CELL GROWTH & DIVISION

CELL GROWTH & DIVISION

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1. Diffusion limits size An oxygen molecule follows a path to the mitochondria (Oxygen) plasma membrane cytoplasm mitochondria Because of the small size of the cell, oxygen molecules take a fraction of a second to reach the mitochondria. Smaller size allows the cell to be more efficient

2. DNA content limits size Cells usually contain only one nucleus DNA is found in the nucleus DNA makes RNA RNA will travel through the cytoplasm to the ribosomes RNA assists the ribosomes in making proteins DNA is responsible for the whole above process If the cell was very large, there would not be enough DNA to support the cell.

3. Surface area to volume ratio limits size As a cell increases, it volume increases much faster than its surface area If a cell doubled, the cell would require 8X more nutrients and have 8X more waste to get rid of FYI If E.coli ( a bacterium)were left unregulated, it could engulf the Earth in one day because it doubles in volume every 30 minutes!!

THE CELL CYCLE PHASES G1 (GAP 1) The Cell Grows Physically Larger, Copies Organelles, Makes The Molecular Building Blocks It Will Need In Later Steps. G0: Cell not preparing to divide; doing its job S PHASE Synthesizes A Complete Copy Of The DNA Duplicates A Microtubuleorganizing Structure Called The Centrosome. G2 (GAP PHASE) The Cell Grows More Makes Proteins And Organelles Begins To Reorganize Its Contents In Preparation For Mitosis. M PHASE The Cell Divides Its Copied DNA & Cytoplasm Makes Two New Cells.

CELL CYCLE REGULATION

INTERNAL AND EXTERNAL FACTORS REGULATE CELL DIVISION. AN INTERNAL SIGNAL INVOLVES THE CELL SENSING THE PRESENCE OF PROTEINS- GROWTH FACTORS (ENZYMES) INSIDE THE CELL. CYCLINS CONTROL THE TIMING OF THE CELL CYCLE KINASES ENZYMES THAT HELP CYCLINS WORK

REGULATORY PROTEINS MANY TYPES OF CYCLINS & KINASES CONTROL THE CELL CYCLE INTERNAL PROTEINS- MONITOR EVENTS WITHIN THE CELL EXTERNAL PROTEINS MONITOR EVENTS OUTSIDE THE CELL GROWTH FACTORS STIMULATE GROWTH & DIVISION ( DEVELOPMENT & REPAIR)

AN EXTERNAL SIGNAL INVOLVES THE CELL SENSING THE PRESENCE OF A CHEMICAL (SUCH AS A GROWTH FACTOR) WHICH WAS PRODUCED IN OTHER SPECIALIZED CELLS. CELLS CAN ALSO RESPOND TO PHYSICAL SIGNALS FROM THEIR ENVIRONMENT. CELLS SENSE WHEN THEY ARE TOO CLOSELY PACKED AND CELL DIVISION IS TURNED OFF. CELLS SENSE WHEN THEY ARE NOT IN CONTACT WITH A SURFACE AND CELL DIVISION IS TURNED ON.

APOPTOSIS: programmed cell death. A NORMAL FEATURE OF HEALTHY ORGANISMS CAUSED BY A CELL S PRODUCTION OF SELF-DESTRUCTIVE ENZYMES OCCURS IN DEVELOPMENT OF INFANTS webbed fingers

UNCONTROLLED CELL DIVISION: CELL CYCLE REGULATION BREAKS DOWN CANCER -the normal signals which shut down the cell division process DO NOT WORK (fig.3.3 p 493) Cancer cells divide even when they are very densely packed and/or there is no growth factor present. Cancer begins when a single cell is transformed into a cancer cell

CELL DIVISION IS UNCONTROLLED IN CANCER. CANCER CELLS FORM DISORGANIZED CLUMPS CALLED TUMORS. Benign tumors remain clustered and can be removed. Malignant tumors metastasize, or break away, and can form more tumors. normal cell cancer cell bloodstream

Normally the body s immune system will recognize that the cell is damaged and destroy it If it evades destruction, it will continue to divide and each daughter cell will become a cancer cell. A mass of these cells that invades and impairs the functions of one or more organs is called a malignant tumor. A benign tumor is a mass of abnormal cells that remains at the original site. METASTASIZED cancer cells separate from the original tumor enter the blood and lymph vessels of the circulatory system invade other parts of the body, where they grow to form new tumors.

CANCER CELLS DO NOT CARRY OUT NECESSARY FUNCTIONS. Cancer cells come from normal cells with damage to genes involved in cell-cycle regulation. p53 gene Many Cancers Have a defect in this gene p53 gene stops cell cycle until replication of chromosomes is finished

CARCINOGENS ARE SUBSTANCES KNOWN TO PROMOTE CANCER. Standard cancer treatments typically kill both cancerous and healthy cells. LUNG CANCER CELLS