UNIT 3: CELL REPRODUCTION

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1 UNIT 3: CELL REPRODUCTION What are Chromosomes? Cell structures that contain genetic material. Where are they found? Found inside a cell, inside the nucleus.

2 VOCABULARY Somatic cells (body cells) Sex cells (gametes) Haploid Diploid Chromosomes Chromatin Centrioles Spindle fibers Mitosis Cytokinesis Meiosis all cells in body except egg and sperm sperm cells and egg cells only Having a single set of chromosomes. A result of MEIOSIS. Only SPERM and EGG cells are HAPLOID. In humans = 23 chromosomes. Having two sets of chromosomes. A result of MITOSIS. Only BODY CELLS are DIPLOID. In humans = 46 chromosomes. A cellular structure that contains DNA Coiled chromosomes that are unable to be seen individually (clump of spaghetti) Organelle that forms the spindle fibers Fibers that guide the movement of the chromosomes during mitosis is the process in which the cell divides to form two identical cells. completes the cell division process by dividing the cytoplasm into two daughter cells, each with its own nucleus process of cell division where the number of chromosomes are cut in

3 cancer half. Uncontrolled cell division What is the Cell Cycle? A series of events that takes place in a cell leading to its division and duplication... Interphase: This part of the cell s life cycle occupies most of the cell s "life". At this phase the cell grows and carries out all of its activities. Mitosis: is the process in which the cell divides to form two identical cells. This portion of the cycle may last only hours while the whole cycle can last for weeks.

4 MITOSIS is how ONE cell becomes TWO! Each minute your body needs to make...oh...about 300 MILLION NEW CELLS! Cells wear out, break down and suffer injuries. As organisms grow and change, they need new cells to make more skin tissue, bone tissue, muscle tissue. These new cells can only come from one place: OTHER CELLS - through the process of cell division, or mitosis. INTERPHASE Chromatin is present, individual chromosomes cannot be seen yet. Chromosomes duplicate PROPHASE Chromatin condenses enough to see individual chromosomes. Nuclear membrane breaks down. Spindle fibers begin to form from the centrioles. METAPHASE Chromosomes attach to the spindle fibers. Chromosomes line up

5 in the middle of the cell. There is no nucleus. ANAPHASE Duplicated chromosomes split in half. Pulled towards opposite poles of the cell. TELOPHASE Chromosomes at opposite ends of cell. TWO nuclear membranes form around chromosomes. Chromosomes begin to coil back into chromatin. CYTOKINESIS Completes the cell division process by dividing the cytoplasm into two daughter cells, each with its own nucleus Mitosis in a plant cell occurs differently by forming a cell plate that grows into a cell wall. MITOSIS. Who does it? All SOMATIC cells (body cells)

6 Type of reproduction? Asexual Reproduction How many cells are there when process is done? 2 Are the two daughter cells identical? YES (They are DIPLOID, meaning 2 sets of chromosomes, one from mom and one from dad) SIMULATION:

7 CANCER What is cancer? Uncontrolled cell division. Cancer is essentially a disease of mitosis. Why? Often this is because of a change in function or a DNA mutation that occurs in one of several genes that normally function to control growth. Cancer Growth Animation View the cancer growth animation by clicking on the link Answer the following questions from the animation 1. What type of cancer is studied in the animation and where does it form? Carcinoma 2. How many cells are in the human body? 30 trillion!!!!!!!! 3. Identify two things that can cause mutation? 1. Mis- copying during mitosis 2. Environmental exposure to carcinogens ( cancer causing chemicals/toxins)4. Why do normal cells usually reproduce? To replace old, damaged, or injured cells.

8 MEIOSIS is a process of cell division by which the number of chromosomes is cut in half. Why? Meiosis process of nuclear division where the number of the chromosomes is halved. produces 4 daughter cells all daughter cells are haploid chromosomes are shuffled in the process, so that each daughter cell has a unique combination used to create SEX CELLS ONLY (gametes) (sperm and egg)

9 COMPARISON OF MITOSIS AND MEIOSIS Characteristic Mitosis Meiosis Number of daughter cells Number of cell divisions Daughter cells are diploid or haploid Daughter cells are identical or different from parent cells Parent cells are diploid or haploid Diploid Identical Diploid Haploid Different Diploid When is it used? Body cells Sex cells (gametes)

10 DNA What is it? A molecule that contains an organism s genetic code What does it stand for? Deoxyribose Nucleic Acid Where is it found? Cell Nucleus Chromosome Gene DNA What type of ORGANIC compound is it? Nucleic Acid What does it do? It makes us who we are. It can be referred to as the blueprint for life because ALL the instructions or directions for making an organism are found within DNA. What does it look like? A twisted ladder, called a double helix A Little History For many years, the structure of a DNA molecule was a puzzle to scientists. In the 1950 s, two scientists deduced the structure while experimenting with chemical models. They later won a Nobel Prize for helping to solve this DNA puzzle.

11 THE STRUCTURE OF DNA DNA is a molecule that is made up of many repeating units called NUCLEOTIDES. Nucleotide + Nucleotide + Nucleotide + Nucleotide = DNA Monomer + Monomer + Monomer + Monomer = Polymer All the nucleotides are composed of three parts. 1. Phosphate group 2. Sugar group called dexoyribose 3. Nitrogen base group (A,T,C,G) There are 4 different kinds of nucleotides found in DNA. Phosphate, Sugar, Nitrogen Base Adenine (A) Phosphate, Sugar, Nitrogen Base Guanine (G) Phosphate, Sugar, Nitrogen Base Thymine (T) Phosphate, Sugar, Nitrogen Base Cytosine (C) All nucleotides have all 3 parts

12 Remember these nucleotides are molecules made from many elements. So their chemical structure really looks something like this: When the 4 nucleotides are strung together in repeating units in various orders, a double stranded molecule of DNA results. Double Helix (Twisted Ladder) The sides of the ladder are made up of repeating phosphates and sugars. The rungs of the ladder are made up of the nitrogen bases.

13 Base Pair Rule: Scientists noticed that the nitrogen bases always pair up with another particular nitrogen base. Adenine pairs up with Thymine Guanine pairs up with Cytosine To help you remember: ALL TEACHERS GO CRAZY The nitrogen bases of each nucleotide are bonded by a very weak bond called a hydrogen bond. Vocabulary DNA Nucleotide Mutation A molecule that contains an organism s genetic code The basic unit of DNA that consist of a sugar, a phosphate, and a nitrogen base. A change in DNA

14 DNA REPLICATION Recall that when a cell is preparing for cell division the chromosomes or the DNA is copied in interphase of the cell cycle. The process of copying a cell s DNA before cell division is called DNA replication. 1. The Double helix unwinds by an enzyme DNA helicase. It breaks the hydrogen bonds between the nitrogen bases. 2. An enzyme called DNA polymerase move along the DNA strand adding new nitrogen bases or (nucleotides) following the BASE-PAIR RULE. 3. The end result is two separate, identical DNA molecules. DNA Replication is semiconservative. That means when a copy is made, one half of the old strand is always kept attached to the new strand. This helps to reduce the number of copy errors (mutations). Each side of the DNA molecule is complementary to the other side. Meaning the base-pair rule is always followed. In picture: BLACK STRAND = New strand WHITE STRAND = Old strand Mutation