You can easily find out what RPM package provides the file. For example find out what provides the /etc/passwd file:

# yum whatprovides /etc/passwd
Sample output:

Loading "installonlyn" plugin
Loading "security" plugin
Setting up repositories
Reading repository metadata in from local files

setup.noarch                             2.5.58-1.el5           base
Matched from:
/etc/passwd

setup.noarch                             2.5.58-1.el5           installed
Matched from:
/etc/passwd

You can use same command to list packages that satisfy dependencies:
# yum whatprovides {dependency-1} {dependency-2}
Refer yum command man page for more information:
# man yum