Chapter 6 - A Tour of the Cell

Chapter 6 - A Tour of the Cell  Cell Structure and Function Outline Cell Theory Microscopes : Light and Electron Cell Size Prokaryotic Cells Eukaryotic Cells: Plant vs Animal  Origin of Eukaryotic Cells  Organel...

Chapter 6 - A Tour of the Cell  Cell Structure and Function Outline Cell Theory Microscopes : Light and Electron Cell Size Prokaryotic Cells Eukaryotic Cells: Plant vs Animal  Origin of Eukaryotic Cells  Organelles ­ Nucleus and Ribosomes ­ Endomembrane System ­ Lysosomes and Vacuoles ­ Chloroplasts and Mitochondria ­ Cytoskeleton  Organisms and Some organisms are unicellular Cells and some are multicellular  Cell Structure and Function Cell Theory Cells were discovered with microscopes (1665) Led to the development of the cell theory: (1838 – 1850) All organisms are composed of one or more cells. Cells are the smallest units of life. Cells arise only by division of a previously existing cell.  Visualizing Cells Different types of microscopes are used to visualize different sized cellular Unaided eye structures  Light Microscopes (LMs) Use light and magnify with lenses Image formed on the retina of the eye Limitations: low magnification (1000x) and resolving power Best for viewing living cells and general cell shape and structure  Electron Microscopes (EMs) Use beams of electrons and electromagnets Image formed on a screen Greater resolving and magnification powers  Up to 2,000,000X Limitation: can’t view living cells Two types: TEM & SEM Virtual electron microscope: http://school.discoveryeducation.com/lessonplans/interact/vemwindow.html Microscopy and Amoeba proteus  Cell Structure and Function Why Are Cells So Small? Some as small as one micrometer (m) Size restricted by Surface/Volume (S/V) ratio  As cell grows, volume increases faster than surface  Cells specialized to greatly increase surface area per unit volume: frilly, long, concave  Cell Structure Prokaryotic Cells and Function  Lack a membrane-bound nucleus  Simple Structure  Two Domains: Bacteria and Archaea  Prokaryotic Cells All have DNA, cytoplasm with ribosomes, a plasma membrane and cell wall. Genome - one single circular chromosome  Found in a region called the nucleoid  Some have plasmids - small rings of DNA Bacterial Plasmids Prokaryotic Cell Structure  Check for Understanding Can you identify each part of the prokaryotic cell? What is the function of each part?  Cell Structure and Function Eukaryotic Cells Found in all eukaryotes  Domain Eukarya Larger than prokaryotes Membrane-bound nucleus Internal membranes - Increase surface area - Form specialized organelles - Form an endomembrane system  Origin of Eukaryotic Cells Invagination of plasma membrane gave rise to the nuclear envelope and endomembrane system Endosymbiotic theory: mitochondria and chloroplasts originated from aerobic and photosynthetic prokaryotes that were eaten but not digested; became permanent residents and eventually organelles Animation: Origin of Eukaryotic Organelles  Differences in Structure & Function Eukaryotic cells vary in structure Division of labor In multicellular eukaryotes - Cells are specialized - Structure fits function Animal Cell Plant Cell Animation: Tour of An Animal Cell Animation: Tour of a Plant Cell  Cell Walls Found in plants, bacteria, fungi, some protists Protect, support and prevents excessive water uptake Composition varies: ­Plants – cellulose ­Fungi – chitin ­Bacteria - peptidoglycan  Plasma Membrane Structure: lipid bilayer embedded with proteins attached with carbohydrates; semipermeable Controls passage of materials into and out of the cell Also plays role in cell communication and identification  Nucleus Containing genetic material packaged in chromatin Chromatin – DNA plus protein; when highly coiled forms a chromosome. Nuclear envelope – separates nucleoplasm from cytoplasm; has pores Nucleolus - produces subunits of ribosomes  Cell Structure and Function Ribosomes: Protein Factories Site of protein synthesis Consists of a 2 subunits Many locations is cell Animation: Protein Synthesis  Endomembrane System System of membranes that functions in synthesis, storage, and export of cell proteins and lipids  Endoplasmic reticulum (ER)  Golgi apparatus  Vesicles  Plasma membrane Rough and Smooth Endoplasmic Reticulum Rough ER - studded with ribosomes which synthesize cellular proteins (membrane proteins, enzymes, antibodies, hormones) Allows proteins to fold inside its lumen Smooth ER- embedded with enzymes that synthesize cellular lipids (fats, oils, steroids) Also detoxifies poisons such as drugs and alcohol Protein synthesis by Rough ER  Golgi Apparatus Modifies, sorts, packages and distributes ER products (proteins and lipids) Has a receiving and shipping side Some products are exported ER products move to Golgi in transport vesicles Golgi products may: be secreted from the cell or exported. become part of membranes become organelles such as lysosomes Animation: Vesicles and Golgi  Cell Structure and Function Endomembrane System Check  Cell Structure and Function Lysosomes: Digestive Compartments Membranous vesicles with hydrolytic-digestive enzymes Functions: Intracellular digestion of food or pathogens Autophagy – digest nonfunctional organelles; recycle of cellular resources  Cell Vacuoles: Storage Sacs Membranous sacs that store materials Food vacuole – stores food Contractile vacuole – stores and eliminates water Central vacuole – stores water, nutrients, pigments, enzymes, and wastes Maintains turgor pressure for support  Chloroplasts: Sugar Factories Energy transforming organelles in plants and some protists Light energy  Chemical energy (sugar) Site of photosynthesis: process of making food using visible light from sun CO2 + H2O  C6H12O6 + O2  Mitochondria: Powerhouses Energy transforming organelles in all eukaryotes Sites of cellular respiration: process of making ATP using the energy in organic molecules such as - C6H12O6 + O2  CO2 + H2O + Energy (Energy released is used to build ATP) Origin of Chloroplasts and Mitochondria  Cytoskeleton Scaffold of protein fibers throughout cytoplasm  Three types Function: Maintain shape of cell Cell motility Anchor organelles Movement of organelles  Cell Structure and Function Cytoskeleton: Actin Filaments Thinnest filaments Dense web just under plasma membrane Function:  Support shape of cell  Ameoboid movement  Cytoplasmic steaming  Muscle contraction Cytoskeleton: Intermediate Filaments Rope-like assembly of fibrous polypeptides Found in cells that require strength (Ex. epithelial cells) Functions: Support and strength Form cell junctions which hold cells tightly together Anchor organelles Animation: Intermediate filaments of the Cytoskeleton  Cell Structure The Cytoskeleton: and Function Microtubules Hollow cylinders made of globular proteins Interacts with motor proteins (kinesin and dynein) Function: Movement of organelles Movement of cells by flagella and cilia  Cell Structure and Function Cilia and Flagella Locomotor appendages of some cells  Contain specialized arrangements of paired microtubules  How do flagella and cilia bend to produce motility? The protein dynein is responsible for the bending movement of cilia and flagella Powered by ATP, the dynein arms of one microtubule pair grip the adjacent doublet, push it up, release and grip again. Microtubule Outer doublets ATP doublets ATP cross-linking proteins Anchorage in cell Dynein arm (a) (b)  Animal Cell: Check for Understanding Can you identify each part and describe its function?  Plant Cell: Check for Understanding Can you identify each part and describe its function?  Additional Web Resources http://www.usoe.k12.ut.us/curr/science/sciber00/7th/cells/sciber/ micrpart.htm *Quick study sheet on parts of a compound light microscope. http://www.udel.edu/Biology/ketcham/microscope/scope.html *Interactive tutorial on how to use the microscope. Excellent site!!! http://www.microscopy-uk.org.uk/micropolitan/index.html * Beautiful micrographs taken with light microscopes. http://www.cellsalive.com *Select Cell Biology: How Big Is A Cell? Cell Models http://www.biology4kids.com/files/cell_main.html *Great site for learning about cell organelles