1. Cell Division Students: Model the processes involved in cell replication, including but not limited to: Mitosis and meiosis Mitosis Cell division is the process that cells undergo in order to form new cells. Mitosis occurs in somatic (or body) cells for the purpose of growth and repair. This process produces two daughter cells that are genetically identical to the original parent cell. Mitosis involves division of the nucleus (nuclear division) and separation into daughter cells (cytokinesis). When an organism can reproduce via asexual reproduction, it undergoes a process similar to mitosis in order to create a genetically identical version of itself. Can you think of any examples of organisms that reproduce asexually? 1 Mitosis is part of the cell cycle. By Simon Caulton (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons Copyright MATRIX EDUCATION 2019 Page 80 of 309 Our Students Come First!
Can you still remember the stages of mitosis? Watch this brief VIDEO (Length 1:10) as a refresher! Interphase is often included in discussions of mitosis, but interphase is technically not part of mitosis, but rather encompasses stages G1, S, and G2 of the cell cycle. The various stages of mitosis are summarised in the diagram below. By Schemazeichnung_Mitose.svg: *Diagrama_Mitosis.svg: Jpablo cad translation: Matt (talk) Diagrama_Mitosis.svg: juliana osorio derivative work: M3.dahl (Schemazeichnung_Mitose.svg Diagrama_Mitosis.svg) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons Copyright MATRIX EDUCATION 2019 Page 81 of 309 Our Students Come First!
Mitosis vs. Meiosis Before we focus on the process of meiosis and its role in inheritance, we will first revise the differences between mitosis and meiosis. Recall that mitosis is the process of nuclear division required for the formation of new body (or somatic) cells, whereas meiosis is the process of nuclear division required for the formation of new sex cells (or gametes). The following diagrams compare these processes side by side. Mitosis by Mysid - Vectorized in CorelDraw by Mysid from http://www.ncbi.nlm.nih.gov/about/primer/genetics_cell.html., Public Domain, https://commons.wikimedia.org/w/index.php?curid=1414818 Meiosis by Rdbickel - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=49599354 Copyright MATRIX EDUCATION 2019 Page 82 of 309 Our Students Come First!
Use the information in the diagram to help you complete the following table summarising the differences. 2 Mitosis Meiosis Where it occurs What it produces Ploidy of parent cells Ploidy of daughter cells Rounds of nuclear division What it is used for You may want to refer to this ANIMATION that compares mitosis and meiosis side by side. Copyright MATRIX EDUCATION 2019 Page 83 of 309 Our Students Come First!
Meiosis Basics We established that meiosis is the process of nuclear division required for the formation of new sex cells or gametes (eggs and sperm). Why is it important for gametes to be haploid cells? Hint: What would happen if normal diploid cells, with the full complement of chromosomes, were used in fertilisation? 3 Importantly, the process of meiosis results in genetically unique gametes. This occurs due to the processes of crossing over (recombination), random segregation and independent assortment (all of which will be explained by the end of this lesson!). Therefore, meiosis introduces variability into offspring populations i.e. offspring are not identical to their parents. \ The process of meiosis can be divided into two stages of nuclear division: 1. Meiosis I 2. Meiosis II Copyright MATRIX EDUCATION 2019 Page 84 of 309 Our Students Come First!
Meiosis I Meiosis I is quite distinct from mitosis although it is broken into the same four stages (PMAT), many important differences exist. Pay close attention to these differences! Later you will see that meiosis II is actually quite similar to mitosis in its overall process. INTERPHASE Interphase refers to the 'growth phase' of a cell's lifecycle. As you can see in the following diagram, interphase takes up the majority of a cell's lifecycle. In preparation for meiosis I genetic material must be replicated so the daughter cells will have the right number of chromosomes. Is genetic material organised in the form of chromosomes during interphase and DNA replication? 4 Modified from work by Ali Zifan - Own work; Used information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=49630204 Copyright MATRIX EDUCATION 2019 Page 85 of 309 Our Students Come First!
PROPHASE I During prophase I, genetic material condenses into chromosomes. The nuclear envelope and nucleolus disappear, and spindle fibres form and spread across the cell, as shown below. Importantly, pairing homologous of chromosomes occurs this event is called synapsis. Ali Zifan - Own work; Used information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., CC BY- SA 4.0, https://commons.wikimedia.org/w/index.php?curid=49630204 During prophase I, crossing-over may occur. Homologous maternal and paternal chromosomes overlap and sections of genetic material may be swapped between these chromosomes, as shown below. This increases genetic variability because it increases the possible combination of alleles for different traits. That is, it mixes maternal and paternal alleles, resulting in new combinations of traits. By Boumphreyfr - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6925174 Watch this ANIMATION to consolidate your understanding of crossing over. Copyright MATRIX EDUCATION 2019 Page 86 of 309 Our Students Come First!
METAPHASE I Tetrads (pairs of homologous chromosomes) now move to the metaphase plate, halfway between the two poles of the cell. Spindle fibres then attach to the centromeres of each chromosome. Metaphase I of Meiosis Metaphase of Mitosis By Ali Zifan - Own work; Used information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=49630204 How is metaphase I of meiosis different from metaphase of mitosis? 5 ANAPHASE I The cell begins to elongate and sister chromatids from pairs of homologous chromosomes separate together, moving to opposite poles of the cell. How does this differ to what occurs in anaphase of mitosis? 6 Anaphase I of Meiosis Anaphase of Mitosis By Ali Zifan - Own work; Used information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=49630204 Copyright MATRIX EDUCATION 2019 Page 87 of 309 Our Students Come First!
TELOPHASE I The chromosomes have reached opposite poles at this stage. The chromosomes decondense and a nuclear envelope begins to reform around them. By Ali Zifan - Own work; Used information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=49630204 CYTOKINESIS I The cell physically divides into two new daughter cells. Organelles are distributed evenly to each new cell. By Ali Zifan - Own work; Used information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=49630204 What does the genetic material look like at this stage? 7 Copyright MATRIX EDUCATION 2019 Page 88 of 309 Our Students Come First!
Meiosis II Remember that meiosis II will actually be very similar to mitosis no crossing over will occur, and the chromosomes will align and separate exactly as they would in mitosis. PROPHASE II Meiosis II begins WITHOUT any further replication of genetic material. Why not? Hint: What would happen to chromosome number of the final daughter cells if replication did occur? 8 The nuclear envelope and nucleoli disappear, and spindle fibres form and spread across the two daughter cells formed during meiosis I, as shown below. By Ali Zifan - Own work; Used information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php? curid=49630204 Crossing over does NOT occur at this stage (unlike in prophase I). METAPHASE II The chromosomes line up again on the metaphase plate. Notice that chromosomal alignment in metaphase I differs from what occurred in metaphase I. Describe these differences. 9 Importantly, this alignment results in separation of the sister chromatids of each chromosome pair (as in mitosis). By Ali Zifan - Own work; Used information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php? curid=49630204 Copyright MATRIX EDUCATION 2019 Page 89 of 309 Our Students Come First!
ANAPHASE II The sister chromatids of each chromosome pair separate and move to opposite poles of the cell. By Ali Zifan - Own work; Used information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php? curid=49630204 TELOPHASE II The sister chromatids (now called individual chromosomes) have reached opposite poles at this stage. They decondense and a nuclear envelope begins to reform around them. By Ali Zifan - Own work; Used information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php? curid=49630204 CYTOKINESIS II The cells then physically divide into FOUR new daughter cells. What is the ploidy (chromosome number) of these new daughter cells? Hint: Are they diploid or haploid cells? 10 Modified from Ali Zifan - Own work; Used information from Campbell Biology (10th Edition) by: Jane B. Reece & Steven A. Wasserman., CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php? curid=49630204 How do these new daughter cells compare to the original parent cell? Are they genetically identical or unique? 11 Watch this ANIMATION to review the stages of meiosis. Copyright MATRIX EDUCATION 2019 Page 90 of 309 Our Students Come First!
Concept Check 1.1 [2012 HSC Q29(a)] Complete the following diagram to show the process by which gametes are formed. 12 3 Copyright MATRIX EDUCATION 2019 Page 91 of 309 Our Students Come First!
Concept Check 1.2 [2005 HSC Q23] The flow diagram below is a representation of one pair of homologous chromosomes in a cell during meiosis. (a) Identify ONE characteristic of the cells labelled D. 13 1 (b) Identify what occurs in Process 1. 14 1 (c) Identify where crossing over will occur, and explain how crossing over affects the inheritance of genes. 15 3 Copyright MATRIX EDUCATION 2019 Page 92 of 309 Our Students Come First!
Concept Check 1.3 (a) Which stage of meiosis I helps to increase the amount of genetic variation within a population, and how? 16 3 (b) Outline THREE distinct differences between meiosis I and mitosis. 17 1 Copyright MATRIX EDUCATION 2019 Page 93 of 309 Our Students Come First!
2. The Structure of DNA Students: Model the processes involved in cell replication, including but not limited to: DNA replication using the Watson and Crick DNA model, including nucleotide composition, pairing and bonding. What is DNA? DNA stands for deoxyribonucleic acid. DNA is the molecule which carries all the genetic information coding for proteins that enable cells to undergo growth, repair and other specialised functions. It is a long double-stranded helix found within a specific organelle in eukaryotic cells. What is the name of this organelle? 18 There is also a small amount of DNA in the mitochondria and chloroplasts. Drawing by OpenStax College - Anatomy & Physiology, Connexions Web site. http://cnx.org/content/col11496/1.6/, Jun 19, 2013., CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=30131165 Copyright MATRIX EDUCATION 2019 Page 94 of 309 Our Students Come First!
Specifically, DNA is a biopolymer made up of repeating subunits called nucleotides. Each individual nucleotide contains three basic components: 3. A sugar (in the case of DNA, the sugar deoxyribose). 4. A phosphate group. 5. A nitrogenous base. Sugar and phosphate molecules covalently join together to form the twisted double helix backbone. The nitrogenous bases are joined together by hydrogen bonding, forming the rungs of the double helix ladder. There are four types of nitrogenous bases found in DNA adenine (A), thymine (T), guanine (G) and cytosine (C). Due to their chemical structure, adenine always pairs with thymine and cytosine always pairs with guanine. HINT: Remember A-T and C-G "Apple Tart", "Chocolate Gateau"! Copyright MATRIX EDUCATION 2019 Page 95 of 309 Our Students Come First!
The following diagram shows the molecular structure of a SINGLE nucleotide. Label the three components that make up this nucleotide. 19 The following diagram shows the molecular structure of a DNA molecule made up of repeating nucleotides joined together by covalent bonds and hydrogen bonding. See if you can identify phosphate groups, deoxyribose sugars and nitrogenous bases. You will often see each end of a DNA or RNA strand labelled as 5' and 3' meaning five prime and three prime. This refers to the numbered carbon atoms in the sugar part of the backbone and gives the strand a "direction". By Boumphreyfr - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=7190747 Copyright MATRIX EDUCATION 2019 Page 96 of 309 Our Students Come First!
DNA, Genes and Chromosomes Genes are sequences of DNA that contain specific information for making proteins. Each gene has a particular sequence of nitrogenous bases. Chromosomes are macrostructures containing highly packaged DNA. What do you think the term macrostructure means? 20 Chromosomes are composed of chromatin. Chromatin fibres contain DNA (40%) and proteins (60%) DNA is wound around histone proteins, forming a beaded necklace which is coiled over and over, so that a very long strand of DNA can be densely packed into a small space. These structures are shown in context in the following diagram. Copyright MATRIX EDUCATION 2019 Page 97 of 309 Our Students Come First!
Genes are therefore found on chromosomes. These genes can be 'expressed' by the cell to form polypeptides and proteins for both structural and functional purposes. We will learn about this process in the next lesson. There are many genes on each chromosome and each gene is located at a different place (or locus ) along a chromosome. For example, the following diagram shows the various genes found on human chromosome number 20. By Office of Biological and Environmental Research of the U.S. Department of Energy Office of Science, the Biological and Environmental Research Information System, Oak Ridge National Laboratory. - Human Chromosomes from "Human Genome Landmarks: Selected Genes, Traits, and Disorders" Poster, 2002. (Gene Gateway) from Human Genome Project (1990-2003) Image Gallery Archive, Public Domain, https://commons.wikimedia.org/w/index.php?curid=41867620 Watch this VIDEO (Length 1:44) about chromosome and gene structure, and answer the following questions. What is the reason for the tight packaging of DNA? 21 Are chromosomes always visible? If not, when are they visible? 22 Copyright MATRIX EDUCATION 2019 Page 98 of 309 Our Students Come First!
Concept Check 2.1 Provide the complementary DNA sequence if one strand is: 5 -AGGTCAGCCACA-3. 23 1 Concept Check 2.2 Draw a simple, labelled diagram showing the structure of DNA molecule. 2 Copyright MATRIX EDUCATION 2019 Page 99 of 309 Our Students Come First!
Concept Check 2.3 (a) What is DNA? 24 1 (b) What is the shape of DNA called? 25 1 (c) What is the sugar-phosphate chain referred to as? 26 1 (d) What are the nitrogenous bases said to be like? 27 1 (e) What are the names of the four bases, and which bases pair together? 28 2 (f) What is a gene? 29 1 (g) What is a chromosome? 30 1 Copyright MATRIX EDUCATION 2019 Page 100 of 309 Our Students Come First!