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6.2 Replication

5 min readdecember 19, 2022

Samantha Himegarner

Samantha Himegarner

Haseung Jun

Haseung Jun

Samantha Himegarner

Samantha Himegarner

Haseung Jun

Haseung Jun

Replication is the process in which genetic information is passed on to the next generation. In eukaryotes, this process takes place in the nucleus of the cell. Because prokaryotes do not have a nucleus, this process occurs in the cytoplasm. This is a multi-step process that employs the help of multiple enzymes.

DNA Replication

The DNA is twisted by nature, so the first step is to unwind and break the . A protein called unwinds the DNA strands and breaks the hydrogen bond between each of the bases. But you know how twisted things behave when they are untwisted. They tend to twist back right? So protein called and comes to the scene and relaxes the coil in front of the and prevents it from recoiling. Then comes the actual replicating part.

The DNA polymerase III has the main job of going through the and adding the corresponding . But here's the problem: the is a little timid, so it can't start anything on its own. This is when the comes into play. The is a protein and it adds something called a , which is a short strand of RNA . The only starts replication after the is added.

Once it's done adding the corresponding , the comes into play. Not only is the timid, it also makes a lot of mistakes. So it always needs a second pair of eyes to look over its work. The goes through the DNA replicated by and fixes any mistakes. It also goes through the and changes it out with appropriate DNA . Lastly, the comes over and glues the newly replicated segment that used to be the with the rest of the DNA strand. Here's a short list of what each protein does in an analogy.

Players of DNA replications:

  • - scissors

  • and single-strand binding protein - relaxers

  • - copier

  • - initiator (with )

  • - editor

  • - glue

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F512px-DNA_replication_en.png?alt=media&token=84c8dade-6736-4fbf-bd53-9d573dd2c0c3

Image courtesy of WikiMedia Commons.

The Leading and Lagging Strand

But then we're hit with a huge problem. Replication is a “semiconservative” process, meaning it conserves one strand of DNA, unchanged, to serve as a template to create another. The DNA is processed in the 5’ → 3’ direction, or what is called the . can only work in the . That's a problem because the other side of the DNA is in the , called the . This is a huge problem right? 😱

Well this problem is semi-solved. Instead of simply working in one direction, works in the from A to B, for example. Then, it moves to a new location, C, and works in the again up A, which is where it started last time. Then, the DNA is unwound more, and works on another segment. These small segments are called . Once these fragments are made, goes around and glues all the fragments together. Instead of a simple one-way replication, the is a little more complicated, but in the end, two copies of DNA are made!

Side Notes

Unfortunately, as much as we would love for our body to be perfect in replicating our DNA, it's not. There are a few bases that are not replicated because the needs space to bind to the (talk about inefficient proteins!). This means that every time our DNA is replicated, the chromosome loses a few base pairs. Our body tries to compensate for the loss by putting bits of unimportant DNA at the end, called . However, in the end, this doesn't really help, and our body ends up losing DNA. Unfortunately, when we lose all our DNA and end up only having , our body stop functioning 💀😭.

Conclusion

is done through essentially unwinding DNA and then using the existing strand as a template. The proteins involved do their part in replicating. The acts as "scissors" of the DNA and cuts the DNA by breaking between the . The and then keep the DNA from recoiling and messing things up. (highly inefficient, needs a lot of conditions satisfied before actually working) is the copier and adds the corresponding . But remember! It can't start without a , so the has to go and add a primer consisting of RNA . Then, can do its job. But since it makes a lot of mistakes, the goes back and edits any mistakes and replaces the with actual DNA . Lastly, the is the glue!

Also remember that the only in the , so the is replicated through a series of . The is simply just replicated without much difficulty!

Try to explain this to a friend or yourself; explaining concepts out loud always proves to be the best study tip when trying to understand complicated processes.

Key Terms to Review (19)

3'→5' Direction

: This refers to how template strands of DNA are read during replication or transcription. Enzymes read these strands in this direction but synthesize new strands in the opposite direction (5’→3’).

5' → 3' Direction

: This refers to the direction in which new nucleotides are added during DNA replication or transcription. The numbers 5' and 3' refer to the carbon atoms in a deoxyribose sugar molecule to which phosphate groups can attach, forming the backbone of the DNA strand.

DNA Polymerase I

: A type of enzyme called a polymerase that replaces RNA primers with DNA nucleotides during DNA replication.

DNA Polymerase III

: DNA Polymerase III is an enzyme that synthesizes new DNA strands by adding nucleotides to the 3' end of a pre-existing or newly synthesized DNA strand.

DNA Replication

: DNA replication is the process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules.

Helicase

: Helicase is an enzyme that unwinds the double helix of a DNA molecule, separating it into two single-stranded molecules during replication.

Hydrogen Bonds

: Hydrogen bonds are weak interactions between two molecules caused by electrostatic attraction between a proton in one molecule and an electronegative atom in another.

Lagging Strand

: The lagging strand is the other new DNA strand synthesized during replication. It's called 'lagging' because it is synthesized discontinuously, in fragments that are later joined together.

Leading Strand

: The leading strand is one of the two new strands of DNA that are synthesized during replication. It's called 'leading' because it is synthesized continuously in the direction towards the replication fork.

Ligase

: Ligase is an enzyme that facilitates the joining of DNA strands together by forming a bond between them. It plays a crucial role in DNA replication and repair.

Nucleotides

: Nucleotides are the basic building blocks of DNA and RNA. They consist of a sugar, a phosphate group, and a nitrogenous base.

Okazaki Fragments

: Short sequences of DNA nucleotides synthesized discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA replication.

Replication Fork

: The Replication Fork is a point in a DNA molecule where the two strands separate during replication, resembling a fork in the road.

RNA Primase

: RNA primase is an enzyme that creates a short RNA segment, known as a primer, which serves as a starting point for DNA synthesis.

RNA Primer

: The RNA primer is a short sequence of RNA nucleotides synthesized by RNA primase. It provides a 3' end onto which DNA polymerases can add nucleotides to synthesize a new strand of DNA.

Single-Strand Binding Proteins

: Single-strand binding proteins are proteins that bind to the single-stranded DNA during replication to prevent the separated strands from reannealing or being degraded.

Telomeres

: Telomeres are the protective caps at the ends of chromosomes that prevent them from deteriorating or fusing with neighboring chromosomes. They play a key role in cellular aging and cancer.

Template Strand

: The template strand is the DNA strand that serves as a guide for synthesizing an RNA molecule during transcription.

Topoisomerase

: Topoisomerase is an enzyme that alters the supercoiled form of a DNA molecule. It helps in unwinding the DNA helix by cutting one or both strands, allowing it to unwind and then resealing it.

6.2 Replication

5 min readdecember 19, 2022

Samantha Himegarner

Samantha Himegarner

Haseung Jun

Haseung Jun

Samantha Himegarner

Samantha Himegarner

Haseung Jun

Haseung Jun

Replication is the process in which genetic information is passed on to the next generation. In eukaryotes, this process takes place in the nucleus of the cell. Because prokaryotes do not have a nucleus, this process occurs in the cytoplasm. This is a multi-step process that employs the help of multiple enzymes.

DNA Replication

The DNA is twisted by nature, so the first step is to unwind and break the . A protein called unwinds the DNA strands and breaks the hydrogen bond between each of the bases. But you know how twisted things behave when they are untwisted. They tend to twist back right? So protein called and comes to the scene and relaxes the coil in front of the and prevents it from recoiling. Then comes the actual replicating part.

The DNA polymerase III has the main job of going through the and adding the corresponding . But here's the problem: the is a little timid, so it can't start anything on its own. This is when the comes into play. The is a protein and it adds something called a , which is a short strand of RNA . The only starts replication after the is added.

Once it's done adding the corresponding , the comes into play. Not only is the timid, it also makes a lot of mistakes. So it always needs a second pair of eyes to look over its work. The goes through the DNA replicated by and fixes any mistakes. It also goes through the and changes it out with appropriate DNA . Lastly, the comes over and glues the newly replicated segment that used to be the with the rest of the DNA strand. Here's a short list of what each protein does in an analogy.

Players of DNA replications:

  • - scissors

  • and single-strand binding protein - relaxers

  • - copier

  • - initiator (with )

  • - editor

  • - glue

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F512px-DNA_replication_en.png?alt=media&token=84c8dade-6736-4fbf-bd53-9d573dd2c0c3

Image courtesy of WikiMedia Commons.

The Leading and Lagging Strand

But then we're hit with a huge problem. Replication is a “semiconservative” process, meaning it conserves one strand of DNA, unchanged, to serve as a template to create another. The DNA is processed in the 5’ → 3’ direction, or what is called the . can only work in the . That's a problem because the other side of the DNA is in the , called the . This is a huge problem right? 😱

Well this problem is semi-solved. Instead of simply working in one direction, works in the from A to B, for example. Then, it moves to a new location, C, and works in the again up A, which is where it started last time. Then, the DNA is unwound more, and works on another segment. These small segments are called . Once these fragments are made, goes around and glues all the fragments together. Instead of a simple one-way replication, the is a little more complicated, but in the end, two copies of DNA are made!

Side Notes

Unfortunately, as much as we would love for our body to be perfect in replicating our DNA, it's not. There are a few bases that are not replicated because the needs space to bind to the (talk about inefficient proteins!). This means that every time our DNA is replicated, the chromosome loses a few base pairs. Our body tries to compensate for the loss by putting bits of unimportant DNA at the end, called . However, in the end, this doesn't really help, and our body ends up losing DNA. Unfortunately, when we lose all our DNA and end up only having , our body stop functioning 💀😭.

Conclusion

is done through essentially unwinding DNA and then using the existing strand as a template. The proteins involved do their part in replicating. The acts as "scissors" of the DNA and cuts the DNA by breaking between the . The and then keep the DNA from recoiling and messing things up. (highly inefficient, needs a lot of conditions satisfied before actually working) is the copier and adds the corresponding . But remember! It can't start without a , so the has to go and add a primer consisting of RNA . Then, can do its job. But since it makes a lot of mistakes, the goes back and edits any mistakes and replaces the with actual DNA . Lastly, the is the glue!

Also remember that the only in the , so the is replicated through a series of . The is simply just replicated without much difficulty!

Try to explain this to a friend or yourself; explaining concepts out loud always proves to be the best study tip when trying to understand complicated processes.

Key Terms to Review (19)

3'→5' Direction

: This refers to how template strands of DNA are read during replication or transcription. Enzymes read these strands in this direction but synthesize new strands in the opposite direction (5’→3’).

5' → 3' Direction

: This refers to the direction in which new nucleotides are added during DNA replication or transcription. The numbers 5' and 3' refer to the carbon atoms in a deoxyribose sugar molecule to which phosphate groups can attach, forming the backbone of the DNA strand.

DNA Polymerase I

: A type of enzyme called a polymerase that replaces RNA primers with DNA nucleotides during DNA replication.

DNA Polymerase III

: DNA Polymerase III is an enzyme that synthesizes new DNA strands by adding nucleotides to the 3' end of a pre-existing or newly synthesized DNA strand.

DNA Replication

: DNA replication is the process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules.

Helicase

: Helicase is an enzyme that unwinds the double helix of a DNA molecule, separating it into two single-stranded molecules during replication.

Hydrogen Bonds

: Hydrogen bonds are weak interactions between two molecules caused by electrostatic attraction between a proton in one molecule and an electronegative atom in another.

Lagging Strand

: The lagging strand is the other new DNA strand synthesized during replication. It's called 'lagging' because it is synthesized discontinuously, in fragments that are later joined together.

Leading Strand

: The leading strand is one of the two new strands of DNA that are synthesized during replication. It's called 'leading' because it is synthesized continuously in the direction towards the replication fork.

Ligase

: Ligase is an enzyme that facilitates the joining of DNA strands together by forming a bond between them. It plays a crucial role in DNA replication and repair.

Nucleotides

: Nucleotides are the basic building blocks of DNA and RNA. They consist of a sugar, a phosphate group, and a nitrogenous base.

Okazaki Fragments

: Short sequences of DNA nucleotides synthesized discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA replication.

Replication Fork

: The Replication Fork is a point in a DNA molecule where the two strands separate during replication, resembling a fork in the road.

RNA Primase

: RNA primase is an enzyme that creates a short RNA segment, known as a primer, which serves as a starting point for DNA synthesis.

RNA Primer

: The RNA primer is a short sequence of RNA nucleotides synthesized by RNA primase. It provides a 3' end onto which DNA polymerases can add nucleotides to synthesize a new strand of DNA.

Single-Strand Binding Proteins

: Single-strand binding proteins are proteins that bind to the single-stranded DNA during replication to prevent the separated strands from reannealing or being degraded.

Telomeres

: Telomeres are the protective caps at the ends of chromosomes that prevent them from deteriorating or fusing with neighboring chromosomes. They play a key role in cellular aging and cancer.

Template Strand

: The template strand is the DNA strand that serves as a guide for synthesizing an RNA molecule during transcription.

Topoisomerase

: Topoisomerase is an enzyme that alters the supercoiled form of a DNA molecule. It helps in unwinding the DNA helix by cutting one or both strands, allowing it to unwind and then resealing it.


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© 2024 Fiveable Inc. All rights reserved.

AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.