  We present a panoramic view of the utility of coarse-grained (CG) models to
study folding and functions of proteins and RNA. Drawing largely on the methods
developed in our group over the last twenty years, we describe a number of key
applications ranging from folding of proteins with disulfide bonds to functions
of molecular machines. After presenting the theoretical basis that justifies
the use of CG models, we explore the biophysical basis for the emergence of a
finite number of folds from lattice models. The lattice model simulations of
approach to the folded state show that non-native interactions are relevant
only early in the folding process - a finding that rationalizes the success of
structure-based models that emphasize native interactions. Applications of
off-lattice $C_{\alpha}$ and models that explicitly consider side chains
($C_{\alpha}$-SCM) to folding of $\beta$-hairpin and effects of macromolecular
crowding are briefly discussed. Successful application of a new class of
off-lattice model, referred to as the Self-Organized Polymer (SOP), is shown by
describing the response of Green Fluorescent Protein (GFP) to mechanical force.
The utility of the SOP model is further illustrated by applications that
clarify the functions of the chaperonin GroEL and motion of the molecular motor
kinesin. We also present two distinct models for RNA, namely, the Three Site
Interaction (TIS) model and the SOP model, that probe forced unfolding and
force quench refolding of a simple hairpin and {\it Azoarcus} ribozyme. The
predictions based on the SOP model show that force-induced unfolding pathways
of the ribozyme can be dramatically changed by varying the loading rate. We
conclude with a discussion of future prospects for the use of coarse-grained
models in addressing problems of outstanding interest in biology.
