CELL CYCLE The life cycle of a cell consists of a repeating set of events

Phases of Cell Cycle Interphase G 1 : Normal cell function S: DNA Replication G 2 : Preparation for cell division M Phase (Red ) Mitosis Cytokinesis

G 1 Phase Period of normal cell function Cell growth and synthesis of materials needed for proper cell function take place Certain cells never leave G 1 Known as G 0 Red blood cells, neurons, skeletal muscle cells These cells will not divide or grow, but will continue to function until cell death Cells which will divide pass through a "point of no return" and proceed through S, G 2 and mitosis.

S Phase DNA synthesis occurs. Genes copy themselves by the process known as replication. Chromosomes consist of two identical strands once replication is completed. Each of these strands is called a chromatid. During mitosis the chromatids will separate and each chromatid will become a separate chromosome.

M Phase Mitosis: division of the nucleus Prophase Metaphase Anaphase Telophase Cytokinesis: division of cell cytoplasm Animals—Cleavage Furow Plants—Cell plate

Timing for a Typical Cell Cycle Plants: usually hours Animals: hours Varies from 20 minutes to several days or weeks Greatest variation in G 1 See Cell Cycle Animation

Interphase Most cells are in interphase, the phase between cell divisions. The chromosomes are uncondensed with their strands existing as chromatin in the nucleus. They become condensed as chromosomes during mitosis. Label- centrioles, chromatin, nucleus,

MITOSIS Mitosis: the nuclear division of a cell Cytokinesis- produces two identical daughter cells. Recognizable phases of mitosis: Prophase Metaphase Anaphase Telophase

Early Prophase Chromosome condensation – get thicker Nuclear envelope breaks down Centrioles move toward opposite poles and pulls the spindle fibers with them

Late Prophase Chromosomes very thick Nuclear Membrane disappears

The centromere attaches the chromosome to the spindle fibers. Do NOT have to know kinetochore

Metaphase Chromosomes are aligned at the equator and are attached to the spindle.

Anaphase Individual chromatids pull apart..

Telophase and Cytokinesis Telophase Chromosomes reach the poles Nuclear envelope forms around each chromosome set Cytokinesis- Daughter cells become separated by cell membranes.

Cytokinesis and Late Telophase Chromosomes de-condense / get thinner A nucleolus forms as the cells enter into interphase.

Onion Root Tip: Interphase

Onion Root Tip: Prophase

Onion Root Tip: Metaphase

Onion Root Tip: Anaphase

Onion Root Tip: Telophase

Interphase

Prophase

Metaphase

Anaphase

Telophase

Which Stage is This?