The Cell Cycle

When do cells divide?

• Reproduction• Replacement of damaged cells• Growth of new cells• In replacement and growth cell divisions how

should daughter cells compare to parent cell?• The daughter cells should be identical copies

of the parent cell.

How can identical daughter cells form?

• The chromosomes must be copied and then divided such that each daughter cell gets one of the copies.

Important terms in eukaryotic cell division

• Chromosome =

Important terms in eukaryotic cell division

• Chromosome = threadlike structures that are composed of DNA + protein

• replication =

Important terms in eukaryotic cell division

• Chromosome = threadlike structures that are composed of DNA + protein

• mitosis =

Important terms in eukaryotic cell division

• Chromosome = threadlike structures that are composed of DNA + protein

• mitosis = division of the nucleus• cytokinesis =

Important terms in eukaryotic cell division

• Chromosome = threadlike structures that are composed of DNA + protein

• mitosis = division of the nucleus• cytokinesis = division of the cytoplasm

• Chromatid =

• Chromatid = after copying the chromosome consists of 2 sister chromatids joined at the centromere.

• Centromere =

• Chromatid = after replication the chromosome consists of 2 sister chromatids joined at the centromere.

• Centromere = special region of the chromosome, where chromatids are joined.

The Cell Cycle

Interphase

• 90% of cell cycle is spent in this phase• Chromosome copying (replication) occurs here

Interphase in animal cells:

• Nuclear envelope is visible• nucleoli are present• Centrioles are near nucleus• asters form around each pair of centrioles• chromosomes are loosely packed (chromatin),

not visible w/microscope

General Overview of Mitosis

Prophase:

• In the Nucleus:• Nucleoli disappear• chromosomes condense –become visible• each chromosome consists of 2 sister

chromatids joined at the centromere

• In the Cytoplasm:• spindle begins to form – these will be tracks

for chromosome movement• Nuclear envelope breaks apart

Metaphase• Chromosomes move to the middle of cell and

line up• Each sister chromatid is attached to a spindle

fiber

Anaphase

• Centromeres divide sister chromatids are separated

• the cell is stretched into an oval shape

Telophase• new nuclear envelopes are formed around

the chromosomes at each end of the cell• nucleoli reappear• chromosomes uncoil into chromatin fiber• last phase of mitosis

Cytokinesis

• Begins before telophase has completed