A Tour of the Cell. Chapter 4. Most cells are microscopic. Cells vary in size and shape

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1 Chapter 4 A Tour of the Cell Most cells are microscopic Cells vary in size and shape 10 m Human height 1 m Length of some nerve and muscle cells 100 mm (10 cm) 10 mm (1 cm) Chicken egg Unaided eye 1 mm Frog egg 100 µm 10 µm Most plant and animal cells Light microscope 1 µm Most bacteria Mitochondrion 100 nm 10 nm Mycoplasmas (smallest bacteria) Viruses Ribosome Proteins Electron microscope Birgit Woelker, PhD Figure 4.2A 1 nm 0.1 nm Lipids Small molecules Atoms The microscopic size of most cells ensures a sufficient sur face area Across which nutrients and wastes can move to ser vice the cell volume A small cell has a greater ratio of sur face area to volume Than a large cell of the same shape 30 µm 10 µm 30 µm 10 µm Figure 4.2B Surface area of one large cube = 5,400 µm 2 Total surface area of 27 small cubes = 16,200 µm 2 1

2 Prokaryotic cells are structurally simpler than eukar yotic cells There are two kinds of cells Prokaryotic and eukaryotic Nucleoid region Prokaryotic cell Colorized TEM 15,000 Prokaryotic cells are small, relatively simple cells That do not have a -bound nucleus Capsule Cell wall Plasma Prokar yotic flagella Nucleoid region (DNA) Figure 4.3A Eukar yotic cell Organelles Figure 4.3B Pili Eukaryotic cells are par titioned into functional compar tments All other forms of life are composed of more complex eukaryotic cells Distinguished by the presence of a true nucleus Membranes form the boundaries of many eukar yotic cells Compar tmentalizing the interior of the cell and facilitating a variety of metabolic activities 2

3 A typical animal cell Contains a variety of membranous organelles Smooth endoplasmic Rough endoplasmic A typical plant cell has some structures that an animal cell lacks Such as chloroplasts and a rigid cell wall Rough endoplasmic Not in most plant cells Flagellum Lysosome Golgi apparatus Smooth endoplasmic Microtubule Centriole Peroxisome Golgi apparatus Not in animal cells Central vacuole Chloroplast Cell wall Intermediate filament Microfilament Cytoskeleton Microtubule Plasma Figure 4.4A Cytoskeleton Intermediate filament Microfilament Mitochondrion Figure 4.4B Mitochondrion Peroxisome Plasma ORGANELLES OF THE ENDOMEMBRANE SYSTEM The nucleus is the cell s genetic control center The largest organelle is usually the nucleus Which is separated from the cytoplasm by the nuclear envelope The nucleus is the cellular control center Containing the cell s DNA, which directs cellular activities Nucleolus Chromatin Two s of nuclear envelope Pore Rough endoplasmic Figure 4.5 3

4 Over view: Many cell organelles are connected through the endo system The endo system is a collection of membranous organelles Smooth endoplasmic has a variety of functions Smooth endoplasmic, or smooth ER Synthesizes lipids Processes toxins and drugs in liver cells Stores and releases calcium ions in muscle cells That manufactures and distributes cell products Smooth ER Nuclear envelope Smooth ER Figure 4.7 TEM 45,000 Rough endoplasmic makes and proteins The rough ER Manufactures s on the sur face of the rough ER Produce proteins that are secreted, inser ted into s, or transpor ted in vesicles to other organelles Transport vesicle buds off 4 Ribosome 1 3 Secretory (glyco-) protein inside transport vesicle Sugar chain Figure 4.8 Polypeptide 2 Glycoprotein 4

5 The Golgi apparatus finishes, sor ts, and ships cell products Stacks of membranous sacs receive and modify ER products Then ship them to other organelles or the cell sur face Lysosomes are digestive compar tments within a cell Lysosomes are sacs of enzymes That function in digestion within a cell 1 Transport vesicle (containing inactive hydrolytic enzymes) Figure 4.9 Receiving side of Golgi apparatus Transport vesicle from ER New vesicle forming Shipping side of Golgi apparatus Golgi apparatus Transport vesicle from the Golgi Golgi apparatus TEM 130,000 Figure 4.10A Food Plasma 3 Engulfment of particle Food vacuole Golgi apparatus Lysosome 2 engulfing damaged organelle Lysosomes 5 4 Digestion Lysosomes in white blood cells Lysosomes also recycle damaged organelles Destroy bacteria that have been ingested Lysosome Lysosome containing two damaged organelles Mitochondrion fragment Peroxisome fragment TEM 42,500 Figure 4.10B TEM 8,500 Figure 4.10C 5

6 Vacuoles function in the general maintenance of the cell Plant cells contain a large central vacuole, Which has lysosomal and storage functions Some protists have contractile vacuoles That pump out excess water Chloroplast Central vacuole Figure 4.12A Colorized TEM 8,700 Figure 4.12B Contractile vacuoles LM 650 A review of the endo system The various organelles of the endo system Are interconnected structurally and functionally Transport vesicle from ER to Golgi Transport vesicle from Golgi to plasma ENERGY-CONVERTING ORGANELLES Chloroplasts conver t solar energy to chemical energy Chloroplasts, found in plants and some protists Conver t solar energy to chemical energy in sugars Plasma Chloroplast Stroma Inner and outer s Vacuole Granum TEM 9,750 Figure 4.13 Smooth ER Nuclear envelope Lysosome Golgi apparatus Figure 4.14 Inter space 6

7 Mitochondria har vest chemical energy from food Mitochondria carry out cellular respiration Which uses the chemical energy in food to make ATP for cellular work Mitochondrion THE CYTOSKELETON AND RELATED STRUCTURES The cell s internal skeleton helps organize its structure and activities A network of protein fibers Make up the cytoskeleton. Outer Inter space Figure 4.15 Inner Cristae Matrix TEM 44,880 Figure 4.16 Actin subunit Microfilament 7 nm Fibrous subunits Intermediate filament 10 nm Tubulin subunit Microtubule 25 nm Microfilaments of actin Enable cells to change shape and move Intermediate filaments Reinforce the cell and anchor cer tain organelles Cilia and flagella move when microtubules bend Eukaryotic cilia and flagella Are locomotor appendages that protrude from cer tain cells Microtubules give the cell rigidity And provide anchors for organelles and act as tracks for organelle movement Figure 4.17A Figure 4.17B Colorized SEM 4,100 LM 600 7

8 Clusters of microtubules Drive the whipping action of these organelles Flagellum Electron micrographs of cross sections: CELL SURFACES AND JUNCTIONS Cell sur faces protect, suppor t, and join cells Cells interact with their environments and each other via their sur faces. Outer microtubule doublet Central microtubules Radial spoke Dynein arms Plasma Figure 4.17C Basal body (structurally identical to centriole) Flagellum Basal body TEM 206,500 TEM 206,500 Plant cells Are suppor ted by rigid cell walls made largely of cellulose Connect by plasmodesmata, which are connecting channels Vacuole Walls of two adjacent plant cells Plasmodesmata Animal cells are embedded in an extracellular matrix Which binds cells together in tissues Figure 4.18A Layers of one plant cell wall Cytoplasm Plasma 8

9 FUNCTIONAL CATEGORIES OF ORGANELLES Tight junctions can bind cells together into leakproof sheets Anchoring junctions link animal cells into strong tissues Gap junctions allow substances to flow from cell to cell Tight junctions Eukaryotic organelles comprise four functional categories Eukar yotic organelles fall into four functional groups Manufacturing Breakdown Figure 4.18B Anchoring junction Gap junctions Extracellular matrix Space between cells Plasma s of adjacent cells Energy processing Suppor t, movement, and communication between cells Eukar yotic organelles and their functions Table