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Lecture 8 Cells Structure: A Tour of the Cell The Cell: A basic unit of living matter separated from its environment by a plasma membrane. The smallest structural unit of life. Discovery First observations of cells were made with light microscopes: Robert Hooke (1665): Used primitive microscope to observe cork (dead plant cells). Coined the word cell. Cell Theory Developed 200 years ago. 1. All living organisms are made up of one or more cells. 2. The smallest living organisms are single cells, and cells are the functional units of multi-cellular organisms. 3. All cells arise from pre-existing cells. Relative Sizes of Procaryotic and Eucaryotic Cells and Viruses Different Classes of Cells • Prokaryotic • Eukaryotic - Animal - Plant • All possess a cell membrane. Called the plasma membrane in bacterial cells and cytoplasmic membrane in animal/plant cells. The Cell Membrane • Functions as a semi-permeable barrier, allowing a very few molecules across it while fencing the majority of organically produced chemicals inside the cell. • Structure is a lipid bilayer (also referred to as the fluidmosaic model). • The most common molecule in the model is the phospholipid, which has a polar (hydrophilic) head and two nonpolar (hydrophobic) tails. These phospholipids are aligned tail to tail so the nonpolar areas form a hydrophobic region between the hydrophilic heads on the inner and outer surfaces of the membrane. Lipid Bilayer Functions of Cell Membranes • Separate cell from nonliving environment. Form most organelles and partition cell into discrete compartments • Regulate passage of materials in and out of the cell and organelles. Membrane is selectively permeable. • Receive information that permits cell to sense and respond to environmental changes. Hormones Growth factors Neurotransmitters • Communication with other cells and the organism as a whole. Surface proteins allow cells to recognize each other, adhere, and exchange materials. Prokaryotic Cells • • • • • • Bacteria and blue-green algae. Small size: Range from 1- 10 micrometers in length. About one tenth the size of a eukaryotic cell. No nucleus: DNA in cytoplasm or nucleoid region. Ribosomes are used to make proteins Cell wall: Hard shell around membrane Other structures that may be present: 1. Capsule: Protective, outer sticky layer. May be used for attachment or to evade immune system. 2. Pili: Hair-like projections (attachment) 3. Flagellum: Longer whip-like projection (movement) Prokaryotic Cells • • • • • • Bacteria and blue-green algae. Small size: Range from 1- 10 micrometers in length. About one tenth the size of a eukaryotic cell. No nucleus: DNA in cytoplasm or nucleoid region. Ribosomes are used to make proteins Cell wall: Hard shell around membrane Other structures that may be present: 1. Capsule: Protective, outer sticky layer. May be used for attachment or to evade immune system. 2. Pili: Hair-like projections (attachment) 3. Flagellum: Longer whip-like projection (movement) Prokaryotic Cells: Prokaryotic Cell Wall • Made up of peptidoglycans, molecules that have a carbohydrate (polysaccharide) attached to a polypeptide chain. The polysaccharide chains are liked by short amino acid chains. • Forms a net like structure that surrounds the whole cell. • Function – support and prevention of lysis • Use to identify different types of bacteria • Gram positive and Gram negative Gram negative and Gram positive • Gram because of inventor. • Bacteria with small amounts of peptidoglycan and, characteristically, lipopolysaccharide, are Gram-negative. Cells are a pink colour after staining. • Bacteria containing relatively large amounts of peptidoglycan and no lipopolysaccharide are Gram-positive. Cells are a purple colour after staining. Eukaryotic Cells • E.g protists, fungi, plant, and animal cells. • Nucleus: Protects and houses DNA • Membrane-bound Organelles: Internal structures with specific functions such a: Separate and store compounds Store energy Work surfaces Maintain concentration gradients Eukaryotic Cell Surfaces • Cell wall: Much thicker than cell membrane, (10 to 100 X thicker). • Provides support and protects cell from lysis. • Plant and algae cell wall: Cellulose • Fungi and bacteria have other polysaccharides. • Not present in animal cells or protozoa. • Breaks in surface: Channels between adjacent plant cells form a circulatory and communication system between cells. Sharing of nutrients, water, and chemical messages Membrane-Bound Organelles of Eukaryotic Cells • • • • • • • Nucleus Rough Endoplasmic Reticulum (RER) Smooth Endoplasmic Reticulum (SER) Golgi Apparatus Lysosomes Vacuoles Chloroplasts Mitochondria Membrane Bound Organelles Nucleus Processing and transport Rough ER Smooth ER Golgi Body Completed Protein Eucaryotic Cells: Typical Animal Cell Eucaryotic Cells: Typical Plant Cell Chloroplasts • Site of photosynthesis in plants and algae. CO2 + H2O + Sun Light -----> Sugar + O2 • Number may range from 1 to over 100 per cell. • Disc shaped structure with three different membrane systems: – 1. Outer membrane: Covers chloroplast surface – 2. Inner membrane: Contains enzymes needed to make glucose during photosynthesis. Encloses stroma (liquid) and thylakoid membranes. – 3. Thylakoid membranes: Contain chlorophyll, green pigment that traps solar energy. Organized in stacks called grana. Chloroplasts Trap Solar Energy and Convert it to Chemical Energy Chloroplasts • Contain their own DNA, ribosomes, and make some proteins. • Can divide to form daughter chloroplasts. • Type of plastid: Organelle that produces and stores food in plant and algae cells. • Other plastids include: Leukoplasts: Store starch. Chromoplasts: Store other pigments that give plants and flowers color. Mitochondria • Change chemical energy of molecules into the useable energy of the ATP molecule. • Oval or sausage shaped. • Contain their own DNA, ribosomes, and make some proteins. • Can divide to form daughter mitochondria. • Structure: Inner and outer membranes. Intermembrane space. Cristae (inner membrane extensions), Matrix (inner liquid) Mitochondria Harvest Chemical Energy From Food The Cytoskeleton • Complex network of thread-like and tube-like structures. • Functions: Movement, structure, and structural support. • Three Cytoskeleton Components: 1. Microfilaments: Smallest cytoskeleton fibres. Important for: Muscle contraction: Actin & myosin fibres in muscle cells “Amoeboid motion” of white blood cells . 2. Intermediate filaments: Medium sized fibres Anchor organelles (nucleus) and hold cytoskeleton in place. Abundant in cells with high mechanical stress. 3. Microtubules: Largest cytoskeleton fibres. Found in structures that help move chromosomes during cell division (mitosis and meiosis). Found in animal cells, but not plant cells. Movement of flagella and cilia. Components of the Cytoskeleton are Important for Structure and Movement The Cytoskeleton Cilia and Flagella • Projections used for locomotion or to move substances along cell surface. • Enclosed by plasma membrane and contain cytoplasm. • Consist of 9 pairs of microtubules surrounding two single microtubules (9 + 2 arrangement). • Flagella: Large whip-like projections. Move in wavelike manner, used for locomotion. Example: Sperm cell • Cilia: Short hair-like projections. Example: Human respiratory system uses cilia to remove harmful objects from bronchial tubes and trachea. Lysosomes, Aging, and Disease • As we get older, our lysosomes become leaky, releasing enzymes which cause tissue damage and inflammation. Example: Cartilage damage in arthritis. • Steroids or cortisone-like antiinflammatory agents stabilize lysosomal membranes, but have other undesirable effects (affect immune function). Important Differences Between Plant and Animal Cells Plant cells Cell wall Chloroplasts Large central vacuole Flagella rare No Lysosomes No Centrioles Animal cells None No chloroplasts No central vacuole Flagella more usual Lysosomes present Centrioles present Organelles and Function • Manufacture Nucleus Ribosomes Rough ER Smooth ER Golgi Apparatus • Breakdown Lysosomes Vacuoles • Energy Processing Chloroplasts (Plants and algae) Mitochondria • Support, Movement, Communication Cytoskeleton (Cilia, flagella, and centrioles) Cell walls (Plants, fungi, bacteria, and some protists) Extracellular matrix (Animals) Cell junctions Viruses are not cells! • They are referred to as particles. • They are the smallest living organisms on the planet. • They are obligate parasites • Core of nucleic acids surrounded by a protein coat (capsid) • Some viruses have a DNA genome and others have an RNA genome.