CELL CYCLE AND MITOSISObjectives:

- to describe the phases on mitosis

- to compare the differences between cell division in plant cells and animal cells

- to analyze the link between mitosis and cancer

Reasons Why a Cell Would Divide

To repair or heal damaged tissue For multicellular organisms to grow To keep cell sizes small for increased efficiency For reproduction in unicellular organisms

Activity

Brainstorm in at your tables what is needed for a cell to divide.

Reading Assignment

Read Section 10-1, p.241-243 titled Cell Growth. Table 1 – Describe to the class “DNA Overload” Table 2 – Describe to the class “ Exchanging

Materials” Table 3 – Describe to the class “Ratio of Surface

Area to Volume” Table 4 - Describe to the class “Division of the

cell” Complete Worksheet 10-1 “Cell Growth”

Activity

Using your biological intellect, put these slides in order from first to last. Analyze each of the slides and on the slide list what actions you think are taking place.

Put the Slides in Order

The Correct Sequence is …

1 2 3

4 5

The Stages of Cell Cycle

The actual division of the cell is broken into 2 stages Mitosis is the division of the cell nucleus Cytokinesis is the division of the cytoplasm

In reality the cell cycle is much more complex and is broken into four phases

The Stages of the Cell Cycle

Interphase includes: G1 Phase

S Phase G2 Phase

M PhaseMitosis

Prophase Metaphase Anaphase Telophase

Cytokinesis

The Stages of Cell Division

Cell Division Video

G1 Phase

Cells increase in size Synthesis of new proteins and organelles

S Phase

Chromosomes replicate and the synthesis of DNA molecules takes place.

DNA Replication Helicase “unzips” the double helix by breaking the

hydrogen bonds between the nitrogen bases. Each single strand of the DNA acts as a template. DNA polymerase allows free floating nucleotides to

bond to the single strand of DNA to create two daughter molecules.

S Phase

Activity

Draw a DNA triplet with the base sequence ATG on the left side. Make the 5’ the top left.

S Phase

DNA Replication Video

G2 Phase

Centrioles replicate The proteins required for cell division are

produced.

M Phase

Replicated centrioles split and start moving to opposite sides of the cell forming asters.

Nuclear envelop disappears.

Replicated chromatin shortens, thickens and forms chromatid pairs

Early Prophase

M Phase

Centrioles have reached opposite poles of the cell

Spindle forms Plant cells have no

centrioles but the mitotic spindle still forms in a similar manner.

Chromatid pairs float throughout the cytoplasm.

Late Prophase

M Phase

Chromatid pairs align at the equator of the spindle

Microtubules connect the centromere of each chromosome to the two poles of the spindle.

Metaphase

M Phase

Chromatid pairs split

Spindle fibers contract and the single chromosomes are pulled to opposite poles

Anaphase

M Phase

Often described as the opposite of prophase

Nuclear envelop reappears

The chromosomes unravel to become chromatin

Cleavage furrow begins to form (cytokinesis)

Early Telophase

M Phase

Cleavage furrow completes it’s indentation.

“Mother” cell splits into 2 identical “Daughter” cells in a process called cytokinesis

Late Telophase

M Phase

This is the last stage of the cell cycle. Cytokinesis takes place during telophase. Cytokinesis starts with the cleavage furrow and continues

until the cytoplasm is in two separate parts and two new daughter cells have formed.

In plants a structure referred to as the cell plate forms between the two nuclei.

This cell plate gradually forms into a separating membrane. A cell wall then begins to form inside the cell plate

Cytokinesis

M Phase

Cytokinesis in plants

Activity

Draw a DNA triplet with the base sequence TAG on the left side. Make the 5’ the top left

Summary of Cell Division

Prophase: Replicated chromatin condense into chromatid pair Centrioles move to opposite poles Nuclear envelope disappears Spindle fibers start to form

Metaphase Chromatid pairs line up at the equator

Anaphase Chromatid pairs split Chromosomes are pulled to opposite poles by the spindle fibers

Telophase Chromosomes de-condense into chromatin Nuclear envelope reappears Cytoplasm is divided into 2 cells Cytokinesis

Try these….

1. Cells divide to keep cells sizes small for greater _________.

2. As a cell becomes larger its ________ increases faster than its _________.

3. As a cell grows, it places more demands on its _____.

4. Division of the cell nucleus is called ________.

5. Division of the ________ is called cytokinesis.

6. The four phases of the cell cycle are _____, _____, _____and _______.

7. Cells carry out their specialized functions during _______.

8. During the ______, DNA replicates.

9. The enzyme _______ “unzips” the DNA, the enzyme __________attached free floating nucleotides.

10. The ____________breaks down during prophase

11. Spindle fibers contract and the single chromosomes are pulled to opposite poles during _________.

12. During metaphase, _________align at the equator of the spindle

13. Chromosomes unravel to become chromatin during ________.

Try these….

1. Cells divide to keep cells sizes small for greater efficiency.

2. As a cell becomes larger its volume increases faster than its surface area.

3. As a cell grows, it places more demands on its DNA.

4. Division of the cell nucleus is called mitosis.

5. Division of the cytoplasm is called cytokinesis.

6. The four phases of the cell cycle are G1 phase, S phase, G2

phase and M phase.

7. Cells carry out their specialized functions during G1 phase.

8. During the S phase, DNA replicates.

9. The enzyme helicase “unzips” the DNA, the enzyme DNA polymerase attached free floating nucleotides.

10. The nuclear envelope breaks down during prophase

11. Spindle fibers contract and the single chromosomes are pulled to opposite poles during anaphase.

12. During metaphase, chromatid pairs align at the equator of the spindle

13. Chromosomes unravel to become chromatin during telophase.

I don't watch television when I can talk about Cell Division!

G0 Phase

Certain cells lose their ability to divide.

They do not replicate their centrioles.

They enter the Gap 0 stage

Examples are neurons of the spinal cord / brain cells

Mitosis in Plant Cells

Mitosis in Animal and Plant Cells

Plant Cells Animal Cells

Cancer

Starts with a single cell that loses its control mechanisms due to a genetic mutation (mistakes in DNA replication)

Can be caused naturally or by carcinogens (i.e.: tobacco smoke, chemicals, etc.)

That cell starts dividing without limit, possibly killing the host (without treatment)

Cancer

Cancer Treatment Three basic treatments:

Surgery to remove cancer Radiation to kill affected cells New drugs are becoming available (Chemotherapy)

It is hard to remove cancer (tumors often lack clear boundaries) Some tumors are very small and are found throughout the body (advanced

stages) Radiation and chemotherapy are aimed at killing cancer cells

The body then has to replace those dead cells which requires a lot of energy Therefore treatment must be balanced with overall patient health

Unfortunately due to natural selection cancer that seems to have disappeared can come back in the future in a form that is resistant to the radiation / chemotherapy

Using multiple drugs can decrease the risk of relapse Multiple drugs decrease the probability of cells acquiring immunity

Another Type of Cell Division - Meiosis

Special cell division that produces Haploid sex cells

Consists of one replication and two cell divisions