Chapter 7
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CHAPTER 7 Cell Structure and Function CH 7-1 LIFE IS CELLULAR Goals: Explain the Cell Theory Describe how researchers explore living cells Distinguish between eukaryotes and prokaryotes DISCOVERY OF THE CELL Cells- basic units of life Robert Hooke (1665)- first to use the term cell while looking at cork cells using compound microscope Anton van Leeuwenhoek (1674) uses single lens microscope to see microorganisms Matthias Schleiden (1838) concludes all plants are made of cells Theodor Schwann (1839) concludes all animals are made of cells Rudolph Virchow (1855) proposes all cells come from existing cells CELL THEORY These observations led to Cell Theory: All living things are composed of cells Cells are the basic unit of structure and function in living things All cells come from existing cells IMPROVED CELL EXPLORATION Compound light microscope- magnify up to 1000x Staining can improve visibility of organelles Fluorescent staining may also be used Confocal light microscope- scans cells with laser beam to make 3-D images Electron microscopes- magnify up to 100,000x and resolve biological structures as small as 2 nanometers and • gave biologists the ability to see with great clarity the structures that make up cells FIGURE 4.1B 10 m 100 mm (10 cm) Length of some nerve and muscle cells Chicken egg 10 mm (1 cm) Unaided eye Human height 1m Frog egg 10 m 1 m 100 nm Most plant and animal cells Nucleus Most bacteria Mitochondrion Smallest bacteria Viruses Ribosome 10 nm Proteins Lipids 1 nm 0.1 nm Small molecules Atoms Electron microscope 100 m Paramecium Human egg Light microscope 1 mm FIGURE 4.1B_2 Frog egg 10 m 1 m 100 nm Most plant and animal cells Nucleus Most bacteria Mitochondrion Smallest bacteria Viruses Ribosome 10 nm Proteins Lipids 1 nm 0.1 nm Small molecules Atoms Electron microscope 100 m Paramecium Human egg Light microscope 1 mm FIGURE 4.1B_3 TYPES OF ELECTRON MICROSCOPES Transmission electron microscopes (TEMs) pass a beam of electron through a thin specimen Scanning electron microscopes (SEMs) scan a beam of electrons over the surface of a specimen Create excellent 3-D images Specimens from electron microscopy are viewed in a vacuum, are preserved and dehydrated, so living cells cannot be viewed NEW MICROSCOPE TECHNOLOGY Scanning probe microscopes- trace surface of specimens with fine probe while electronically recording the position Non-contact atomic force microscope (Nc AFM) (also called dynamic force microscope (DFM)) http://news.berkeley.edu/2013/05/30/scientists-capture-firstimages-of-molecules-before-and-after-reaction/ IMAGES PRODUCED BY ELECTRON MICROSCOPES Cyanobacteria (TEM) House ant Lactobacillus (SEM) Avian influenza virus Campylobacter (SEM) Human eyelash Deinococcus (SEM) Yeast PROKARYOTES AND EUKARYOTES Prokaryotes Eukaryotes Cell membrane Cell membrane DNA (coiled into a region called the nucleoid) Nucleus (a membrane surrounds the DNA) Cytoplasm Cytoplasm Ribosomes Generally larger and more complex No true organelles Generally smaller than eukaryotes Contain dozens of structures (including ribosomes) and internal membranes Bacteria Highly specialized Single celled protists, RBC, etc. FIGURE 4.3 Fimbriae Ribosomes Nucleoid Plasma membrane Cell wall Bacterial chromosome A typical rod-shaped bacterium Capsule Flagella A TEM of the bacterium Bacillus coagulans Generalized Prokaryotic Cell CH 7-2 EUKARYOTIC CELL STRUCTURE Goals: Describe the function of the nucleus Describe the function of major cell organelles Identify main roles of cytoskeleton EUKARYOTIC CELL STRUCTURES The structures and organelles of eukaryotic cells can be organized by their basic functions Rough Smooth endoplasmic endoplasmic reticulum reticulum NUCLEUS: Nuclear envelope Chromatin Nucleolus NOT IN MOST PLANT CELLS: Centriole Lysosome Peroxisome Ribosomes Golgi apparatus CYTOSKELETON: Microtubule Intermediate filament Microfilament Mitochondrion Plasma membrane FIGURE 4.4B NUCLEUS: Nuclear envelope Chromatin Nucleolus Golgi apparatus NOT IN ANIMAL CELLS: Central vacuole Chloroplast Cell wall Plasmodesma Mitochondrion Peroxisome Plasma membrane Cell wall of adjacent cell Rough endoplasmic reticulum Ribosomes Smooth endoplasmic reticulum CYTOSKELETON: Microtubule Intermediate filament Microfilament CYTOPLASM Clear, gelatinous fluid inside of the cells Organelles are suspended in this jelly-like matrix NUCLEUS Central, membrane-bound organelle that contains DNA (in the form of chromatin) which controls cellular functions Contains directions to make proteins Therefore controls activity of all other organelles Membrane is a porous, double-membrane referred to as the nuclear envelope CHROMATIN (IN NUCLEUS) Like a tangled ball of yarn in the nucleus Becomes organized into chromosomes just before a cell divides NUCLEOLUS Prominent organelle within the nucleus Appears as a prominent dark area in the nucleus Assembly of ribosomes begins FIGURE 4.5 Two membranes of nuclear envelope Chromatin Nucleolus Pore Endoplasmic reticulum Ribosomes Nucleus RIBOSOMES (RRNA) Sites where the cell produces proteins according to directions of DNA Simple structure made of RNA and protein Must leave the nucleus and enter cytoplasm to make proteins A DNA copy with instructions for making proteins is sent to a ribosome in the cytoplasm or one attached to the ER FIGURE 4.6 Ribosomes ER Cytoplasm Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Colorized TEM showing ER and ribosomes mRNA Protein Diagram of a ribosome ENDOPLASMIC RETICULUM (ER) Highly-folded membranes make up the ER Allows for lots of surface area for chemical reactions to take place Fits into a compact space Rough ER has ribosomes imbedded in surface Newly made proteins leave the ribosome and are inserted into the ER where they are chemically modified Smooth ER has no ribosomes Produces enzymes responsible for the synthesis of membrane lipids and detoxification of drugs (liver cells) Nuclear envelope Smooth ER Ribosomes Rough ER Transport vesicle buds off 4 Secretory protein inside transport vesicle mRNA Ribosome 3 Sugar chain 1 2 Polypeptide Glycoprotein Rough ER GOLGI APPARATUS Made of a series of tubular membranes Receives proteins synthesized on ribosomes of the ER Modifies the proteins Then sorts and packs them into vesicles for secretion or to be shipped to other parts of the cell LYSOSOMES Contain digestive enzymes Digest excess or worn out organelles, food particles (lipids, carbohydrates, and proteins), engulfed viruses, or bacteria Membrane prevents enzymes from leaking out, but membrane can fuse with vacuole to digest its contents Lysosomes can ingest the cell itself Digestive enzymes Lysosome Plasma membrane Digestive enzymes Lysosome Food vacuole Plasma membrane Digestive enzymes Lysosome Food vacuole Plasma membrane Digestive enzymes Lysosome Digestion Food vacuole Plasma membrane Lysosome Vesicle containing damaged mitochondrion Lysosome Vesicle containing damaged mitochondrion Lysosome Digestion Vesicle containing damaged mitochondrion VACUOLES Vacuoles are large vesicles that have a variety of functions. Can store water, salts, proteins, and carbohydrates Large, central vacuole in plants gives plant turgor pressure Some protists have contractile vacuoles that help to eliminate water In plants, vacuoles may have digestive functions, contain pigments, or contain poisons that protect the plant. Contractile vacuole Nucleus Central vacuole Chloroplast Nucleus MITOCHONDRIA Mitochondria are organelles that carry out cellular respiration in nearly all eukaryotic cells. Cellular respiration converts the chemical energy in foods to chemical energy in ATP (adenosine triphosphate). MITOCHONDRIA Mitochondria have two internal compartments. 1. 2. The intermembrane space is the narrow region between the inner and outer membranes. The mitochondrial matrix contains the mitochondrial DNA, ribosomes, and many enzymes that catalyze some of the reactions of cellular respiration. Mitochondrion Outer membrane Intermembrane space Inner membrane Cristae Matrix CHLOROPLASTS Chloroplasts are the photosynthesizing organelles of all photosynthesizing eukaryotes. Photosynthesis is the conversion of light energy from the sun to the chemical energy of sugar molecules (glucose). CHLOROPLASTS Chloroplasts are partitioned into compartments. Between the outer and inner membrane is a thin intermembrane space. Inside the inner membrane is a thick fluid called stroma that contains the chloroplast DNA, ribosomes, and many enzymes and a network of interconnected sacs called thylakoids. In some regions, thylakoids are stacked like poker chips. Each stack is called a granum, where green chlorophyll molecules trap solar energy. FIGURE 4.14 Inner and outer membranes Granum Chloroplast Stroma Thylakoid EVOLUTION CONNECTION: MITOCHONDRIA AND CHLOROPLASTS EVOLVED BY ENDOSYMBIOSIS Mitochondria and chloroplasts have DNA and ribosomes. The structure of this DNA and these ribosomes is very similar to that found in prokaryotic cells. The endosymbiont theory proposes that mitochondria and chloroplasts were formerly small prokaryotes and they began living within larger cells. Idea first suggested by biologist Lynn Margulis Mitochondrion Nucleus Endoplasmic reticulum Some cells Engulfing of oxygenusing prokaryote Engulfing of photosynthetic prokaryote Chloroplast Host cell Mitochondrion Host cell BENEFITS OF MEMBRANE-BOUND ORGANELLES Separates cell functions into distinct compartments Allows chemical reactions to occur simultaneously CYTOSKELETON Network of tiny rods and filaments within the cytoplasm that provides support and structure for the cell Help anchor and support organelles Involved in movement Microtubules- thin hollow cylinders made of protein Microfilaments- smaller, solid protein fibers made of actin CYTOSKELETON Cells contain a network of protein fibers, called the cytoskeleton, which functions in structural support and motility. Scientists believe that motility and cellular regulation result when the cytoskeleton interacts with proteins called motor proteins. CYTOSKELETON The cytoskeleton is composed of three kinds of fibers. 1. 2. 3. Microfilaments (actin filaments) support the cell’s shape and are involved in motility. Intermediate filaments reinforce cell shape and anchor organelles. Microtubules (made of tubulin) give the cell rigidity and act as tracks for organelle movement. Nucleus Nucleus Actin subunit 7 nm Microfilament Fibrous subunits Tubulin subunits 10 nm 25 nm Intermediate filament Microtubule CILIA AND FLAGELLA MOVE WHEN MICROTUBULES BEND While some protists have flagella and cilia that are important in locomotion, some cells of multicellular organisms have them for different reasons. Cells that sweep mucus out of our lungs have cilia. Animal sperm are flagellated. Outer microtubule doublet Central microtubules Radial spoke Dynein proteins Plasma membrane CENTRIOLES Play an important role in cell division Found in cells of animals and most protists CH 7-2 CELL BOUNDARIES Goals: Identify the main functions of the cell membrane and cell wall Describe what happens during diffusion Explain the processes of osmosis, facilitated diffusion, and active transport CELL WALL Fairly rigid structure located outside the plasma membrane in some cells Plants, fungi, bacteria, and some protists Provides support and protection Composed of cellulose Very porous, so it is NOT selectively permeable That is the job of the cell membrane CELL MEMBRANE Flexible phospholipid bilayer with proteins responsible for maintaining homeostasis Surrounds all cells Outside of cell Proteins Carbohydrate chains Cell membrane Inside of cell (cytoplasm) Protein channel phospholipid bilayer CELL MEMBRANE Maintains homeostasis by: Regulating what enters and leaves the cell Also provides protection and support Composed of a double-layered sheet called the lipid bilayer which includes embedded and attached proteins in a structure biologists call a fluid mosaic CELL MEMBRANE Fluid Mosaic Model Fluid: in motion -Mosaic: “pattern” of phospholipids and proteins on cell surface Outside of cell Carbohydrate chains Proteins Cell membrane Inside of cell (cytoplasm) Protein channel phospholipid bilayer http://telstar.ote.cmu.edu/Hughes/tutorial/cellmembranes/bil.swf CELL MEMBRANE Many phospholipids are made from unsaturated fatty acids that have kinks in their tails. These kinks prevent phospholipids from packing tightly together, keeping them in liquid form. In animal cell membranes, cholesterol helps stabilize the membranes prevent the fatty acid tails from sticking together CELL MEMBRANES • Membranes may exhibit selective permeability, allowing some substances to cross more easily than others. Diffusion Brownian motion- random movement of atoms and molecules caused by their collisions with one another Diffusion is the net movement of molecules across a concentration gradient Move from an area of high concentration to and area of low concentration http://www.biosci.ohiou.edu/introbioslab/Bios170/diffusion/Diffusion.html Slow process because it relies on random motion of atoms and molecules Diffusion does not require energy so it is referred to as passive transport Eventually, the particles reach equilibrium where the concentration of particles is the same throughout FIGURE 5.3A Molecules of dye Membrane Pores Net diffusion Net diffusion Dynamic Equilibrium OSMOSIS Diffusion of water across a membrane OSMOSIS High concentration of water to low concentration of water Fresh water to salt water http://www.stolaf.edu/people/giannini/flashanimat/transport/osmosis.swf HYPOTONIC SOLUTION ‘Hypo-’ means less Concentration of solute (dissolved solids) is less outside of cell than inside Therefore a higher concentration of water outside the cell Water will enter cell Cell may lyse (burst) Cell wall prevents lysis in plant cells HYPERTONIC SOLUTION ‘Hyper-’ means more Concentration of solute is higher outside of cell Therefore a lower concentration of water outside the cell Water leaves the cell Results in plasmolysis in plant cells ISOTONIC SOLUTION ‘Iso-’ means equal Solute concentration is the same outside and inside the cell Water moves in and out of the cell but in equal amounts No change in cell size Animals prefer this WHEN MOLECULES DON’T DIFFUSE Some molecules diffuse easily Others do not because of their size, shape, or polarity PHOSPHOLIPIDS Fatty acid tails are nonpolar Heads are polar Tails don’t want to be near water because water is polar Polar ♥ Polar Non-polar ≠ Polar PROTEINS Transport Proteins- needed for the movement of certain substances and waste materials across the plasma membrane Channel or carrier FACILITATED DIFFUSION Hydrophobic substances easily diffuse across a cell membrane. However, polar or charged substances do not easily cross cell membranes and, instead, move across membranes with the help of specific transport proteins Process is called facilitated diffusion, which does not require energy and relies on the concentration gradient. ACTIVE TRANSPORT Requires energy (ATP) Used for large molecules or substances moving against their concentration gradient (low to high) ENDOCYTOSIS AND EXOCYTOSIS Endocytosis- taking materials into the cell by means of infolding of membrane to form a vacuole 2 types: phagocytosis- cytoplasmic extensions surround food particle and package it in a vacuole Cell then engulfs it pinocytosis- formation of tiny pockets in cell membrane to take in liquids ENDOCYTOSIS AND EXOCYTOSIS Exocytosis- membrane of a vacuole fuses with cell membrane and releases contents out of cell FUNCTIONS OF MEMBRANE PROTEINS CYTOPLASM Enzymatic activity Fibers of extracellular matrix (ECM) Phospholipid Cholesterol Cell-cell recognition Receptor Signaling molecule Transport Attachment to the cytoskeleton and extracellular matrix (ECM) Signal transduction ATP Intercellular junctions Glycoprotein Microfilaments of cytoskeleton CYTOPLASM OTHER PROTEIN FUNCTIONS Other proteins serve as tags on the surface to ID chemical signals and other cells On inner surface help anchor membrane to cell’s internal support structure
