Slide 2:Chapter: Cell Reproduction Table of Contents Section 3: DNA Section 1: Cell Division and Mitosis Section 2: Sexual Reproduction and Meiosis


Slide 3:Many organisms start as just one cell. That cell divides and becomes two, two become four, four become eight, an so on. Many-celled organisms, including you, grow because cell division increases the total number of cells in an organism. Why is cell division important? Cell Division and Mitosis 1


Slide 4:Even after growth stops, cell division is still important. Every day, billions of red blood cells in your body wear out and are replaced. During a few seconds, your bone marrow produced about six million red blood cells. Why is cell division important? Cell Division and Mitosis 1 Cell division is important to one-celled organisms, too—it’s how they reproduce themselves.


Slide 5:A living organism has a live cycle. A life cycle begins with the organism’s formation, is followed by growth and development, and finally ends in death. Individual cells also have life cycles. The Cell Cycle Cell Division and Mitosis 1 Click image to view movie.


Slide 6:The cell cycle is a series of events that takes place from one cell division to the next. The time is takes to complete a cell cycle is not the same in all cells. Length of Cycle Cell Division and Mitosis 1


Slide 7:Most of the life of any eukaryotic cell—a cell with a nucleus—is spent in a period of growth and development called interphase. Cells in your body that no longer divide, such as nerve and muscle cells, are always in interphase. Interphase Cell Division and Mitosis 1 During interphase, a cell duplicates its chromosomes and prepares for cell division.


Slide 8:Before a cell divides, a copy of the hereditary material must be made so that each of the two new cells will get a complete copy. Each cell needs a complete set of hereditary material to carry out life functions. Interphase Cell Division and Mitosis 1


Slide 9:Interphase Cell Division and Mitosis 1 After interphase, cell division begins. The nucleus divides, and then cytoplasm separates to form two new cells.


Slide 10:Mitosis (mi TOH sus) is the process in which the nucleus divides to form two identical nuclei. Each new nucleus also is identical to the original nucleus. Mitosis Cell Division and Mitosis 1 Mitosis is described as a series of phases, or steps. The steps of mitosis in order are named prophase, metaphase, anaphase, and telophase.


Slide 11:A chromosome (KROH muh sohm) is a structure in the nucleus that contains hereditary material. Steps of Mitosis Cell Division and Mitosis 1


Slide 12:During interphase, each chromosome duplicates. Steps of Mitosis Cell Division and Mitosis 1


Slide 13:Steps of Mitosis Cell Division and Mitosis 1


Slide 14:During prophase, the pairs of chromatids are fully visible when viewed under a microscope. The nucleolus and the nuclear membrane disintegrate. Steps of Mitosis Cell Division and Mitosis 1 Two small structures called centrioles (SEN tree olz) move to opposite ends of the cell.


Slide 15:Between the centrioles, threadlike spindle fibers begin to stretch across the cell. Plant cells also form spindle fibers during mitosis but do not have centrioles. Steps of Mitosis Cell Division and Mitosis 1


Slide 16:In metaphase, the pairs of chromosomes line up across the center of the cell. The centromere of each pair usually becomes attached to two spindle fibers—one from each side of the cell. Steps of Mitosis Cell Division and Mitosis 1


Slide 17:In anaphase, each centromere divides and the spindle fibers shorten. Each pair of chromatids separates, and chromatids begin to move to opposite ends of the cell. Steps of Mitosis Cell Division and Mitosis 1 The separated chromatids are now called chromosomes.


Slide 18:In the final step, telophase, spindle fibers start to disappear, the chromosomes start to uncoil, and a new nucleus forms. Steps of Mitosis Cell Division and Mitosis 1


Slide 19:For most cells, after the nucleus has divided, the cytoplasm separates and two new cells are formed. Division of the Cytoplasm Cell Division and Mitosis 1 In animal cells, the cell membrane pinches in the middle, like a balloon with a string tightened around it, and the cytoplasm divides.


Slide 20:In plant cells, the appearance of a cell plate tells you that the cytoplasm is being divided. Division of the Cytoplasm Cell Division and Mitosis 1 New cell walls form along the cell plate, and new cell membranes develop inside the cell walls.


Slide 21:Results of Mitosis Cell Division and Mitosis 1 Mitosis is the division of the nucleus, and it produces two new nuclei that are identical to each other and the original nucleus.


Slide 22:Results of Mitosis Cell Division and Mitosis 1 Each new nucleus has the same number and type of chromosomes. Every cell in your body, except sex cells, has a nucleus with 46 chromosomes—23 pairs.


Slide 23:Each of the trillions of cells in your body, except sex cells, has a copy of the same hereditary material. Results of Mitosis Cell Division and Mitosis 1 Allows growth and replaces worn out or damaged cells.


Slide 24:In asexual reproduction, a new organism (sometimes more than one) is produced from one organism. Asexual Reproduction Cell Division and Mitosis 1 The new organism will have hereditary material identical to the hereditary material of the parent organism.


Slide 25:Organisms with eukaryotic cells asexually reproduce by cell division. Cellular Asexual Reproduction Cell Division and Mitosis 1 However, bacteria do not have a nucleus so they can’t use mitosis. Instead, bacteria reproduce asexually by fission. During fission, an organism whose cells do not contain a nucleus copies its genetic material and then divides into two identical organisms.


Slide 26:Budding is a type of asexual reproduction made possible because of cell division. Budding and Regeneration Cell Division and Mitosis 1 When the bud on the adult becomes large enough, it breaks away to live on its own.


Slide 27:Some organisms can regrow damaged or lost body parts. Budding and Regeneration Cell Division and Mitosis 1 Regeneration is the process that uses cell division to regrow body parts. Sponges, planaria, sea stars, and some other organisms can use regeneration for asexual reproduction.


Slide 28:Section Check Question 1 Answer Many-celled organisms grow by _______. The answer is cell division. Cell division increases the total number of cells in an organism. 1


Slide 29:Section Check Question 2 What is the longest part of the cell cycle? 1


Slide 30:Section Check Answer The answer is interphase. Interphase is the period of growth and development in a eukaryotic cell. 1


Slide 31:Section Check Question 3 Answer _______ is the process in which the nucleus divides to form two identical nuclei. The answer is mitosis. Each new nucleus that is produced is identical to the original nucleus. 1


Slide 32:Sexual Reproduction During sexual reproduction, two sex cells, sometimes called an egg and a sperm, come together which is called fertilization.. Sex cells are formed from cells in reproductive organs. Sperm are formed in the male reproductive organs. Sexual Reproduction and Meiosis 2 Eggs are formed in the female reproductive organs.


Slide 33:Sexual Reproduction The joining of an egg and a sperm is called fertilization, and the cell that forms is called a zygote (ZI goht). Following fertilization, cell division begins. A new organism with a unique identity develops. Sexual Reproduction and Meiosis 2


Slide 34:Diploid Cells A typical human body cell has 46 chromosomes. Each chromosome has a mate that is similar to it in size and shape and has similar DNA. Sexual Reproduction and Meiosis 2 Human body cells have 23 pairs of chromosomes. When cells have pairs of similar chromosomes, they are said to be diploid (DIH ployd).


Slide 35:Haploid Cells Because sex cells do not have pairs of chromosomes, they are said to be haploid (HA ployd). Sexual Reproduction and Meiosis 2 They have only half the number of chromosomes as body cells. Haploid means “single form.” Human sex cells have only 23 chromosomes—one from each of the 23 pairs of similar chromosomes.


Slide 36:Meiosis and Sex Cells A process called meiosis (mi OH sus) produces haploid sex cells. Sexual Reproduction and Meiosis 2


Slide 37:Meiosis and Sex Cells Sexual Reproduction and Meiosis 2 Meiosis ensures that the offspring will have the same diploid number as its parent.


Slide 38:Meiosis and Sex Cells Sexual Reproduction and Meiosis 2


Slide 39:Meiosis and Sex Cells During meiosis, two divisions of the nucleus occur. These divisions are called meiosis I and meiosis II. Sexual Reproduction and Meiosis 2


Slide 40:Meiosis and Sex Cells Sexual Reproduction and Meiosis 2 The steps of each division have names like those in mitosis and are numbered for the division in which they occur.


Slide 41:Meiosis I Before meiosis begins, each chromosome is duplicated, just as in mitosis. Sexual Reproduction and Meiosis 2


Slide 42:Meiosis I Sexual Reproduction and Meiosis 2 When the cell is ready for meiosis, each duplicated chromosome is visible under the microscope as two chromatids.


Slide 43:Meiosis I The events of prophase I are similar to those of prophase in mitosis. Sexual Reproduction and Meiosis 2 In meiosis, each duplicated chromosome comes near its similar duplicated mate. In mitosis they do not some near each other.


Slide 44:Meiosis I In metaphase I, the pairs of duplicated chromosomes line up in the center of the cell. Sexual Reproduction and Meiosis 2 The centromere of each chromatid pair becomes attached to one spindle fiber, so the chromatids do not separate in anaphase I.


Slide 45:Meiosis I In anaphase I, the two pairs of chromatids of each similar pair move away from each other to opposite ends of the cell. Sexual Reproduction and Meiosis 2 Each duplicated chromosome still has two chromatids.


Slide 46:Meiosis I In telophase I, the cytoplasm divides, and two new cells form. Sexual Reproduction and Meiosis 2 Each new cell has one duplicated chromosome from each similar pair.


Slide 47:Meiosis II The two cells formed during meiosis I now begin meiosis II. Sexual Reproduction and Meiosis 2


Slide 48:Meiosis II Sexual Reproduction and Meiosis 2 The chromatids of each duplicated chromosome will be separated during this division.


Slide 49:Meiosis II In prophase II, the duplicated chromosomes and spindle fibers reappear in each new cell. Sexual Reproduction and Meiosis 2


Slide 50:Meiosis II In metaphase II, the duplicated chromosomes move to the center of the cell. Sexual Reproduction and Meiosis 2 Unlike what occurs in metaphase I, each centromere now attaches to two spindle fibers instead of one.


Slide 51:Meiosis II The centromere divides during anaphase II, and the chromatids separate and move to opposite ends of the cell. Sexual Reproduction and Meiosis 2 Each chromatid now is an individual chromosome.


Slide 52:Meiosis II As telophase II begins, the spindle fibers disappear, and a nuclear membrane forms around the chromosomes at each end of the cell. Sexual Reproduction and Meiosis 2 When meiosis II is finished, the cytoplasm divides.


Slide 53:Summary of Meiosis Sexual Reproduction and Meiosis 2 Remember that meiosis produces haploid sex cells. Click box to view movie.


Slide 54:Mistakes of Meiosis Meiosis occurs many times in reproductive organs. Sexual Reproduction and Meiosis 2 Mistakes can produce sex cells with too many or too few chromosomes.


Slide 55:Mistakes of Meiosis Sometimes, zygotes produced from these sex cells die. Sexual Reproduction and Meiosis 2 If the zygote lives, every cell in the organism that grows from that zygote usually will have the wrong number of chromosomes. Organisms with the wrong number of chromosomes may not grow normally.


Slide 56:Section Check Question 1 Answer _______ is the joining of an egg and a sperm. The answer is fertilization. Fertilization occurs during sexual reproduction. 2


Slide 57:2 Section Check Question 2 _______ and _______ are the two types of cells your body forms. A. body and sex B. egg and sperm C. meiosis and mitosis D. zygote and embryo


Slide 58:2 Section Check Answer The answer is A. Egg cells and sperm cells are both types of sex cells.


Slide 59:2 Section Check Question 3 Which best describes the sperm and egg?


Slide 60:2 Section Check A. typical body cells B. haploid cells C. zygotes D. diploid cells


Slide 61:2 Section Check Answer The answer is B. Sperm and eggs are sex cells that do not have pairs of chromosomes.


Slide 62:What is DNA? A cell uses a code in its hereditary material. The code is a chemical called deoxyribonucleic (dee AHK sih ri boh noo klay ihk) acid, or DNA. It contains information for an organism’s growth and function. DNA 3


Slide 63:What is DNA? DNA is stored in cells that have a nucleus. When a cell divides, the DNA code is copied and passed to the new cells. DNA 3 In this way, new cells receive the same coded information that was in the original cell.


Slide 64:DNA’s Structure In 1952, scientist Rosalind Franklin discovered that DNA is two chains of molecules in a spiral form. DNA 3 In 1953, scientists James Watson and Francis Crick made a model of a DNA molecule. The structure of DNA is similar to a twisted ladder.


Slide 65:A DNA Model According to the Watson and Crick DNA model, each side of the ladder is made up of sugar-phosphate molecules. DNA 3 Each molecule consists of the sugar called deoxyribose (dee AHK sih ri bohs) and a phosphate group.


Slide 66:A DNA Model The rungs of the ladder are made up of other molecules called nitrogen bases. DNA 3


Slide 67:A DNA Model DNA 3


Slide 68:A DNA Model DNA 3 The bases are represented by the letters A, G, C, and T.


Slide 69:A DNA Model The amount of cytosine in cells always equals the amount of guanine, and the amount of adenine always equals the amount of thymine. DNA 3 Adenine always pairs with thymine, and guanine always pairs with cytosine.


Slide 70:Copying DNA When chromosomes are duplicated before mitosis or meiosis, the amount of DNA in the nucleus is doubled. DNA 3 The two sides of DNA unwind and separate.


Slide 71:Copying DNA DNA 3 Each side then becomes a pattern on which a new side forms. The new DNA has bases that are identical to those of the original DNA and are in the same order.


Slide 72:Genes Most of your characteristics, such as the color of your hair, your height, and even how things taste to you, depend on the kinds of proteins your cells make. DNA 3 DNA in your cells stores the instructions for making these proteins.


Slide 73:Genes DNA 3 Proteins build cells and tissues or work as enzymes. The instructions for making a specific protein are found in a gene which is a section of DNA on a chromosome.


Slide 74:Making Proteins DNA 3 Genes are found in the nucleus, but proteins are made on ribosomes in cytoplasm. The codes for making proteins are carried from the nucleus to the ribosomes by another type of nucleic acid called ribonucleic acid, or RNA.


Slide 75:Ribonucleic Acid DNA 3 RNA is made in the nucleus on a DNA pattern. However, RNA is different from DNA. RNA is like a ladder that has all its rungs sawed in half. RNA has the bases A, G, and C like DNA but has the uracil (U) instead of thymine (T). The sugar-phosphate molecules in RNA contain the sugar ribose, not deoxyribose.


Slide 76:Ribonucleic Acid DNA 3 The three main kinds of RNA made from DNA in a cell’s nucleus are messenger RNA (mRNA), ribosomal (rRNA), and transfer RNA (tRNA). Protein production begins when mRNA moves into the cytoplasm. There, ribosomes attach to it.


Slide 77:Ribonucleic Acid DNA 3 Ribosomes are made of rRNA. Transfer RNA molecules in the cytoplasm bring amino acids to these ribosomes. Inside the ribosomes, three nitrogen bases on the mRNA temporarily match with three nitrogen bases on the tRNA.


Slide 78:Ribonucleic Acid DNA 3 The same thing happens for the mRNA and another tRNA molecule. The amino acids that are attached to the two tRNA molecules bond. This is the beginning of a protein.


Slide 79:Ribonucleic Acid DNA 3 The code carried on the mRNA directs the order in which the amino acids bond. After a tRNA molecule has lost its amino acid, it can move about the cytoplasm and pick up another amino acid just like the first one. The ribosome moves along the mRNA. New tRNA molecules with amino acids match up and add amino acids to the protein molecule.


Slide 80:Controlling Genes DNA 3 In many-celled organisms like you, each cell uses only some of the thousands of genes that it has to make proteins. Each cell uses only the genes that direct the making of proteins that it needs. For example, muscle proteins are made in muscle cells but not in nerve cells.


Slide 81:Controlling Genes DNA 3 Cells must be able to control genes by turning some genes off and turning other genes on. Sometimes the DNA is twisted so tightly that no RNA can be made. Other times, chemicals bind to the DNA so that it cannot be used. If the incorrect proteins are produced, the organism cannot function properly.


Slide 82:Mutations DNA 3 If DNA is not copied exactly, the proteins made from the instructions might not be made correctly. These mistakes, called mutations, are any permanent change in the DNA sequence of a gene or chromosome of a cell. Outside factors such as X rays, sunlight, and some chemicals have been known to cause mutations.


Slide 83:Results of a Mutation DNA 3 Genes control the traits you inherit. Without correctly coded proteins, an organism can’t grow, repair, or maintain itself. A change in a gene or chromosome can change the traits of an organism.


Slide 84:Results of a Mutation DNA 3 If the mutation occurs in a body cell, it might or might not be life threatening to the organism. If a mutation occurs in a sex cell, then all the cells that are formed from that sex cell will have that mutation. Mutations add variety to a species when the organism reproduces.


Slide 85:Results of a Mutation DNA 3 Many mutations are harmful to organisms, often causing their death. Some mutations do not appear to have any effect on the organism, and some can even be beneficial.


Slide 86:Section Check Question 1 Answer _______ is the chemical code that is stored in the cell’s hereditary material. The answer is deoxyribonucleic acid, or DNA. DNA contains information for an organism’s growth and function. 3


Slide 87:3 Section Check Question 2 Which is not a nitrogen base of DNA? A. adenine B. guanine C. kerosene D. thymine


Slide 88:3 Section Check Answer The answer is C. The forth kind of nitrogen base is cytosine.


Slide 89:3 Section Check Question 3 This illustration represents the production of _______? A. DNA B. genes C. proteins D. RNA


Slide 90:3 Section Check Answer The answer is C. Cells need DNA, RNA, and amino acids to make proteins.


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