Helicase Function in DNA Replication

Yazan Hamzeh, April Koch
  • Author
    Yazan Hamzeh

    I am an inspiring budding scientist, who currently works at a fertility unit. I graduated with BSc (honors) in Genetic Engineering from Jordan University of Science and Technology, and then pursued an MSc in Clinical Embryology at the University of Oxford where I graduated with merit. During the course of academic endeavors, I found a passion in writing, whether it being scientific writing or blog writing. Therefore, I am so glad to be a part of Study.com! I am looking forward to hopefully inspire the many budding students out there.

  • Instructor
    April Koch

    April teaches high school science and holds a master's degree in education.

Learn about the function of helices in DNA replication. Know the DNA double helix definition. Discover DNA unwinding enzymes, with diagrams. Updated: 01/09/2022

What is DNA Replication?

During its lifetime, the cell undergoes several stages of molecular characteristics, referred to as the cell cycle. The cell cycle is composed of 4 main stages: G1, S, G2, and M. All stages that occur prior to the last stage, M, in which the cell divides, occur to ensure the cell divides properly. An important factor ensuring correct division is the transmittance of the same of amount of genetic material between the daughter cells. If genetic balance is disrupted, a myriad of abnormalities can occur, leading to cell death, or apoptosis. Therefore, the parent cell's genetic material is duplicated, in order to ensure the correct amount of genetic material is present between the daughter cells. This process is referred to as DNA replication. DNA replication occurs in the S phase of the cell cycle, and is controlled by many proteins called enzymes. Enzymes work together, each responsible for a certain step of DNA replication, in order to ensure its correct progression. DNA replication is vital for tissue growth and repair, as these two phenomena are built upon the process of cell division.


DNA Replication

DNA replication employs the use of many enzymes.


The Semi-Conservative Model

This model states that one parental strand of DNA is conserved in each new daughter molecule.
Semi-Conservative Model

The work of Meselson and Stahl in the 1950s helped us to understand that DNA replication occurs by a semi-conservative model, but it doesn't explain all of the intricate molecular movements that are necessary in order to achieve such a complicated feat. Remember that many scientists didn't agree with the semi-conservative model at first. In fact, they didn't agree with Watson and Crick's DNA model altogether because it was so elaborate. They argued that even if a molecule like this did exist in our bodies, there'd be no way for it to make copies of itself. Once they discovered the truth about the semi-conservative model, they had even more tough questions to answer. The biggest question they had was: how could a twisted, convoluted molecule like DNA open itself up for semi-conservative replication?

Remember that the semi-conservative model states that one parental strand of DNA is conserved in each of the new daughter DNA molecules. The parental strand, which is the original DNA strand, acts as a template for the daughter strand, or a strand of newly synthesized nucleotides. In order for that to happen, DNA must actually split down the middle so that all of the nitrogenous bases are exposed. Once the bases are left out in the open, then new nucleotides can be added on. Remember that there is a rule about which nucleotides pair with which; we call it the rule of complementary base pairing. So the bases adenine and thymine will always pair together, and cytosine and guanine will always pair together. That means that as the new nucleotides are being added on to form the daughter strand, they can only add on at the places where they match a complementary base. So still the question remains: how do we actually get in there to the center of the DNA double helix, unwind all the twisted strands and expose those nucleotides in the first place?

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: How DNA Polymerase and RNA Primase Initiate DNA Replication

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
 Replay
Your next lesson will play in 10 seconds
  • 0:05 The Semi-Conservative Model
  • 1:56 How to Unwind the DNA…
  • 2:30 DNA Helicase
  • 3:30 Replication Bubbles
  • 4:30 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Timeline
Autoplay
Autoplay
Speed Speed

Molecular Mechanism of DNA Replication

DNA replication is dependent on many enzymes, in order to be carried out efficiently. DNA is double stranded in nature, and in order to be replicated, this structure has to be unzipped. The site of initial unwinding is referred to as the origin of replication. After that, other enzymes add new pieces of DNA to the unzipped strands in order to synthesize two new DNA molecules. This is referred to as semi-conservative replication, and is the most accepted way of DNA replication. Other proposed mechanisms of DNA replication include conservative DNA replication and dispersive DNA replication, but these have been disproven. The Y-shaped structure that is brought about by DNA unwinding and replication is known as the replication fork.

Semi-conservative replication

This mode of replication involves the parental strands separating, meaning that the two daughter molecules would each have a strand from the parent DNA molecule. This mode of replication was proven to be the correct one by studies involving centrifugation and fluorescent DNA.


Semi-conservative Replication

This mode of replication preserves one old strand into the daughter molecules.


Conservative replication

This mode of replication involves the lack of any of the old DNA in the daughter DNA molecule. The newly synthesized DNA strand is made of entirely new DNA.


Conservative Replication

This mode of replication births a completely new DNA molecule


Dispersive replication

This mode of replication involves the distribution of the parental DNA into the newly synthesized DNA. The daughter DNA molecules would have a mosaic of new DNA and parental DNA.


Dispersive Replication

New DNA molecules contain a mix of new and old pieces of DNA.


Helicases in DNA Replication

The first step of DNA replication is to unwind the double stranded structure, in order to promote semi-conservative replication. This process is mediated by an enzyme, referred to as the helicase enzyme. Helicase, in DNA replication, breaks the hydrogen bonds that hold the double strand together to expose the single strands, in order to kickstart replication. Helicases form a class of enzymes that differ between species; however, the function remains the same. They were first discovered in 1976 in bacteria called E.coli.


DNA Replication

DNA replication employs various enzymes.


What is DNA Double Helix?

DNA is a double stranded molecule, where the shape of it, is sometimes referred to as the double helix. DNA is composed of monomers, referred to as nucleotides. Nucleotides are further composed of a sugar, phosphate group, and a nitrogen containing base. The sequence of nitrogen containing bases in DNA is what is known as the genetic code, and is vital for DNA function in directing protein synthesis. The double helix is formed as a result of hydrogen bonds between opposite strands of DNA, thus generating the distinct DNA structure.

DNA helicase unwinds the DNA double helix.
DNA Helicase

How to Unwind the DNA Double Helix

Well, it looks like we've got some bond-breaking to do. Remember that the nitrogenous bases in DNA are linked in the center by hydrogen bonds. Hydrogen bonds are generally weaker than all the other bonds in the molecule, so this is a perfect spot to start separating the nucleic acid strands. But keep in mind that DNA is a very important molecule; it holds all of our genetic information, and it can't just split open at the drop of a hat. It needs a specialized helper to assist in orchestrating that movement. That helper is an enzyme that we call DNA helicase.

DNA Helicase and Its Function in Replication

DNA helicase is an enzyme that unwinds the DNA double helix by breaking the hydrogen bonds between the complementary bases. It's easy to remember the name because it has part of the word helix in it. You can imagine it sort of as a wedge that forces apart the two strands, just like the slider on a zipper wedges apart the two long rows of teeth. DNA helicase is responsible for taking apart our DNA double helix.

To unlock this lesson you must be a Study.com Member.
Create your account

Video Transcript

The Semi-Conservative Model

This model states that one parental strand of DNA is conserved in each new daughter molecule.
Semi-Conservative Model

The work of Meselson and Stahl in the 1950s helped us to understand that DNA replication occurs by a semi-conservative model, but it doesn't explain all of the intricate molecular movements that are necessary in order to achieve such a complicated feat. Remember that many scientists didn't agree with the semi-conservative model at first. In fact, they didn't agree with Watson and Crick's DNA model altogether because it was so elaborate. They argued that even if a molecule like this did exist in our bodies, there'd be no way for it to make copies of itself. Once they discovered the truth about the semi-conservative model, they had even more tough questions to answer. The biggest question they had was: how could a twisted, convoluted molecule like DNA open itself up for semi-conservative replication?

Remember that the semi-conservative model states that one parental strand of DNA is conserved in each of the new daughter DNA molecules. The parental strand, which is the original DNA strand, acts as a template for the daughter strand, or a strand of newly synthesized nucleotides. In order for that to happen, DNA must actually split down the middle so that all of the nitrogenous bases are exposed. Once the bases are left out in the open, then new nucleotides can be added on. Remember that there is a rule about which nucleotides pair with which; we call it the rule of complementary base pairing. So the bases adenine and thymine will always pair together, and cytosine and guanine will always pair together. That means that as the new nucleotides are being added on to form the daughter strand, they can only add on at the places where they match a complementary base. So still the question remains: how do we actually get in there to the center of the DNA double helix, unwind all the twisted strands and expose those nucleotides in the first place?

DNA helicase unwinds the DNA double helix.
DNA Helicase

How to Unwind the DNA Double Helix

Well, it looks like we've got some bond-breaking to do. Remember that the nitrogenous bases in DNA are linked in the center by hydrogen bonds. Hydrogen bonds are generally weaker than all the other bonds in the molecule, so this is a perfect spot to start separating the nucleic acid strands. But keep in mind that DNA is a very important molecule; it holds all of our genetic information, and it can't just split open at the drop of a hat. It needs a specialized helper to assist in orchestrating that movement. That helper is an enzyme that we call DNA helicase.

DNA Helicase and Its Function in Replication

DNA helicase is an enzyme that unwinds the DNA double helix by breaking the hydrogen bonds between the complementary bases. It's easy to remember the name because it has part of the word helix in it. You can imagine it sort of as a wedge that forces apart the two strands, just like the slider on a zipper wedges apart the two long rows of teeth. DNA helicase is responsible for taking apart our DNA double helix.

To unlock this lesson you must be a Study.com Member.
Create your account

Frequently Asked Questions

What is the function of helicase in DNA replication?

Helicase is an enzyme vital for the initiation of DNA replication. Helicase breaks the hydrogen bonds forming the double helix structure of DNA.

Is DNA a double helix?

DNA is composed of two strands that coil around each other to form a double helix. This occurs as a result of hydrogen bonding between nucleotides.

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back

Resources created by teachers for teachers

Over 30,000 video lessons & teaching resources‐all in one place.
Video lessons
Quizzes & Worksheets
Classroom Integration
Lesson Plans

I would definitely recommend Study.com to my colleagues. It’s like a teacher waved a magic wand and did the work for me. I feel like it’s a lifeline.

Jennifer B.
Teacher
Jennifer B.
Create an account to start this course today
Used by over 30 million students worldwide
Create an account