How does our government protect our unalienable rights?

How does our government protect our unalienable rights?
I have to work on this one essay for history class and for one of the topics it asks me:

In which way does the government protect our rights to life, liberty, and the pursuit of happiness?

I am aware that the pursuit of happiness means that you have every right to pursue what makes you content. The bill of rights protects these 3 things… your life, your liberty and your right to pursue whatever makes you happy. But how is our liberty and life protected? Please be specific.

You have to remember that the Bill of Rights protects us only from the government itself. We have freedom of speech. Meaning we can’t be imprisoned for speaking our mind. That doesn’t mean we can’t be say fired from work. I can mail the president, or my governor, or my mayor, or any member of government a letter and tell him I think he’s a blithering fool if I want and no one can do anything about it. But I guarantee that if I went to work and told my boss the same thing I’d be looking for a new job. Life is protected by due process. The government can not execute someone without going through all the legal processes. This does not imply that the government has some responsibility to protect us from being a serial killer’s victim or something. Same as liberty. People can’t be arrested and thrown in jail without at least probable cause, and can not be convicted and kept in prison without proof beyond a shadow of a doubt. Liberty just means freedom. But more than just physical freedom. The government can’t tell me that I can’t go get a job as a theoretical physicist if I want to. I have the freedom to do so, especially if it makes me happy… But that doesn’t mean someone has to hire me to do it. The checks and balances put in place by our 3 branches of government, in theory at least, are the protection. Congress can pass an unconstitutional law (and they have many times in the past), but then the Supreme Court can come in and declare it unconstitutional, or the president can veto it.