What are the requirements for doing PhD in molecular biology in us??

I have currently done 3 years of bachelors and 1 year of masters…how much years of education is needed to apply???

To be accepted into any PhD program in the USA, usually you need a bachelor’s degree (but not a specific number of years of study). There may be a strong expectation that your undergraduate major was in the same (or closely related) field as the one you now intend to pursue. The decision probably will hinge on several factors including the quality of your undergraduate preparation, your grades, your GRE scores, and whether you seem to have mature research interests that align with the interests of prospective mentors.

Are you saying you started but did not complete work toward two different degrees? There may be an expectation that you complete the bachelor degree before enrolling in the new doctoral program. If you are in some kind of dual bachelor/master program (3 year BA + 2 year MA or some such) and expect to be awarded both degrees before starting on the PhD, that ought to be fine.

No I have 3 year bsc and 1 year msc from UK…will I get to be in PhD programme???

If you already have a bachelor’s degree and a master’s degree, then I don’t see any obstacle in the fact that it only took you 3 years + 1 year to earn them. A bachelor’s degree (or imminent bachelor’s degree) is likely to be a necessary … but not sufficient … qualification for admission to a strong PhD program. There may be other important factors. Nobody here can predict, based on the little information you’ve provided, whether you’re likely to get in wherever you apply.

I was asking if I am eligible to apply as masters is only of 1 year …so will it cause hindrance for applying to them??

no.
PhD programs generally dont require an applicant to have a masters degree.
but what you WILL need is great LOR’s, great GRE test scores and very good GPA in the classes required for a Biology degree.
Plus experience doing research.
Do/ will you have some by the time you earn your BS degree?

Thanks so I can apply as long as I fulfill above conditions??

The people who are best situated to advise you about this are your own professors. Go speak with them. Ask them where their previous students have been admitted. Did those students go directly into Ph.D. programs, or were they sometimes required to complete a second masters degree?

@Manika16
PhD programs, such as those at Caltech, require all PhD candidates to take 1 year of classes, [which may duplicate those that they took for their masters degree], and then pass a rigorous qualifying oral exam in order to move forward with their degree.
Students who enter rigorous PhD programs with a masters degree at hand often have an educational advantage.
Students who do pass their “quals”, do fulfill the qualifications for a masters degree, but most students don’t ask to have a masters degree awarded, since that is not the primary reason they are attending a PhD program…

You are eligible to apply to a Ph.D. program with a 3 year degree from the UK. The fact that you have also completed a Masters may reduce the number of courses you will be required to take in a Ph.D. program.