Cell Structure and Function

Early Discoveries Early 1600s - Galileo Galilei used microscope to observe insect eye Mid 1600s - Robert Hooke observed and described cells in cork Late 1600s - Anton von Leeuwenhoek observed sperm, microorganisms 1820s - Robert Brown observed and named nucleus in plant cells

Developing Cell Theory Matthias Schleiden (1839) plants Theodor Schwann (1839) animals Rudolf Virchow (1840) Cell reproduction

Cell Theory 1) Every organism is composed of one or more cells 2) Cell is smallest unit having properties of life 3) Continuity of life arises from growth and division of single cells

Cell Smallest unit of life Can survive on its own or has potential to do so Is highly organized for metabolism Senses and responds to environment Has potential to reproduce

Structure of Cells All start out life with: Two types: Plasma membrane Region where DNA is stored Cytoplasm Two types: Prokaryotic Eukaryotic

Why Are Cells So Small? Surface-to-volume ratio The bigger a cell is, the less surface area there is per unit volume Above a certain size, material cannot be moved in or out of cell fast enough

Microscopes Create detailed images of something that is otherwise too small to see Light microscopes Simple or compound Electron microscopes Transmission EM or Scanning EM

Limitations of Light Microscopy Wavelengths of light are 400-750 nm If a structure is less than one-half of a wavelength long, it will not be visible Light microscopes can resolve objects down to about 200 nm in size Magnifies up to 2000X

Electron Microscopy Uses streams of accelerated electrons rather than light Electrons are focused by magnets rather than glass lenses Can resolve structures down to 0.5 nm SEM = Scanning EM Up to 100,000 X TEM = Transmission EM Up to 200,000 X

Prokaryotic Cells Archaebacteria and Eubacteria DNA is not enclosed in nucleus Generally the smallest, simplest cells No organelles

Prokaryotic Structure pilus cytoplasm with ribosomes DNA flagellum capsule cell wall plasma membrane

Lipid Bilayer Main component of cell membranes Gives the membrane its fluid properties Two layers of phospholipids with proteins Hydrophilic heads = “water loving” Hydrophobic tails = “water fearing” one layer of lipids Figure 4.3 Page 56

Protein pump across bilayer Protein channel across bilayer Membrane Proteins Recognition protein Receptor protein extracellular environment lipid bilayer cytoplasm Protein pump across bilayer Protein channel across bilayer Protein pump Figure 4.4 Page 57

Eukaryotic Cells Have a nucleus and other organelles Eukaryotic organisms Plants Animals Protistans Fungi

Functions of Nucleus Keeps the DNA molecules of eukaryotic cells separated from metabolic machinery of cytoplasm Makes it easier to organize DNA and to copy it before parent cells divide into daughter cells

Components of Nucleus nuclear envelope nucleoplasm nucleolus chromatin Figure 4.11b Page 62

bilayer facing nucleoplasm Nuclear Envelope Two outer membranes (lipid bilayers) Innermost surface has DNA attachment sites Nuclear pore bilayer facing cytoplasm Nuclear envelope bilayer facing nucleoplasm Figure 4.12b Page 63

Cytomembrane System Group of related organelles in which lipids are assembled and new polypeptide chains are modified Products are sorted and shipped to various destinations

Components of Cytomembrane System Endoplasmic reticulum Golgi bodies Vesicles

Endoplasmic Reticulum In animal cells, continuous with nuclear membrane Extends throughout cytoplasm Two regions - rough and smooth

Endoplasmic Reticulum

Golgi Body Puts finishing touches on proteins and lipids that arrive from ER Packages finished material for shipment to final destinations Material arrives and leaves in vesicles budding vesicle Figure 4.15 Page 65

Golgi Body

Vesicles Membranous sacs that move through cytoplasm Lysosomes Peroxisomes Glyoxisomes

Assorted Vesicles Lysosomes Peroxisomes Glyoxisomes

Mitochondria ATP-producing powerhouses Membranes form two distinct compartments ATP-making machinery embedded in inner mitochondrial membrane

Mitochondria

Plant Cell Features Plasma membrane Nucleus Ribosomes Endoplasmic reticulum Golgi body Vesicles Mitochondria Cytoskeleton Cell wall Central vacuole Chloroplast Figure 4.10a Page 61

Specialized Plant Organelles Plastids Central Vacuole Cell Wall

Chloroplasts Convert sunlight energy to ATP through photosynthesis

Chloroplasts

Other Plastids Chromoplasts Amyloplasts No chlorophyll Abundance of carotenoids Color fruits and flowers red to yellow Amyloplasts No pigments Store starch

Other Plastids Chromoplasts Amyloplasts

Plant Cell Walls Secondary cell wall (3 layers) Primary cell wall

Plant Cuticle Cell secretions and waxes accumulate at plant cell surface Semitransparent Restricts water loss

Cytoskeleton Present in all eukaryotic cells Basis for cell shape and internal organization Allows organelle movement within cells and, in some cases, cell motility

Cytoskeletal Elements intermediate filament microtubule microfilament

Microtubules Largest elements Composed of tubulin subunit Microtubules Largest elements Composed of tubulin Arise from microtubule organizing centers (MTOCs) Involved in shape, motility, cell division Figure 4.21 Page 71

Microfilaments Thinnest elements Composed of actin Take part in movement, formation, and maintenance of cell shape actin subunit Figure 4.21 Page 71

Flagella and Cilia microtubule Structures for cell motility 9 + 2 internal structure Figure 4.25 Page 73

Cell-to-Cell Junctions Plants Plasmodesmata plasmodesma

Matrixes between Animal Cells Animal cells have no cell walls Some are surrounded by a matrix of cell secretions and other material

Animal Cell Junctions Tight junctions : prevent the passage of molecules and ions through the space between cells Adhering junctions : provide strong mechanical attachments between adjacent cells Gap junction : permit free passage of ions and small molecules between cells

Animal Cell Junctions tight junctions gap junction adhering junction