Cell Structure and Function Chapter 4

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

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 Cell

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

Main component of cell membranes Gives the membrane its fluid properties Two layers of phospholipids Lipid Bilayer one layer of lipids one layer of lipids Figure 4.3 Page 56

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

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

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

Plasma membrane Nucleus Ribosomes Endoplasmic reticulum Golgi body Vesicles Mitochondria Cytoskeleton Figure 4.10b Page 61

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

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 4.4 Functions of Nucleus

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

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

Group of related organelles in which lipids are assembled and new polypeptide chains are modified Products are sorted and shipped to various destinations 4.5 Endomembrane System

Components of Endomembrane System Endoplasmic reticulum Golgi bodies Vesicles

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

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

Vesicles Membranous sacs that move through cytoplasm Lysosomes Peroxisomes

ATP-producing powerhouses Membranes form two distinct compartments ATP-making machinery embedded in inner mitochondrial membrane 4.6 Mitochondria

Mitochondrial Origins Mitochondria resemble bacteria –Have own DNA, ribosomes –Divide on their own May have evolved from ancient bacteria that were engulfed but not digested

Plastids Central Vacuole 4.7 Specialized Plant Organelles

Chloroplasts Convert sunlight energy to ATP through photosynthesis

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

Present in all eukaryotic cells Basis for cell shape and internal organization Allows organelle movement within cells and, in some cases, cell motility 4.9 Cytoskeleton

Cytoskeletal Elements microtubule microfilament intermediate filament

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

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

Intermediate Filaments Only in animal cells of certain tissues Most stable cytoskeletal elements Six known groups one polypeptide chain Figure 4.21 Page 71

4.10 Flagella and Cilia Structures for cell motility internal structure dynein microtubule Figure 4.25 Page 73

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

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

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

Cell-to-Cell Junctions Plants –Plasmodesmata Animals –Tight junctions –Adhering junctions –Gap junctions plasmodesma

Animal Cell Junctions tight junctions adhering junction gap junction

Archaebacteria and Eubacteria DNA is not enclosed in nucleus Generally the smallest, simplest cells No organelles 4.12 Prokaryotic Cells

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