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Unit 6: cell division. liver cell undergoing cell division splits into two daughter cells. 1 All organisms, including humans, have the ability to regenerate something in the body. Cells must divide and specialize to replace a lost limb or to repair damaged tissue. Chapter 10 Mystery.
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Unit 6: cell division liver cell undergoing cell division splits into two daughter cells
1 All organisms, including humans, have the ability to regenerate something in the body. Cells must divide and specialize to replace a lost limb or to repair damaged tissue. Chapter 10 Mystery
2 How do living things grow? By increasing cell number, not cell size. For instance, how many cells did you personally start out as? And how many do you have now?
3 Cell Growth – why do cells have a limit to how large they can grow? • The nucleus is not big enough to control a bigger cell. Remember, it has the instructions for all of the cell’s functions. Ex. Rome was too far away from the borders of its empire to effectively control it, and it eventually fell.
4 Limit to Cell Growth Continued • The cell membrane’s surface area is not large enough to get food and oxygen in and to expel waste for a bigger cell. Problem: The cell membrane (surface area) increases slower than the volume. So, when looking at surface to volume ratio, we need enough surface area to meet the cell’s needs, so cells need to be small.
6 Cell Division So, since the cells have a limit to how big they can grow, cells must divide in order for an organism to grow, develop, repair, and reproduce. Cell Division is the process by which one cell divides to create two daughter cells. These two daughter cells will be identical to the parent cell.
7 What very important step must occur prior to cell division? • cell replicates, or copies, all of its DNA so that each daughter cell will get one complete set of genetic information • Chromosomes – genetic information bundled into packages of DNA
8 prokaryotic chromosomes Bacteria have no nucleus and a single, circular DNA chromosome.
10 Eukaryotic chromosomes chromosomes are neat packages of DNA that make it easier to divide up
11 Chromatin versus Chromatids • Chromatin is relaxed DNA that is wrapped around proteins called histones. • Before cell division, the chromatin is copied. • When the histones start to coil together, they form nucleosomes. • Once the whole strand is coiled, it forms a chromatid. • This condensing allows it to be more organized during division so that the DNA is equally divided.
13 chromosome number • species specific • fruit flies - 8 • human cells - 46 • carrot cells – 18 • Gorillas – 48 • Chimps - 48
14 eukaryote cell cycle The Cell Cycle describes the series of events as a cell grows and divides. During the cycle, a cell grows, prepares for division, and divides to form two daughter cells.
15 Interphase Period growth that occurs before cell division. Divided into three phases: G1 phase: cell increases in size and makes proteins and organelles S phase: DNA is copied G2 phase: organelles and molecules needed for cell division are made. Interphase is the longest phase of the cell cycle, with G2 being the shortest of the three. G is for “gap” and S if for “synthesis.”
16 M Phase The M Phase is cell division, and is broken down into two stages. The first stage is Mitosis, the division of the nucleus and its contents, which is broken down into four stages. The second stage is Cytokinesis, the division of the cytoplasm and organelles. May overlap with last phases of Mitosis
17 Prophase – 1st phase of Mitosis Chromatin in the nucleus condenses and becomes visible. A spindle of microtubules begins to form outside the nucleus. It grows between the two sets of centrioles in animal cells. Nucleolus disappears, and nuclear envelope breaks down. Prophase is the longest phase of Mitosis and takes half of the time required for Mitosis.
18 Metaphase – 2nd phase of mitosis Centrosomes (area around the centrioles where spindle originates) are not at the poles of the cell (opposite ends) Centromeres of each chromosome are attached to the spindle, and they are lined up on the equator of the cell Shortest phase of Mitosis.
19 centrioles – centrosomeasters, polar fibers, kinetochore fibers
20 Anaphase – 3rd phase of Mitosis The sister chromatids separate, and each chromatid is now a separate chromosome. Sister chromatids are pulled by the spindle to opposite ends of the cells towards the centrosome.
21 Telophase – 4th phase of Mitosis Chromosomes begin to detangle into chromatin. Nuclear envelope reforms around the two clusters of chromosomes and nucleolus reappears. Spindle breaks down. Mitosis is now complete, but we are still in the M Phase. Cytokinesis, which happens next, may already be started during telophase.
22 Cytokinesis in Animal Cells Follows Mitosis, last stage of the cell cycle. Cell membrane is drawn inward, creating a cleavage furrow. As they pinch off, cytoplasm and organelles are divided among the two daughter cells.
23 Cytokinesis in Plant Cells Since cell membrane cannot fold in, a cell plate forms down the middle between the two nuclei. This cell plate will develop into the cell membrane and then the cell wall.
