Only the first 255 characters of the meta description will be read by most search engine "spiders".
Just make sure that your title, your meta description and meta keywords.. all match the content of your webpage. If not, you will be penalized by google.
Also, this has diddly squat to do with pagerank.
All this has to do with is that search engine robots actually know what is in the pages. That's all. Your google ranking is not affected by the content of your pages, but by what and who links to that page.