Episode 1: DNA and DNA Replication (Synthesis)

By: Shivani Kanjerla

Hello and welcome to the first official episode of The Secrets of Science! This is part of an ongoing series which covers a multitude of information from the basics of biology all the way to gene editing technologies such as CRISPR-Cas 9. Within today's episode, I will be covering DNA and the process of DNA replication in full detail. This will lead into the next episode in which I will discuss RNA and Protein synthesis. To access the transcript version along with images, make sure to check out my recent blog post on my website. Within the blog post, there will be links to videos, textbook information, and other resources for aiding guided learning. Although national DNA day was on April 25th, it is still important to learn about the importance of DNA and genetics and the role it plays in our everyday lives. Before diving into the deep end of biotechnology, it is essential to start off with a basic stand point of heredity. This begins with information such as DNA, RNA, and genetic mutations among others.

DNA: Stands for Deoxyribose Nucleic Acid

• It is made of two strands of nucleotides which are twisted into a double helix structure

  • The nucleotides have 3 parts (phosphate group, deoxyribose sugar, and nitrogen base).

    • Sugar and phosphate groups are responsible for the “backbones” and structure of the DNA molecule.

• DNA is represented as the “hereditary material” which is passed down from generation to generation through different forms of reproduction such as asexual (binary fission) and sexual (such as performed by mammals).

• There are 4 nitrogen bases that are included, each in a nucleotide that are paired together.

  • The 4 bases are adenine, guanine, cytosine, and thymine

    • Cytosine and thymine are known as pyrimidines. They have one ring of carbon atoms along with nitrogen and oxygen atoms.

    • Guanine and adenine are known as purines. They have two rings of carbon atoms as opposed to one and also have the nitrogen and oxygen atoms like cytosine and thymine.

    • The pairs are Adenine-Thymine and Cytosine-Guanine, each pair has one purine and one pyrimidine.

Image credit: https://www.diffen.com/difference/Nucleoside_vs_Nucleotide

• In order to form the double helix structure, the nitrogen bases are paired with hydrogen bonds. The adenine and thymine pairs use 2 hydrogen bonds and the cytosine and guanine pairs use 3 hydrogen bonds. This should not be confused with the covalent bonds that hold the nucleotides together.

• The nitrogen bases are bonded to the number 1 carbon which is located on the right hand side and the phosphate groups bond to the number 5 carbon located on the left hand side.

• The right hand side runs 3 prime to 5 prime and the left hand side runs 5 prime to 3 prime (the numbers 5 prime and 3 prime are rendered to the carbon numbers on the sugar phosphate backbone).

Image credit: https://commons.wikimedia.org/wiki/File:DNA_Nucleotides.jpg

DNA replication: AKA DNA synthesis

• Occurs during cell division when cells duplicate their DNA during the S-phase of the cell cycle (mitosis and meiosis, before interphase) so their future daughter cells will have a complete set of chromosomes.

  • Chromosomes are located in the nucleus of cells and are made of DNA double helices along with proteins.

Image credit: "The cell cycle: Figure 1" by OpenStax College, Biology (CC BY 3.0).

• The new DNA will be exactly identical to the original DNA molecule.

1. To begin the process, there is an enzyme known as DNA helicase which unzips the two strands of DNA (unwinds the double helix). The location the DNA helicase attaches to is referred to as the “origin of replication.” Additionally, this area is located within the parts of the DNA strands which are primarily composed of adenine, thymine pairs because as mentioned previously, these pairs are held together with 2 hydrogen bonds as opposed to the cytosine guanine pairs which are held together by 3 hydrogen bonds. As the helicase begins to unwind the helix by breaking the hydrogen bonds, a “replication fork” is formed. Furthermore, an area of “bubble of replication” is also created which is where the dna replication is currently taking place. There are multiple “bubbles” which all will eventually enlarge in both directions later joining to form a set of duplicate DNA strands.

2. In order to perform the process of “copying the DNA,” the enzyme DNA polymerase is used. This enzyme has the responsibility of replicating DNA molecules in order to build a new strand. It does this by adding on new nucleotides to the strand left exposed by the helicase enzyme. When the DNA strands are single and being added on to, they are to be referred to as “template strands.” New complementary base pairs and a new sugar phosphate backbone are developed. It is essential to remember that DNA polymerase only builds the DNA in a 5 prime to 3 prime direction. The 5 prime to 3 prime direction strand is referred to the leading strand. As a result, there will be a lagging strand in which okazaki fragments (short sections) are formed.

3. This process continues until the whole DNA molecule is copied. When complete, the molecule is referred to as semi conservative because the replication process is semi conservative. This refers to the idea that one side is from the previous strand and the other is newly added.

4. DNA polymerase can attach nucleotides at the speed of 50 nucleotides per second but in bacteria this can increase to 1000 nucleotides per second. Over 3.4 billion base pairs have the ability to be copied within an hour but the enzyme DNA polymerase makes a mistake in this process every billion nucleotides.

   1. The polymerase will re-check DNA through a proofreading process and if any errors are detected, they can be altered through a “mismatch repair.”

Image credit: https://study.com/academy/lesson/dna-replication-fork-definition-lesson-quiz.html

Thank you for joining me in this episode of the Secrets of Science where we discussed DNA and DNA replication. During the next episode, we will be discussing RNA, the three main types of RNA, and the process of translation (protein synthesis). In order to access the transcribed version of this podcast as well as additional resources, make sure to check out my blog post (link in the description).

To access the podcast on multiple platforms you can visit: https://anchor.fm/shivani-kanjerla1

Thank you for your time,

Shivani Kanjerla

Works cited +More resources:

Amoeba sisters:

• (OLD VIDEO) DNA Structure and Function

• DNA, Chromosomes, Genes, and Traits: An Intro to Heredity

• DNA Replication (Updated)

• DNA Replication Fork: Definition & Overview - Video & Lesson Transcript

• Designer Genes - Wiki (Scioly)

• Heredity - Wiki (Scioly)

• Textbook:

  • AP Edition Biology Seventh Edition by: Campbell Reece