Lecture Notes on Chapter 12: The Cell Cycle

Introduction

• Speaker: Dr. D
• Textbook: Biology 12th Edition Campbell
• Chapter Focus: The Cell Cycle
• Topics: Cell division, DNA, chromosomes, the genome, mitosis, cytokinesis, cell cycle control

The Cell Cycle Overview

• Definition: Process of cell division where one cell divides into two.
• Reasons for Cell Division:
  • Asexual reproduction
  • Growth and development
  • Tissue renewal and healing

Understanding DNA and Chromosomes

• Genome: All DNA in a cell.
  • Prokaryotic cells: Single DNA molecule or chromosome
  • Eukaryotic cells: Multiple DNA molecules or chromosomes
• Chromosomes: DNA is packaged into chromosomes.
  • DNA wraps around histone proteins to form chromatin.
• Human Chromosomes:
  • Humans have 46 chromosomes (2 sets of 23)
  • Genes: Segments on chromosomes that code for proteins
  • Homologous chromosomes: Contain same types of genes but not identical

DNA Replication Before Cell Division

• Cells must replicate DNA before dividing to ensure each cell has full set of chromosomes.
• Sister Chromatids: Identical copies of a chromosome, formed during DNA replication

Phases of the Cell Cycle

• Interphase (90% of cell cycle):
  • G1 phase: Cell growth
  • S phase: DNA synthesis (replication)
  • G2 phase: Preparation for cell division, replication of centrosomes
• Mitotic (M) phase (10% of cell cycle):
  • Mitosis: Separation of chromosomes
  • Cytokinesis: Division of the cell

Stages of Mitosis

• Prophase: Chromatin condenses into chromosomes, centrosomes move apart
• Prometaphase: Nuclear envelope breaks, microtubules attach to kinetochores
• Metaphase: Chromosomes align at metaphase plate
• Anaphase: Sister chromatids separate and move to opposite poles
• Telophase: Nuclear envelopes reform, chromosomes decondense

Cytokinesis

• Animal Cells: Forms cleavage furrow via microfilaments
• Plant Cells: Vesicles form cell plate, developing into a cell wall

Cell Cycle Control System

• Checkpoints: Points where the cell cycle stops until go-ahead signals are received
  • G1 checkpoint: Decides whether the cell will divide
  • G2 checkpoint: Ensures DNA was copied correctly
  • M checkpoint: Ensures all chromosomes are properly attached to spindle
• Cancer: Caused by failure in cell cycle control, often due to mutations in checkpoint genes

Key Terms

• Homologous Chromosomes: Non-identical chromosomes with same types of genes
• Sister Chromatids: Identical copies of a chromosome
• Centromere: Region where sister chromatids are joined
• Kinetochore: Protein structure on chromatids where microtubules attach
• Mitotic Spindle: Structure involved in chromosome movement

Conclusion

• Understanding of cell cycle is crucial for grasping cell division, growth, and the development of conditions like cancer.
• For further clarification, questions can be left for discussion.