Recall that M phase is the part of the cell cycle when the cell divides. GROWTH DNA LOOSENS G1 CYTOPLASM DIVIDES INTERPHASE M PHASE NUCLEUS DIVIDES S DNA REPLICATION G2 CHROMOSOMES FORM CHECK FOR ERRORS

M phase is divided into two main parts. GROWTH DNA LOOSENS G1 CYTOPLASM DIVIDES (CYTOKINESIS) INTERPHASE M PHASE NUCLEUS DIVIDES S (MITOSIS) DNA REPLICATION G2 CHROMOSOMES FORM CHECK FOR ERRORS

Mitosis First part of M phase; division of the nucleus. Nucleus

Cytokinesis SKIP ½ PAGE Nucleus Nucleus Nucleus Nucleus Last part of M phase; division of the cytoplasm and organelles. L C O

WHAT PROBLEMS DOES A CELL FACE DURING MITOSIS? Nucleus Nucleus Nucleus

Chromosomes are trapped in the nucleus PROBLEM SOLUTION Chromosomes are trapped in the nucleus Get rid of the nucleus!

Chromosomes didn’t divide equally PROBLEM SOLUTION Chromosomes didn’t divide equally Line up the chromosomes in the middle!

Chromosomes are stuck together Pull the chrosomes apart! PROBLEM SOLUTION Chromosomes are stuck together Pull the chrosomes apart!

Chromosomes need to be enclosed in a nucleus PROBLEM SOLUTION Chromosomes need to be enclosed in a nucleus

Chromosomes need to be enclosed in a nucleus PROBLEM SOLUTION Chromosomes need to be enclosed in a nucleus Form two new nuclei!

Mitosis occurs in 4 careful steps… GROWTH DNA LOOSENS C G1 CYTOPLASM DIVIDES (Cytokinesis) INTERPHASE M PHASE NUCLEUS DIVIDES S DNA REPLICATION (Mitosis) G2 CHROMOSOMES FORM CHECK FOR ERRORS

…to ensure that the daughter cells get an equal number of chromosomes.

INTERPHASE M PHASE G1 S PROPHASE G2 GROWTH DNA LOOSENS CYTOPLASM DIVIDES (Cytokinesis) INTERPHASE M PHASE NUCLEUS DIVIDES S DNA REPLICATION (Mitosis) PROPHASE G2 CHROMOSOMES FORM CHECK FOR ERRORS

Prophase NEW PAGE First step of mitosis; fully-formed chromosomes appear, and the nucleus starts to disappear. M C N

Organelles called centrioles move to opposite ends of the cell.

The centrioles will pull the chromosomes apart.

Additionally, spindle fibers appear during prophase Additionally, spindle fibers appear during prophase. They grow out from the centrioles and attach to the chromosomes. S F P C C Chromosomes Spindle fiber Centrioles

Prophase “Before” Centrioles Fully-formed chromosomes Nucleus disappears Spindle fibers

INTERPHASE M PHASE G1 METAPHASE S PROPHASE G2 GROWTH DNA LOOSENS CYTOPLASM DIVIDES (Cytokinesis) INTERPHASE M PHASE NUCLEUS DIVIDES METAPHASE S DNA REPLICATION (Mitosis) PROPHASE G2 CHROMOSOMES FORM CHECK FOR ERRORS

Metaphase “Middle” Step 2 of mitosis; chromosomes line up along the middle of the cell. M L U M

Motor proteins pushing chromosomes into position during metaphase (discovered in 2012):

INTERPHASE M PHASE G1 ANAPHASE METAPHASE S PROPHASE G2 GROWTH DNA LOOSENS G1 CYTOPLASM DIVIDES (Cytokinesis) INTERPHASE M PHASE ANAPHASE NUCLEUS DIVIDES METAPHASE S DNA REPLICATION (Mitosis) PROPHASE G2 CHROMOSOMES FORM CHECK FOR ERRORS

Anaphase “Not” Step 3 of mitosis; chromosomes are pulled apart by the spindle fibers. M C A S F

The spindle fibers pull the chromosomes apart by contracting (getting shorter).

INTERPHASE M PHASE G1 TELOPHASE ANAPHASE METAPHASE S PROPHASE G2 GROWTH DNA LOOSENS G1 CYTOPLASM DIVIDES (Cytokinesis) INTERPHASE M PHASE TELOPHASE ANAPHASE NUCLEUS DIVIDES METAPHASE S DNA REPLICATION (Mitosis) PROPHASE G2 CHROMOSOMES FORM CHECK FOR ERRORS

Telophase “Away” Final step of mitosis; chromosomes move away from each other, and a nucleus re-forms around each set of chromosomes. M A N C

What happens if mitosis does not occur correctly?

It is EXTREMELY important that chromosomes split equally….

…especially during the division of sex cells.

If chromosomes don’t split equally during the formation of sex cells… Wrong number of chromosomes

…the resulting baby could have the wrong number of chromosomes. Mother Father

Which stage of mitosis is this? Prophase Metaphase Anaphase Telophase Cytokinesis

Cytokinesis occurs immediately after mitosis.

Cytokinesis is different in animal and plant cells. Rigid Cell wall

Cytokinesis in Animal Cells vs. Plant Cells

In animal cells, protein fibers in the middle of the cell contract, pinching the cell in two.

In plant cells, the cell wall is too rigid to pinch In plant cells, the cell wall is too rigid to pinch. Instead, a cell plate forms. P C W R P

After cytokinesis, the DNA loosens so that the cell cycle can start over.

Mitosis + Cytokinesis

Go Sally Go Make Children Interphase M Phase Go Sally Go Make Children G1 S G2 Mitosis Cytokinesis P M A T

Identifying Cells in M Phase

Identifying Cells in the Cell Cycle Fully-formed chromosomes No chromosomes G1 Small (just divided) Fully-grown Interphase S End of G2 DNA starting to condense Fully-formed chromosomes Prophase & no nucleus Metaphase M phase Anaphase Mitosis Telophase

Mitosis cells: fully-formed chromosomes, no nucleus

Prophase?

Identifying Cells in the Cell Cycle No chromosomes G1 Small (just divided) Fully-grown Interphase S End of G2 DNA starting to condense Before chromosomes have lined up Fully-formed chromosomes Prophase & no nucleus Metaphase M phase Anaphase Mitosis Telophase

Metaphase?

Identifying Cells in the Cell Cycle No chromosomes G1 Small (just divided) Fully-grown Interphase S End of G2 DNA starting to condense Before chromosomes have lined up Fully-formed chromosomes Prophase Chromosomes lined up in the middle & no nucleus Metaphase M phase Anaphase Mitosis Telophase

Anaphase?

Identifying Cells in the Cell Cycle No chromosomes G1 Small (just divided) Fully-grown Interphase S End of G2 DNA starting to condense Before chromosomes have lined up Fully-formed chromosomes Prophase Chromosomes lined up in the middle & no nucleus Metaphase Chromosomes are not attached (still close) M phase Anaphase Mitosis Telophase

Telophase?

Identifying Cells in the Cell Cycle No chromosomes G1 Small (just divided) Fully-grown Interphase S End of G2 DNA starting to condense Before chromosomes have lined up Fully-formed chromosomes Prophase Chromosomes lined up in the middle & no nucleus Metaphase Chromosomes are not attached (still close) M phase Anaphase Chromosomes move away; divided nucleus Mitosis Telophase

What about this cell?

Identifying Cells in the Cell Cycle No chromosomes G1 Small (just divided) Fully-grown Interphase S End of G2 DNA starting to condense Before chromosomes have lined up Fully-formed chromosomes Prophase Chromosomes are lined up in the middle & no nucleus Metaphase Chromosomes are not attached (still close) M phase Anaphase Chromosomes move away from each other Mitosis Telophase DNA starting to loosen; Cytokinesis

Additionally, during cytokinesis, a line starts to form between the two daughter cells. Contracting protein fibers Cell plate

Identifying Cells in the Cell Cycle No chromosomes G1 Small (just divided) Fully-grown Interphase S End of G2 DNA starting to condense Before chromosomes have lined up Fully-formed chromosomes Prophase Chromosomes are lined up in the middle & no nucleus Metaphase Chromosomes are not attached (still close) M phase Anaphase Chromosomes move away from each other Mitosis Telophase DNA starting to loosen; Cytokinesis Line starts to form