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Transcript
A Tour of the Cell Cell Structure Chapter 4 The Fundamental Units of Life All organisms are made of one or more cells The cell is the simplest collection of matter that can be alive All cells are related by their descent from earlier cells Though cells can differ substantially from one another, they share common features Biologists use microscopes and the tools of biochemistry to study cells Most cells are between 1 and 100 m in diameter, too small to be seen by the unaided eye-Scientists use Microscopes In a light microscope (LM), visible light is passed through a specimen and then through glass lenses LMs can magnify effectively to about 1,000 times the size of the actual specimen Lenses refract (bend) the light, so that the image is magnified Fluorescence 50 m 10 m Light Microscopy (LM) Confocal Three important parameters of microscope 1. 2. 3. 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 between two distinguishable points Contrast: visible differences in parts of the sample 0.1 m Human height Length of some nerve and muscle cells Chicken egg 1 cm 100 m 10 m 1 m 100 nm 10 nm 1 nm 0.1 nm Frog egg Human egg Most plant and animal cells Nucleus Most bacteria Mitochondrion EM 1 mm LM 1m Unaided eye 10 m Smallest bacteria Viruses Ribosomes Proteins Lipids Small molecules Atoms Superresolution microscopy Electron Microscopes Electron microscopes (EMs) are used to study subcellular structures 2 types of Electron Microscopes 1. Scanning electron microscopes (SEMs) focus a beam of electrons onto the surface of a specimen, providing images that look threedimensional 2 Types of Electron Microscopes 2. Transmission electron microscopes (TEMs) focus a beam of electrons through a specimen TEM is used mainly to study the internal structure of cells Electron Microscopy (EM) Longitudinal section of cilium Cross section of cilium Cilia Scanning electron microscopy (SEM) 2 m Transmission electron microscopy (TEM) History of the Microscope Invention & development of the microscope enabled scientists to discover the cell Simple Microscopes: The microscope van Leeuwenhoek used is considered a simple light microscope because it contained one lens and used natural light to view objects Light Microscopes: The microscope Hooke used to look at thin slices of cork Cell Discovery through Microscopes Robert Hooke-the first to observe cells;built a microscope and looked at cork cells from the bark of a tree “coined the term cells” (1665) Van Leeuwenhoek-observed the first living cells from pond water-protists. He called them (animalcules) & scraped tarter from his teeth 1838-Schleiden-botanist-all plants are made of cells 1839-Schwann-zoologists-all animals made of cells 10 yrs later-Virchow (1821-1902)-all cells come from cells—Cell Theory Cell Theory 1. All living organisms are composed of one or more cells 2. Cells are the basic units of structure and function in an organism 3. Cells come only from the reproduction of existing cells Comparing Prokaryotic and Eukaryotic Cells The basic structural and functional unit of every organism is one of two types of cells: 1. Prokaryotic Cells: Organisms of the domains Bacteria and Archaea 2. Eukaryotic Cells: Protists, fungi, animals, and plants Comparing Prokaryotic and Eukaryotic Cells Basic features of all cells Plasma membrane (phospholipids) Semifluid substance called cytosol Chromosomes (carry genes) Ribosomes (make proteins) Pili: (Fimbriae: attachment pili) Nucleoid Ribosomes Plasma membrane Bacterial chromosome (a) A typical rod-shaped bacterium Cell wall Capsule Flagella 0.5 m (b) A thin section through the bacterium Bacillus coagulans (TEM) Prokaryotic cells are characterized by having: No nucleus DNA in an unbound region called the nucleoid No membrane-bound organelles Cytoplasm bound by the plasma membrane Eukaryotic Cells Eukaryotic cells are characterized by having DNA in a nucleus that is bounded by a membranous nuclear envelope Membrane-bound organelles Cytoplasm in the region between the plasma membrane and nucleus Eukaryotic cells are generally much larger than prokaryotic cells ENDOPLASMIC RETICULUM (ER) Flagellum Smooth ER Rough ER Nuclear envelope Nucleolus NUCLEUS Chromatin Centrosome Plasma membrane CYTOSKELETON: Microfilaments Intermediate filaments Ribosomes Microtubules Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome Nuclear envelope Nucleolus Chromatin Rough endoplasmic reticulum Smooth endoplasmic reticulum NUCLEUS Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate filaments Microtubules Mitochondrion Peroxisome Plasma membrane Cell wall Wall of adjacent cell Chloroplast Plasmodesmata CYTOSKELETON In animal Cells but not plant cells: 1. Lysosomes 2. Centrosomes with centrioles 3. Flagella (but present in some plant reproductive cells) In plant cells but not animal cells: 1. Chloroplast 2. Central Vacuole Cell Wall Plasmodesmata 3 Features All Cells have in Common: All cells have an outer boundary, inner substance, and a control region: 1. Plasma membrane: the delicate skin of lipids with embedded protein molecules 2. Nucleoid Region or Nucleus-the brain of the cell 3. Cytoplasm: region within the plasma membrane that is fluid based 1. Plasma Membrane Cells outer boundary AKA Cell Membrane Covers a cells surface and acts as a barrier between the inside and outside of the cell All material enter and exit through here Phospholipid bilayer with globular proteins embedded (proteins may be markers, transporters or receptors) 2. Cytoplasm A semi-fluid matrix (gel-like) that contains sugars, amino acids, and proteins; organelles are suspended within it The Cytosol is the part of the cytoplasm that includes molecules and small particles like ribosomes, but do not include membranebound organelle. 3. Nucleoid Region or Nucleus Control center; a membrane bound organelle that contains a cell’s DNA Center of the cell (usually); most prominent structure Most eukaryotes have a single nucleus, but fungi and some other groups have many nuclei. Organelles Eukaryote cells have a variety of internal membranes that divide the cell into compartments called organelles or little organs Well-defined, intracellular bodies that perform specific functions for the cell They carry out cellular processes Bacteria Cell Walls Strong cell wall made of peptidoglycan, a carbohydrate matrix (polymer of sugars) All bacteria is classified by into 2 types based on their cell wall: 1. Gram-positive bacteria 2. Gram-negative bacteria Gram Staining Procedures Gram-positive bacteria have a thick, single layered cell wall that stains violet Gram-negative bacteria have a multi-layered cell layer and does not stain purple, but a pinkish red See Notes Bacterial Cell Wall Function Protect the cell Maintain the cell’s shape Prevents excessive uptake of water Some bacterial cell walls are covered with a polysaccharide-this helps the bacteria to stick to substances like teeth, skin, and food Some bacteria secrete a jellylike capsule Bacterial Flagella Flagella are long threadlike structures that protrude from the surface of a cell They are used for locomotion & feeding Bacteria swim by rotating their flagella (rotary motor) They are made of protein Bacteria may have one flagellum or many flagella (depends on the species) Interior Organization of a Bacterial Cell Cytoplasm (no support structures) A few ribosomes (but no other membrane bound organelles) make protein Plasma (cell) membrane-controls what goes in and out of bacterium Nucleoid: area within cytoplasm where DNA is located Flagella: whip-like tail (with Rotary motor) Pili: hairlike growths on the outside of the cell Eukaryotic Cells More complex than prokaryotic cells Many membrane organelles; functions important for cell division Made of tiny organelles/little organs -Nucleus Region - Cytoskeleton -ER Region -Centriole - Lysosome - Mitochondria - Vacuole - Golgi Apparatus Cell Organelles and Features Plasma membrane AKA: cell membrane; has several functions Allows only certain molecules to enter or leave the cell It separates internal metabolic reactions from external conditions & Allows the cell to excrete waste & interact with its environment Made of phospholipids with embedded proteins Nucleus “Control Center” Nucleus controls most of the functions in eukaryote cells Filled with a jellylike liquid called nucleoplasm holds the contents in place The nucleus is surrounded by a double membrane called the nuclear envelope Covering the surface of the nuclear envelope are tiny protein-lined holes called nuclear pores. They provide passageways for RNA and other materials to enter and leave the nucleus Nucleus “Control Center” The nucleolus is the site where DNA concentrated by processing ribosomes DNA in the form of thread-like materials is called chromatin. Before the cell divides, chromatin changes to chromosomes Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Rough ER Pore complex Ribosome Close-up of nuclear envelope Chromatin Mitochondria Transfer energy from organic molecules to adenosine triphosphate (ATP) High active cells (muscle cells) have hundreds of mitochondria Low active cells (fat storage cells) have few mitochondria Mitochondria have their own DNA-contains genes that make proteins needed for cellular respiration Mitochondria can divide-but also involves nuclear enzymes Parts of the Mitochondria Double membrane: 1. Outer Membrane: separates the mitochondrion from the cytosol 2. Inner Membrane: has many folds called cristae Cristae contain proteins that carry out energyharvesting chemical reactions The matrix (fluid) is inside the inner membrane This is were cellular respiration occurs-glucose is metabolized into ATP (energy molecules) Ribosomes “Protein Makers” Where amino acids are assembled to make proteins Has 2 subunits: a large and a small Subunits are made of ribosomal RNA (rRNA) and protein The subunits are made in the nucleolus then move through the nuclear pores to the cytoplasm The subunits assemble when mRNA is present (mRNA carries the DNA code) Ribosomes on the ER make protein to be exported Ribosomes in the cytoplasm make proteins to used within the cell Endoplasmic Reticulum “Highway” A system of membranous tubes and sacs called cisternae (sis-TUHR-nee) Functions as an intracellular highway or path that molecules move from one part of the cell to another It is a Network of internal membranes made of a lipid bilayer embedded with proteins 2 Types of ER 1. Rough ER: interconnected flattened sacs covered with proteins; the ER transports the newly made protein Ex: Ribosomes on the rough ER make digestive enzymes that accumulate inside the ER. Distributes Vesicles: little sacs that pinch off from the ends & store them until they are released from the cell 2 Types of ER 2. Smooth ER: lacks ribosomes; contain very little smooth ER contain enzymes involved in making carbs and lipids Ex: 1. In ovaries & testes: makes steroid hormones estrogen and testosterone 2. In skeletal & heart muscle: releases calcium 3. Abundant in liver, kidney cells to help detoxify drugs & poisons ( long-term use causes more smooth ER) Functions of Smooth ER The smooth ER Synthesizes lipids Metabolizes carbohydrates Detoxifies drugs and poisons Stores calcium ions Smooth ER Rough ER Nuclear envelope ER lumen Cisternae Ribosomes Transport vesicle Transitional ER The Golgi Apparatus: Shipping and Receiving Center The Golgi apparatus consists of flattened membranous sacs called cisternae Functions of the Golgi apparatus Modifies products of the ER Manufactures certain macromolecules Sorts and packages materials into transport vesicles Golgi Apparatus The sacs nearest the nucleus receive vesicles from the ER containing newly made proteins or lipids Vesicles travel from 1 part of the Golgi body to the next transporting substances as they go Proteins get “address labels” that direct them to other parts of the cell cis face (“receiving” side of Golgi apparatus) Cisternae trans face (“shipping” side of Golgi apparatus) Lysosomes “suicide sacs” Digestive vesicles Arise from the Golgi Contain enzymes that can digest carbs, proteins, lipids and nucleic acids Break down worn out organelles and recycle molecules In White Blood cells they phagocytize bacteria Can merge with food vesicles and digest food Other Vesicles Enzyme-bearing, membrane-enclosed vesicles Found in the cells of plants, animals, fungi, and protists 2 types: 1. glyoxysome: specialized peroxisomes; found in seeds of some plant cells; contain enzymes that convert fats to carbs. 2. peroxisomes: contain catalase enzymes, which convert hydrogen peroxide into water and oxygen; Similar to lysosomes Cytoskeleton Made of protein fibers that assemble and disassemble Support the shape of the cell Anchor organelles to fixed locations Functions based on 3 structural elements 1. Microtubules 2. Microfilaments 3. Intermediate Filaments 3 Types of Cytoskeleton Microtubules: Hollow tubes made of a protein called tubulin which consist of 2 slightly different subunits Function: 1. holds organelles in place 2. maintain a cells shape 3. acts as tracks that guide organelles and molecules as they move within the cell 3 Types of Cytoskeleton Microfilaments (Actin Filaments): long threads of protein actin that are linked end to end & wrapped around each other like two strands of a rope Function: 1. Contribute to cell movement (crawling, or swim) 3 Types of Cytoskeleton Intermediate Filaments: are rods that anchor the nucleus and other organelles to their places in the cell They maintain internal shape of the nucleus Found in : hair-follicles (produce large quantities which makes up most of the hair shaft) Cell Movement Cell Crawling: Essential to inflammation, clotting, wound healing, and spread of cancer Cell Movement Cell Swimming: Flagella: Long, whip-like tail (sperm) In Eukaryotes: flagella (different from prokaryotes Cell Movement Cell Swimming: Cilia: Short, hair-like projections Organized in rows Move mucus in respiratory passage, Move egg in fallopian tube Centrioles Barrel- shaped organelles in animals & protists Occur in pairs: usually at right angles to one another and situated in the cytoplasm near the nuclear envelope Usually near the nucleus The region around them is called the centrisome Some centrioles have DNA which makes structural protein Centrioles help to organize microtubules and are found in areas called microtubule-organizing centers Replicate and move to opposite ends of the cell during mitosis (cell division) Plant Cells Have 3 additional structures that are important to plant function 1. Cell Walls 2. Large Central Vacuoles 3. Plastids Plants lifestyle Differ from Animals 1. 2. Plants make their own carbon-containing molecules directly from carbon taken from the environment Plant cells take carbon dioxide gas from the air and process it as photosynthesis (convert carbon dioxide & water into sugars Cell Wall A ridged layer that lies outside the cell’s plasma membrane Contain a carbohydrate called cellulose Pores in the cell wall allow water, ions, and some molecules to enter and exit the cell Cell Walls: made of cellulose; protect and support plant cell Primary cell wall-laid down while cell is growing Middle lamella-sticky substance that glues cells together Secondary walls: are deposited inside the primary walls in some plants Central Vacuole Is a large, fluid filled organelle that stores water, enzymes, metabolic waste, and other materials Forms as smaller vacuoles fuse together Make up 90% of the plant cell’s volume & can push all other organelles into a thin layer against the plasma membrane Other Vacuoles Other vacuoles store toxic materials Ex: Acacia Trees store poisons that provide a defense against plant-eating animals Ex: Tobacco plant cells store the toxic nicotine in a storage vacuole Other vacuoles store plant pigments like the pigment found in rose petals Plastids Surrounded by a double membrane & have their own DNA (like mitochondria) Several types of plastids 1. Chloroplasts 2. Chromoplasts 3. Leucoplasts: 1. Chloroplasts “Photo synthesizers” Carry out photosynthesis; manufacture own food Contain photosynthetic pigment chlorophyll that gives most plants their green color Double membrane Have their own DNA Bodies of Chloroplast Each chloroplast contains a system of flattened membranous sacs called thylakoids; contain the green pigment chlorophyll (absorbs light & captures light energy for the cell) The stroma is an area inside of the chloroplast where reactions occur and starches (sugars) are created; fluid matrix One thylakoid stack is called a granum Outer & inner membranes: lie close to each other 2. Chromoplasts Are plastids that contain colorful pigments that may or may not take part in photosynthesis Ex: carrot root cells contain chromoplasts filled with orange pigment carotene Chromoplasts in flower petal cells contain red, purple, yellow or white pigments Other Plastids Leucoplasts: starch (white) storage sites in root cells and other plant cells A leucoplast that stores starch is sometimes called an amyloplast Comparing Cells Plant Cell have a Cell Wall Plant Cells contain a large central vacuole Plant cells contain a variety of plastids