Cell division - mitosis

Cell division

Cell division is needed for:

• reproduction in unicellular organisms

• growth in multicellular organisms

• replacement of damaged or dying cells

• repair of damaged organs or tissues

Mitosis

Involves:

• replication of DNA

• controlled division of the nuclear material so new each cell has the same DNA or number of chromosomes

• division of cytoplasm and organelles so each new cell has similar contents

Chromosomes• Chromosomes are only

visible during cell division

• They consist of two strands (chromatids) of tightly coiled DNA joined at the centromere

• They hold all the genetic information that controls the activities of cells

DNA replication• Occurs in interphase – before

mitosis starts• One set of enzymes split the

strands• Another set of enzymes join new

nucleotides to each strand• Nucleotides match up by the

base pairing rule (C – G, A - T)• The end result is two identical

strands, joined at a point called the centromere

Cell cycle

Stages of mitosis

Interphase

• Phase of growth and normal metabolism

• Nucleus and nucleolus visible

• DNA replication occurs just before cell division occurs

Prophase

• First stage of division• Nucleus and

nucleolus disappear• Spindle starts to form• DNA condenses and

becomes visible as chromosomes

• Centrioles move to opposite poles (animal cells)

Metaphase

• Chromosomes line up on spindle at the equator of the cell

Anaphase

• Chromatids pull apart at the centromere

• One chromatid from each chromosome moves to each end of the cell

Telophase

• Chromosomes uncondense and a new nucleus forms around them

• The cytoplasm splits (cytokinesis) to form two new cells identical to the original except smaller

Interphase

• Phase of growth and normal metabolism• Nucleus and nucleolus visible

Identify the stages of mitosis

telophase

anaphase

metaphase

early prophase

interphase

early prophase

metaphase

early prophase