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| Why don't cells grow indefinitely? | 1) the larger the cell, the more demands placed on its DNA; 2) The cell has more trouble moving enough nutrients and wastes across the cell membrane. |
| How to you calculate surface area? | length X width X number of sides |
| When the length of a cell increases, what happens to the volume? | The volume increases faster than does the surface area. (See chart pg. 243) |
| As the volume of a cell increases, what happens to the ratio of surface area to volume of the cell? | The ratio of surface area to volume decreases. (242-243)...think of the street analogy in your book: even when population in a town increases, the main road remains the same size, so people encounter more traffic. In a cell, the area for diffusion decreases, so it can't get all the nutrients in and wastes out. |
| Before a cell divides, what important thing occurs? | The cell replicates (copies) all of its DNA. Thus, when the cell divides, each cell gets one set of genetic information. |
| When eukaryotic cells divide, there are two important stages. Name both. | 1) mitosis: division of the cell nucleus; 2) cytokinesis: division of the cytoplasm. |
| Is reproduction by mitosis sexual or asexual? | It's asexual because the cells produced by mitosis are genetically identical to the parent cell. (Review: asexual reproduction is the process by which one parent reproduces by itself.) |
| In humans, when does mitosis start? | It begins shortly after the egg is fertilized. |
| What is the composition of chromosomes? | They're made up of DNA (genetic information) and proteins. |
| How many chromosones do humans have? | 46 |
| What are chromatids? | They're identical "sister" parts of a duplicated chromosome. |
| What is a centromere? | It is the area where the chromatids of a chromosome are attached. (Picture on 244) |
| What are the BASIC EVENTS (not the 4 phases) that occur during the cell cycle? | The cell grows, prepares for division, and divides to form 2 daughter cells, each of which starts the cycle again. |
| What are the 4 phases of the cell cycle? | first 3 are INTERPHASE: G1: cell does most of its growing & synthesizes new proteins & organelles; S phase: chromosome replication or synthesis; G2: the shortest phase where many organelles & molecules needed for cell division are produced. These are followed by the M phase: mitosis & cytokinesis [Mitosis consists of prophase, metaphase, anaphase, telophase (when cytokinesis usually occurs, too)] |
| What happens during prophase? | It's the first and longest phase of mitosis (see 246 for picture) The chromosomes become visible & the centrioles (2 tiny structures in cytoplasm near the nuclear envelope) separate, taking up positions at opposite sides of the nucleus. A spindle (located in the area called the centrosome) helps separate the chromosomes. The condensed chromosomes become attached to fibers in the spindle at a point near the centromere of each chromatid. Near the end of prophase, the chromosomes coil more tightly; the nucleolus disappears, and the nuclear envelope breaks down. |
| What occurs during metaphase? | It lasts a short time, and the chromosomes line up across the center of the cell; microtubules connect the centromere (area where chromatids are attached) of each chromosome to the 2 poles of the spindle. (See 247 picture!) |
| What happens during anaphase? | During the 3rd stage of mitosis, the centromeres that are joining the sister chromatids split; so there are now 2 individual chromosomes. These move until they have separated into 2 groups near the poles of the spindle. Anaphase ends once chromosomes are no longer moving. |
| What happens in telophase? | During the 4th stage of mitosis, the chromosomes start to disperse into a tangle of dense material at opposite ends of the cell; they lose their distinct shapes, and 2 new nuclear envelopes form around each cluster of chromosomes. The spindle starts to break apart, and the nucleolus is visible in each daughter nucleus. |
| In the final state of human cell division, cytokinesis, what happens? | The cytoplasm "pinches" in half, and each daughter cell has an identical set of duplicate chromosomes. |
| Give examples of human cells that do not divide once developed. | Most muscle & nerve cells do not divide once developed. |
| Give examples of human cells that grow and divide rapidly throughout life. | Skin cells, digestive tract cells, cells in the bone marrow that make blood cells. |
| What happens when cells come into contact with other cells? | They stop growing (unless they are given more space, in which casse they start dividing again.) |
| In eukaryotic cells, what regulates the timing of the cell cycle? | It's regulated by proteins called cyclins. |
| What 2 scientists discovered "cyclin"? | Tim Hunt of Great Britain & Mark Kirschner of the U.S. |
| What are internal regulators & what do they do? | Proteins that allow the cell cycle to continue ONLY when certain processes have happened within the cell (Examples on 251). |
| What are external regulators & what do they do? | Proteins that direct cells to speed up or slow down the cell cycle. Growth regulators are among the most important during embryonic development & wound healing. |
| What do cancer cells lack that allow them to continue developing? | They lack responses to the signals that regulate the growth of most cells. Thus, they divide uncontrollably, forming tumors that damage surrounding tissues. They can break lose and spread throughout the body, too. |
| What is ONE of the genes that is defective in many types of cancer? | Gene p53 usually halts the cell cycle until all chromosomes have been properly replicated. Defective p53 genes cause cells to lose the information needed to respond to signals that normally control their growth. |
| What are stem cells? | They are unspecialized cells that have the potential to become specialized in structure & function into a wide variety of cell types. In early embryonic development, stem cells produce every tissue in the body. Some stem cells are also found in adults. |
| How can stem cells help people injured by disease or injury? | It is thought that implants of stem cells will help healing. Stem cells are capable of growing into various types of tissues. |
| What are some problems associated with stem cell research? | 1) Obtaining & using cells taken from human embryos is controversial; 2) rejection problems in a recipient must be dealt with; 3) more research involving adult, human stem cells must be done. |
