Overview The Fundamental Units of Life All organisms are made of cells The cell is the simplest collection of matter that can live Cell structure is correlated to cellular function All cells are related by their descent from earlier cells 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 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 Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings 10 m Human height Length of some nerve and muscle cells 0 1 m Chicken egg 1 cm Frog egg 100 m 10 m Most plant and animal cells Nucleus Most bacteria 1 m 100 nm 10 nm 1 nm 0 1 nm Mitochondrion Smallest bacteria Viruses Ribosomes Proteins Lipids Small molecules Atoms Electron microscope 1 mm Light microscope 1m Unaided eye Fig 6 2 Most subcellular structures including organelles membrane enclosed compartments are too small to be resolved by an LM 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 Fig 6 4 TECHNIQUE a Scanning electron microscopy SEM RESULTS Cilia 1 m b Transmission electron Longitudinal Cross section section of of cilium microscopy TEM 1 m cilium Cell Fractionation Cell fractionation takes cells apart and separates the major organelles from one another Ultracentrifuges fractionate cells into their component parts Cell fractionation enables scientists to determine the functions of organelles Biochemistry and cytology help correlate cell function with structure Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 6 5 TECHNIQUE Homogenization Tissue cells Homogenate 1 000 g 1 000 times the force of gravity Differential centrifugation 10 min Supernatant poured into next tube 20 000 g 20 min Pellet rich in nuclei and cellular debris 80 000 g 60 min 150 000 g 3 hr Pellet rich in mitochondria and chloroplasts if cells are from a plant Pellet rich in microsomes pieces of plasma membranes and cells internal membranes Pellet rich in ribosomes Concept 6 2 Eukaryotic cells have internal membranes that compartmentalize their functions The basic structural and functional unit of every organism is one of two types of cells prokaryotic or eukaryotic Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells Protists fungi animals and plants all consist of eukaryotic cells Basic features of all cells 1 Plasma membrane 2 Chromosomes carry genes 3 Semifluid substance called cytosol 4 Ribosomes make proteins Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Prokaryotic cells are characterized by having like a bacteria cell simple cells 1 No nucleus no nuclear membrane 2 DNA in an unbound region called the nucleoid 3 No membrane bound organelles 4 Cytoplasm bound by the plasma membrane Eukaryotic cells are characterized by having 1 DNA in a nucleus that is bounded by a membranous nuclear envelope 2 Membrane bound organelles 3 Cytoplasm in the region between the plasma membrane and nucleus Cytosol Cytoplasm region where cytosol is present fluid like substance jelly cytoplasm Fig 6 6 Fimbriae 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 A Panoramic View of the Eukaryotic Cell Eukaryotic cells are generally much larger than prokaryotic cells A eukaryotic cell has internal membranes that partition the cell into organelles Plant and animal cells have most of the same organelles The nucleus contains most of the DNA in a eukaryotic cell Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 6 9a ENDOPLASMIC RETICULUM ER Flagellum Rough ER Smooth ER Nuclear envelope NUCLEUS Nucleolus Chromatin Centrosome Plasma membrane CYTOSKELETON Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome Fig 6 9b NUCLEUS Nuclear envelope Nucleolus Chromatin Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate filaments Microtubules Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Wall of adjacent cell Plasmodesmata CYTOSKELETON The Nucleus Information Central The nucleus contains most of the cell s genes and is usually the most conspicuous organelle The nuclear envelope encloses the nucleus separating it from the cytoplasm The nuclear membrane is a double membrane each membrane consists of a lipid bilayer In the nucleus DNA and proteins form genetic material called chromatin Chromatin condenses to form discrete chromosomes The nucleolus is located within the nucleus and is the site of ribosomal RNA rRNA synthesis Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 6 10 Nucleus 1 m Nucleolus Chromatin Nuclear envelope Inner membrane Outer membrane RNA enters into the cytoplasm Nuclear pore Pore complex Surface of nuclear envelope Called rough where it has ribosomes on its surface Rough ER Ribosome 1 m 0 25 m Close up of nuclear envelope Pore complexes TEM Nuclear lamina TEM Ribosomes Protein Factories Ribosomes are particles made of ribosomal RNA and protein Ribosomes carry out protein synthesis in two locations In the cytosol free ribosomes On the outside of the endoplasmic reticulum or the nuclear envelope bound ribosomes 50 S Large 30 s Small mRNA Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 6 11 Cytosol Endoplasmic reticulum ER Free ribosomes Bound ribosomes Large subunit 0 5 m