You should punctuate dialogue exactly the way you would punctuate the same sentence if it were not in dialogue (excepting the typographic rules around the placement of quotation marks).
A sentence is a sentence. A sentence fragment is a sentence fragment. Two independent clauses joined together are two independent clauses joined together. There are specific punctuation rules for all these things and they remain the same whether the sentence is in quotation marks or not.
You should not attempt to use punctuation as a way to inflect a sentence to show how an actor might speak it in a movie. There simply are no punctuation marks for that. Insead, recast your sentence so the the emphasis naturally falls where you want it. (You could use italics or bolding to indicate emphasis, though personally that makes me shudder.)
EDIT: It seems necessary to address this issues of pauses (though it is not part of the original question). There is a lot of confusion, including in published sources, about the relationship between punctuation in writing and pauses in speech. A lot of people seem to think that punctuation in writing is used to indicate pauses in speech. This is not so.
Language, whether spoken or written, consists of grammatical units -- groups of words used together to express a meaning. A sentence expresses a complete thought, which may be composed of one grammatical unit or of several. In the case where it consists of several grammatical units, there is the possibility of confusion about which words belong to which grammatical units, and that confusion can change the meaning of the grammatical units, thus creating ambiguity in the sentence. In order to avoid this ambiguity, we need to find a way to indicate which words belong to which grammatical units.
In written language, we do this with punctuation. (In English, that is. In inflected languages it is done, in part at least, with inflection, greatly reducing the need for punctuation.)
But in spoken language, we don't have punctuation, unless you want to adapt Victor Borge's audible punctuation system (Google that if you have never heard it; it's hilarious.) So in spoken language, we need a different way to indicate which words belong together to make up grammatical units. We do this with a combination of inflections and pauses.
There are far fewer pauses in speech than people imagine. We speak in a constant stream without pauses between words. The brain separates that stream of syllables into words and we imagine that we are actually hearing pauses between the words. But those pauses are not there. You can demonstrate this to yourself by listening to a language you don't understand. You won't hear pauses. You can also demonstrate it by attempting to speak without the pauses you think you hear between words. You can't do it, because there never were pauses in the first place. At some of the places where you would insert punctuation in writing, you will find a genuine pause in speaking, but not in most of them.
So, this notion that punctuation indicates pauses is incorrect. Rather, what punctuation indicates in writing, inflection, and (occasionally) pauses, indicates in speech. One is not a sign for another, they are different signs for the same thing in different media.
But there is no one to one correspondence between these two sign systems. They work quite differently from one another. What commas do in writing is sometimes done by inflection in speech and sometimes by a pause. It is not even a given that everything that is indicated by the punctuation rules of writing is indicated at all in speech (there is no Oxford comma debate in spoken language, for instance). We don't rely on either of these systems alone to disambiguate language. A lot of disambiguation is done simply by choosing the most likely meaning. And, of course, sometimes genuine ambiguity arises in both speech and writing, and not always in the same place or in the same way.
All of which does pose a problem for writing dialogue, which is supposed to represent speech, not written language. There is an obvious temptation for the writer to want to indicate how the dialogue would actually have been spoken -- to act it out, as it were.
But the literary mainstream has never done this. It has, with only isolated exceptions, always punctuated dialogue as written language. The reason for this, I believe, is precisely that there is no direct correspondence between our written and spoken systems for delineating grammatical units. They don't correspond to each other, and therefore one cannot be used reliably to indicate the other.
This means that if you try to use punctuation not as it is used in written language, but as means to simulate the use of inflections and pauses in spoken language, you are certain to fail, for some or all of your readers, because the two systems simply don't correspond.
The solution that has been used down through the ages is, therefore, to punctuate dialogue as written language and allow the reader to translate it into spoken language in their heads (if, indeed, they read that way). And this works very well almost all the time because we are used to doing this translation anyway.
SECOND EDIT: For a further demonstration that we don't pause between words in speech, and don't pause for most punctuation either, consider singing. Music and singing form a continuous sound with no pauses between notes. This makes a rest, when it does occur in music, an incredibly powerful device because of how rare it is and how disruptive it is to the flow of the music. Pauses in speech are equally powerful rhetorical devices, and are used more often. But such pauses often don't correspond to where commas would occur in text. For instance, when Jeremy Clarkson says that some car is "The fastest car in the world." he puts a huge dramatic pause before "in the world." But there is no punctuation mark there.
We generally speak in a continuous flow of sound, just as we sing. Occasionally we pause in speech, either for dramatic effect, or to indicate a grammatical break. Sometimes we pause at the same place where we would put a comma in written language, but we don't pause for most commas and we when we do pause, it is often not at a place where a comma or any other kind of punctuation would occur in writing.
