Biology 93 is the first biology class that UCI Biology majors take in their journey to pursue a degree in biological sciences. Although this class is extremely interesting and full of facts, it can also be a little difficult for students. Typically, this is the class that makes students realize that Biology either is or is not for them. Biology 93 can be a challenging course, but knowing these important concepts can get you off to the right step!

1. DNA Replication

DNA replication is a process that occur when the DNA makes a copy of itself during cell division. First, the double helix of the DNA becomes unzipped, which is done by the enzyme helicase. The enzyme helicase breaks the hydrogen bonds that hold the complementary bases of DNA together. One of the strands is in the 3′ to 5′ direction, while the other strand is in the 5′ to 3′ direction. Therefore, one strand is referred to as the leading strand, while the other stand is referred to as the lagging strand.


2. Leading Strand

The enzyme primase primes the leading strand of the DNA. The primer that is inserted by primate acts as the starting point so that complementary nucleotide bases can be added to the strand of DNA. This enzyme is important because without primase, DNA replication would not be able to happen. There must be a primer inserted on the DNA before DNA replication begins.


3. Lagging Strand

The lagging strand has many RNA primers since the lagging strand of DNA is essentially being replicated backwards. Segments of DNA, called Okazaki fragments, are added to the lagging strand once the primer is laid down in the 5′ to 3′ direction. Replication on the lagging strand is discontinuously happening and requires DNA ligase to seal all the segments together. The difference between the leading and lagging strand is that the lagging strand has Okazaki fragments and is replicated backwards so that it goes in the 5′ to 3′ direction.


4. Result of DNA Replication

After DNA replication is complete, there will be two DNA molecules that consist of one old chain of nucleotides and one new chain of nucleotides. Because of the old and new chain of nucleotides, many scientists commonly describe DNA replication as semi-conservative. After replication is complete, the DNA molecule winds into a double helix. Replication is necessary for living organisms to survive.


Biology 93 is typically offered year round, depending on what the biology department at UC Irvine feels is necessary. It is safe to say that it is always offered in the fall quarter and during summer school. The course code for this course always changes each quarter, so be sure that the title of the course is Bio 93. Biology is an interesting course that allows students to investigate life and living organisms. In fact, if you are ever confused about a DNA topic in class, you can always tell your teacher that you don’t under-strand and that you are lagging behind! Enjoy!


Ari Zaed

Related Articles

Final Exam
Study Guide

Get the best notes at

View All

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.