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Transcript
Quick Recap!! You need to know this stuff for your exam!!! Overview: The Fundamental Units of Life “The Cell Theory” • The modern tenets of the Cell Theory include: 1. all known living things are made up of cells. 2. the cell is structural & functional unit of all living things. 3. all cells come from pre-existing cells by division. (Spontaneous Generation does not occur). 4. cells contains hereditary information which is passed from cell to cell during cell division. 5. All cells are basically the same in chemical composition. 6. all energy flow (metabolism & biochemistry) of life occurs within cells. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings To study cells, biologists use microscopes and the tools of biochemistry • Though usually too small to be seen by the unaided eye, cells can be complex Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Microscopy • Scientists use microscopes to visualize cells too small to see with the naked eye • In a light microscope (LM), visible light passes through a specimen and then through glass lenses, which magnify the image Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The quality of an image depends on • Magnification, the ratio of an object’s image size to its real size • Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points • Contrast, visible differences in parts of the sample Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • LMs can magnify effectively to about 1,000 times the size of the actual specimen • Various techniques enhance contrast and enable cell components to be stained or labeled • Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to be resolved by an LM Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Two basic types of electron microscopes (EMs) are used to study subcellular structures • Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look 3-D • Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen • TEMs are used mainly to study the internal structure of cells Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Robert Hooke- used a compound microscope to see chambers within a cork and named them “cells” • Schleiden and Swann- works states that all plant and animals are made of cells. Cell Structure Chapter 6 YOU MUST KNOW • Three differences between prokaryotic and eukaryotic cells • The structure and function of organelles common to plant and animal cells • The structure and function of organelles found only in plant cells or animal cells • How different cell types show difference in subcellular components • How internal membranes or organelles contribute to cell function • How cell size and shape affect the overall rate of nutrient intake and waste elimination Prokaryotes • • • • Found in the domains Bacteria and Archaea(single-celled microorganisms. ) Contain a single, circular chromosome in nucleoid region Contain no membrane-bound organelles Very small in comparison to eukaryotes Interesting Facts • Prokaryotes dominate the biosphere • Collective mass outweighs all eukaryotes combined by at least 10fold • More prokaryotes inhabit a handful of fertile soil or in the mouth or skin of a human than the total number of people who have ever lived! • Found wherever there is life • Especially in extreme environments • There are a hundred billion prokaryotes per milliliter of fluid in the human colon. Eukaryotes • • • • Belong to domain Eukarya, includes animals, plants, fungi, protists (mainly unicellular animals and plants, that do not form tissues.) Membrane bound nucleus containing linear chromosomes Membrane-bound organelles Much larger than prokaryotes Plasma Membrane Ribosomes Membrane-bound organelles Nucleus Size Prokaryotes Yes Yes No Eukaryotes Yes Yes Yes No 1-10um Yes 10-100um The Nucleus • Contains DNA • Surrounded by a lipid bilayer (membrane) called the nuclear envelope which is connected to the rough endoplasmic reticulum and contains nuclear pores to allow things to enter and leave the nucleus • Nucleolus – region (not really a structure) where rRNA combines with proteins to form ribosomal subunits Ribosomes • Composed of rRNA and protein – one large subunit and one small • Sites of protein synthesis • Can be free-floating or bound to endoplasmic reticulum • Free-floating – produce proteins to be used in the cell • Bound – produce proteins that will be exported out of the cell Endoplasmic Reticulum • Network or folded membranes and sacs – space between called cisternal space • Smooth– no ribosomes associated • Metabolism of lipids and carbs • Detoxification of drugs and poisons • Rough – covered in ribosomes • Ribosomes synthesize proteins which are then wrapped in vesicles made of the membrane of the ER Golgi Apparatus • Stacks of flattened sacs of membrane called cisternae • Modifies, stores, and ships out proteins • Sacs are polar with cis side receiving incoming proteins from the RER and shipping them out from the trans side Camilo Golgi Lysosomes • Membrane-bound sacs of hydrolytic enzymes to digest unwanted or old molecules and organelles in the cell • Release to monomers produced by their reactions back in to the cell • Enzymes involved require a low pH to function, so if lysosome breaks open, they do not work Peroxisomes • Membrane-bound sacs • Transfer hydrogen from compounds to oxygen, forming H2O2 (toxic to cell) • Contains enzymes to break down the H2O2 • Breaks down fatty acids so that they can be used by the mitochondria • Detoxify substances (alcohol) by transferring its hydrogen to oxygen Peroxisomes • Membrane-bound sacs • Transfer hydrogen from compounds to oxygen, forming H2O2 (toxic to cell) • Contains enzymes to break down the H2O2 • Breaks down fatty acids so that they can be used by the mitochondria • Detoxify substances (alcohol) by transferring its hydrogen to oxygen Vacuoles • Membrane-bound sacs used for various reasons • Contractile vacuoles in protists – contracts to expel water out of the cell to prevent lysis in hypotonic environments https://www.youtube.com/watch?v=pahUt0RCKYc • Central vacuole in plants – can make up as much as 80% of a cell, used for storage Mitochondria • • • • • Sites of cellular respiration – energy conversion from food to ATP 2 membranes – outer and inner Cristae – folds of the inner membrane, increase surface area Matrix – fluid filled inner compartment Contains its own circular DNA and its own ribosomes Chloroplasts • Site of photosynthesis in plants – energy conversion from light to food • Also contains its own circular DNA and ribosomes • Double membrane structure Endosymbiotic theory • Mitochondria and chloroplasts have many characteristics of prokaryotic cells – circular DNA, ribosomes • Double membrane indicates they were engulfed by another cell by endocytosis • Eukaryotes arose from one prokaryote engulfing others and the engulfed cells developing specialized functions Cytoskeleton • Network of protein fibers for support, motility, and regulation • Microtubules – tubulin fibers, shape and support, tracks for molecules to travel along, separate chromosomes during mitosis and meiosis, form cilia and flagella • • • Flagella – long tails to propel cells Cilia – shorter and more numerous than flagella, can be used to move the cell itself or to move things along outside the cell Both in 9+2 pattern – 9 pairs of microtubules around a core of 2 microtubules • Microfilaments – composed of actin, smaller than microtubules, involved in muscle contractions • Intermediate filaments – maintain shape, fix position of oragnelles Centrosomes – near nucleus, region where where microtubules grow Centrioles – located within centrosomes, used during mitosis and meiosis Extracellular components • Cell wall • In plants, composed of cellulose, for shape and support • Also in prokaryotes & fungi, composed of peptidoglycan & chitin • Plasmodesmata – channels in cell walls between cells to allow passage of materials from one cell to another • Extracellular Matrix (ECM) • Animal cells • Composed of glycoproteins secreted by cell, mostly collagen • Strengthens tissues, allows for transmittal of stimuli into the cell • Intercellular junctions (in animal cells) • Tight junctions – two neighboring cells are fused by their cell membranes • Desmosomes – proteins that link adjacent cells like rivets, making strong sheets • Gap junctions – protein channels connecting adjacent cells so small molecules can pass from one to the next