Mitosis

“The Life and Times of the Cell”

Objectives

List factors that influence when cells divide

Understand & describe the ‘Cell Cycle’

Study the events of cell division (Mitosis)

Compare Mitosis in plant & animal cells

Cell Division Animation

Reading Assignment

Read Section 10-1, p.241-243 titled Cell Growth.

From the diagram indicating the Ratio of Surface area to Volume onp.243, sketch in your notes the smallest cell and the related statistics for Surface Area, Volume, and Surface Area to Volume Ratio and then sketch the largest cell with it’s related statistics.

Answer the 4 questions in 10-1 Section Assessment on p.243.

Cell Cycle – 4 Phases

Gap 1 (G1)– Typical cell growth &

metabolism.

S Phase (S)– DNA Replication

Gap 2 (G2)– Centrioles Replicate– Protein synthesis

M Phase (M)– Mitosis phase / cell division

occurs

Cell Cycle

The G1, S and G2 stages of the Cell Cycle happen during INTERPHASE.

The M phase consists of: Prophase;

Metaphase; Anaphase;

Telophase; Cytokinesis

S Phase - DNA ReplicationAn enzyme called Helicase causes the hydrogen bonds that hold DNA together to break or ‘unzip’

Then DNA Polymerase allows free floating nucleotides to attach to the single strand of DNADNA is Replicated

Draw DNA Replication

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

DNA Replication

Separate the original DNA strands.

With different colors, show the attachment of free-floating nucleotides.

DNA Replication

Where do the free-floating nucleotides come from?

Foods we eat!

How do the 2 strands compare?

They are exactly the same!

What happens if there is a mistake made during replication?

A mutation occurs!

Replication

DNA Replication..Who wants to try?

Replication Song

M Phase – Mitosis (4/5 Phases)

1. Interphase– G1, S, & G2 phases

2. Prophase– Early & Late

3. Metaphase4. Anaphase5. Telophase– Early & Late

Cytokenesis

Interphase

Early Prophase

Replicated centrioles split and start moving to opposite sides of the cell forming ASTERS.Nuclear envelop disappearsReplicated chromatin shortens, thickens and forms CHROMATID PAIRS

Remember this Diagram?

Early Prophase

Late Prophase

Centrioles have reached opposite poles of the cell

SPINDLE forms

Chromatid Pairs float throughout the cytoplasm.

Late Prophase

MetaphaseShortest stage of Mitosis

Chromatid pairs align at the equator of the spindle

Metaphase

Anaphase

Chromatid pairs split

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

Anaphase

Early Telophase

Often described as the opposite of prophase

Nuclear envelop reappears

The chromosomes unravel to become chromatin

Cleavage furrow begins to form

Late Telophase

Cleavage furrow completes it’s indentation.

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

Early/Late Telophase

Summary of MitosisProphase:

Replicated chromatin condense into chromatid pairCentrioles move to opposite polesNuclear envelope disappearsSpindle fibers start to form

MetaphaseChromatid pairs line up at the equator

AnaphaseChromatid pairs splitChromosomes are pulled to opposite poles by the spindle fibers

TelophaseChromosomes de-condense into chromatinNuclear envelope reappearsCytoplasm is divided into 2 cells Cytokenesis

Mitosis

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

One more Phase – GAP 0 (G0)

Some cells do not replicate their centrioles during Prophase.

They lose their ability to divide

They enter the Gap 0 stage

Neurons of the Spinal cord / Brain cells

Mitosis in Plant vs. Animal CellsThe Rivalry Continues

Plants have no centrioles but still form spindle fibers

Plant cells divide from the inside out

Cell Plate

“Messy Metaphase”

Plant Cell Mitosis

Importance of Mitosis

Method of reproduction for all single celled organisms

Allows us to regenerate cells (tissue) repair cuts, bone breaks, etc

Growth – one cell to trillions

How Long does the Cell Cycle Last?

Pick up a textbook and turn to page 249.

Read the section titled “Life Spans of Cells” and answer the 4 questions that follow.

Regulating the Cell Cycle

Turn in your textbook to page 250. Read pages 250 to 252.

Answer the 5 questions that follow.

Terms: Contact Inhibition; Cyclins; Internal regulators; External regulators; Cancer;

Meiosis

Special cell division that produces Haploid sex cells

Consists of one replication and two cell divisions

Sexual vs. Asexual

Asexual Reproduction

Reproduction that doesn't involve sex cells

Produces ‘clones’ of previous cells

Ex: 1. Binary Fission

2. Fragmentation

3. Budding

Sexual Reproduction

Reproduction involving sex cells

Produces genetically different offspring

Sperm + egg = Zygote

(n) + (n) = (2n)

CancerA disease of uncontrolled cell divisionStarts 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 TreatmentThree 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 / chemotherapyUsing multiple drugs can decrease the risk of relapse– Multiple drugs decrease the probability of cells acquiring immunity