TMJC The Cell Cycle Notes

Page 1 of 55 Tampines Meridian Junior College JC1 H2/9744 Biology 2023 Core Idea 2 4. Genetics & Inheritance (I) – The Cell Cycle SYLLABUS OVERVIEW No. Overarching Idea Topics 1 Core Idea 1 The Cell and Biomolecules of Life Cell – The Basic Unit of Life 2 Biomolecules of Life and Cellular Transport 3 Core Idea 3 Energy and Equilibrium Transformation of Energy – Photosynthesis and Cellular Respiration 4 Core Idea 2 Genetics and Inheritance Genetics and Inheritance (I) – The Cell Cycle 5 Genetics and Inheritance (II) – DNA Replication and Gene Expression 6 Genetics and Inheritance (III) – DNA Mutations and their Consequences 7 Genetics and Inheritance (IV) – Molecular Techniques in DNA Analysis 8 Genetics and Inheritance (V) – Organization of Genome & Control of Gene Expression in Eukaryotes [Includes Core Idea 1D: Stem Cells] 9 Genetics and Inheritance (VI) – Organization and Inheritance of Viral Genomes 10 Genetics and Inheritance (VII) – Organization of Genome & Control of Gene Expression in Prokaryotes 11 Genetics and Inheritance (VIII) - Inheritance 12 Core Idea 3 Energy and Equilibrium Communication and Equilibrium in Multicellular Organisms 13 Core Idea 4 Biological Evolution Biological Evolution 14 Extension Topic A Infectious Diseases Immunity and Infectious Diseases 15 Extension Topic B Impact of Climate Change on Animals & Plants Climate Change – Causes and Impacts on Animals and Plants

Page 2 of 55 NARRATIVES An understanding of Genetics and Inheritance that would help make sense of the transition from molecular to organismal level. Genetics and Inheritance provides the molecular basis to the understanding of how variations in populations arise and this is important in the study of biological evolution. At the cellular level, expression of genes involves cellular structures such as the nucleus, endoplasmic reticulum and ribosome. Many essential products of gene expression are enzymes involved in biochemical pathways which control physiological functions. As such, mutation of genes may give rise to dysfunctional proteins which in turn could result in diseases. Sickle cell anemia and cancer are raised as examples of a monogenic and a mul ti-genic disease respectively. The following questions should help students frame their learning: • How does the genetic make-up of an organism influence its appearance, behavior and survival? • How does the inheritance of genetic information ensure the continuity of humans as a species? The cell cycle is tightly regulated The cell cycle comprises interphase, nuclear division and cytokinesis. There are two types of nuclear division: mitosis and meiosis. A cell cycle that involves mitosis will give rise to genetically identical cells and this is important for growth, repair a nd asexual reproduction of organisms. This cycle is coupled intricately and inexplicably with another important process of the living cell i.e. DNA replication, which occur during synthesis phase of interphase. The mitotic cell cycle is tightly regulated a t various checkpoints that control the rate of cell division; uncontrolled cell division could result in cancer. A cell cycle that involves meiosis occurs in reproductive organs of organisms and is important for sexual reproduction. Meiosis results in sex cells having half the amount of genetic mate rial present in somatic cells. The crossing-over of non-sister chromatids and independent assortment of bivalents in meiosis, together with random fertilisation of male and female gametes, give rise to genetic variation in populations. Genetic variation is necessary for natural selection to occur. Homogeneity of a population can result in the entire population being wiped out by diseases or climatic changes. LEARNING OUTCOMES Core Idea 2E: The Cell Cycle There are two different types of cell cycles: mitotic and meiotic. Cell cycles are tightly regulated at various checkpoints. The mitotic cell cycle is necessary for growth and repair while the meiotic cell cycle is necessary to generate gametes. Meiosis gives rise to genetic variation between gametes through crossing over of homologous chromosomes and independent assortment of bivalents. Candidates should be able to: n) Describe the events that occur during the mitotic cell cycle and the main stages of mitosis (including the behavior of chromosomes, nuclear envelope, cell surface membrane and centrioles). o) Explain the significance of the mitotic cell cycle (including growth, repair and asexual reproduction) and the need to regulate it tightly (knowledge that dysregulation of checkpoints of cell division can result in uncontrolled cell division and cancer is required, but detail of the mechanism are not required.) s) Describe the events that occur during the meiotic cell cycle and the main stages of meiosis (including the behavior of chromosomes, nuclear envelope, cell surface membrane and centrioles). (Names of the main stages are expected, but not that sub-divisions of prophase). t) Explain the significance of the meiotic cell cycle (including how meiosis and random fertilization can lead to variation).

Page 3 of 55 LECTURE OUTLINE 1. Introduction 1.1 Somatic cells, Germ cells and Gametes 1.2 Gene 1.3 Alleles 1.4 Locus / Loci 1.5 Chromosomes 1.6 Amount / Mass of DNA 1.7 Ploidy: Number of sets of Chromosomes in a cell 1.8 Homologous Chromosomes 1.9 Mendel’s Law of Independent Assortment and Segregation 2. Cell Theory and the Cell Cycle 3. Interphase 3.1 Features of the Interphase 3.2 Organization and Structure of the Eukaryotic Chromosome 4. Mitosis 4.1 Stages of Mitosis 4.2 Significance of Mitosis 4.3 Functions of Mitosis 5. Cytokinesis 6. Control of Cell Cycle 6.1 The Three Main Checkpoints 6.2 Loss of Cell Cycle Control in Cancer Cells 7. Meiosis 7.1 Stages of Meiosis 7.2 Significance of Meiosis 7.3 How Meiosis gives rise to Genetic Variation 8. Comparisons 8.1 Differences between Cell Division in Animal and Plant Cells 8.2 Differences between Mitosis and Meiosis

Page 4 of 55 1. Introduction 1.1 Somatic cells, Germ cells and Gametes • In this topic, we will be mainly talking about cell division in eukaryotic cells and multicellular organisms. • A somatic cell (diploid) is any cell in a multicellular organism other than those involved in gamete formation (Fig. 1.1). Examples: muscle cell, liver cell, neurons, blood cells, bone marrow cells, etc. • A germ cell (diploid) is a cell that develops into an egg or a sperm (usually haploid). • A gamete is a sperm or an egg cell (usually haploid). They typically carry half the amount of DNA and half the number of chromosomes that a somatic cell in the same organism carries. Fig. 1.1: The relationship between somatic cells, germ cells and gametes. 1.2 Gene • A gene (Fig. 1.2) is an inheritable and specific sequence of nucleotides on a DNA molecule, which codes for a RNA (e.g. tRNA, rRNA, telomerase RNA) or polypeptide (e.g. amylase). • A single chromosome can carry many genes. Fig. 1.2: Genes are found on chromosomes. One chromosome contains many genes.

Page 5 of 55 1.3 Alleles • An allele is an alternative form of a gene . Alleles of a gene have different nucleotide sequences (Fig. 1.3). o E.g. the allele for brown eye pigment and the allele for blue eye pigment are alternative forms of the gene that codes for eye color. o E.g. the allele for normal haemoglobin and the allele for sickle cell haemoglobin differ by just one base pair (Fig. 1.3). o E.g. the gene that codes for flower colour has two alleles, one which codes for purple flowers and the other which codes for white flowers. Fig. 1.3: The allele for wild-type haemoglobin (right) differs from the allele for sickle cell haemoglobin (left) by one base pair. • Alleles of a gene occupy the same