Focus Questions: Why do cells need to grow and divide? How do cells divide? What happens when cells divide incorrectly?

Reasons we need our cells to grow! Growth of organisms Repair of tissues

There are limits to a cell’s growth A larger cell may experience “DNA overload” As cells get larger they become less efficient at exchanging nutrients and materials such as oxygen, water, and food with its environment

DNA Overload If a cell is large, there are more demands on its single copy of DNA Think of a book in a library: the more people there are, the greater the likelihood that they will have to wait to read it

Exchanging Nutrients As a cell gets larger, what gets bigger? Its volume! Its surface area also gets larger, but not large enough! Only so many materials are able to pass through the cell membrane at once The surface area of many small cells is greater than one cell (or ever a few large cells)

Remember, cells must use diffusion and osmosis to obtain important nutrients, like oxygen and glucose

Cell Division - process by which a cell splits into two identical daughter cells Occurs in two main phases:  Interphase – cell copies its DNA and prepares for division Mitosis – chromosomes separate into two new cells

Chromosomes DNA containing cell’s genetic code During interphase, chromosomes are copied - this produces two identical “sister chromatids”

The Cell Cycle

The Cell Cycle Interphase (longest phase) G1 - first growth (gap) phase, new organelles produced Synthesis - DNA makes a copy G2 - second growth (gap) phase, preparing for mitosis G0 - no growth phase, a cell may enter this phase Mitosis - nucleus divides, ensuring each new cell has the exact number of chromosomes as parent

Life Cycle of the Cell Mitosis = nuclear division Mitosis is followed by cytokinesis (cell division) The steps of mitosis ensure that each new cell has the exact same number of chromosomes as the original

First, a little background info Centrioles – produce spindle fibers during cell division Spindle fiber – a tiny protein that helps chromatids separate during mitosis

Anatomy of a chromosome Chromosome is composed of a pair of chromatids (sister chromatids) Centromere is the center, where the two chromatids connect

Interphase • Prophase • Metaphase • Anaphase • Telophase IPMAT

Interphase Most of the time in the cell cycle is spent in interphase (95%) Technically, it is not mitosis (Includes G1, S, G2) Most cellular activity occurs in interphase Reproduction of DNA and organelles

Prophase Chromatin (stringy DNA) condenses into chromosomes (more compact DNA, which is more visible)

Prophase Centrioles migrate to opposite poles of the cell. Spindle fibers form Nuclear envelope (covering around nucleus) disappears.

Draw Prophase

Metaphase Nuclear envelope is gone Microtubules connect to chromosomes Chromosomes aligned along middle of nucleus (on the equator)

Draw Metaphase

Anaphase Chromosomes pulled apart by spindle

Draw Anaphase

Telophase Chromatids arrive on opposite sides of cell Nuclear envelope begins to reform around each set of chromatids Chromosomes unwind Spindle fibers disperse

Draw Telophase

Cytokinesis Cell membrane pinches off New cell wall forms in plants

Interphase Two new genetically identical cells Cell Cycle continues

Mitosis: Can you name the stages? 1 2 3 4 5

Mitosis: Can you name the stages? Prophase 2 3 4 5

Mitosis: Can you name the stages? Prophase Metaphase 3 4 5

Mitosis: Can you name the stages? Prophase Metaphase Anaphase 4 5

Mitosis: Can you name the stages? Prophase Metaphase Anaphase Telophase 5

Mitosis: Can you name the stages? Prophase Metaphase Anaphase Telophase Cytokinesis

Important People Must Analyze Tasks Correctly Phases of cell cycle - IPMATC Important People Must Analyze Tasks Correctly

Cell Cycle Images

1. chromosomes visible (chromatids) 2. centrioles migrate to the poles 3. nuclear membrane disappears 4. nucleolus disappears 5. spindle forms

1. chromosomes line up on the equator, spindle attaches

1. chromatids separate and move to opposite poles

1. chromosomes disappear • chromatin 2. nuclear membrane reforms 3. nucleoli reappears 4. spindle disappears 5. centrioles duplicate

- division of the cytoplasm to form 2 new daughter cells - organelles are divided - daughter cells are genetically identical Cells return to interphase

Important People Must Analyze Tasks Correctly Impatient People May Phases of cell cycle - IPMATC Important People Must Analyze Tasks Correctly Impatient People May Attack Teachers Constantly

Name the phases starting at the top.

Name the phase Identify X Identify Y

5. Name the phase

6. Name the phase