Accessing SharePoint:SPAppIFrame contents in a SharePoint hosted app

I've created a SharePoint hosted app that will display a page from its host web. This SP hosted app's home page consists of a SharePoint:SPAppIFrame element with its 'src' attribute set to the host web page. I've added the following entry in the master page:

<WebPartPages:AllowFraming runat="server" />

and, hence, allowing the iframe to display the host web's page content. 

Now, I want hide certain content within this iframe (such as Quick launch, top navigation etc.). How to achieve this? I tried adding accessing the iframe and its contents using jQuery, but that is not fetching the required data.

Thanks Arut