How many stages of cell division do you see in this image?

Genetics Unit: Mitosis

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Cell Cycle

Mitosis will be our main focus.

First, we will look at Interphase…

Interphase

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• Longest stage of cell division (90% of cell cycle)

• Nucleus is visible

• Cell is growing and DNA is being replicated.

Interphase:3 Phases

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1. G1: Cell is Growing

2. S: DNA is Synthesized (DNA Replication)

3. G2: Organelles duplicate in preparation for division

Most of these cells are in Interphase

Limits to Cell Growth

6 150 750

1 125 125

6 61.2

Total Surface Area:

Height x Width x Number of sides x Number of boxes

Total Volume:

Height x Width x Length x Number of boxes

Surface-to-volume ratio:

Surface Area/ Total Volume

What’s the problem with a low surface-to-volume ratio?

1. Materials have trouble entering and leaving the cell.

2. The cell can’t make enough mRNA to meet the demands of the cell.

O2

O2

What are the key roles of cell division?

1. Cell division functions in:a. Reproduction for some organisms

b. Growth of an organism from a fertilized egg

c. Repair of cells that die from normal wear and tear or accidents

2. Cell division distributes identical sets of chromosomes to daughter cells

Key Vocabulary

• DNA molecules are packaged into .– Human (body cells)

have 46 – Human (sperm or eggs)

have 23

• Chromosomes are made of a material called .

chromosomessomatic cells

gametes

chromosomes.

chromosomes.

chromatin

Key Vocabulary

• Chromatin is composed of and .

• It is supercoiled around proteins, called .

• Together the DNA and histone molecules form bead-like structures called

DNAproteins

histones

nucleosomes

Key Vocabulary

sisterchromatids

centromere

• The chromosome is duplicated.

• Each duplicated chromosome consists of two

.

• These are connected by a .

Mitosis (M Phase)

The M Phase consists of:• Mitosis and Cytokinesis

Four Stages of Mitosis:

• Prophase

• Metaphase

• Anaphase

• Telophase

Late Interphase: GLate Interphase: G22

Centrosomes (with centriole pairs)Centrosomes (with centriole pairs)

Preparing for Division

1.Nuclear membrane still visible1.Nuclear membrane still visible

Nucleolus Nucleolus

2.Chromatin has been replicated2.Chromatin has been replicated

Late Interphase: GLate Interphase: G22

Preparing for Division

4.Chromosome consisting of two sister chromatids4.Chromosome consisting of two sister chromatids

CentromereCentromereEarly Spindle ApparatusEarly Spindle Apparatus

ProphaseProphase

3.Nuclear 3.Nuclear membrane membrane disappearsdisappears

MetaphaseMetaphase

5. Chromosomes line up5. Chromosomes line up at an at an imaginary line between the imaginary line between the centrosomes at opposite ends centrosomes at opposite ends of the cell.of the cell.

6.The spindle attaches to 6.The spindle attaches to the centromeres.the centromeres.

AnaphaseAnaphase

7.Spindles pull the 7.Spindles pull the “daughter” “daughter” chromosomes appart chromosomes appart

Telophase & CytokinesisTelophase & CytokinesisTelophase8.Two nuclei become visibleIn animal cells, a Cleavage Furrow is visible

In plant cells, a cell plate is now visible

Cytokinesis9.The cytoplasm and organelles divide.

What’s the end product?

• Two identical daughter cells ready to start the cycle again… or not.

• Some cells (like your nerve and muscle cells) do not undergo division.

• For those that do (your skin and the lining of your intestinal tract) how would you know how quickly division takes place?