I've lived a sedentary existence for awhile now. I am about 312 lbs. 5 feet 10 inches. l do not look obese, but obviously l am. l have no health conditions except a fractured lower vertebrae that only affects me once in awhile. If l mountain bike on the streets for 35 minutes, with added resistence(left speed on 3 right on 5 or 4) and lift weights(dumbells, enough weight to do 3 sets of 10 and not be able to do more) is that enough? And should l consume extra protein because of it? l just bought powder whey protein. 26g per scoop. l take two scoops a day.

You want to pedal at a faster rate around 70-90 rpm is with lite pressure on the pedals, that will use fat for fuel. Pedaling at a slow rate like u r doing will tire out ur muscles very quickly & ur muscles use glycogen as fuel & require a longer time to recover. Select a gear that feels easy to pedal at the higher rpm is u will be able to ride longer without ur legs giving out. You can tell how hard u r working by how hard u r breathing. You want to be able to talk but not sing. It will take a while for ur body to get use to it.

When l lift weights l do about 12 reps & increase the weight when its easy to do 16 or more. Cut back on the protein supplements u do not need that much if u have protein in ur diet. Eating too much protein wont increase ur muscle size, it just ads calories.

You should sit down with your doctor and possibly a good personal trainer and consult with them about this before you get started, assuming you have not already done so. I'd give that advice to virtually anyone who intends to go from completely sedentary into a training regimen, regardless of their weight. Just for starters, that 35-minute bike ride sounds pretty ambitious, maybe too much so.

Protein in your diet serves one purpose- it builds muscle condition. If you want to build condition then take protein otherwise don't. It will in fact increase your muscle size provided you're involved in some form of exercise.

l gave this exact answer to someone who asked a similar question a while ago:
To obtain maximum benefit from ur exercise routine u need to work within ur target heart rate zone. It will require a little research on ur part based upon ur age, body type & resting heart rate to determine what yours is.
I'd take advice from either ur doctor or a trained professional who will likely direct u to ur doctor first.
No one here is qualified to offer u advice on ur exercise regime, & if they were, u have not given enough information for them to give an accurate or responsible answer.
Your health is no a matter for idle speculation & as a rule undertaking any strenuous exercise requires careful consideration if it is something you're not used to doing.
l could tell u all about what works for me or my mates, but this would almost certainly not apply to you.
For all l know, u could be recovering from heart surgery & my advice might kill you.
Please look to professionals for ur advice.
Good luck.

For the cycling part, like Bob A said, u should pedal fast & pedal light as it involves ur slow-twitch muscles in ur legs that uses fats & fuel & does not tire out easily compared to pedalling hard & slow with the higher resistance.

If u r trying to lose weight, which l believe u are, u need to do more cardio exercise, like cycling & running. Weight lifting is more for building muscles.
If u r serious about building more muscles, then drink the protein whey, if u r not working out, l do not think u need to drink it.

i'd suggest u cycle more instead, its much more fun than lifting weights :P

Good luck!