Can I deploy a django app which uses sqlite3 as backend on google app engine?
Unfortunately, no you can't. Google App Engine does not allow you to write files, and that is needed by SQLite.
Until recently, it had no support of SQL at all, preferring a home-grown solution (see the "CAP theorem" as for why). This motivated the creation of projects like "Django-nonrel" which is a version of Django that does not require a relational database.
Recently, they opened a beta service that proposes a MySQL database. But beware that it is fundamentally less reliable, and that it is probably going to be expensive.
EDIT: As Nick Johnson observed, this new service (Google Cloud SQL) is fundamentally less scalable, but not fundamentally less reliable.
I created a simple bookmarking app using django which uses sqlite3 as the database backend.
Can I upload it to appengine and use it? What is "Django-nonrel"?