The threat of a possible downgrade of the nation's debt rating sent the markets tumbling to a sharply lower close with the Dow plummeting 248 points to 11,547. Nasdaq stumbled 49 points to 2523.

On the upside

Bargain hunters lifted shares of Geron (Nasdaq: GERN), whose stock price tumbled last week after announcing that it was shuttering its stem cell research programs.

Kodiak Oil & Gas (NYSE: KOG) expanded its stock offering on Friday to 42 million common shares to raise an additional $34.8 million.

Pennystocksinsiders.com issued an equity research report on Central European Distribution (Nasdaq: CEDC).

On the downside

Renren (NYSE: RENN) sold its stake in eLong (Nasdaq: LONG) to Expedia for approximately $72.4 million.

Shares of E-Commerce China Dangdang (NYSE: DANG) continued falling after swinging to a third quarter loss last week.

Camelot Information Systems (NYSE: CIS) will release third quarter results next Wednesday, November 30.

In the broad market, declining issues outpaced advancers by a margin of nearly 6 to 1 on the NYSE and by 5 to 1 on Nasdaq. The Russell 2000 which tracks small cap stocks plunged 17 points to 701.