Making a responsive HTML5 mobile app

I have recently started using LinkedIn and Google's mobile apps like Gmail/G+ etc and they are so fast, intuitive and simple to use.

My question is what steps the engineers would have taken to 开发者_开发百科make such apps? Are they rendering entire HTML or just update the portion of it?

"fast, intuitive and simple to use" - This isn't entirely a technology based question. A lot of design and user experience design would have gone into the building of these app. Which is what makes them "intuitive and simple to use".

To answer your questions within your question. Yes a lot of the new apps are HTML5 apps. Which uses the new HTML5 spec as well as a lot of JavaScript and CSS.

Ajax is used extensively to develop those applications.