Cyclic Prefix length of 5G NR Frame Structure?

Hello,

I was trying to understand the frame structure importance and its requirement along with the cyclic prefix attachment.

I have basic two questions here:

1) Why is a frame structure requires in sending traffic and control signals in 5G/LTE?Can’t we send just series of symbols as it is? Why is a frame structure defined in first place?

2) Why is cyclic prefix for 1st and 7th symbol more when compared to other symbols in the slots. The time/length of cyclic prefix for 1st and 7th symbol is more. Why can’t it be same for all the symbols? What is the purpose.

Thank you