Cell Cycle & Mitosis Overview

Cell Cycle & Mitosis

• Cell Cycle Phases:
  • G₁ (Gap 1): Cell growth, normal functions, DNA replication preparation.
  • S (Synthesis): DNA replication, chromosome duplication.
  • G₂ (Gap 2): Cell growth, resource production for mitosis.
  • M (Mitosis): Nucleus division.
  • Cytokinesis: Cytoplasm division, two daughter cells.
  • Longest Phase: G₁
• DNA Structure & Replication:
  • Base Pairing: A-T, C-G
  • Backbone: Phosphate and sugar molecules.
  • Ends: 5' and 3' indicate DNA strand direction.
  • Bonds: Phosphodiester (sugar-phosphate), hydrogen (base pairs).
• Cell Cycle Checkpoints:
  • Cyclins and checkpoint proteins regulate cell progression.
  • DNA damage and cell readiness are checked.
  • Checkpoint failure leads to uncontrolled cell division (cancer).
• Cancer and Genetic Mutations:
  • Proto-oncogenes: Mutated to oncogenes, promote uncontrolled division.
  • Tumor Suppressor Genes: Prevent uncontrolled growth; mutations disable them.

Cancer Risk Factors

• General Risks:
  • Genetic predisposition (family history).
  • Environmental factors (radiation, smoking, toxins).

DNA Damage & Consequences

• G₁ Phase Damage: Unfixed damage leads to accumulated mutations, potentially causing cancer.

Stem Cells

• Stem Cell Types: Pluripotent stem cells (differentiate into any cell type).
• Location: Embryonic stem cells in blastocysts.

Villi in the Small Intestine

• Function: Increase surface area for nutrient absorption.
• Structure: Contain microvilli for further nutrient uptake.

Surface Area & Cell Exchange

• Optimal Shape: Small, cube-shaped cells have a larger surface area-to-volume ratio for efficient exchange.

Mitosis Stages

• Prophase: Chromosomes condense, spindle fibers form, nuclear membrane breaks down.
• Metaphase: Chromosomes align at the cell center.
• Anaphase: Sister chromatids separate to opposite poles.
• Telophase: Nuclear membranes reform around chromosomes.
• Cytokinesis: Cytoplasm divides into two daughter cells
  • Chromosome Count: Without DNA replication, daughter cells have half the normal number of chromosomes.

Chromosome Structures

• Unreplicated Chromosomes: Single-stranded DNA.
• Chromatin: Loose, uncoiled DNA during interphase.
• Replicated Chromosomes: Two sister chromatids connected at a centromere.

DNA Replication

• Leading Strand: Continuous synthesis.
• Lagging Strand: Synthesis in short fragments (Okazaki).
• Key Enzymes:
  • Helicase: Unwinds DNA.
  • DNA Polymerase: Adds nucleotides.
  • Ligase: Seals gaps in the lagging strand.