What might explain how 20,000 genes encode for 87,000 proteins in human cells? Select one:
a. proteins must be spliced together to be functional
b. genes are cut into proteins by RNA
c. viruses leave behind remnant DNA
d. alternative splicing of genes into different mRNA
e. one gene encodes for one protein

Oxytocin and cholecystokinin are transported through the bloodstream and arrive at the uterus at the same time. oxytocin causes the uterus to contract, whereas cholecystokinin has no effect. why? oxytocin blocks the activity of cholecystokinin. oxytocin is at a higher concentration in the bloodstream than cholecystokinin. oxytocin can diffuse through the plasma membrane of uterine cells, whereas cholecystokinin cannot. oxytocin alters gene expression patterns, whereas cholecystokinin does not. the uterus has receptors for oxytocin, but not for cholecystokinin.