Chapter 4. Cell Structure and Function. Including some materials from lectures by Gregory Ahearn University of North Florida Ammended by John Crocker

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2 What Is the Cell Theory? Tenets of Modern Cell Theory Every living organism is made of one or more cells The smallest organisms are made of single cells while multicellular organisms are made of many cells All cells arise from pre-existing cells

3 4.1 What Features Are Shared By All Cells? Cells are the smallest unit of life. Cells are enclosed by a plasma membrane. Cells use DNA as a hereditary blueprint. Cells contain cytoplasm, which is all the material inside the plasma membrane and outside the DNA-containing region. Cells obtain energy and nutrients from their environment.

5 4.1 What Features Are Shared By All Cells? Cell function limits cell size. Most cells are small, ranging from 1 to 100 micrometers in diameter Cells need to exchange nutrients and wastes with the environment No part of the cell can be far away from the external environment

6 Cell Function Limits Cell Size Diffusion of molecules across cell membranes limits the diameter of cells. As cells get bigger, their nutrient and waste elimination needs grow faster than the membrane area to accommodate them.

7 4.1 What Features Are Shared By All Cells? The volume of cytoplasm grows faster than the plasma membrane area. Fig. 4-2

Relative sizes Diameter 100 m 10 m tallest trees 1 m 10 cm 1 cm visible with unaided human eye chicken egg adult human 1 mm frog embryo Units of measurement: 1 meter (m) = 39.

8 Relative sizes Diameter 100 m 10 m tallest trees 1 m 10 cm 1 cm visible with unaided human eye chicken egg adult human 1 mm frog embryo Units of measurement: 1 meter (m) = inches 1 centimeter (cm) = 1/100 m 1 millimeter (mm) = 1/1,000 m 1 micrometer ( m) = 1/1,000,000 m 1 nanometer (nm) = 1/1,000,000,000 m 100 m 10 m 1 m 100 nm 10 nm 1 nm 0.1 nm visible with special electron microscopes visible with light microscope visible with conventional electron microscope most eukaryotic cells mitochondrion most bacteria virus proteins diameter of DNA double helix atoms Fig. 4-1

9 All Cells Share Common Features A plasma membrane encloses all cells and regulates material flow

11 All Cells Share Common Features Cytoplasm is the fluid interior where a cell s metabolic reactions occur Contains organelles Fluid portion (cytosol) contains water, salts, and organic molecules

12 All Cells Share Common Features All cells use DNA (deoxyribonucleic acid) as a hereditary blueprint All cells use RNA (ribonucleic acid) to copy DNA to make proteins

13 All Cells Share Common Features All cells obtain energy and nutrients from the environment All cells use common building blocks to build the molecules of life

14 Some Cell Types Have Cell Walls Stiff coatings on outer surfaces of bacteria, plants, fungi, and some protists are cell walls Cells walls support and protect fragile cells and are usually porous

15 Cell Walls Cell walls are composed of polysaccharides like cellulose or chitin

16 Cell Walls Cell walls in plants may have multiple layers Primary cell walls in plants are outermost Secondary cell walls are innermost Cell walls of adjacent cells joined by middle lamellae

18 4.2 How Do Prokaryotic And Eukaryotic Cells Differ? There are two kinds of cells. Prokaryotic cells Are found only in two groups of singlecelled organisms the bacteria and archaea Eukaryotic cells Are structurally more complex cells Possess a membrane-enclosed nucleus Probably arose from prokaryotic cells

19 There Are Two Basic Cell Types Prokaryotic Before nucleus

20 4.7 What Are The Features Of Prokaryotic Cells? Prokaryotic cells are much smaller than eukaryotic cells (< 5 µm long) Are very reproductively successful and so are more abundant Have a simple internal structure Surrounded by a stiff cell wall, which provides shape and protection Can take the shape of rods, spheres, or helices

23 Prokaryotic Cells Some bacteria are propelled by flagella Infectious bacteria may have polysaccharide adhesive capsules and slime layers on their surfaces Pili and fimbriae are protein projections in some bacteria that further enhance adhesion

25 Prokaryotic Cells No nuclear membrane or membranebound organelles present Some have internal membranes used to capture light Cytoplasm contains ribosomes used for protein synthesis Cytoplasm may contain food granules

27 Prokaryotic Cells Single, circular chromosome of DNA Chromosome found coiled in an area called the nucleoid Small rings of DNA (plasmids) located in the cytoplasm

28 Prokaryotic Cells A generalized prokaryotic cell chromosome (nucleoid region) ribosomes food granule prokaryotic flagellum cell wall cytoplasm plasma membrane Fig. 4-11

29 There Are Two Basic Cell Types Eukaryotic True nucleus Includes Protist, Fungi, Plant, and Animal cells

30 4.3 What Are The Main Features Of Eukaryotic Cells? Eukaryotic cells are > 10 µm long The cytoskeleton provides shape and organization A variety of membrane-enclosed organelles perform specific functions

31 Major Features Nucleus: contains DNA Mitochondria: produce energy Endoplasmic reticulum: synthesizes membrane components and lipids Golgi apparatus: molecule sorting center Lysosomes: digest cellular membranes or defective organelles Microtubules: make up the cytoskeleton

Major Features A generalized animal cell flagellum cytoplasm rough endoplasmic reticulum ribosome lysosome nuclear pore chromatin (DNA) nucleus nucleolus nuclear

32 Major Features A generalized animal cell flagellum cytoplasm rough endoplasmic reticulum ribosome lysosome nuclear pore chromatin (DNA) nucleus nucleolus nuclear envelope centriole intermediate filaments plasma membrane microtubules free ribosome smooth endoplasmic reticulum mitochondrion vesicle Golgi apparatus vesicle Fig. 4-3

33 Major Features Animal and plant cells differ with regards to cell walls, chloroplasts, plastids, central vacuoles, and centrioles

Major Features A generalized plant cell microtubules (part of cytoskeleton) mitochondrion chloroplast Golgi apparatus smooth endoplasmic reticulum vesicle rough endoplasmic

34 Major Features A generalized plant cell microtubules (part of cytoskeleton) mitochondrion chloroplast Golgi apparatus smooth endoplasmic reticulum vesicle rough endoplasmic reticulum nucleolus nuclear pore chromatin nuclear envelope nucleus central vacuole plasmodesma cell wall plasma membrane intermediate filaments ribosomes free ribosome Fig. 4-4

35 4.4 What Role Does The Nucleus Play? The nucleus is the largest organelle in the cell. It is bounded by a nuclear envelope. It contains granular-looking chromatin. It contains the nucleolus.

36 The Nucleus The nuclear envelope separates chromosomes from cytoplasm Envelope is a double membrane with nuclear pores for transport Some smaller materials can move through the pores, while others, such as DNA, are excluded. Outer membrane is studded with ribosomes

37 The Nucleus The nucleus nucleolus nuclear envelope nuclear pores nucleus chromatin nuclear pores (a) Structure of the nucleus (b) Yeast cell Fig. 4-5

39 The Nucleus The nucleus contains DNA in various configurations Compacted chromosomes (during cell division) Diffuse chromatin (as DNA directs reactions through an RNA intermediate by coding for proteins)

41 The Nucleus Darker area within the nucleus called the nucleolus Functions as the site of ribosome synthesis Ribosomes synthesize proteins Ribosomes are composed of RNA and proteins

42 The Nucleus Ribosome components are made at the nucleolus. The nucleolus contains DNA, RNA, proteins, and ribosomes in various stages of construction. This is the site where components of ribosomes are constructed. Ribosome components leave the nucleus and are assembled in the cytoplasm.

43 4.5 What Roles Do Membranes Play In Eukaryotic Cells? The plasma membrane isolates the cell, and alternately, helps it interact with its environment. The phospholipid bilayer contains globular proteins that regulate the transport of molecules into and out of the cell. Plant, fungi, and some protist cells also have a cell wall outside the plasma membrane, which acts as a protective coating.

44 System of Membranes The endoplasmic reticulum (ER) forms a series of enclosed, interconnected channels within cell There are two forms of ER: Rough endoplasmic reticulum: is studded with ribosomes Smooth endoplasmic reticulum: has no ribosomes

45 System of Membranes Vesicles are membranous sacs that transport substances among the separate regions of the membrane system

47 System of Membranes Smooth ER has no ribosomes Contains enzymes that detoxify drugs (in liver cells) Synthesizes phospholipids and cholesterol. Together with rough ER are the sites of new membrane synthesis for the cell.

49 System of Membranes Rough ER is studded with ribosomes on outside Produces proteins and phospholipids destined for other membranes or for secretion (export) Together with rough ER are the sites of new membrane synthesis for the cell.

51 System of Membranes The Golgi Apparatus is a set of stacked flattened sacs Receive proteins from ER (via transport vesicles) and sorts them by destination Modify some molecules (e.g. proteins to glycoproteins) Package material into vesicles for transport

53 System of Membranes Three fates of substances made in the membrane system: 1. Secreted proteins made in RER, travel through Golgi, then are exported through plasma membrane The following figure illustrates this process for antibodies Antibodies are proteins produced by white blood cells to inactivate foreign diseasecausing agents

55 System of Membranes 2. Digestive proteins made in RER, travel through Golgi, and are packaged as lysosomes for use in cell Lysosomes fuse with food vacuoles and digest food into basic nutrients In the cytoplasm, they digest defective organelles or pieces of membrane into component parts that can be recycled.

57 System of Membranes 3. Membrane proteins and lipids made in ER, travel through Golgi, and replenish or enlarge organelle and plasma membranes

59 4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Vacuoles Mitochondria Chloroplasts Plastids Cytoskeleton Cilia and flagella

60 Vacuoles Fluid-filled sacs with a single membrane Functions of vacuoles Contractile vacuoles in freshwater organisms used to collect and pump water out Many plant cells have a large central vacuole.

62 Vacuoles Functions of vacuoles (continued) Plant central vacuoles used in several ways Maintain water balance Store hazardous wastes, nutrients, or pigments Provide turgor pressure on cytoplasm to keep cells rigid

63 Mitochondria Extract Food Energy Mitochondria are round, oval, or tubular sacs of double-membranes Inner membrane is folded into cristae Intermembrane compartment lies between inner and outer membranes Matrix space within inner membrane

67 Mitochondria Extract Food Energy Mitochondria may be remnants of free-living prokaryotes (endosymbiotic hypothesis)

68 Mitochondria Extract Food Energy Function as the powerhouses of the cell Mitochondria extract energy from food molecules Extracted energy is stored in high-energy bonds of ATP Energy extraction process involves anaerobic and aerobic reactions

69 Chloroplasts Chloroplasts are specialized organelles surrounded by a double membrane Outer membrane Inner membrane encloses the stroma space Stacked hollow membranous sacs (grana) within stroma are called thylakoids

73 Chloroplasts The thylakoid membranes contain chlorophyll and other pigments that capture sunlight and make sugar, CO 2, and water (photosynthesis)

74 Plants Use Plastids for Storage Plastids found only in plants and photosynthetic protists Surrounded by a double membrane

75 Plants Use Plastids for Storage Functions Storage for photosynthetic products like starch Storage of pigment molecules giving color to ripe fruit

77 Cytoskeleton The cytoskeleton provides shape, support, and movement. All organelles in the cell do not float about the cytoplasm, but instead, are attached to a network of protein fibers called the cytoskeleton.

78 Cytoskeleton Several type of protein fibers make up the cytoskeleton. Microfilaments: thin fibers Intermediate filaments: medium-sized fibers Microtubules: thick fibers

79 Cytoskeleton plasma membrane microfilaments mitochondrion microtubules (red) intermediate filaments ribosomes endoplasmic reticulum microtubule nucleus vesicle microfilaments (blue) (a) Components of the cytoskeleton (b) Cell with stained cytoskeleton Fig. 4-9

80 Cilia and Flagella Cilia and flagella are extensions of the plasma membrane

82 Cilia and Flagella Cilia and flagella are composed of microtubules in a 9+2 arrangement formed by centrioles which become membrane-anchored structures called basal bodies Cilia are short (10-25 µm) and numerous while flagella are long (50-75 µm) but few in any cell

84 Cilia and Flagella Long pairs of microtubules slide along each other (using ATP) causing movement of cilia and flagella

85 Cilia and Flagella Functions Cilia or flagella may be used to move cell about Cilia may be used to create currents of moving fluid in their environment

86 4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Cilia provide force parallel to the plasma membrane, which can be described as a rowing motion. propulsion of fluid power stroke plasma membrane return stroke cilia lining the trachea (a) Cilium Fig. 4-10a

87 4.6 What Other Structures Play Key Roles In Eurkaryotic Cells? Flagella provide a force perpendicular to plasma membrane, like the engine on a motorboat. direction of locomotion propulsion of fluid continuous propulsion flagellum of human sperm (b) Flagellum Fig. 4-10b

89 Evolution of Membrane-Enclosed Organelles The first eukaryotes (cells that possess membrane-bound organelles) appeared about 1.7 billion years ago

90 Membrane-Enclosed Organelles Several organelles (mitochondria, chloroplasts, centrioles) may have arisen when primitive cells engulfed certain types of bacteria (the endosymbiont hypothesis)

91 Evolution of Mitochondria Anaerobic, predatory prokaryotic cell engulfs an aerobic bacterium that it failed to digest Predatory cell and bacterium gradually enter into a symbiotic relationship

92 Evolution of Mitochondria Descendants of engulfed bacterium evolve into mitochondria

94 Evolution of Chloroplasts Mitochondria-containing predatory prokaryotic cell engulf a photosynthetic bacterium Predatory cell and bacterium gradually enter into a symbiotic relationship Descendants of engulfed bacterium evolve into chloroplasts

96 Evidence for Endosymbionts Many biochemical features are shared by eukaryotic organelles and living bacteria Mitochondria, chloroplasts, and centrioles contain their own supply of DNA

97 Evidence for Endosymbionts Living intermediates (modern cells that host bacterial endosymbionts) Pelomyxa palustris harbors aerobic bacteria Paramecium harbors photosynthetic bacteria

Biology: Life on Earth

Teresa Audesirk Gerald Audesirk Bruce E. Byers Biology: Life on Earth Eighth Edition Lecture for Chapter 4 Cell Structure and Function Copyright 2008 Pearson Prentice Hall, Inc. Chapter 4 Outline 4.1 What