With the evolution of quantum computing, classical cryptographic techniques such as RSA and ECDSA have become vulnerable to quantum attacks. Generally, classical cryptographic techniques use smaller key sizes, which are feasible for a block in a blockchain. However, in a post-quantum scenario, the block size increases significantly due to the larger key sizes required for security. To address this challenge, this paper introduces a new blockchain structure that separates public keys into a dedicated block instead of storing them within transaction blocks. Rather than securing public keys in every transaction block, a new block is introduced that stores the public keys of only a limited number of blocks. Furthermore, a lattice-based digital signature scheme (Dilithium) is used to sign all transactions, making the system quantum-resistant. Additionally, a Merkle tree-based structure is employed to manage public keys within the public key block. The system follows a consensus mechanism for block validation. To ensure the presence of honest miners, block signing is implemented using threshold cryptography. This proposed structure could serve as a viable solution for transitioning classical blockchain systems toward post-quantum security.