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LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 6 A Tour of the Cell Lectures by Erin Barley Kathleen Fitzpatrick © 2011 Pearson Education, Inc.

Overview: The Fundamental Units of Life • All organisms are made of cells • Cell structure function • All cells are related by their descent from earlier cells © 2011 Pearson Education, Inc.

Microscopy • Scientists use microscopes to visualize cells too small to see with the naked eye • In a light microscope (LM), visible light is passed through a specimen and then through glass lenses • Lenses refract (bend) the light, so that the image is magnified © 2011 Pearson Education, Inc.

• Three important parameters of microscopy – Magnification, the ratio of an object’s image size to its real size – Resolution, the measure of the clarity of the image, or the minimum distance of two distinguishable points – Contrast, visible differences in parts of the sample © 2011 Pearson Education, Inc.

10 m Human height 1 m 0. 1 m Length of some nerve and muscle cells Chicken egg 1 cm Unaided eye Frog egg 1 mm Human egg Most plant and animal cells 10 m 100 nm Nucleus Most bacteria Mitochondrion Smallest bacteria Viruses Ribosomes 10 nm Proteins Lipids 1 nm 0. 1 nm Small molecules Atoms Superresolution microscopy Electron microscopy 100 m Light microscopy Figure 6. 2

Figure 6. 3 Light Microscopy (LM) Electron Microscopy (EM) Brightfield (unstained specimen) Confocal Longitudinal section of cilium Cross section of cilium 50 m Cilia 50 m Brightfield (stained specimen) 2 m Deconvolution 10 m Phase-contrast Differential-interferencecontrast (Nomarski) Super-resolution 10 m 1 m Fluorescence Scanning electron microscopy (SEM) Transmission electron microscopy (TEM)

• LMs can magnify effectively to about 1, 000 times the size of the actual specimen • Stain/contrast techniques reveal detail • Most subcellular structures, including organelles (membrane-enclosed compartments), are too small to see with light microscope © 2011 Pearson Education, Inc.

• Two kinds of electron microscopes (EMs) 1. Scanning electron microscopes (SEMs) look at surface of a specimen, take 3 -D photos 2. Transmission electron microscopes (TEMs) focus a beam of electrons through a thin slice of a specimen – TEMs are used to study the internal structure of cells © 2011 Pearson Education, Inc.

• light microscopy – more detail than in the past – Confocal microscopy, deconvolution • sharper images of 3 -D tissues and cells – New techniques for labeling cells improve resolution © 2011 Pearson Education, Inc.

Cell Fractionation • Cell fractionation – taking cells apart to look at the organelles & study function • Centrifuges separate organelles by fractionate • Biochemistry and cytology help correlate cell function with structure © 2011 Pearson Education, Inc.

Concept 6. 2: Eukaryotic cells have internal membranes that compartmentalize their functions • two types: 1. 2. prokaryotic (bacteria/Archaea) eukaryotic (nucleus) • Protists, fungi, animals, and plants all consist of eukaryotic cells © 2011 Pearson Education, Inc.

Comparing Prokaryotic and Eukaryotic Cells • Basic features of all cells – Plasma membrane – Semifluid substance called cytosol – Chromosomes (carry genes) – Ribosomes (make proteins) © 2011 Pearson Education, Inc.

Comparing Prokaryotic and Eukaryotic Cells • Many cell types have walls – Some bacteria (peptidoglycans) – Some fungi (chitin) – Some protists (silicon) – Most plants (cellulose) – NOT ANIMALS (no wall) © 2011 Pearson Education, Inc.

Comparing Prokaryotic and Eukaryotic Cells • Many cell types can do photosynthesis – Some bacteria – Some protists – Almost ALL plants (exception: dodder) – NOT ANIMALS or fungi (unless stolen organelle or symbiont) © 2011 Pearson Education, Inc.

• Prokaryotic cells are characterized by having – No nucleus – DNA in an unbound region called the nucleoid – No membrane-bound organelles – Cytoplasm bound by the plasma membrane © 2011 Pearson Education, Inc.

Figure 6. 5 Fimbriae Nucleoid Ribosomes Plasma membrane Bacterial chromosome Cell wall Capsule 0. 5 m (a) A typical rod-shaped bacterium Flagella (b) A thin section through the bacterium Bacillus coagulans (TEM)

• Eukaryotic cells have – DNA in a nucleus (“nuclear envelope”) – organelles – Cytoplasm between the plasma membrane and nucleus • Eukaryotic cells are usually prokaryotic cells © 2011 Pearson Education, Inc.

plasma membrane • Semi-permeables: controls what gets in or out of cell (oxygen, nutrients, waste) • Mostly a double layer of phospholipids • Other parts of membrane include Lots of other proteins and carbohydrates © 2011 Pearson Education, Inc.

Figure 6. 6 Outside of cell Inside of cell 0. 1 m (a) TEM of a plasma membrane Carbohydrate side chains Hydrophilic region Hydrophobic region Hydrophilic region Phospholipid Proteins (b) Structure of the plasma membrane

• Why cells don’t get too big: • They need enough surface area to exchange oxygen/waste/nutrients • Small cells have a greater surface area relative to volume © 2011 Pearson Education, Inc.

A Panoramic View of the Eukaryotic Cell • A eukaryotic cell: membrane-bound organelles • Plant and animal cells have most of the same organelles Bio. Flix: Tour of an Animal Cell Bio. Flix: Tour of a Plant Cell © 2011 Pearson Education, Inc.

Concept 6. 3: The eukaryotic cell’s genetic instructions are housed in the nucleus and carried out by the ribosomes • The nucleus contains most of the DNA in a eukaryotic cell • Ribosomes use the information from the DNA to make proteins • Chef cartoon! © 2011 Pearson Education, Inc.

The Nucleus: Information Central • The nucleus contains most of the cell’s genes and is usually the most conspicuous organelle • Mitochondria have own DNA and ribosomes • The nuclear envelope around nucleus • a double membrane; each membrane consists of a lipid bilayer © 2011 Pearson Education, Inc.

Figure 6. 9 1 m Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Outer membrane Nuclear pore Rough ER Surface of nuclear envelope Pore complex Ribosome Chromatin 1 m 0. 25 m Close-up of nuclear envelope Pore complexes (TEM) Nuclear lamina (TEM)

Nuclear Pores (windows on the castle) • Pores regulate the entry and exit of molecules from the nucleus • The shape of the nucleus is maintained by the nuclear lamina, which is composed of protein • Proteins control membrane shape (true of many membranes, not just this one) © 2011 Pearson Education, Inc.

• DNA = deoxyribonucleic acid • Chromatin = DNA wrapped around histone proteins • Chromosomes = long chain of chromatin (one long DNA molecule and the histone proteins it is wrapped around) Looks like this @ cell division spread out the rest of time © 2011 Pearson Education, Inc.

nucleolus • Part of the nucleus • Where we make r. RNA – Major part of ribosome (chef) All RNA is made in the nucleus Reading DNA to make RNA is called “transcription” (monk-like “scribe”) © 2011 Pearson Education, Inc.

Ribosomes: Chef that makes Proteins • Part r. RNA, part protein • Found in two places in cell – In the cytosol (free ribosomes) Floating between nucleus and plasma memb. – Stuck to endoplasmic reticulum or nuclear envelope (bound ribosomes) May be able to move in or out of ER © 2011 Pearson Education, Inc.

Figure 6. 10 0. 25 m Free ribosomes in cytosol Endoplasmic reticulum (ER) Ribosomes bound to ER Large subunit TEM showing ER and ribosomes Small subunit Diagram of a ribosome

Concept 6. 4: The endomembrane system regulates protein traffic and performs metabolic functions in the cell • Components of the endomembrane system – Nuclear envelope – Endoplasmic reticulum – Golgi apparatus – Lysosomes – Vacuoles – Plasma membrane • These components are either continuous or connected via transfer by vesicles © 2011 Pearson Education, Inc.

The Endoplasmic Reticulum: Biosynthetic Factory • ER >50% of membranes in eukaryotic cells • continuous with the nuclear envelope • There are two distinct regions of ER – Smooth ER, no ribosomes – Rough ER, covered in ribosomes © 2011 Pearson Education, Inc.

Functions of Smooth ER • The smooth ER – makes lipids – Metabolizes carbohydrates – Detoxifies drugs and poisons – Stores calcium ions • “sarcoplasmic reticulum” © 2011 Pearson Education, Inc.

Functions of Rough ER • The rough ER – bound ribosomes • Make glycoproteins (proteins + carb) – Gives off transport vesicles, proteins surrounded by membranes – Is a membrane factory for the cell © 2011 Pearson Education, Inc.

Golgi Apparatus: Shipping & Receiving Center Golgi apparatus: membranous sacs (cisternae) • Functions of the Golgi apparatus – Modifies ER products – Sorts & packages stuff into transport vesicles – Makes some macromolecules © 2011 Pearson Education, Inc.

Lysosomes: Digestive Compartments • Cell’s mobile stomach unit • Lysosome: membranous sac full of hydrolytic enzymes (work best in acid) – digests macromolecules • • Proteins Fats Polysaccharides nucleic acids Animation: Lysosome Formation © 2011 Pearson Education, Inc.

• Some types of cell can eat another cell by phagocytosis; this forms a food vacuole • A lysosome fuses with the food vacuole and digests the molecules (breaks it apart) • Lysosomes also do “autophagy” (self eating) – Break down cell’s own old or unneeded organelles and macromolecules, – Can reuse parts © 2011 Pearson Education, Inc.

Vacuoles: Maintenance Compartments • In plant cell or fungal cell • can have one or several vacuoles • derived from ER and Golgi apparatus © 2011 Pearson Education, Inc.

• Food vacuoles are formed by phagocytosis • Contractile vacuoles, found in many freshwater protists, pump excess water out of cells – Water wants to dilute stuff, often flowing into cells – Must pump extra out • Central vacuoles, found in many mature plant cells, hold organic compounds and water Video: Paramecium Vacuole © 2011 Pearson Education, Inc.

The Endomembrane System: A Review • The endomembrane system is a complex and dynamic player in the cell’s compartmental organization © 2011 Pearson Education, Inc.

Concept 6. 5: Mitochondria and chloroplasts change energy from one form to another • Mitochondria: where respiration happens • Uses sugar and oxygen to make ATP Found in ALL eukaryotes • Chloroplasts: where photosynthesis happens – found in plants and some protists (algae) – Not found in animals or fungi no photosynthesis unless symbiosis or theft © 2011 Pearson Education, Inc.

Weird Stuff • Prokaryotes don’t have chloroplasts • No membrane bound organelles • Some still do photosynthesis • Peroxisomes are oxidative organelles © 2011 Pearson Education, Inc.

Evolutionary Origins: Mitochondria & Chloroplasts • Similar to bacteria – free ribosomes and circular DNA molecules – Can grow & reproduce independently in cells • Enveloped by a double membrane © 2011 Pearson Education, Inc.

• The Endosymbiont theory – An early ancestor of eukaryotic cells engulfed a nonphotosynthetic prokaryotic cell, which formed an endosymbiont relationship with its host – The host cell and endosymbiont merged into a single organism, a eukaryotic cell with a mitochondrion – At least one of these cells may have taken up a photosynthetic prokaryote, becoming the ancestor of cells that contain chloroplasts © 2011 Pearson Education, Inc.

Figure 6. 16 Endoplasmic reticulum Nucleus Engulfing of oxygen. Nuclear using nonphotosynthetic envelope prokaryote, which becomes a mitochondrion Ancestor of eukaryotic cells (host cell) Mitochondrion Nonphotosynthetic eukaryote At least one cell Engulfing of photosynthetic prokaryote Chloroplast Mitochondrion Photosynthetic eukaryote

Mitochondria: Chemical Energy Conversion • Mitochondria in nearly all eukaryotic cells • smooth outer membrane & inner membrane folded into cristae • two compartments: – intermembrane space • H+ pumped to here – mitochondrial matrix • H+ flows passively to here © 2011 Pearson Education, Inc.

Mitochondria: Chemical Energy Conversion • Some metabolic steps of cellular respiration are catalyzed in the mitochondrial matrix • Cristae present a large surface area for enzymes that synthesize ATP © 2011 Pearson Education, Inc.

Chloroplasts: Capture of Light Energy • Chloroplasts have chlorophyll • found in – Leaves – other green organs of plants – algae © 2011 Pearson Education, Inc.

• Chloroplast structure includes – Thylakoids, membrane sacs (hydrogen ions) – Granum: stacks of thylakoids – Stroma, fluid filled space around thylakoids • The chloroplast is one of a group of plant organelles, called plastids © 2011 Pearson Education, Inc.

Peroxisomes: Oxidation • • specialized metabolic compartments single membrane Make hydrogen peroxide & convert to water Peroxisomes perform reactions with many different functions • How peroxisomes are related to other organelles is still unknown © 2011 Pearson Education, Inc.

Concept 6. 6: cytoskeleton - protein fibers to organize structures and activities in the cell • • fibers extend throughout cytoplasm Organizes cell’s structures and activities anchors many organelles three types – Microtubules – Intermediate filaments – Microfilaments © 2011 Pearson Education, Inc.

10 m Figure 6. 20

Cytoskeleton job: Support and Motility • Supports cell and maintains shape • Interacts with motor proteins to produce motility • vesicles can travel along microtubules • Recent evidence suggests that the cytoskeleton may help regulate biochemical activities © 2011 Pearson Education, Inc.

Components of the Cytoskeleton • Three main types of fibers – Microtubules: thickest – Intermediate filaments are fibers with diameters in a middle range – Microfilaments: thinnest © 2011 Pearson Education, Inc.

Table 6. 1 10 m 5 m Column of tubulin dimers Keratin proteins Fibrous subunit (keratins coiled together) Actin subunit 25 nm 7 nm Tubulin dimer 8 12 nm

Microtubules • Microtubules are hollow rods about 25 nm in diameter and about 200 nm to 25 microns long • Functions of microtubules – Shaping the cell – Guiding movement of organelles – Separating chromosomes during cell division © 2011 Pearson Education, Inc.

Centrosomes and Centrioles • The centrosome is a “microtubule-organizing center” • In many cells, microtubules grow out from a centrosome near the nucleus • In animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a ring © 2011 Pearson Education, Inc.

Figure 6. 22 Centrosome Microtubule Centrioles 0. 25 m Longitudinal section of one centriole Microtubules Cross section of the other centriole

Cilia and Flagella • Microtubules control the beating of cilia and flagella, locomotor appendages of some cells • Cilia and flagella differ in their beating patterns Video: Chlamydomonas Video: Paramecium Cilia © 2011 Pearson Education, Inc.

• Cilia and flagella share a common structure – microtubules sheathed by plasma membrane – basal body to anchor the cilium or flagellum – Dynein: motor protein that bends cilia/flagella Animation: Cilia and Flagella © 2011 Pearson Education, Inc.

• How dynein “walking” moves flagella and cilia − Dynein arms alternately grab, move, and release the outer microtubules – Protein cross-links limit sliding – Forces exerted by dynein arms cause doublets to curve, bending the cilium or flagellum © 2011 Pearson Education, Inc.

Microfilaments (Actin Filaments) • Microfilaments: twisted double chain of actin • resist pulling forces within the cell • Cortex: 3 -D network inside plasma membrane support the cell’s shape © 2011 Pearson Education, Inc.

Microfilaments (Actin Filaments) • Bundles of microfilaments make up the core of microvilli of intestinal cells © 2011 Pearson Education, Inc.

• Microfilaments: part of muscle contraction • Actin fibers pulled on by myosin fibers © 2011 Pearson Education, Inc.

• Localized contraction brought about by actin and myosin also drives amoeboid movement • Pseudopodia (cellular extensions) extend and contract through the reversible assembly and contraction of actin subunits into microfilaments © 2011 Pearson Education, Inc.

• Cytoplasmic streaming is a circular flow of cytoplasm within cells • This streaming speeds distribution of materials within the cell • In plant cells, actin-myosin interactions and solgel transformations drive cytoplasmic streaming Video: Cytoplasmic Streaming © 2011 Pearson Education, Inc.

Intermediate Filaments • Intermediate filaments range in diameter from 8 – 12 nanometers, larger than microfilaments but smaller than microtubules • They support cell shape and fix organelles in place • Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes © 2011 Pearson Education, Inc.

Concept 6. 7: Extracellular components and connections between cells help coordinate cellular activities • Most cells synthesize and secrete materials that are external to the plasma membrane • These extracellular structures include – Cell walls of plants – The extracellular matrix (ECM) of animal cells – Intercellular junctions © 2011 Pearson Education, Inc.

Cell Walls of Plants • The cell wall is an extracellular structure that distinguishes plant cells from animal cells • Prokaryotes, fungi, and some protists also have cell walls • The cell wall protects the plant cell, maintains its shape, and prevents excessive uptake of water • Plant cell walls are made of cellulose fibers embedded in other polysaccharides and protein © 2011 Pearson Education, Inc.

• Plant cell walls may have multiple layers – Primary cell wall: relatively thin and flexible – Middle lamella: thin layer between primary walls of adjacent cells – Secondary cell wall (in some cells): added between the plasma membrane and the primary cell wall • Plasmodesmata are channels between adjacent plant cells © 2011 Pearson Education, Inc.

Figure 6. 28 Secondary cell wall Primary cell wall Middle lamella 1 m Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata

The Extracellular Matrix (ECM) of Animal Cells • Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM) • The ECM is made up of glycoproteins such as collagen, proteoglycans, and fibronectin • ECM proteins bind to receptor proteins in the plasma membrane called integrins © 2011 Pearson Education, Inc.

Figure 6. 30 Collagen Polysaccharide molecule EXTRACELLULAR FLUID Proteoglycan complex Fibronectin Carbohydrates Core protein Integrins Proteoglycan molecule Plasma membrane Proteoglycan complex Microfilaments CYTOPLASM

• Functions of the ECM – Support – Adhesion – Movement – Regulation © 2011 Pearson Education, Inc.

Cell Junctions • Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact • Intercellular junctions facilitate this contact • There are several types of intercellular junctions – Plasmodesmata – Tight junctions – Desmosomes – Gap junctions © 2011 Pearson Education, Inc.

Plasmodesmata in Plant Cells • Plasmodesmata are channels that perforate plant cell walls • Through plasmodesmata, water and small solutes (and sometimes proteins and RNA) can pass from cell to cell © 2011 Pearson Education, Inc.

Figure 6. 31 Cell walls Interior of cell 0. 5 m Plasmodesmata Plasma membranes

Tight Junctions, Desmosomes, and Gap Junctions in Animal Cells • At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid • Desmosomes (anchoring junctions) fasten cells together into strong sheets • Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells © 2011 Pearson Education, Inc.

Animation: Tight Junctions Animation: Desmosomes Animation: Gap Junctions © 2011 Pearson Education, Inc.

Figure 6. 32 Tight junctions prevent fluid from moving across a layer of cells Tight junction TEM 0. 5 m Tight junction Intermediate filaments Desmosome TEM 1 m Gap junction Space between cells Plasma membranes of adjacent cells Extracellular matrix TEM Ions or small molecules 0. 1 m

The Cell: A Living Unit Greater Than the Sum of Its Parts • Cells rely on the integration of structures and organelles in order to function • For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the cytoskeleton, lysosomes, and plasma membrane © 2011 Pearson Education, Inc.

5 m Figure 6. 33

Figure 6. UN 01 Nucleus (ER) (Nuclear envelope)

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