DNA Replication Lecture Notes

Overview

• Focus: DNA Replication
  • Why DNA replication is necessary
  • Phases and steps involved

Importance of DNA Replication

• Purpose:
  • To make new DNA for cell creation
  • Replacement or repair of cells ensures identical DNA across cells
  • Avoid mutations which can be harmful
  • Pass on genetic code to offspring ensuring species survival
  • Essential for cellular replication to repair/replace damaged cells

Interphase and DNA Replication

• Interphase:

  • Cell spends majority of its time here
  • Features: Intact nucleus, DNA in chromatin network (thread-like structure), centrioles without spindle fibers
  • DNA replication occurs in the S phase (DNA synthesis phase) of interphase

• Stages of Mitosis:

  • Interphase → Prophase → Metaphase → Anaphase → Telophase
  • Goal: Ensure identical DNA in daughter cells by making a full copy of chromosomes

DNA Replication Process

1. Unwinding the DNA

   • DNA is a double helix (two wound strands)
   • To replicate, it must be unwound into a ladder-like structure
   • Nucleotides (A, T, G, C) hold genetic code

2. Strand Separation

   • Strands separate by breaking hydrogen bonds between nitrogenous bases
   • Enzyme (unnamed) catalyzes this separation
   • Each strand serves as a template for a new complementary strand

3. Base Pairing

   • Complementary nucleotides pair with exposed bases:
     • Adenine (A) pairs with Thymine (T)
     • Guanine (G) pairs with Cytosine (C)
   • Floating nucleotides in the nucleus attach to their complements with sugar-phosphate backbones

4. Strand Formation

   • Enzyme (DNA polymerase) ensures correct nucleotide attachment and sequence
   • Two identical strands result, each with an original and a new strand
   • Hydrogen bonds reform between base pairs

5. Rewinding into Double Helix

   • Enzyme rewinds strands into double helix structure

Outcomes of DNA Replication

• Result:
  • Two identical DNA strands
  • Each strand consists of one original and one new strand
  • Necessary for cell division into two identical sister cells

Common Confusions

• Protein Synthesis vs. DNA Replication:
  • Often confused due to similar components
  • Important to distinguish between their processes and products
  • Utilize exam guidelines to clarify differences

Conclusion

• DNA replication is critical for genetic consistency and cellular functions
• Ensures the production of identical cells for growth, repair, and inheritance

Note:

• Refer to exam guidelines for detailed differences between DNA replication and protein synthesis.
• Understanding the steps and phases is crucial for exams.