Lecture #3 The Cell Cycle & Cancer Unit 5: Cell Reproduction

The Cell Cycle Cell cycle- a repeating cycle of cellular growth and division during the life of an organism. What’s the result? 2 daughter cells genetically identical to the parent cell they came from.

2 Basic Parts of the Cell Cycle 1.Interphase- composed of G1, S, G2 stages This is the longest part of cell cycle. A cell spends 90% of its time in interphase. 2.M= Mitosis = Nuclear division Interphase

G1 Phase - Cell Growth In the G1 phase, the cell increases in size due to rapid growth. Cells also synthesize new proteins and organelles.

S Phase: DNA Replication In the S (or synthesis) phase, new DNA is synthesized when the chromosomes are replicated. The cell has DOUBLE the genetic material at this point (sister chromatids rather than chromosomes)

G2 Phase: Preparing for Cell Division In the G2 phase, growth continues. The cell prepares for cell division by producing organelles and molecules required for cell division.

M Phase In eukaryotes, cell division occurs in two stages: mitosis and cytokinesis. Mitosis is the division of the cell nucleus. Cytokinesis is the division of the cytoplasm.

Regulating the Cell Cycle The cell cycle has key checkpoints at which feedback can trigger the next phase of the cell cycle ( like a green light). There are also feedback signals that can delay the passage to the next phase (red light). This allows the current phase to be completed.  In other words, checkpoints CONTROL the rate of cell division  

These checkpoints are actually controlled by a family of proteins called cyclins. Their job is to regulate the timing of the cell cycle in eukaryotic cells.

Checkpoints Cell Growth (G1) checkpoint – This checkpoint makes the decision of whether or not the cell will divide. If conditions are favorable, synthesis phase (S phase) begins and the cells DNA is copied. If conditions are NOT favorable, the cell will stop division at this checkpoint.  

Checkpoints (continued) DNA synthesis checkpoint (G2) – DNA is checked by DNA repair enzymes. If this checkpoint is passed, proteins help to trigger mitosis. Mitosis checkpoint ~ this checkpoint triggers the end of mitosis. It indicates that the new cell is in the initial growth phase (G1)

What do you think? forever………………………..???????????????? Do cells continue going through the cell cycle forever………………………..????????????????

Apoptosis Definition- the process of programmed cell death. This is important for development, homeostasis and elimination of pathogens and tumor cells Example: the foot of a mouse is shaped the way it is partly because the toes undergo apoptosis during tissue development.

When Control is Lost Sometimes, there may be a mutation on one of the genes that regulates cell growth and division. This means that the proteins necessary to monitor cell growth are absent.   Cancer - is a disorder in which body cells lose the ability to control cell growth.

Cancer cells do not respond to the body’s control mechanisms. They may cause cell division to either speed up, or to slow down. Either way, this is damaging to the organism

What causes mutations (defects in genes) that can lead to cancer? 1. Mutations can arise spontaneously; meaning that normal cells become cancer cells for no apparent reason. Other sources of gene defects are smoking tobacco, radiation exposure, and viral infection.

What happens in your body if a cell becomes cancerous? Normally, your body’s immune cells destroy cancer cells. Sometimes cancer cells can go undetected. These cells can continue to grow and divide and eventually will form a tumor. Tumor ~ a mass of cancer cells within otherwise healthy tissue.

Types of Tumors Benign tumors ~ Tumors formed from a mass of cells that remain at the original site that cancerous growth began. Malignant tumor ~ tumors that form if cancer cells spread to and destroy healthy neighboring tissues and other parts of the body. Metastasis ~ the spread of cancer cells beyond their original site.   Cancer cells absorb nutrients needed by other cells, block nerve connections, and prevent organs from functioning.

Tumor treatment Surgical removal (for localized tumors) Chemotherapy ( poisonous chemicals) Targeted radiation (high-energy radiation) Chemotherapy and radiation are especially harmful to actively dividing cells (both cancerous and normal) Most cancer drugs interfere with the cell cycle of cancer cells.