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Transcript
Chatper 4 – A Tour of the Cell I. Intro A. Cell theory - All living organisms are made of cells and all cells came from other cells (how do we know?) B. Cells are invisible to our eyes – need microscope C. Cells are highly ordered and organized (city building analogy) II. Microscopes provide windows to the world of the cell A. Two important aspects of microscope 1. Magnification 2. Resolution (resolving power) a) Ability to tell 2 points apart as separate points b) ex: If a microscope has a resolving power of 2um, two points must be at least 2um apart to see them as separate points. Any closer and they will look like one point. B. Three different types of microscopes – each with pluses and minuses compared to others 1. Light Microscope (LM) a) Pass visible light through specimen; lenses bends light to magnify image to the human eye b) 1000 to 2000X magnification limit c) Great for observing living organisms d) Micrograph – photo taken with any microscope 2. Scanning Electron Microscope (SEM) a) Instead of light you bounce electrons off the surface of the sample that has been coated with a metal and use a computer to collect the bounced electrons and generate an image. b) 10,000 to 20,000X magnification c) Great for showing the surface of organisms d) Organism cannot be living (in a vacuum, etc…) 3. Transmission Electron Microscope (TEM) a) Take a thin slice of specimen and hit with electrons b) Electrons are bent just like light in LM, but by using magnetic lenses c) 100,000 – 200,000X magnification d) Great for showing internal cell structures (specimen is dead – vacuum). III. Cell sizes vary with their function (structure-function relationship again!) A. Need to use smaller units when discussing cells – discuss going from mm to um to nm B. Nerve cells – signal transduction across great distances (electrical wires) C. Bird Eggs (Ostrich especially)- nutrient storage (ovalbumin) D. Blood Cells – surface area for gas exchange, fit through capillaries IV. Natural Laws Limit Cell Size A. Maximum - Large cells have a smaller ratio of surface area to volume than small cells (small house vs. large house analogy). Not enough surface area to get nutrients from outside!! B. Minimum – need to be able to hold all the things necessary to live (DNA, proteins, internal structure, etc…) Nanoarchaeum equitans – 400nm diameter V. Two very different cell types have evolved – prokaryotic and eukaryotic A. Prokaryotic cells – small and structurally simple – bacteria and archaea 1. Small - .5 to 10um in length (.0005 to .01mm or 1/100th of mm) 2. No nucleus – DNA is in the cytoplasm in a distinct “nucleoid” region 3. Ribosomes – found in semifluid– machines that assemble amino acids into polypeptide chains 4. Plasma membrane – surrounds the contents of the cells, separating is from outside world (skin) – made of phospholipids 5. Prokaryotic cell wall – rigid, protective covering, made of amino acid/monosaccharide polymer called peptidoglycan 6. Capsule – found around some prokaryotes – sticky outer protective coat (made of carbohydrates) 7. Some prokaryotes have projections a) Pili – assist in surface attachment b) Prokaryotic Flagella – swimming B. Eukaryotic cells – animals, plants, fungi, protests (a city) 1. Much larger than prokaryotic cells (10 to 100um in width or .01 to .1mm – 1/100th to 1/10th of a mm) 2. DNA enclosed in a special membrane called the nucleus 3. More complex than prokaryotes 4. cytosol – fluid region of the cell between nucleus and plasma membrane 5. Cytoplasm – cytosol plus organelles 6. Organelles – structures within the cell having specialized function – membranous and nonmembranous a) Membranous – nucleus, ER, golgi apparatus, mitochondria, lysosomes, peroxisomes and others (1) Compartments, each can maintain conditions that are different than the others for cellular metabolism (reactions in the cell) – different offices in the same building doing different jobs simultaneously (2) Increases membrane surface area b) Non-membranous – ribosomes, microtubules, centrioles, flagella, cytoskeleton and others (disputed!) 7. Plant cells have similar organelles as animal cells except: a) Plant cells DON’T have lysosomes or centrioles and usually don’t have flagella b) Animal cells don’t have rigid cell walls like plant cells or chloroplasts VI. Organization of the Eukaryotic Cell A. The nucleus is the cell’s genetic control center 1. DNA – a parts list, instructions on how to combine amino acids to make every protein in the cell. 2. Chromatin – nuclear DNA does not hang alone, its attached to different proteins, forming long fibers 3. Chromosome – each fiber 4. Nuclear Envelope – double-membrane with nuclear pores (holes/gates) that control what comes in and out (you need a pass to enter and exit). 5. Nucleolus – Dense region of chromtin, proteins and RNA where ribosome components are made (factory for ribosome parts). B. Overview: Many cell organelles are related through the endomembrane system 1. Endomembrane system – composed of the different membranes that are suspended in the cytoplasm within a eukaryotic cell. a) the nuclear envelope, the endoplasmic reticulum, the golgi apparatus, vacuoles, vesicles, and the cell membrane. 2. compartmentalize the cell into various membranous organelles 3. protein trafficking, digestion, etc… a) Endoplasmic reticulum (ER) – two flavors: rough and smooth – continuous with nuclear envelope (1) Rough ER – interconnected, flattened sacs studded with ribosomes (a) New membrane for other organelles (b) Ribosomes make polypeptides that snake into the ER. ER is the way out of the cell. Many of these proteins are destined to be secreted from the cell (antibody, digestive proteins, etc…) (mail system) (c) Glycoprotein (d) Transport vesicle (e) functions (i) lysosomal enzymes, secreted proteins, membrane proteins (2) Smooth ER – variety of functions, continuous with rough ER, but no ribosomes. (a) Site of lipid synthesis – fats, steroids, phospholipids (remind – enzymes within at work here, not membrane part) (b) In liver – helps to regulate amount of sugar released into blood, break down drugs/toxins (i) Exposure to drugs tells liver cells to increase amount of smooth ER and its detoxifying enzymes within – drug resistance (barbiturate – antibiotic problem) (c) Calcium storage – needed for muscle contraction b) Golgi Apparatus – modifies, sorts, and ships proteins/membrane to appropiate places in the cell. (1) Series of flattened sacs separate from ER (2) Molecular warehouse and shipping factory (outgoing mail room) (3) Receives transport vesicles from ER on the “receiving side”, chemically modifies glycoproteins, then ships to proper destination from the “shipping side”. c) Lysosomes – “break down body” – contains hydrolytic digestive enzymes –pH 4.8 compared to 7.2 of cytosol (1) digest the cells food/recycle old organelles/apoptosis (programmed cell death) (2) Produced by rough ER and golgi (3) Fuse with food vacuoles, help destroy bacteria (don’t engulf bacteria – too large – find video of this!), recycling of damaged organelles – break to monomers and release, apoptosis d) Abnormal lysosomes can cause fatal disease (1) Lysosomal storage diseases – hereditary – impedes enzyme function of lysosome – missing an enzyme, lysosomes fill up with stuff they can’t digest (2) Most fatal in childhood (3) Pompe’s disease – accumulation of glycogen – lack glycogen-digesting enzyme. (4) Tay-Sachs – destroys nervous system – lack lipiddigesting enzyme, nerve cells damaged by excess lipids – show video e) Vacuoles function in the general maintenance of cells. (1) Different shapes and sizes, variety of functions (a) Store excess water, waste, other chemicals, food (b) Generally larger than vesicles (2) Central Vacuole in plants – (a) can act as a large lysosome (plants don’t have typical lysosomes) (b) or absorb water to increase cell volume, store chemicals or waste products (3) Contractile Vacuole – collects excess water from cell and expels it to outside (a) Found in paramecium and other freshwater protests (freshwater fish don’t drink) f) A review of the endomembrane system VII. Energy-Converting Organelles A. Chloroplasts (plants and eukaryotic algae) – converts solar energy to chemical energy 1. Double-membrane 2. Site of photosynthesis 3. Structure-function – light captured on grana and chemical reactions that form food-storage molecules occur in stroma. B. Mitochondria harvest chemical energy from food – found in ALL eukaryotic cells with rare exception (including plants!!!) 1. Double membrane 2. Site of Cellular Respiration – conversion of unusable chemical energy (sugar) into usable chemical energy (ATP). (crude oil to gasoline – sort of) VIII. The Cytoskeleton and Related Structures A. The cell’s internal skeleton helps organize its structure and activities 1. Supportive structure of protein fibers (steel framework of building, “bones of the cell”) 2. Involved in cell movement 3. Vesicle trafficking 4. 3-flavors of protein fibers a) Microfilaments – thinnest – solid rods – double chain of actin proteins flexible, strong, movement b) Microtubules – thickest – hollow tubes of globular proteins – tubulins (1) Anchor organelles (2) Conveyor belts for vesicles and organelles (3) Basis of ciliary and flagellar movement c) Intermediate filaments – ropelike strands of fibrous proteins B. Cilia and Flagella move when microtubules bend 1. Cilia – short, numerous, hair-like projections involved in propulsion 2. Flagella – longer, fewer in number, less complexly organized 3. Both are small extension of the plasma membrane surround a complex microtubule arrangement. a) Function to move whole cells or to move materials across the surface of or into cells (show examples) 4. Basal Body – anchors the microtubule or cilia at the base/ foundation for growth – similar construction to centrioles 5. Dynein arms - protein knobs attached to each microtubule doublet – held in place, grab, push up a) Using ATP, exert a force which causes tubules to bend IX. Eukaryotic cell surfaces and junctions A. Cell surfaces protect, support, and join cells 1. Singled celled organisms – plasma membrane too weak to interact directly with environment, capsule and cell wall covering of prokaryotes 2. Plants – cell wall – 10 to 100X thicker than plasma membrane, also protect and support cells (how plants can stand upright without skeletons), and involved in joining neighboring cells – sticky polysaccharide glue a) Cell wall is a mixture of polysaccharides (predominantly cellulose) and proteins – multilayered b) Plasmodesmata – channels through PM and cell wall connecting cytoplasm of one cell to the adjacent cell in plants – circulatory and communication system 3. In animals, cells are usually covered with sticky layers of polysaccharides and proteins, not too supportive though (Extracellular matrix ECM) 4. Cell junctions in animal tissues – structures connecting one cell to another – 3 flavors a) Tight Junctions – leak proof barriers (rain coat) b) Anchoring Junctions – attach cells to each other, but allow passage of materials between cells (cotton shirt) or attach cells to an extracellular matrix (sticky layer of glycoproteins which cells are embedded in) c) Communicating Junctions – channels between cells for the movement of small molecules X. Functional categories of organelles A. Eukaryotic organelles comprise four functional categories 1. GENERAL FUNCTION : MANUFACTURE and TRANSPORT a) Nucleus b) Ribosomes c) Rough ER d) Smooth ER e) Golgi Apparatus 2. GENERAL FUNCTION : ENERGY PROCESSING a) Chloroplasts b) Mitochondria 3. GENERAL FUNCTION : BREAKDOWN a) Lysosomes b) Peroxisomes c) Vacuoles 4. GENERAL FUNCTION: SUPPORT, MOVEMENT, AND COMMUNICATION BETWEEN CELLS a) Cytoskeleton b) Cell Walls c) Extracellular Matrix d) Cell Junctions XI. Extraterrestrial life forms may share features with life on Earth A. All life-forms on Earth share fundamental features – cell theory 1. Consist of highly structured units called cells, membrane bound and separate from environment 2. Have DNA as genetic material 3. Carry out metabolic processes B. These features are likely to be characteristic of other life in our universe, the materials might be different