A researcher has coated the wells in a multiwell plate with human plasma fibronectin. She introduces integrin-expressing cells into these wells in the presence of different concentrations of a synthetic peptide. She then washes the wells to remove unbound cells and counts the number of cells that remain attached to each well. The results of her experiment are presented in the following schematic graph. The synthetic peptide sequences used in these experiments were GRGDSPC (1) or GGDRSLN (2). Which one of these peptides (1 or 2) would you expect to correspond to curve a in the graph? Which curve (a or b) would you expect if a synthetic peptide with the sequence GDGRSPC was used? C is cysteine, D is aspartic acid, G is glycine, L is leucine, N is asparagine, P is proline, R is arginine, and S is serine.
A) 1; a
B) 1; b
C) 2; a
D) 2; b

Question

A researcher has coated the wells in a multiwell plate with human plasma fibronectin. She introduces integrin-expressing cells into these wells in the presence of different concentrations of a synthetic peptide. She then washes the wells to remove unbound cells and counts the number of cells that remain attached to each well. The results of her experiment are presented in the following schematic graph. The synthetic peptide sequences used in these experiments were GRGDSPC (1) or GGDRSLN (2). Which one of these peptides (1 or 2) would you expect to correspond to curve a in the graph? Which curve (a or b) would you expect if a synthetic peptide with the sequence GDGRSPC was used? C is cysteine, D is aspartic acid, G is glycine, L is leucine, N is asparagine, P is proline, R is arginine, and S is serine. 
A) 1; a 
B) 1; b 
C) 2; a 
D) 2; b

Quizplus · Accepted Answer

The synthetic peptide containing the RGD sequence (1) competes with fibronectin for integrin binding. At higher concentrations, its presence results in fewer cells attaching to the fibronectin on the well surface, as shown in curve B. A sequence that lacks the RGD motif would be expected to result in curve A.

A Researcher Has Coated the Wells in a Multiwell Plate