  The mechanism for the formation of the $\Lambda(1405)$ resonance is studied
in a chiral quark model that includes quark-meson as well as contact (four
point) interactions. The negative-parity $S$-wave scattering amplitudes for
strangeness $-1$ and $1$ are calculated within a unified coupled-channel
framework that includes the $KN$, $\bar{K}N$, $\pi\Sigma$, $\eta\Lambda$,
$K\Xi$, $\pi\Lambda$, and $\eta\Sigma$ channels and possible genuine
three-quark bare singlet and octet states corresponding to $\frac12^-$
resonances. We show that in order to reproduce the scattering amplitudes in the
$S_{01}$ partial wave it is important to include the pertinent three-quark
octet states as well as the singlet state, while the inclusion of the contact
term is not mandatory. The Laurent-Pietarinen expansion is used to determine
the $S$-matrix poles. Following their evolution as a function of increasing
interaction strength, the mass of the singlet state is strongly reduced due to
the attractive self-energy in the $\pi\Sigma$ and $\bar{K}N$ channels; when it
drops below the $KN$ threshold, the state acquires a dominant $\bar{K}N$
component which can be identified with a molecular state. The attraction
between the kaon and the nucleon is generated through the $\bar{K}N\Lambda^*$
interaction rather than by meson-nucleon forces.
