Mitosis and DNA Replication

Cell Division Occurs in humans and other organisms at different times in their life. Cell Division differs depending on type of organism: Eukaryotic organisms undergoing growth, development, repair, or asexual reproduction divide by mitosis. EXAMPLE: new hair, nails, skin, liver, cells, etc… are produced.

Interphase 95% of cell cycle in interphase Cells replicate their DNA

Mitosis Mechanism used by cells to replicate DNA and produce identical cell copies. 5% of cell cycle is mitosis Happens in all cells

Mitosis It is broken down into 5 major stages: Prophase Metaphase Anaphase Telophase

Prophase 1st phase of Mitosis Nucleolus breaks down & Nuclear membrane disappears Chromosomes condense –sister chromatids stay attached by the centromere Kinetochore fibers form

Metaphase 2nd phase of Mitosis The kinetochore fibers move the Chromosomes to the equator (middle) Each chromatid is attached to the fibers at the centromere.

Anaphase 3rd phase of Mitosis Centromeres split Sister chromatids are pulled apart to opposite poles of the cell After chromatids separate, they are considered to be individual chromosomes.

Telophase 4th phase of Mitosis Chromosomes begin to uncoil back into chromatin state. Cytokinesis Cytoplasm divides Two new daughter cells are now separate 2 nuclear membranes form around each set of chromosomes. Nucleolus forms in each of the newly formed cells.

Mitosis Animation

Deoxyribose Nucleic Acid DNA double-stranded sugar = deoxyribose bases = A,T,C,G

Free Nucleotide

DNA Replication

DNA Replication DNA copies itself exactly (Occurs within the nucleus) Any mistake in copying = mutation

Basic Facts of DNA Replication Complementary base pairing makes replication possible C - G A - T

Basic Facts of DNA Replication One side of DNA molecule is a template for making the other side (strand)

DNA Replication Step 1: Uncoil & unzip DNA molecule This occurs because of a weak hydrogen bond between the bases.

DNA Replication Step 2: Enzyme brings in complementary N-bases

DNA Replication Each new DNA molecule contains one old strand & one new strand

DNA Replication Animation

The Cell Cycle and Cancer

Cancer: Why does it exist?

There are several factors that regulate the cell cycle and assure a cell divides correctly. 1.Before a cell divides, the DNA is checked to make sure it has replicated correctly. (If DNA does not copy itself correctly, a gene mutation occurs. DNA replication animation:click on DNA picture

2. Chemical Signals tell a cell when to start and stop dividing. (Target cells animation: click on go sign)

3. Neighboring cells communicate with dividing cells to regulate their growth also. (Normal contact inhibition animation: click on petri dish)

Cancer is a disease of the cell cycle Cancer is a disease of the cell cycle. Some of the body’s cells divide uncontrollably and tumors form. Tumors in Liver Tumor in Colon

DNA mutations disrupt the cell cycle. Mutations may be caused by: 1. radiation 2. smoking 3. Pollutants 4. chemicals 5. viruses

While normal cells will stop dividing if there is a mutation in the DNA, cancer cells will continue to divide with mutation.

Due to DNA mutations, cancer cells ignore the chemical signals that start and stop the cell cycle. 2 animations of cancer cells dividing: click on picture

Due to DNA mutations, cancer cells cannot communicate with neighboring cells. Cells continue to grow and form tumors. Skin cancer (cancer cells dividing: click on picture.)

SUMMARY Normal Cell Division DNA is replicated properly. 2. Chemical signals start and stop the cell cycle. 3. Cells communicate with each other so they don’t become overcrowded. Cancer Cells Mutations occur in the DNA when it is replicated. 2. Chemical signals that start and stop the cell cycle are ignored. 3. Cells do not communicate with each other and tumors form.

Cancer Terminology Cancer – a large group of diseases characterized by the uncontrolled growth and spread of abnormal cells Neoplasm – new growth of tissue that serves no physiological function Tumor – clumping of neoplasmic cells Malignant - cancerous Benign - noncancerous Biopsy – microscopic examination of cell development

Cancer Terminology Metastasis – malignant tumors that are not enclosed in a protective capsule have the ability to spread to other organs Mutant cells – disruption of RNA and DNA within normal cells may produce cells that differ in form, quality and function from the normal cell

Factors Believed to Contribute to Global Causes of Cancer Figure 16.2

Treating Cancers Cancer treatments include drugs that can stop cancer cells from dividing. (chemotherapy, radiation)

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