TMJC OCEG & Stem Cells Notes

Page 1 of 95 Tampines Meridian Junior College JC2 H2/9744 Biology 2024 Core Idea 2B | 2C | 1D 8. Genetics & Inheritance (V) Organization of Genome & Control of Gene Expression in Eukaryotes | Stem Cells 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 Before Section II of lecture: Pls revise ‘Gene expression’ topic and complete the pre-lecture qns on pg 33

Page 2 of 95 NARRATIVES An understanding of Genetics and Inheritance helps make sense of the transition from molecular to organismal levels. Genetics and Inheritance provides the molecular basis to the understanding of how variation in populations arises 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 whic h 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 genetic diseases. The following questions should help students frame their learning: • How does the genetic make-up of an organism and the environment influence the organism’s appearance, behavior and survival? • How does the inheritance of genetic information ensure continuity of humans as a species? Heritable information, in the form of DNA (and in some cases RNA), provides for continuity of life Genetic information is stored in an organism’s DNA; expression of genes results in the synthesis of functional products, such as rRNA, tRNA and proteins. These products play a role in intra- and extra-cellular biochemical pathways and influence the physiological processes in organisms. Genomes contain heritable information necessary for continuity of life at all levels: cell, organism and system. This information is stored and passed on to subsequent generations via DNA. Reproduction can occur at the cellular or organismal level; each progeny needs to receive heritable genetic information from its parent(s). An understanding of how eukaryotic, prokaryotic and viral genomes are organised has implications on how gene expression in organisms is controlled. Eukaryotic genomes are organised in a more complex manner (compared to prokaryotic genomes) . DNA is wrapped around histone proteins and compacted to form linear chromosomes; the number of chromosomes varies between eukaryotic species. Structurally, linear chromosomes have centromeres and telomeres, and their DNA consists of coding and non-coding sequences with the latter being in larger proportions. Coding DNA is expressed to give functional products (e.g. proteins, rRNA, tNRA) while non-coding DNA, e.g. control elements and centromeres, are involved in regulation of gene expression and nuclear division respectively. Expression of genetic information involves molecular mechanisms and gene regulation results in differential gene expression. In a single organism, the genes contained in all the nuclei of somatic cells are exactly the same, but the cell types differ morphologically and functionally. The differences between cell types are not due to the different genes being present, but due to differential gene expression, i.e. the expression of different sets of genes by cells with the same genome. Regulation of gene expression gives a cell control cover its structure and function. It allow s cell differentiation to occur. It may be controlled by the way DNA is packed in chromatin and at the var ious steps of protein synthesis, i.e. from the transcription to post -translational modification of a protein. It is the basis for cellular differentiation and morphogenesis which gives an organism versatility and adaptability. Gene expression can be studied using fundamental techniques of molecular biology such as the polymerase chain reaction (PCR), gel electrophoresis, Southern blotting and nucleic acid hybridization (covered in Topic 7). Stem cells have the potential to divide and differentiate into different cell types. Following fertilization, a single-cell zygote develops into a multicellular organism. The zygote can replicate its DNA, divide its nucleus, and divide into two genetically-identical cells. Cell potency describes a cell's ability to differentiate into other cell types. The zygote and cells formed from the first few cell divisions during embryonic development (up to the eight-cell stage) produce totipotent cells. Beyond the eight-cell stage, one of the two daughter cells remains undifferentiated, retaining the ability to divide indefinitely as a stem cell, while the other daughter cell differentiates. After the eight-cell stage, the cells begin to special ise into pluripotent stem cells. Pluripotent stem cells undergo further specialis ation into multipotent cells, which can f urther differentiate t o become unipotent stem cells. Environment signals triggers the differentiation of a cell into a more speciali sed form. Cell differentiation involves changing or regulating the expression patterns of genes . Each specialised cell type in an organism

Page 3 of 95 expresses a subset of all the genes that constitute the genome and this expression is regulated by various mechanisms resulting in differential gene expression of the same genome. It is important to recognise that a cell is dynamic in nature and not a static structure. At any point of time, numerous activities are occurring in the cell. In a plant cell, photosynthesis and respiration can be occurring simultaneously. This causes the biochemical changes in the cytoplasm of the plant cell. If it is necessary to produce more chlorophyll pigments or increase the amount of cellulose, the rate of protein synthesis in those biochemical pathways will increase. REFERENCES Organisation and Control Eukaryotic Genome 1. Campbell Biology by Reece et al. (9th Edition) 2. Molecular Biology of The Cell by Alberts, Bray, Lewis, Raff, Roberts and Watson (4 th or 5 th Edition) 3. Essential Cell Biology by Alberts, Bray, Hopkins, Johnson, Lewis, Raff, Roberts & Walter (3 rd edition) 4. http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Promoter.html Stem cells 5. Molecular Biology of the Cell by Bruce Alberts, Dennis Bray, Julian Lewis, Martin Raff and Keith Roberts 6. Application of Genetics, Cambridge Advanced Sciences by Gregory, J (2000) 7. Taylor, D J, Green, N P O, Stout, G W and Soper R (1997) Biological Science 1 and 2 (Third Edition) 8. Taylor, D (2001), Growth, Development an