YIJC [H2] CI1.1 Organelles and Cellular Structures (N)

2024 JC1 BIOLOGY LECTURE NOTES CORE IDEA 1: THE CELL AND BIOMOLECULES OF LIFE TOPIC 1.1: ORGANELLES AND CELLULAR STRUCTURES Learning Outcomes You should be able to: (a) outline the cell theory with the understanding that cells are the smallest unit of life, all cells come from pre-existing cells, and living organisms are composed of cells (b) interpret and recognise drawings, photomicrographs and electronmicrographs of the following membrane systems and organelles: rough and smooth endoplasmic reticulum, Golgi body, mitochondria, ribosomes, lysosomes, chloroplasts, cell surface membrane, nuclea r envelope, centrioles, nucleus and nucleolus (for practical assessment, candidates may be required to operate a light microscope, mount slides and use an eyepiece graticule and a stage micrometer) (c) outline the functions of the membrane systems and organelles listed in (b) (d) describe the structure of a typical bacterial cell (small and unicellular, peptidoglycan cell wall, circular DNA, 70S ribosomes and lack of membrane-bound organelles) Textbooks and References Campbell, Urry, Cain, Wasserman, Minorsky, Reece (2018) Biology – A Global Approach (11th Edition)(Global Edition) Chapter 7: Cell Structure & Function pg. 163 – 195 (Pearson Publication) ISBN-10 1-292-17043-3 Note: These textbooks and references are available in our library. You may wish to borrow them to supplement your reading when necessary. H2

2 Contents Introduction 3 A bridge to O Level Biology 4 The Cell Theory 6 Cell Types 9 Cell Size 10 A bridge to O Level Biology 12 Functions of membrane systems and organelles in cells 13 Cell Surface Membrane 16 Nucleus 17 Nuclear Envelope 19 Nucleolus 19 Endomembrane system 20 Endoplasmic Reticulum (ER) 21 Rough Endoplasmic Reticulum (rER) 22 Smooth Endoplasmic Reticulum (sER) 23 Golgi Apparatus (Golgi body) 24 Lysosomes 26 Ribosomes 34 Centrioles 35 Cytoskeleton 36 A bridge to O Level Biology 37 Structure of a Typical Bacterial Cell 38 Peptidoglycan cell wall 38 Circular DNA 39 70S ribosomes 39 Summary: Overview of an animal cell ultrastructure with the associated functions 40 Annex A: Microscopy 41 Annex B: Cell Fractionation 42 Annex C: Steps involved in the secretory pathway 44 Annex D: Answers 47

3 Introduction The following questions should help you frame your learning: 1. Why is a cell the basic unit of life and how does it promote continuity of life? 2. How is the basic unit crucial in understanding life? 3. What are the differences between cells of prokaryotes and eukaryotes, between cells of plants and animals, and between cells of unicellular and multicellular organisms? Sub-cellular structures provide the means to drive cellular processes Knowing how cellular structures facilitate specific cellular processes is fundamental to explaining how life ‘works’. The cell theory states that the cell is the smallest and most basic unit of life and that cells grow from existing cells. Understanding the role of cellular organelles (such as the nucleus, ribosome, chloroplast and mitochondrion) and cellular structures (for example, the cytoskeleton) will help in understanding the concept of how structure relates to function. There are significant differences between cells of prokaryotes and eukaryotes. Using bacteria as a model, the nucleoid is not enclosed by any membrane. Plasmids may be present as extra-chromosomal DNA. Membrane -bound organelles, such as mitochondria and en doplasmic reticulum, are absent. Prokaryotic ribosomes are different from eukaryotic ribosomes. Some bacterial cells have cell walls that comprise peptidoglycan rather than cellulose. Within the eukarya domain, the cell model of plants is also different from that of animals. Eukaryotic cells also contain internal membrane structures that partition the cell into specialised compartments so that cellular processes can occur with optimal activity e.g. chloroplasts and mitochondria. The endomembrane system, consisting of rough and smooth endoplasmic reticulum and Golgi apparatus, is responsible for protein processing and vesicular transport within the cell. Prokaryotes generally lack such membrane -bound organelles and endomembrane systems; yet they survive and reproduce. In the endosymbiotic theory, organelles like mitochondria and chloroplasts represent formerly free-living prokaryotes that were taken inside another cell, and this could explain the link between the two domains in the tree of life.

4 A bridge to O Level Biology (6093 syllabus and 5078 syllabus) You should have learnt: A. identify cell structures (including organelles) of typical plant and animal cells from diagrams, photomicrographs and as seen under the light microscope using prepared slides and fresh material treated with an appropriate temporary staining technique: ● chloroplasts ● cell surface membrane ● cell wall ● cytoplasm ● cell vacuoles (large, sap-filled in plant cells, small, temporary in animal cells) ● nucleus B. identify the following membrane systems and organelles from diagrams and electron micrographs: ● endoplasmic reticulum (6093 only) ● mitochondria ● Golgi body (6093 only) ● ribosomes

5 Check Your Understanding (1) Question: The diagram below shows plant and animal cells. Identify structures A to J. Structure G had been identified for you. A F B G centrioles C H D I E J

6 The Cell Theory Learning Outcome (a) Outline the cell theory with the understanding that cells are the smallest unit of life, all cells come from pre-existing cells, and living organisms are composed of cells ● Cell theory has a very solid foundation largely because of the use of the microscope. ● Many scientists have contributed to developing the three main principles of this theory. ● These three principles are: 1. all organisms are composed of one or more cells Practices of Science ● Robert Hooke first described cells in 1665 after looking at cork with a self-built microscope. Fig. 1.1 Cork cells seen by Robert Hooke ● A few years later Antonie van Leeuwenhoek observed the first living cells and referred to them as ‘animalcules’, meaning little animals. ● In 1838, the botanist Matthias Schleiden stated that plants are made of ‘independent, separate beings’ called cells. ● One year later, Theodor Schwann made a similar statement about animals. This shows that scientific knowledge is generated from consensus within the community of scientists through a process of critical debate and peer review.

7 2. cells are the smallest units of life ● Cells vary considerably in size and shape but they share certain common features: ○ Every living cell is surrounded by a membrane, which separates the cell contents from everything else outside. ○ Cells contain genetic material which stores all of the instructions needed for the cells activities. ○ Many of these activities are chemical reactions, catalysed by enzymes produced inside the cell. ○ Cells have their own energy release system that powers all of the cells activities. ● Therefore, cells can be thought of as the smallest living structures as nothing smaller is considered a living structure.

8 3. all cells come from pre-existing cells. • Cells do not formed spontaneously from its component • They divide from pre-existing cells via mitosis, meiosis and binary fission Practices of Science (POS) ● Louis Pasteur sterilized chicken broth by boiling it. ● He showed that living organisms would not ‘spontaneously’ reappear. ● Only after exposure to pre-existing cells was life able to re-establish itself in the sterilized chicken broth. Fig. 1.2 Experiment to show that cells only arise from pre-existing cells This shows that science is an evidence-based, model-building