A DNA toolkit

You will write functions that handle a strand of DNA written as a string. They find the partner strand, the GC content, the hydrogen bonds and a rough melting temperature.

The idea. A pairs with T and G pairs with C. The partner strand runs the other way, so we reverse it. A G-C pair has 3 hydrogen bonds and an A-T pair has 2. For a very short stretch, a rule of thumb gives the melting temperature in degrees C as $2 \times (\text{A-T pairs}) + 4 \times (\text{G-C pairs})$.

Your tasks.

1. Complete reverse_complement(seq) so that it returns the partner strand, read from 5′ to 3′.
2. Complete gc_percent(seq).
3. Complete hydrogen_bonds(seq) for the duplex that the strand makes with its partner.
4. Complete melting_temperature(seq) by the rule above.