Transcript cell cycle
Mitosis & Cancer Cell reproduction in multicellular and unicellular organisms • Unicellular: reproduce by binary fission, asexual reproduction • Multicellular: reproduce by cell division; process of growth and repair depend on cell division; Chapter 9 Cellular Reproduction 9.1 Cellular Growth Ratio of Surface Area to Volume Chapter 9 Cellular Reproduction 9.1 Cellular Growth As the cell grows, its volume increases much more rapidly than the surface area. What’s the problem? The cell would not be able to supply itself with nutrients and expel all waste products. Chapter 9 Cellular Reproduction 9.1 Cellular Growth The Cell Cycle Cell division prevents the cell from becoming too large. It also is the way the cell reproduces so that you grow and heal certain injuries. Cells reproduce by a cycle of growing and dividing called the cell cycle. • The cell cycle is an orderly series of events in which a cell duplicates its contents and divides to produce two new daughter cells. • Muscle and nerve cells do not typically divide The length of the cell cycle differs. at all in the adult human. The length of the cell cycle differs. • Liver cells divide once every year or so. The price you pay - stages of alcohol-induced liver damage Fatty Liver Liver Fibrosis Cirrhosis Deposits of fat cause liver enlargement. Strict abstinence can lead to a full recovery. Scar tissue forms. Recovery is possible, but scar tissue remains. Growth of connective tissue destroys liver cells. Damage is irreversible. • Epithelial cells lining the gut divide more than once a day. Chapter 9 Cellular Reproduction 9.1 Cellular Growth Interphase is the stage during which the cell grows, carries out cellular functions, and replicates DNA. Cell Division (mitosis) is the stage of the cell cycle during which the cell’s nucleus and nuclear material divide. Cytokinesis is the method by which a cell’s cytoplasm divides, creating a new cell. 9.1 Cellular Growth The Stages of Interphase The first stage of interphase, G1 The cell is growing, carrying out normal cell functions, and preparing to replicate DNA. Chapter 9 Cellular Reproduction 9.1 Cellular Growth The Second Stage of Interphase, S The cell copies its DNA in preparation for cell division. Chapter 9 Cellular Reproduction 9.1 Cellular Growth The Third Stage of Interphase, G2 The cell prepares for the division of its nucleus. Chromosomes • Carriers of genetic material found in nucleus • Made up of DNA • Information is copied and passed to future generations • Usually DNA exists as chromatin which is long, winding strands which condense into chromosomes before dividing Chromosome structure • Chromosomes are made up of two chromatids which are held together with a centromere • Human chromosome number is 46 in body cells (diploid); 23 in sex cells (haploid) Replicated chromosomes remain bound together = sister chromatids. Chapter 9 Cellular Reproduction 9.3 Cell Cycle Regulation Normal Cell Cycle Cell regulator Chemical signal telling the cell to divide Cyclins • Cyclins bind to enzymes to control the cell cycle • Different cyclins and cyclin-dependent kinases control the steps of the cell cycle Cell Division • Cell cycle consists of three main stages: ▫ Interphase ▫ Mitosis ▫ Cytokinesis • Mitosis has four phases: ▫ ▫ ▫ ▫ Prophase Metaphase Anaphase Telophase Prophase • Longest phase of mitosis • Chromatin coils into chromosomes • The nucleus disappears • Centrioles form and move to opposite poles of cell • Spindle fibers form from centrioles and begins to cross cell Metaphase • Chromosomes line up in the middle of the cell • Spindle now forms across the cell • Spindle fibers attach to centromere Anaphase • Spindle fibers begin to shorten • This pulls chromosomes apart • Now the chromosome halves are referred to as chromatids Telophase • Chromatids reach poles • Chromosomes unwind into chromatin • Spindle fibers break down • Nucleolus and nucleus re-form • Plasma membrane begins to pinch in (in animal cells) Cytokinesis The cytoplasm divides • Animal Cell ▫ DNA spreads out ▫ 2 nuclei form ▫ Cell membrane pinches in to form the 2 new daughter cells • Plant Cell ▫ DNA spreads out ▫ 2 nuclei form ▫ Cell plate forms between two nuclei to form the 2 new daughter cells Cytokinesis: Plant v. Animal Cleavage furrow in animal cell Cell plate in plant cell Animal Cell Reproduction (Mitosis) Plant Cell Reproduction (Mitosis) Chapter 9 Cellular Reproduction 9.3 Cell Cycle Regulation Abnormal Cell Cycle: Cancer Cancer is the uncontrolled growth and division of cells. Cancer cells can kill an organism by crowding out normal cells, resulting in the loss of tissue function. Cancer • The changes that occur in the regulation of cell growth and division of cancer cells are due to mutations. • Carcinogens are substances and agents that are known to cause cancer Apoptosis • Programmed cell death • Occurs in trees cutting off a leaf • Occurs in the development of hands and feet (cells grow in the space between the fingers, they then die)