In a corporate environment, an organization is implementing a new Identity and Access Management (IAM) system to enhance security and streamline user access. The system will utilize role-based access control (RBAC) to assign permissions based on user roles. If the organization has 5 distinct roles and each role can have a combination of 3 different permissions (read, write, execute), how many unique combinations of permissions can be assigned to a single role? Additionally, if the organization decides to implement a policy where each role must have at least one permission assigned, how does this affect the total number of valid combinations?