A mortgage securing a loan made by an association may contain conditions providing for the payment of insurance, taxes, assessments, levies, maintenance and repairs on the mortgaged property and the assignment to it of rents of the mortgaged property and other conditions required by the association for its security and protection and that any money paid by the association incident thereto may be added to the unpaid balance of the loan and that such payments shall be secured by the mortgage. An association may take an assignment of a life insurance policy issued on the life of the borrower or others as additional security on a real estate loan and may pay premiums thereon for its protection, and any premiums so paid may be added to the amount of the principal debt and become secured by the mortgage. An association may also take as additional security on a real estate loan, securities guaranteed by an agency of the United States Government or other securities listed on a national securities exchange as defined in the Federal Securities Exchange Act up to 75 percent of the market value of such securities. In such case not less than 80 percent of the loan shall be secured by a first mortgage on real estate.