Can I use MD lenses on my Minolta 5D or do I need an adaptor
The two lens mount systems are incompatible.
You can find adapters on ebay (listed as MD to MA or MD to Dynax) but they come in two varieties:-
The first is a straight converter, it allows the MD lens to attach to your camera, but as the lens is further away from the sensor/film plane than it was designed for you lose infinity focussing so the lens is only good for close-ups.
The second type is more expensive as it incorporates corrective optics to compensate and allow infinity focussing. But by introducing additional (and often suspect quality) optical elements you inevitably have a trade-off in image quality and may experience greater lens flare and chromatic aberrations.
Either way, an adapter leaves the MD lens completely unable to communicate any information to the camera body, and the body is unable to automatically stop the lens aperture down when taking photos. In practice, this means that you must use the camera in fully manual mode, manually focus at wide open aperture and then turn the aperture ring down to whatever you wish to use to correctly meter the light level in order to set the correct shutter speed.
All in all, it's a complete waste of time in my opinion and it would be simpler and far cheaper to obtain a suitable Minolta MD mount body to use with those lenses alone. They go for free/peanuts now, like many 35mm SLR bodies and you can try your local FreeCycle/Freegle groups before shelling out anything. Rare/collectable models aside, no MD mount body should go for more than £10-£20 unless it's guaranteed to have been freshly serviced with new batteries.
As you may be aware, newer Sony lenses will fit your 5D as they use the same mount, but they aren't anywhere near as cheap nor plentiful as MD lenses.
Hope this helps, all that I ask in return is for you to take a moment to rate my answer.