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

Cells reproduce by a cycle of growing and dividing called the cell cycle.

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Cell Cycle

Mitosis will be our main focus.

First, we will look at Interphase…

This graph is NOT to scale!!

Interphase

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• Longest stage of cell cycle (90%)

• Nucleus is visible

• Cell is growing during G1 and G2 and DNA is being replicated (copied) during S.

Interphase:3 Phases

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1. G1: Cell is Growing

2. S: DNA is Synthesized (DNA Replication)

3. G2: Cell growth; 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. There are not enough materials entering the cell to meet its demands

2. Materials have trouble leaving the cell.

3. The cell can’t make enough mRNA or proteins to meet the demands of the cell.

O2

O2

CO2

CO2CO2CO2

CO2

CO2

CO2

CO2

What are the key roles of cell division?

• Cell division functions in:– Reproduction for some organisms– Growth of an organism from a fertilized egg– Repair of cells that die from normal wear and

tear or accidents• 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 .

• DNA is supercoiled around proteins called .

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

DNAproteins

histones

nucleosomesHistones

DNA

Chromosome

Key Vocabulary

sisterchromatids

centromere

Sinterphase

• The chromosome is duplicated during ___ in _____________.

• 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 MetaphaseAnaphaseTelophase

Late Interphase: G2

Centrosomes (with centriole pairs)

Preparing for Division

1.Nuclear membrane still visible

Nucleolus

2.Chromatin has been replicated

Late Interphase: G2

Preparing for Division

4.Chromosome consisting of two sister chromatids

CentromereEarly Spindle Apparatus

Prophase

3.Nuclear membrane disappears

Metaphase

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

6.The spindle attaches to the centromeres.

Anaphase

7.Spindles pull the “daughter” chromosomes appart

Telophase & CytokinesisTelophase8. Two nuclei become visible

In animal cells, a cleavage furrow is visible

In plant cells, a cell plate is now visible

Cytokinesis9.The cytoplasm and organelles divide.

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

RE-identify the stages of Mitosis

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?