobility than do the protein–SDS complexes, which, in turn, have lower mobility than the chloride ions (Cl − ) of the loading buffer and the stacking gel buffer. 

[Cl−] > [protein–SDS] > [glycinate].

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#Id: 8991

#Unit 11. Evolution and Behavior

Incomplete lineage sorting (hemiplasy)

If you make a phylogenetic tree of how the alleles are related to each other, it does not mirror how the species split apart.

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#Id: 2397

#Unit 3. Fundamental Processes

Splicing of pre-tRNAs is catalyzed by proteins, not by RNAs.