Recording-2025-03-21T16_34_58.629Z

Cell Growth in Culture:

• Cells in culture require specific growth conditions dependent on their origin.

• Growth medium must be optimal in terms of pH and nutrients to facilitate normal growth.

• Growth factors may be added to simulate conditions within a body.

Learning Objectives:

• Understand the significance of DNA replication.

• Know what happens to each copy post-replication.

Cell Cycle Overview:

• Phases of Cell Cycle:

  • Interphase (includes G1, S, G2 phases).

  • Mitosis (cell division).

• S Phase:

  • Critical for DNA replication where one DNA strand becomes two.

• Importance of DNA Replication:

  • Ensures each daughter cell receives a complete set of DNA during cell division.

Major Enzymes in DNA Replication:

• Helicase:

  • Unwinds and separates the DNA strands at the replication fork.

• DNA Polymerase:

  • Synthesizes new DNA strands by adding nucleotides in a 5’ to 3’ direction.

• DNA Ligase:

  • Joins Okazaki fragments on the lagging strand, ensuring a continuous DNA strand.

Leading vs. Lagging Strand:

• Leading Strand:

  • Synthesized continuously in the same direction as the replication fork opens.

• Lagging Strand:

  • Synthesized in fragments (Okazaki fragments) in the opposite direction to the replication fork.

Semi-Conservative Replication:

• Each new DNA molecule consists of one original (parent) strand and one new strand, reflecting the concept of semiconservativeness.

Automated Relative Directions in DNA:

• DNA strands are anti-parallel (one runs 5' to 3' while the complementary strand runs 3' to 5').

• This orientation affects how strands are replicated.

Review of Key Terms:

• Anabolic vs. Catabolic Reaction:

  • DNA replication is anabolic as it requires energy to synthesize new DNA.

• Okazaki Fragments:

  • Segments of DNA on the lagging strand that need to be joined.

• Replication Fork:

  • Site of DNA replication initiation, forming a bubble as strands unwind.

Equilibrium and Water Movement in Cells:

• Hypertonic:

  • Solution has a higher concentration of solutes than the cell, resulting in water moving out and cell shrinking.

• Hypotonic:

  • Solution has a lower concentration of solutes compared to the cell, allowing water to enter the cell, leading to swelling or bursting.

• Isotonic:

  • Equal concentration of solutes in and outside the cell; no net water movement, maintaining cell shape.

Importance of Accurate DNA Replication:

• Essential for consistent and correct transmission of genetic information during cell division.

• Any mutation during this process can have potentially harmful effects on cellular function.