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Transcript
Introduction to the Cell Copyright CSAN (2005), Images used with permission The Cell Objectives • Briefly discuss the importance of understanding cell structure and function in terms of health, illness and nursing • Give definitions for organism, organ, tissue, cell • Describe the basic difference between Prokaryotic & Eukaryotic cells Objectives • Describe the basic structure of a Eukaryotic cell – Briefly describe the cytoplasm – Describe the cell membrane & briefly explain its functions – Describe Endocytosis and Exocytosis – Describe the structure & function of the following organelles/ cell structures: • Lysosomes ● Nucleolus • Mitochondria ● Chromatin • Centrioles ● Endoplasmic reticulum • Nucleus ● Golgi apparatus Levels of organisation • Think about your body: What are its levels of organisation? 1.Chemical 2.Cellular 3.Tissue 4.Organ 5.System 6.Organism CELL THEORY 1. All living things are made up of cells & the products of those cells 2. All cells carry out their own life functions 3. New cells come from other living cells Cell Theory is based on over 300 years of scientific investigations, beginning with Hooke in 1665 Exceptions to the Cell Theory • Viruses. According to the Cell Theory we have to say they are not alive because a virus is not a cell. Viruses are made protein & nucleic acid, but have no membranes, nucleus, or protoplasm. They appear to be alive when they reproduce after infecting a host cell. (This will be discussed in later sessions) • Mitochondria. These cell organelles (small structures inside the cell) have their own genetic material & reproduce independently from the rest of the cell Cell Basics • The Prokaryotic-Eukaryotic difference • Prokaryotic cells - no nucleus (e.g. bacteria) • Eukaryotic cells - have nucleus (e.g. neutrophil) • All cells have – a cell membrane, – cytoplasm, – genetic material (DNA). • Other variances– Organelles present in the cell, the shape of the cell, or the function of the cell. The Cell organelles • • • • • • • • • • • • • Secretory vesicle plasma membrane Golgi complex nuclear envelope Nuclear envelope Mitochondria Cytoplasm Nucleus Nucleolus Centriole Granular endoplasmic reticulum Agranular endoplasmic reticulum Ribosome Microtubule Lysosome The Cell Cell components • Cytoplasm- a jelly like matrix within the cell – Includes structures called organelles (little organs) – Fluid like cytosol surrounds the organelles Numerous microtubules within the cytosol act like a sort of internal skeleton, forming ‘motorway’ routes for substances, organelles and vesicles to travel Allows for: - communication between components of the cell - communication between the cell and the external environment - microtubules form spindle apparatus involved in cell division The cytoskeleton cell wall The cell ‘plasma’ membrane maintains the boundaries of the cell The Cell ‘plasma’ Membrane • An essential communication link between the cell and its surrounding environment. • Largely made up of phospholipid molecules • Provides specific gateways for substances to pass through, controlling the internal environment & the outflow of substances manufactured in the cell • Contains ‘markers’ that others cells can recognize • Proteins within the phospholipid cell wall are essential; for acceptance of water-soluble substances. Detail of the Cell Membrane Cell membrane proteins are special• Part of them is Lipophilic (fat loving) which means that they can interact with lipids. These proteins can act as: • Transporters to carry substances through the cell wall • Channels that allow substances though the cell membrane • Receptors that detect hormones and transmitter substances • Enzymes that catalyze specific reactions and Markers that give the cell and identity. Cells of the same identity group together to form tissues types (to discussed later) Clinical relevance point – Think about absorption of medicines into cells-– Liposoluble drugs can ‘diffuse’ though the membrane very quickly because lipids are attracted to a cell wall Endocytosis and Exocytosis Endocytosis Exocytosis Exocytosis Transport through the cell wall • ENDOCYTOSIS –A small part of the cell membrane is drawn into the cell and the cell membrane then joins with a vesicle from the outside to reform the external boundaries of the cell. This tiny droplet from the outside is then a part of the cell wall and can be released into the cell • EXOCYTOSIS -Little sacs of substances called ‘vesicles’ join with the cell wall. For this to happen, the cell needs to take away the adjacent phospholipid layer (by endocytosis) to make room for the new part (the vesicle). ORGANELLES & THEIR FUNCTIONS • Organelles within the cell have specific functions. -They support the cell and as a whole, maintain its function -The distribution of organelles varies between cell, depending on their function Nucleus A double layer membrane containing DNA and RNA - genetic codes. Replication of parts of the body = depends on genetic coding Codes = blueprint for the manufacture of proteins that form a part of cell structures and tissues, enzymes, hormones, nucleic acids Genetic codes - contained within the nucleus of the cell embedded within the DNA and RNA complexes Protein synthesis occurs within the cell cytoplasm - you need to understand this process and this is a part of your study to be discussed during Module 2 The nucleus Endoplasmic Reticulum ERConsists of membranes that enclose amino acids and enzymes. Enzymes bring about chemical reactions, producing proteins and lipids. ER is where cellular waste is broken down & converted for re-use or excretion. Rough ER has ribosomes inserted into its membrane Smooth ER does not have ribosomes. Ribosomes Ribosomes are often called the protein factories of the cell (protein synthesis is covered in module 2) They are tiny, and can be found free in the cytoplasm or attached to endoplasmic reticulum This diagram shows a model of the two subunits that make up a ribosome The Golgi apparatus A stack of membranous sacs, associated with the ER It takes up the products made by the ER and may modify them a little Essentially packages the products in transport vesicles to transport to somewhere inside or outside the cell. Mitochondria Originated from bacteriacontain their own DNA and self replicate. Essential for effective energy production. They convert substances like glucose and fats to a form of energy that can be used by the cells (i.e. ATPthis will be discussed later) Clinical relevance point If we fail to feed cells with e.g. glucose, then energy will not be produced • Imagine what would happen to our skin – as these cells need energy to constantly make new cells (to be discussed in module 2) • Without adequate feeding- would wounds heal? Lysosomes Digest materials: Contain Enzymes (acid hydrolases) that digest large molecules like bacteria Breakdown cell materials Sometimes, things have to be broken down and removed to enhance the operating environment of the cell. 'Pinocytosis' - cell drinking, effectively breaking down the bacteria 'Phagocytosis' cell eating Peroxisomes • Peroxisomes are membrane enclosed spherical vesicles that contain several specific enzymes • Peroxisomes- present in most cells – particularly large and active in the liver (think of a substance detoxified by the liver……) • Peroxisomes ‘oxidize’ toxic molecules, removing hydrogen and transferring it to oxygen to form hydrogen peroxide Cell Specialisation Cells become specialized to perform a particular function within an organism, usually as part of a tissue, e.g.: Nerve cells to operate as part of the nervous system Skin cells for waterproof protection and protection against pathogens Cells combine efforts in these tissue types to perform a common cause. Specialized cells The task of the specialized cell will determine in what way it is going to be specialized. e.g. Muscle cells are long and smooth in structure White Blood Cells contain powerful digestive enzymes Specialized cells to detect light at the back of the eye In summary…. • The structural and functional and functional unit of living material is the……….. • It contains functional subunits called…………. • Cell function depends on the presence of specific………….. • Groups of similar cells that perform a similar function are…………… • Structures that contain different tissues organised to perform a general function are……………….. • Groups of organs that work together to carry out a general function are……………. Summary • 1. 2. 3. 4. In this session we reviewed: Levels of organisation Cell Theory Cell structure Organelles and their functions