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DNA Structure and Replication Study Guide

DNA replication is also known as semi-conservative replication and is the process in which the DNA doubles. This is an important process that takes place in the living cells. Let us understand the DNA structure and how the replication steps take place.

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Introduction:

Every cell in our body contains DNA or deoxyribonucleic acid. It is the carrier of genetic instructions that makes every species unique and drives the development and functioning of an organism.

DNA Structure

  • The structure of DNA is a double helix, and it looks like a twisted ladder.

  • A pair of nitrogenous bases make up the steps of the DNA ladder, while the sides of the ladder are made of deoxyribose and phosphate molecules.

  • Each strand of DNA is referred to as a polynucleotide chain.

  • Four different types of nitrogenous bases adenine (A), thymine (T), cytosine (C), and guanine (G) are found in DNA, and these have a specific pairing pattern.

  • In DNA base pairing, adenine will always pair with thymine with a double bond and guanine will always pair up with cytosine with a triple bond.

  • Hydrogen bonds and the stacking of the base pairs stabilize the helical structure.

Chargaff's Rules

The base pairing was based on the observation of Erwin Chargaff:

  1. In any double-stranded DNA, the purine and pyrimidine base pairs are in equal amounts. A + G = T + C

  2. The proportion of A is equal to T, and the proportion of G is equal to C, but the amount of A + T is not necessarily equal to G + C.

DNA Replication

During the S phase of the eukaryotic cell cycle, DNA undergoes a step wherein it makes a copy of the cell's entire DNA. This copying is also called replication.

The replication of DNA takes place in three stages: Initiation, elongation, and termination.

1. Initiation

  • DNA replication starts with unwinding the DNA double helix into two single-stranded DNA molecules.
  • An important enzyme called DNA helicase breaks the hydrogen bonds that join the complementary nucleotide bases to each other.
  • This exposes the strands so that these are used as a template to help in replication.

2. Elongation

  • In this step, nucleotides are added to the new DNA strand. This is carried out by an enzyme called DNA polymerase.
  • This enzyme will addd nucleotides one by one, in the exact order set down by the template strand.

3. Termination

  • After the new DNA strands have been synthesized, the process of replication is terminated.
  • DNA replication is semi-conservative as the outcome of replication, is a double helix composed of both an old strand (half of the parent DNA molecule) and a new strand (synthesized during replication).

Conclusion:

  • DNA is a nucleic acid that contains the genetic instructions or the hereditary materials from the parent.
  • Chargaff's rules state that the amount of A is similar to the amount of T, and the amount of G is similar to the amount of C
  • DNA replication is the process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules.

FAQs:

1. How does the structure of DNA relate to DNA replication?

The double helix structure of the DNA opens when the hydrogen bonds break, and every DNA strand acts as a template in the synthesis of a new and complementary strand.

2. What are DNA structure and replication purposes?

DNA is a nucleic acid that contains the cells genetic instructions and replication produces two double helical DNA copies.

3. What are the 4 steps of DNA replication?

  1. Initiation
  2. Primer binding
  3. Elongation
  4. Termination

4. What DNA structure regulates replication?

The replisome is recruited to regulate DNA replication.

5. What is DNA replication called?

It is called a semi-conservative process.

6. What is the main goal of DNA replication?

The main goal of DNA replication is to produce a second and identical DNA double strand.

7. When and Where does DNA replication take place?

DNA replication occurs in the nucleus of eukaryotes and the cytoplasm of prokaryotes. It occurs in the synthesis phase.

8. What are the 7 steps of DNA replication?

  • Initiation
  • Primer Synthesis
  • Leading strand synthesis
  • Lagging strand synthesis
  • Primer removal
  • Ligation
  • Termination

We hope you enjoyed studying this lesson and learned something cool about DNA Structure and Replication! Join our Discord community to get any questions you may have answered and to engage with other students just like you! Don't forget to download our App and check out our fun VR classrooms - we promise it makes studying much more fun!😎

Sources:

  1. DNA Structure and Replication.https://flexbooks.ck12.org/cbook/ck-12-biology-flexbook-2.0/section/4.3/primary/lesson/dna-structure-and-replication-bio/ Accessed on 2 Dec 2021.
  2. DNA Replication https://teachmephysiology.com/biochemistry/cell-growth-death/dna-replication/ Accessed on 2 Dec 2021.
  3. DNA Structure and Replication https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_Introductory_Biology_(CK-12)/04%3A_Molecular_Biology/4.03%3A_DNA_Structure_and_Replication Accessed on 2 Dec 2021.