How do organisms grow and develop How do

How do organisms grow and develop? • How do we get from a single cell, to a whole organism? • Need to divide and copy cells (and their DNA) • Increase cell NUMBER

Cell Cycle • Events that make up the life of a cell • Consists of – Interphase – M Phase (mitosis, or division) – Cytokinesis

Interphase • • • The cell is “normally” in interphase In the G 1 phase the cell grows to maturity In S phase, the DNA is replicated In the G 2 phase the cell prepares for division Cell can enter G 0 phase where it will not divide but will otherwise function normally – Most nervous system cells are in G 0 phase

Mitosis • The division of the nucleus, and its contents • 4 Phases (PMAT) – Prophase – Metaphase – Anaphase – Telophase

Prophase - “before” • DNA – coils into chromosomes • Nucleus and nuclear membrane – break down • Centrioles – appear in dark spot called centrosome – Begin moving to opposite ends of the cell

Chromosomes • • • Chromatin Chromatid Chromosome Centromere Kinetochore

Centrosome • Centriole • Spindle fibers spread out from centrioles

Metaphase – “middle” • Coiled chromosomes begin to align in the center of the cell • Spindle fibers attach to kinetochore in centromere of chromatids

Anaphase – “apart” • Sister chromatids of each chromosome are pulled apart at the kinetochores • The kinetochores eat the fiber like pac man

Telophase – “end” • • Chromosomes reach opposite ends of the cell Spindle fibers break down Nucleus and nuclear envelope begin to reform Cleavage furrow begins to form between new cells

Cytokinesis • Division of the rest of the cell besides nucleus • Formation of new cell wall in plant cells occurs at the cell plate in the center of the two new cells