Do you have the Mid 2010 model 7,1 MacBook Pro. Those were the first ones that could run audio through the Mini dispayPort http://support.apple.com/kb/HT4241
Go to the Apple in the upper left corner and select About This Mac, then click on More Info. When System Profiler comes up check the Model Identifier.
If you connect the 5,5 MacBook Pro using a Mini DisplayPort to HDMI adapter you will need to use external speakers or a 3.5mm headphone jack to RCA sound plugs connected to a stereo sound system if your TV doesn't have separate RCA input plugs for audio with the HDMI plug. The Mini DisplayPort on the MacBook Pro doesn't carry audio and there're no audio plugs on most TVs to work with the HDMI input plug since it's expecting audio with the HDMI.
Here's the various types of Mini DisplayPort adapters on Amazon.com http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=min i-dvi&x=9&y=13#/ref=nb_sb_ss_sc_2_16?url=search-alias%3Daps&field-keywords=mini+ displayport&sprefix=mini+displayport&rh=i%3Aaps%2Ck%3Amini+displayport
You'll also need audio cables. http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=min i-dvi&x=9&y=13#/ref=nb_sb_ss_i_2_19?url=search-alias%3Daps&field-keywords=macboo k+audio+cable&sprefix=macbook+audio+cable&rh=i%3Aaps%2Ck%3Amacbook+audio+cable