A Tour of the Cell

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

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

Prokaryote vs. eukaryote Prokaryote Less complex (generally bacteria) Has plasma membrane May have cell wall May have some photosynthetic material Does not have membrane bound organelles DNA is not bound (circular) Has ribosomes (not attached to ER) Have proteins and enzymes Have mitochondria Eukaryote More complicated Has membrane bound organelles DNA is stored in the nucleus of the cell Double helix Bound to histone proteins Ribosomes are attached to rough ER Make proteins and enzymes

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

Composite Animal Cell

Nuclear envelope Lysosome Plasma membrane

Next quiz For the quiz, you MUST know the parts of the cell for both the plant and animal cell See pp in your text

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

Nucleolus Located within the nucleus Primarily responsible for the production of ribosomes The different subunits are created within the nucleolus and then transported out of the nucleolus to be assemble along the endoplasmic reticulum (ER) This makes this portion of the ER the rough ER

Ribosomes Protein manufacturing Free cytosol; protein function in cell Bound endoplasmic reticulum; membranes, organelles

Endomembrane system, I 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 (glycoproteins), membrane production

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

Endomembrane system, III Lysosomes sac of hydrolytic enzymes; digestion of macromolecules Phagocytosis Autophagy: recycle cell’s own organic material Tay-Sachs disease: lipid-digestion disorder

Endomembrane system, IV Vacuoles membrane-bound sacs (larger than vesicles) Food (phagocytosis) Contractile (pump excess water) Central (storage in plants)

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

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

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

The Cytoskeleton end here 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

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

Review – plant vs. animal Animal Pretty much there are no additional organelles in an animal cell compared to a plant cell Plant Primarily has 3 extra structures Plastids/ chloroplasts Cell wall Central vacuole

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