Chapter 4 A Tour of the Cell

Cytology: science/study of cells Light microscopy resolving power = measure of clarity Electron microscopy TEM = electron beam to study cell ultrastructure SEM = electron beam to study cell surfaces Cell fractionation = cell separation; organelle study Ultracentrifuges = cell fractionation; 130,000 rpm

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

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

Range of Cell Size

Cell Fractionation

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

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

Compartmentalization Increases internal surface area Sometimes enzymes are incorporated into the membrane. Provide localized environmental areas. Sequester reactions (hydrolytic enzymes in lysosomes)

The Endomembrane System Membranes may be interrelated directly or indirectly via vesicles. Membranes are dynamic structures. Nuclear Envelope Endoplasmic Reticulum Golgi Apparatus Lysosomes Vacuoles Plasma membrane (not actually a member of the system, but related to it).

Continuous with nuclear envelope Smooth ER no ribosomes synthesis of lipids metabolism of carbohydrates detoxification of drugs and poisons Stores Ca 2+ ions Rough ER with ribosomes; synthesis of secretory proteins (glycoproteins), membrane production 1. Endoplasmic Reticulum (ER )

Rough ER Ribosomes 1. Rough ER ribosomes synthesize secretory proteins 2. Growing polypeptide is threaded through the ER membrane into the lumen or cisternal space 3. Protein folds into its native conformation 4. Local enzymes catalyze covalent bonding- modifications 5. Protein departs in a transport vesicle

ER products are modified, stored, and then shipped Cisternae: flattened membranous sacs trans face (shipping) & cis face (receiving) Transport vesicles 2. Golgi Apparatus

Sac of hydrolytic enzymes; digestion of macromolecules Phagocytosis Autophagy: recycle cell’s own organic material Tay-Sachs disease - lipid-digestion disorder Apoptosis 3. Lysosomes

4.Vacuoles Membrane-bound sacs (larger than vesicles) Food vacuole (phagocytosis) Contractile (pump excess water) Central vacuole (storage in plants) Tonoplast (membrane )

Relationships Among Endomembranes

Other Membranous Organelles Not part of endomembrane system Peroxisomes Mitochondria Chloroplasts

Peroxisomes Single membrane Produce hydrogen peroxide in cells Metabolism of fatty acids; detoxification of alcohol (liver) Hydrogen peroxide produced, then converted to water – action of catalase.

Mitochondria quantity in cell correlated with metabolic activity; cellular respiration; double membranous (phospholipid); cristae/matrix; intermembrane space; contain own DNA bacterial origin

Chloroplasts type of plastid; double membranous; thylakoids (flattened disks) grana (stacked thylakoids); stroma; own DNA

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

Tubulin in endothelial cell

Motor Molecules and the Cytoskeleton a.motor molecules on one microtubule ‘grab’ and slide past another microtubule. b. motor molecules attach to receptors on organelles such as vesicles, enabling them to ‘walk’ along the microtubule

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

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

a.ls. cilium b.cs cilium, showing 9+2 arrangement c.cs basal body, anchors the cilium to the cell – third microtubule incorporated (centriole) central 2 lost

How Dynein ‘walking’ Moves Cilia and Flagella The dynein arms of one doublet grip the adjacent doublet. Powered by ATP

Microfilaments and Motility

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 (another glycoprotein-95% carbohydrate) Fibronectins bind to receptor proteins in plasma membrane called integrins (cell communication?)

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

Plamodesmata in a thin plant section

Intercellular Junctions in Animals

The Lives of a Cell Harvard Animation layer/?src=harvard/harvard.swf&width=640 &height=520http://aimediaserver.com/studiodaily/videop layer/?src=harvard/harvard.swf&width=640 &height=520 Assignment Choose 4 images to draw and label Narrated version