Cell Cycle Overview

Overview

This lecture introduces the basics of the cell cycle, focusing on the phases cells go through during growth and division, and highlights exceptions like cancer cells and non-dividing cells.

Cell Size Perspective

• Average humans are about two meters tall, while cells are about 100 micrometers in diameter.
• A cell is roughly one one-millionth the size of a human.

Cell Growth and Division

• The cell cycle describes the lifespan and division process of a cell.
• Cells grow and divide, similar to how humans reproduce.

Phases of the Cell Cycle

• The cycle has two main phases: interphase (growth) and mitosis (division).
• Interphase is where most cell growth occurs, and most cells spend their time here.
• Interphase is split into three parts: G1, S, and G2 phases.

Interphase Details

• G1 phase: Longest phase, cell grows and produces extra organelles and proteins.
• S phase: DNA synthesis (replication) occurs, doubling the sets of chromosomes.
• G2 phase: Prepares for mitosis by producing structures like microtubules.

Alternatives to Division

• Some cells leave the cycle after G1 to enter G0 phase, where they no longer divide (e.g., neurons).
• Cells in G0 generally do not re-enter the cycle.

Mitosis and Cycle Continuity

• Mitosis (M phase): Active cell division creates two new cells.
• After division, new cells re-enter G1 to begin the cycle again.

Cancer Cells Exception

• Cancer cells divide more frequently due to defects in regulation, unlike normal cells that spend most time in interphase.

Key Terms & Definitions

• Cell Cycle — The repeating sequence of growth and division in a cell’s life.
• Interphase — The period of cell growth and DNA replication; includes G1, S, and G2 phases.
• G1 Phase — First growth phase where the cell increases in size and makes organelles and proteins.
• S Phase — DNA synthesis phase where chromosomes are duplicated.
• G2 Phase — Second growth phase preparing the cell for mitosis.
• Mitosis (M Phase) — The phase of active cell division.
• G0 Phase — A resting phase where cells do not divide.
• Microtubules — Structures produced in G2 to help separate chromosomes during cell division.

Action Items / Next Steps

• Review the phases of the cell cycle and their functions.
• Prepare for the next lecture on details of mitosis and chromosome separation.