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Lesson Overview

• Lesson Title: Cell Cycle

• Key Focus: Understanding the steps and phases of the cell cycle, particularly mitosis.

The Cell Cycle

Learning Objectives

• IST-1.B: Describe the events that occur in the cell cycle.

• IST-1.C: Explain how mitosis results in the transmission of chromosomes from one generation to the next.

• Importance of distinguishing between describing (noting characteristics) and explaining (stating why/how).

Phases of the Cell Cycle

General Phases

• G1 Phase: Cell growth, normal function.

• S Phase: Synthesis phase where DNA is replicated.

• G2 Phase: Final preparations for mitosis.

• M Phase: Mitosis and cytokinesis, where cell division occurs.

Steps of Mitosis

• Prophase: Chromosomes condense.

• Metaphase: Chromosomes align at the cell's equator.

• Anaphase: Sister chromatids are pulled apart.

• Telophase: Nuclear membranes re-form around each set of separated chromosomes.

Importance of Cell Division

• Essential for organisms to grow, replace damaged cells, and reproduce asexually.

• G0 Phase: A quiescent state where most cells reside when they are not actively dividing.

DNA Organization Before Division

Key Processes

• DNA Packaging: Cells organize DNA by wrapping it around histones to form nucleosomes, creating chromatin.

• Chromosome Formation: DNA condenses into chromosomes after replication.

• Sister Chromatids: Result from DNA replication; held together at the centromere and linked to the mitotic spindle by kinetochores.

Structure Overview

• Nucleus: Where chromosomes and chromatids are located.

• Chromatin: The less packed form of DNA when the cell is not dividing.

Genome Structure

• Definition: All the genetic information of a cell.

• Types:

  • Prokaryotes: Singular, circular DNA.

  • Eukaryotes: Multiple linear chromosomes, each species has a specific chromosome number.

  • Example Counts: Humans (46), Chimps (48), Elephants (56).

Types of Cells

Somatic Cells

• Characteristics: Body cells, diploid (2n), divide by mitosis.

• Example: Humans have 2n = 46 chromosomes (23 from each parent).

Gametes

• Characteristics: Reproductive cells, haploid (n), divide by meiosis.

• Example: Humans have n = 23 chromosomes in gametes.

Overview of Cell Cycle

Core Components

• Interphase: Longest stage (90% of the cell cycle).

  • G1 Phase: Initial growth and function.

  • S Phase: DNA replication.

  • G2 Phase: Preparation for mitosis.

• M Phase: Actual division of the cell into two identical daughter cells.

Timing of the Cell Cycle

• Overall Duration: Approximately 24 hours.

• Interphase: Takes 23 hours; Mitosis takes about 1 hour.

• Cells may enter a resting state (G0 phase) depending on conditions and needs.

Reasons for Cell Division

• Development: New cells needed for growth.

• Repair: Replacing damaged somatic cells and for tissue repair.

• Reproduction: Asexual organisms use cell division to propagate their DNA.

Interphase and Chromosomes

• Recognizes the significance of interphase and how DNA is configured before undergoing mitosis.

Practice Questions

• Understanding parts of the cell life cycle: Identify which part is not interphase.

• Recognizing phases where cells spend most of their time, particularly in non-dividing cells.