Overview
This lecture gives a concise overview of DNA replication, focusing on the structure of DNA, the importance of replication, key enzymes involved, and the differences in strand synthesis.
Importance and Function of DNA Replication
- DNA replication is essential for cell division so each new cell receives a complete copy of genetic material.
- DNA encodes proteins necessary for various bodily functions.
- Proofreading during replication helps prevent mutations.
Structure of DNA
- DNA is made of nucleotide monomers linked into two strands forming a double helix.
- The two DNA strands are held together by hydrogen bonds between specific base pairs: adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G).
Steps and Enzymes in DNA Replication
- DNA strands must be separated before replication; hydrogen bonds are broken to "unzip" the DNA.
- Helicase unwinds and separates double-stranded DNA by breaking hydrogen bonds.
- Primase signals where DNA polymerase should begin replication.
- DNA polymerase synthesizes new DNA strands by adding complementary nucleotides based on the template strand.
- The leading strand is synthesized continuously, while the lagging strand is synthesized in fragments (discontinuously).
- Ligase connects DNA fragments on the lagging strand to create a continuous strand.
- DNA polymerase also proofreads new DNA for accuracy.
Key Terms & Definitions
- DNA replication — the process of copying DNA before cell division.
- Nucleotide — the building block of DNA, consisting of a sugar, phosphate, and base.
- Helicase — enzyme that unwinds and separates DNA strands.
- Primase — enzyme that provides a starting point for DNA polymerase.
- DNA polymerase — enzyme that synthesizes new DNA strands and proofreads them.
- Ligase — enzyme that joins discontinuous DNA fragments.
- Leading Strand — DNA strand synthesized continuously.
- Lagging Strand — DNA strand synthesized in fragments.
- Hydrogen bond — weak bond connecting complementary DNA bases.
Action Items / Next Steps
- Watch the follow-up video to visualize the process of leading and lagging strand synthesis.
- Answer the practice question regarding the type of bond broken during DNA strand separation (answer: hydrogen bond).