At real estate auctions with reserve, when the hammer falls no contract is formed until the seller accepts the amount, when the seller signs the real estate contract is that when the bid is accepted, and does any part of the UCC code cover real estate

Auction terms vary, but usually in a reserve auction, if the hammer price meets or exceeds the reserve, the sale is automatically confirmed and both buyer and seller are obligated to the sale. If the reserve is not met, an offer is made at the hammer price, and the seller has a predetermined amount of time to accept or decline it (or make a counter-offer).

The UCC doesn't cover the sale real property. The UCC only covers chattels that are part of the transaction that are used as collateral.