No.

First of all, the private key is not actually a string of letters. Rather it is a large 256 bit integer represented as a string of numbers. Represented in decimal it would be ~78 digits long.

Secondly, there is no such object as a Bitcoin. Bitcoin actually uses transaction outputs. Outputs have a value associated with them; that value is the Bitcoin. The private key is what allows you to spend the value from the output. Of course, it is much more complicated than that.