Cell Cycle and Mitosis

Organization of the Process of Cell Division!

What’s Happening in This Picture???

❖ Cells are undergoing various stages of the cell division. ❖ Cell Division Happens at Different Stages

Types of Cell Division

• Binary Fission – Prokaryotic Cell Division

• Mitosis – Eukaryotic Cell Division

• Meiosis – Production of sex cells !

– Two Main Stages – Mitosis and cytokinesis

• Cell cycle is a series of events that cells go through as they grow and divide. !

• During cell cycle: • Cell grows • Prepares for

division. • Divides to form

two daughter cells

Stages of the Cell Cycle

• Is interphase part of mitosis? – NO!!! !

• What percentage of time do cells spend in each phase? – Interphase =

90-95% – Mitosis = 5-10%

Stages of the Cell Cycle

❖ Mitosis is a short but important part of the Cell Cycle

Stages of Interphase

• G0 (Gap0)

– Cell leaves the cell cycle and quit dividing. – Temporary or permanent resting period. – Ex: When cell that has reached an end stage

of development and will no longer divide (e.g. neuron).

Stages of Interphase

• G1 (Gap1) – Cells increase in size. – Produce RNA and synthesize proteins. – G1 Checkpoint ensures that everything is

ready for DNA synthesis. • Cell cycle control mechanism

Stages of Interphase

• S (Synthesis) – DNA replication occurs during this phase. – Once a cell enters this stage, it completes

rest of cell cycle.

Stages of Interphase

• S (Synthesis) – DNA replication occurs during this phase. !

• G2 (Gap2)

– Gap between DNA synthesis and mitosis. – Cell continues to grow and produce proteins and

organelles required for cell division. – G2 Checkpoint determines if the cell can now

proceed to enter M Phase and divide. – Shortest of three phases of interphase

Stages of Mitosis

• There are 4 phases: – Prophase – Metaphase – Anaphase – Telophase

Prophase

• 50-60% of mitosis

Prophase

!• Chromosomes start to become visible,

– Chromatin condenses

Prophase

• 50-60% of mitosis • Chromosomes start to become visible,

– Chromatin condenses • Centrioles separate and go to opposite sides of

the nucleus • Spindle begins to form (helps separate

chromosomes) • Lastly the nucleus disappears and the nuclear

envelope breaks down

Prophase

Metaphase

• 2nd phase, only last a few minutes !

• Chromosomes line up across center of cell !

• Microtubules connect to the centromere of each chromosome

Metaphase

Anaphase• 3rd phase !

• Centromeres that joined the sister chromatids separate !

• Chromosomes separate into 2 groups moving towards the poles !

• Ends when the chromosomes stop moving

Anaphase

Telophase• 4th and final phase of mitosis !

• Chromosomes begin to unravel and disperse !

• Nuclear envelope/membrane begins to reform !

• Spindle breaks apart !

• Daughter cells become visible

Telophase

Cytokinesis

• Cytoplasm pinches in half to create the 2 new daughter cells – Separating the 2 new nuclei !

• Daughter cells now have identical chromosomes

Cytokinesis

Cytokinesis: Animal vs. Plant Cell

Regulating the Cell Cycle

• Not all cells move through the cell cycle at the same rate. !

• External Controls • Proteins respond to events outside of

the cell. • Direct cell to speed up or slow down

cell cycle. • Growth Factors

• Stimulate growth and division of cells !24

Regulating the Cell Cycle

• Not all cells move through the cell cycle at the same rate. !

• Internal Controls • Proteins that respond to events inside the cell.

• Allow cell cycle to proceed only when ready. • Cyclins

• Proteins that regulate the timing of the cell cycle.

• CDK • Binds to cyclins to promote cell cycle

progression.

What Controls the Cell Cycle???

• CDK: always present in cells • Cyclin: level varies throughout the cell cycle • MPF: “mitosis promoting factor” --occurs when

cyclin binds to CDK.

Cancer• Cancer is when the cell cycle

goes wrong. • Body’s cells lose ability to

control growth. • Cancer cells do not respond

to signals that regulate the growth of cells.

• Form masses called tumors.

• Several causes, but common factor is uncontrolled growth.

• p53 gene

Mitosis

Be able to describe and sketch what’s happening:

• Chromosomes • Nuclear Envelope • Spindle

Mitosis Chromosomes Nuclear Envelope

Spindle

DNA coils into c’somes

Begins to disappear

Spindles begin to grow;Centrioles begin to move to opposite poles

C’somes line up along equator

Spindle fibers attach to c’some at centromere

Sister chromatids split -- move to poles

Spindles shorten

C’some have moved to oppostie poles

Begins to reform

Spindle breaks down

Mitosis Animations

• Mitosis Rap !

• Twilight Mitosis !

• Mitosis Animation !

• Mitosis Animation