Sakızı toplantı başlamadan önce çöpe attım.

The -ı here is the accusative case ending, which marks a specific direct object.

• sakız = gum
• sakızı = the gum

So Sakızı attım means I threw away the gum, not just I threw away gum in a general sense.

In Turkish, a definite/specific direct object usually takes the accusative ending.

The -e is the dative case ending, which often means to, into, or toward.

• çöp = trash, garbage
• çöpe = to the trash / into the trash

With atmak meaning to throw, Turkish uses the dative to show the destination:

• çöpe atmak = to throw into the trash

Compare:

• çöpte = in the trash
• çöpten = from the trash

This is a very common Turkish structure:

• verb stem + -madan / -meden
  • önce

It means before doing something or before something happens.

Here:

• başlamak = to start
• başlama-dan önce = before starting / before it started

So:

• toplantı başlamadan önce = before the meeting started

This is a standard way to make a before-clause in Turkish.

Because başlamadan is a non-finite verb form, not a full main verb.

The main tense of the sentence comes from attım:

• attım = I threw

So başlamadan önce does not need its own past tense suffix. English often requires one, so we translate it as:

• before the meeting started

But Turkish leaves that time reference to be understood from the main verb and the context.

Both are possible, but they mean slightly different things.

• toplantıdan önce = before the meeting
• toplantı başlamadan önce = before the meeting started

The version in your sentence is more explicit. It focuses on the moment before the meeting began, not just any time earlier than the meeting.

So toplantı başlamadan önce is a little more specific.

Because Turkish usually drops subject pronouns when they are already clear from the verb ending.

• attım = I threw

The -m at the end already tells you the subject is I.

So:

• Ben sakızı toplantı başlamadan önce çöpe attım is possible, but
• Sakızı toplantı başlamadan önce çöpe attım is more natural unless you want to emphasize I.

It breaks down like this:

• atmak = to throw
• verb stem = at-
• past tense = -tı / -ti / -tu / -tü or -dı / -di / -du / -dü
• first person singular = -m

So:

• at- + tı + m → attım

Why -tı and not -dı?
Because the final t in at- is voiceless, so the past suffix also becomes voiceless: -tı.

The result is written with double t:

• attım = I threw

The most neutral Turkish word order is usually Subject – Object – Other elements – Verb, with the verb at the end.

In this sentence:

• sakızı = object
• toplantı başlamadan önce = time clause
• çöpe = destination
• attım = verb

So the verb comes last, which is very typical in Turkish.

A natural English-style breakdown would be:

• I threw the gum into the trash before the meeting started.

Yes. Turkish word order is fairly flexible, although the verb usually stays at the end.

For example, these are possible:

• Toplantı başlamadan önce sakızı çöpe attım.
• Sakızı çöpe toplantı başlamadan önce attım.

They all mean roughly the same thing, but the emphasis changes.

The original version sounds natural and neutral, with a smooth flow from object to time to destination to verb.

This is a good question, because sakızı can sometimes look ambiguous to learners.

By itself, sakızı could look like:

• sakız + ı = the gum, as a definite object

In other contexts, forms like this can resemble possessive forms, which is why learners often get confused.

But in this sentence, the intended reading is clearly:

• the gum

If you wanted to say his/her gum as the object, you would normally make that clearer, for example:

• onun sakızını attım = I threw away his/her gum

So here, you should understand sakızı as the gum.

Because in Turkish, önce usually comes after the word or phrase it relates to.

So:

• başlamadan önce = before starting
• toplantı başlamadan önce = before the meeting started

This is the normal Turkish pattern. English uses before at the beginning of the phrase, but Turkish uses önce after it.

That is a common word-order difference between the two languages.

Yes, it is a very common combination.

• atmak = to throw
• çöpe atmak = to throw in the trash / throw away

So even though the literal structure is throw to the trash, the natural English meaning is throw away or throw into the trash.

You could also hear:

• çöp kutusuna atmak = to throw into the trash can

That is a bit more specific than just çöpe atmak.