Chapter 6 ~ A Tour of the Cell

Cytology: study of cells Light microscopy: resolving power~ measure of clarity Electron microscopy: TEM~ electron beam to study cell ultra-structure SEM~ electron beam to study cell surfaces Cell fractionation: cell separation; organelle study

Differential- interference- contrast (Nomarski) Fluorescence 50 µm LE 6-3b Differential- interference- contrast (Nomarski) Fluorescence 50 µm Confocal 50 µm

Brightfield (unstained specimen) LE 6-3a Brightfield (unstained specimen) 50 µm Brightfield (stained specimen) Phase-contrast

Cell Types: Prokaryotic Nucleoid: DNA concentration No membrane organelles Ribosomes: protein synthesis Plasma membrane/CM (all cells) semi-permeable Cytoplasm/cytosol (all cells)

Carbohydrate side chain LE 6-8 Outside of cell Carbohydrate side chain Hydrophilic region Inside of cell 0.1 µm Hydrophobic region Hydrophilic region Phospholipid Proteins TEM of a plasma membrane Structure of the plasma membrane

Cell size As cell size increases, the surface area to volume ratio decreases Rates of chemical exchange may then be inadequate for cell size So …cell size remains small

Surface area increases while Total volume remains constant 5 1 1 Total surface area (height x width x number of sides x number of boxes) 6 150 750 Total volume (height x width x length X number of boxes) 1 125 125 Surface-to-volume ratio (surface area  volume) 6 1.2 6

Nucleus Genetic material... Double membrane envelope with pores chromatin chromosomes nucleolus: rRNA; ribosome synthesis Double membrane envelope with pores Protein synthesis (mRNA)

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

Ribosomes Protein manufacture Free Bound cytosol; protein function in cell Bound endoplasmic reticulum; membranes, organelles, and export

Ribosomes ER Cytosol Endoplasmic reticulum (ER) Free ribosomes Bound ribosomes Large subunit 0.5 µm Small subunit TEM showing ER and ribosomes Diagram of a ribosome

ENDOPLASMIC RETICULUM (ER LE 6-9a ENDOPLASMIC RETICULUM (ER Nuclear envelope Flagellum Rough ER Smooth ER Nucleolus NUCLEUS Chromatin Centrosome Plasma membrane CYTOSKELETON Microfilaments Intermediate filaments Microtubules Ribosomes: Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome In animal cells but not plant cells: Lysosomes Centrioles Flagella (in some plant sperm)

LE 6-9b Nuclear envelope Rough endoplasmic NUCLEUS reticulum Nucleolus Chromatin Smooth endoplasmic reticulum Centrosome Ribosomes (small brown dots) Central vacuole Golgi apparatus Microfilaments Intermediate filaments CYTOSKELETON Microtubules Mitochondrion Peroxisome Plasma membrane Chloroplast Cell wall Plasmodesmata Wall of adjacent cell In plant cells but not animal cells: Chloroplasts Central vacuole and tonoplast Cell wall Plasmodesmata

Endomembrane system Endoplasmic reticulum (ER) Continuous with nuclear envelope Smooth ER •no ribosomes •synthesis of lipids •metabolism of carbohydrates •detoxification of drugs and poisons Rough ER •with ribosomes •synthesis of secretory proteins & membrane production

Smooth ER Nuclear Rough ER envelope ER lumen Cisternae Ribosomes Transitional ER Transport vesicle 200 nm Smooth ER Rough ER

Endomembrane system Golgi apparatus Cisternae: Transport vesicles ER products are modified, stored, and then shipped Cisternae: flattened membranous sacs trans face (shipping) cis face (receiving) Transport vesicles

Golgi apparatus cis face (“receiving” side of Golgi apparatus) 0.1 µm LE 6-13 Golgi apparatus cis face (“receiving” side of Golgi apparatus) Vesicles move from ER to Golgi Vesicles coalesce to form new cis Golgi cisternae 0.1 µm Vesicles also transport certain proteins back to ER Cisternae Cisternal maturation: Golgi cisternae move in a cis- to-trans direction Vesicles form and leave Golgi, carrying specific proteins to other locations or to the plasma mem- brane for secretion Vesicles transport specific proteins backward to newer Golgi cisternae trans face (“shipping” side of Golgi apparatus) TEM of Golgi apparatus

Endomembrane system Lysosomes Phagocytosis sac of hydrolytic enzymes digestion of macromolecules Phagocytosis Autophagy: recycle cell’s own organic material (suicide bags) Tay-Sachs disease = lipid-digestion disorder

Phagocytosis: lysosome digesting food LE 6-14a Nucleus 1 µm Lysosome Lysosome contains active hydrolytic enzymes Food vacuole fuses with lysosome Hydrolytic enzymes digest food particles Digestive enzymes Plasma membrane Lysosome Digestion Food vacuole Phagocytosis: lysosome digesting food

two damaged organelles 1 µm LE 6-14b Lysosome containing two damaged organelles 1 µm Mitochondrion fragment Peroxisome fragment Lysosome fuses with vesicle containing damaged organelle Hydrolytic enzymes digest organelle components Lysosome Digestion Vesicle containing damaged mitochondrion Autophagy: lysosome breaking down damaged organelle

Endomembrane system Vacuoles Food (phagocytosis) membrane-bound sacs (larger than vesicles) Food (phagocytosis) Contractile (pump excess water) Central Vacuole (LARGE & storage in plants) Tonoplast = membrane (around vacuole)

Central vacuole Cytosol Tonoplast Nucleus Central vacuole Cell wall Chloroplast 5 µm

Mitochondria quantity in cell correlated with metabolic activity cellular respiration double membranous (phospholipids) cristae/matrix contain own DNA

Mitochondrion Intermembrane space Outer membrane Free ribosomes in the LE 6-17 Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Inner membrane Cristae Matrix Mitochondrial DNA 100 nm

Chloroplast type of plastid double membranous thylakoids (flattened disks) grana (stacked thylakoids) stroma own DNA – other types of plastids

Chloroplast Ribosomes Stroma Chloroplast DNA Inner and outer membranes LE 6-18 Chloroplast Ribosomes Stroma Chloroplast DNA Inner and outer membranes Granum 1 µm Thylakoid

http://www.youtube.com/watch?v=q6_MI1d8ZmI

Peroxisomes Single membrane Produce hydrogen peroxide in cells Metabolism of fatty acids; detoxification of alcohol (liver) Hydrogen peroxide then converted to water

LE 6-19 Chloroplast Peroxisome Mitochondrion 1 µm

Centrosomes/centrioles Centrosome: region near nucleus Centrioles: 9 sets of triplet microtubules in a ring; used in cell replication; only in animal cells

LE 6-22 Centrosome Microtubule Centrioles Longitudinal section of one centriole Microtubules Cross section of the other centriole

The Cytoskeleton Microtubules: Microfilaments : Fibrous network Support, cell motility, biochemical regulation Microtubules: Thickest; tubulin protein, shape, support, transport, chromosome Microfilaments : thinnest; actin protein filaments; motility, cell division, shape Intermediate filaments: middle diameter; keratin, shape, nucleus anchorage

LE 6-20 Microtubule Microfilaments 0.25 µm

Cilia/flagella Locomotive appendages Ultrastructure: “9+2” 9 doublets of microtubules in a ring 2 single microtubules in center connected by radial spokes anchored by basal body & dynein protein

LE 6-25a Microtubule doublets ATP Dynein arm Dynein “walking”

Cross section of basal body LE 6-24 Outer microtubule doublet Plasma membrane 0.1 µm Dynein arms Central microtubule Cross-linking proteins inside outer doublets Microtubules Plasma membrane Radial spoke Basal body 0.5 µm 0.1 µm Triplet Cross section of basal body

* remember to show video clips* Microtubules control the beating of cilia and flagella Cilia and flagella differ in their beating patterns * remember to show video clips*

LE 6-23a Direction of swimming Motion of flagella 5 µm

Direction of active stroke Direction of recovery stroke LE 6-23b Direction of organism’s movement Direction of active stroke Direction of recovery stroke Motion of cilia 15 µm

Cell surfaces & junctions Cell wall: not in animal cells; protection, shape, regulation Plant cell: primary cell wall produced first middle lamella of pectin (polysaccharide); holds cells together some plants, a secondary cell wall; strong durable matrix wood (between plasma membrane and primary wall)

Extracellular matrix (ECM) Glycoproteins: proteins covalently bonded to carbohydrate Collagen (50% of protein in human body) embedded in proteoglycan Fibronectins bind to receptor proteins in plasma membrane called integrins = (cell communication - possibly)

Proteoglycan complex EXTRACELLULAR FLUID Collagen fiber Fibronectin LE 6-29a Proteoglycan complex EXTRACELLULAR FLUID Collagen fiber Fibronectin Plasma membrane CYTOPLASM Integrin Micro- filaments

Intracellular junctions PLANTS: Plasmodesmata: cell wall perforations; water and solute passage in plants ANIMALS: Tight junctions - fusion of neighboring cells prevents leakage between cells Desmosomes - riveted, anchoring junction strong sheets of cells Gap junctions - cytoplasmic channels allows passage of materials or current between cells

Cell walls Interior of cell Interior of cell 0.5 µm Plasmodesmata LE 6-30 Cell walls Interior of cell Interior of cell 0.5 µm Plasmodesmata Plasma membranes

LE 6-31 Tight junctions prevent fluid from moving across a layer of cells Tight junction 0.5 µm Tight junction Intermediate filaments Desmosome 1 µm Gap junctions Space between cells Plasma membranes of adjacent cells Gap junction Extracellular matrix 0.1 µm

Inner life of a Cell https://www.youtube.com/watch?v=FzcTgrxMzZk (~8:00 mins) Viral invasion https://www.youtube.com/watch?v=Rpj0emEGShQ (3:38 mins)