Chapter 6: A Tour of the Cell

The Beginning First Cells - 1665 First Living Cells - 1674 Hooke’s Microscope First Cells - 1665 Leeuwenhoek’s Microscope First Living Cells - 1674

Studying Cells Microscopes Light Electron Cell Fractionation

The Light Microscope Light is transmitted through the specimen Magnified and focused using lenses Maximum magnification is around 1000X Sample can be stained to see various organelles and internal structures Can look at preserved or living specimens

The Light Microscope Light is transmitted through the specimen Magnified and focused using lenses Maximum magnification is around 1000X Sample can be stained to see various organelles and internal structures Can view preserved or living specimens

Micrograph from Light Microscope Euglena, LM 1000X

Resolution

The Electron Microscope Two types: Scanning (SEM) and Transmission (TEM) Electrons are passed through the specimen (TEM) or bounce off the surface (SEM) Maximum magnification is around 100,000X High resolution All specimens MUST BE preserved – no living cells

Micrograph from Transmission Electron Microscope

A single yeast cell (colorized TEM) Figure 6.8bc 1 m Cell wall Vacuole Nucleus Mitochondrion Figure 6.8 Exploring: Eukaryotic Cells A single yeast cell (colorized TEM)

Micrograph from Scanning Electron Microscope

Centrifuged at 1,000 g (1,000 times the force of gravity) for 10 min Fig. 6-5 TECHNIQUE Homogenization Tissue cells Homogenate Centrifugation Differential centrifugation Centrifuged at 1,000 g (1,000 times the force of gravity) for 10 min Supernatant poured into next tube 20,000 g 20 min 80,000 g 60 min Pellet rich in nuclei and cellular debris 150,000 g 3 hr Pellet rich in mitochondria (and chloro- plasts if cells are from a plant) Pellet rich in “microsomes” (pieces of plasma membranes and cells’ internal membranes) Pellet rich in ribosomes Cell Fractionation Technique used to separate organelles and major structures from one another Involves centrifugation Heavier components are pushed to the bottom of the test tube Can separate out using sequential centrifugations at increasing speeds

Cell Theory All organisms are made of cells All cells come from cells

Features of All Cells Plasma membrane - selective barrier Cytoplasm – semifluid substance containing organelles and other components DNA – genetic information Ribosomes – protein making structures

Prokaryotes vs. Eukaryotes DNA Location: Proks: nucleoid region Euks: nucleus Organelles Proks: no true organelles (no internal membranes) Euks: membrane-bound organelles Size Proks: smaller Euks: larger

Nucleoid region Nucleus Organelles Eukaryotic cell Prokaryotic cell Colorized TEM 15,000 Eukaryotic cell Organelles

Surface area increases while total volume remains constant Fig. 6-8 Surface area increases while total volume remains constant 5 1 6 150 750 125 1.2 Total surface area [Sum of the surface areas (height  width) of all boxes sides  number of boxes] Total volume [height  width  length  number of boxes] Surface-to-volume (S-to-V) ratio [surface area ÷ volume] Does size matter?

Features of Prokaryotic Cells Fig. 6-6 Features of Prokaryotic Cells Fimbriae Nucleoid Ribosomes Plasma membrane Cell wall Capsule Flagella Bacterial chromosome (a) A typical rod-shaped bacterium (b) A thin section through the bacterium Bacillus coagulans (TEM) 0.5 µm

Organisms with eukaryotic cells Animals Plants Fungi Protists

Animal Cell ENDOPLASMIC RETICULUM (ER) Nuclear envelope Rough ER Figure 6.8a ENDOPLASMIC RETICULUM (ER) Rough ER Smooth ER Nuclear envelope Nucleolus Chromatin Plasma membrane Ribosomes Golgi apparatus Lysosome Mitochondrion Peroxisome Microvilli Microtubules Intermediate filaments Microfilaments Centrosome CYTOSKELETON: Flagellum NUCLEUS Animal Cell

Rough endoplasmic reticulum Figure 6.8c NUCLEUS Nuclear envelope Nucleolus Chromatin Golgi apparatus Mitochondrion Peroxisome Plasma membrane Cell wall Wall of adjacent cell Plasmodesmata Chloroplast Microtubules Intermediate filaments Microfilaments CYTOSKELETON Central vacuole Ribosomes Smooth endoplasmic reticulum Rough endoplasmic reticulum Plant Cell

Features Found in Plant Cells, but NOT Animal Cells Cell Wall Chloroplast Central vacuole Plasmodesmata

Features Found in Animal Cells, but NOT Plant Cells Lysosomes Centrosomes Flagella

Nucleus Nucleus Nucleolus Chromatin Nuclear envelope: Inner membrane Fig. 6-10 Nucleolus Nucleus Rough ER Nuclear lamina (TEM) Close-up of nuclear envelope 1 µm 0.25 µm Ribosome Pore complex Nuclear pore Outer membrane Inner membrane Nuclear envelope: Chromatin Surface of nuclear envelope Pore complexes (TEM) Nucleus

Ribosome Cytosol Endoplasmic reticulum (ER) Free ribosomes Fig. 6-11 Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit Small subunit Diagram of a ribosome TEM showing ER and ribosomes 0.5 µm Ribosome

Endomembrane System: Overview Transport vesicle from ER to Golgi Rough ER Nucleus Smooth ER Nuclear envelope Golgi apparatus Lysosome Vacuole Plasma membrane Transport vesicle from Golgi to plasma membrane

Endoplasmic Reticulum (ER) Fig. 6-12 Smooth ER Rough ER Nuclear envelope Transitional ER Transport vesicle Ribosomes Cisternae ER lumen 200 nm Endoplasmic Reticulum (ER)

Smooth ER Three functions of the Smooth ER: Lipid production Detoxifying enzymes Calcium ion storage

Rough ER Two functions of the Rough ER: Membrane production Along with ribosomes, produce proteins for use within the endomembrane system or for secretion from the cell Protein modification

Transport vesicle buds off Ribosome Polypeptide Glycoprotein Sugar chain Rough ER Secretary (glyco-) protein inside trans- port vesicle

Golgi Apparatus (Golgi Complex) Figure 6.12 Golgi Apparatus (Golgi Complex) cis face (“receiving” side of Golgi apparatus) 0.1 m Cisternae Figure 6.12 The Golgi apparatus. trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus

Lysosome Figure 6.13 Figure 6.13 Lysosomes. Vesicle containing two damaged organelles 1 m Nucleus 1 m Mitochondrion fragment Lysosome Peroxisome fragment Digestive enzymes Figure 6.13 Lysosomes. Lysosome Lysosome Peroxisome Plasma membrane Digestion Food vacuole Mitochondrion Digestion Vesicle (a) Phagocytosis (b) Autophagy

Central Vacuole Central vacuole Cytosol Central vacuole Nucleus Figure 6.14 Central vacuole Cytosol Central Vacuole Central vacuole Nucleus Figure 6.14 The plant cell vacuole. Cell wall Chloroplast 5 m

Nucleus Rough ER Smooth ER Plasma membrane Figure 6.15-1 Figure 6.15 Review: relationships among organelles of the endomembrane system. Plasma membrane

Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi Figure 6.15-2 Nucleus Rough ER Smooth ER cis Golgi Figure 6.15 Review: relationships among organelles of the endomembrane system. Plasma membrane trans Golgi

Nucleus Rough ER Smooth ER cis Golgi Plasma membrane trans Golgi Figure 6.15-3 Nucleus Rough ER Smooth ER cis Golgi Figure 6.15 Review: relationships among organelles of the endomembrane system. Plasma membrane trans Golgi

Mitochondria: Powerhouse of the Cell Mitochondria are divided into two compartments (separated by the innermembrane): Intermembrane space Mitochondrial matrix

Endoplasmic reticulum Nucleus Figure 6.16 Endoplasmic reticulum Nucleus Engulfing of oxygen- using nonphotosynthetic prokaryote, which becomes a mitochondrion Nuclear envelope Ancestor of eukaryotic cells (host cell) Mitochondrion Engulfing of photosynthetic prokaryote At least one cell Figure 6.16 The endosymbiont theory of the origin of mitochondria and chloroplasts in eukaryotic cells. Chloroplast Nonphotosynthetic eukaryote Mitochondrion Photosynthetic eukaryote

Mitochondria: Powerhouse of the Cell Figure 6.17 Mitochondria: Powerhouse of the Cell 10 m Intermembrane space Outer Mitochondria membrane DNA Inner Mitochondrial DNA Free ribosomes in the mitochondrial matrix membrane Cristae Matrix Nuclear DNA Figure 6.17 The mitochondrion, site of cellular respiration. 0.1 m (a) Diagram and TEM of mitochondrion (b) Network of mitochondria in a protist cell (LM)

Chloroplasts: Site of Photosynthesis Converts solar energy into chemical energy Chloroplasts are divided into three compartments: Intermembrane space Stroma Grana

Chloroplasts: Site of Photosynthesis Figure 6.18 Chloroplasts: Site of Photosynthesis Ribosomes 50 m Stroma Inner and outer membranes Granum Chloroplasts (red) DNA Thylakoid Intermembrane space 1 m Figure 6.18 The chloroplast, site of photosynthesis. (a) Diagram and TEM of chloroplast (b) Chloroplasts in an algal cell

Peroxisome 1 m Chloroplast Peroxisome Mitochondrion Figure 6.19 Figure 6.19 A peroxisome.

Cytoskeleton Microfilaments – thinnest Intermediate filaments Microtubules – thickest

Cytoskeleton 10 m Microfilaments – thinnest Intermediate filaments Figure 6.20 Cytoskeleton 10 m Figure 6.20 The cytoskeleton. Microfilaments – thinnest Intermediate filaments Microtubules – thickest

Table 6.1 The Structure and Function of the Cytoskeleton 10 m 10 m 5 m Table 6.1 The Structure and Function of the Cytoskeleton Column of tubulin dimers Keratin proteins Actin subunit Fibrous subunit (keratins coiled together) 25 nm 7 nm 812 nm   Tubulin dimer

Cilia and Flagella Direction of swimming (a) Motion of flagella 5 m Figure 6.23 Direction of swimming (a) Motion of flagella Cilia and Flagella 5 m Direction of organism’s movement Figure 6.23 A comparison of the beating of flagella and motile cilia. Power stroke Recovery stroke (b) Motion of cilia 15 m

Cross section of cilium Fig. 6-24 Outer microtubule doublet Plasma membrane 0.1 µm Dynein proteins Central microtubule Radial spoke Protein cross-linking outer doublets Microtubules (b) Cross section of cilium Plasma membrane Basal body 0.5 µm (a) Longitudinal section of cilium 0.1 µm Triplet (c) Cross section of basal body

Secondary cell wall Primary cell wall Middle lamella Central vacuole Fig. 6-28 Secondary cell wall Primary cell wall Middle lamella 1 µm Central vacuole Cytosol Plasma membrane Plant cell walls Plasmodesmata

Fig. 6-30 Collagen Proteoglycan Polysaccharide complex molecule EXTRACELLULAR FLUID Carbo- hydrates Fibronectin Core protein Integrins Proteoglycan molecule Plasma membrane Proteoglycan complex Micro- filaments CYTOPLASM

Fig. 6-32 Tight junction Tight junctions prevent fluid from moving across a layer of cells 0.5 µm Tight junction Intermediate filaments Desmosome Desmosome Gap junctions 1 µm Extracellular matrix Space between cells Gap junction Plasma membranes of adjacent cells 0.1 µm

Figure 6.UN01 Summary table, Concepts 6.3–6.5 Nucleus (ER) (Nuclear envelope) Figure 6.UN01 Summary table, Concepts 6.3–6.5