CELL CYCLE

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

Phases of Cell Cycle

• InterphaseG1: Normal cell

functionS: DNA ReplicationG2: Preparation for

cell division

• M Phase (Red ) MitosisCytokinesis

G1 Phase

• Period of normal cell function• Cell growth and synthesis of materials needed for

proper cell function take place• Certain cells never leave G1

Known as G0

Red blood cells, neurons, skeletal muscle cellsThese 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, G2 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 nucleusProphaseMetaphaseAnaphaseTelophase

• Cytokinesis: division of cell cytoplasmAnimals—Cleavage FurowPlants—Cell plate

Timing for a Typical Cell Cycle

• Plants: usually 10-30 hours

• Animals: 18-24 hours

• Varies from 20 minutes to several days or weeks

• Greatest variation in G1

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:

ProphaseMetaphaseAnaphaseTelophase

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

Prophase

Metaphase

Anaphase

Telophase

Telophase

Which Stage is This?