Cell Reproduction Chapter 10, 11-4 Cells Grow! • Living organisms are made of cells. Like living organism, cells also go through periods of growth, and ultimately divide to produce more cells. • Cell growth is limited by: – DNA overload – Information/material exchange Cell Division • Chromosomes: – Condensed chromatin – During the cycle of a cell, chromosomes appear as X during mitosis. – These X-shaped chromosomes are made up of a pair of identical chromosomes, each called a Chromatid. – The chromatid are attached at a point called the Centromere. • During the life of a cell it follows a number of set steps that occur. These steps are called the Cell Cycle. Chromosomes • Each organism has a set number of chromosomes in its cells. – Humans for example have 46 chromosomes – Flies have 8 • There are 2 types of cells: – Autosomal: Non-sex cells. The cells in the rest of the body. – Gamete: Cells involved in sexual reproduction. • Haploid vs. Diploid – The total number of chromosomes in these 2 types of cells differ. In autosomal cells 2 sets of chromosomes exist. – In the sex cells (gametes) only 1 set of chromosomes exist. Chromosomes • In Humans: • 23 unique chromosomes (Haploid number = 23) – In autosomal cells: 46 chromosomes total OR 2 pairs of the 23 unique chromosomes. – In gametes 1 set of the unique 23 chromosomes. Cell Cycle • 2 Major phases to the Cell Cycle: • Occurs in somatic cells of organisms. – Interphase: “inbetween” period – Mitosis – period of cell division • The result of the cell cycle are 2 identical cells called daughter cells. Cell Cycle • Mitosis and Interphase have subphases. In these subphases specific events occur. • Ultimately there needs to be an equal division of the cell contents in order to produce 2 healthy cells. Mitosis • Mitosis begins with one adult cell. • Through a series of steps, this adult cell spits into 2 identical daughter cells. Interphase • Has 3 major subphases. • G1, S, and G2 Interphase • In G1 of Interphase the cell grows normally and performs its regular functions • In the S phase the DNA is replicated (double the DNA) • In G2 the cell makes ready to divide. Mitosis • Within the mitosis phase, there are 4 major subphases. • Each phase is clearly visible and has defining features. Prophase • This is the longest of the 4 mitosis phases. • In animal cells the centrosomes form on either side of the chromosomes. • Spindles (microtubules) attach the chromosomes to the centrosomes • The chromatin condenses to chromosomes. • The nuclear envelope and nucleolus disappear. Metaphase • Most obvious of the mitosis phases. • Chromosomes line up in the center of the cell (called metaphase plate). • Each chromosome is attached by spindle fibers to both centrosomes. Anaphase • The sister chromatids are separated by the pulling centromeres. • The chromosomes continue to move until they reach opposite polls of the cell. Telophase • The daughter cells begin to separate along the metaphase plate. • The chromosomes disperse into chromatin. • Meanwhile, the nuclear envelop begins to reform. As does the nucleolus. • The spindle fibers start to break apart. Cytokinesis • Occurs during Telophase! • Animal Cells – cell membrane pinches inwards • Plant Cells – Cell plate is formed from Golgi in cell membrane – Cell wall forms between this • Cell Plate Formation Regulating the Cell Cycle • Controls of Cell Cycle: – Cells can only divide a certain number of times. – Cells stop dividing when they come in contact with other cells (Known as Contact Inhibition). Regulation of Cell Cycle • Regulators of the Cell Cycle • A group of proteins known as cyclins regulate the timing of the events of the cell cycle. – Internal Regulators: proteins within the cell that respond to events, such as DNA replication, alignment of chromosomes. – External Regulators: proteins that respond to events outside the cell. Signal the cell to speed or slow down the cycle. Cancer • When cell cycle regulation goes wrong, the result is the formation of cancer. • Cancer cells are those that continuously divide, and ignore Cell Cycle regulation signals. • Cancer is caused by altering the regulators of the cell cycle. Many substances such as tobacco smoking, virus infections and radiation have lead to disruption of growth controlling proteins. Cancer • Cancer is caused by a number of mutations within a cell. It is not a one hit wonder!