Chapter 6A

A Tour of the Cell

Cytology: science/study of cells

Light microscopyResolving power~ measure of clarityElectron microscopyTEM~ electron beam to study cell ultrastructureSEM~ electron beam to study cell surfacesCell fractionation~ cell separation; organelle studyUltracentrifuges~ cell fractionation; 130,000 rpm

Electron Micrograph

Cell Types: Prokaryotic

Nucleoid: DNA concentrationNo organelles with membranesRibosomes: protein synthesisPlasma membrane (all cells); semi-permeableCytoplasm/cytosol (all cells)

Cell SizeAs cell size increases, the surface area to volume ratio decreasesRates of chemical exchange may then be inadequate for cell sizeCell size, therefore, remains small

NucleusContains the Genetic materialChromatin (chromosomes)Nucleolus: rRNA; ribosome synthesisDouble membrane envelope with poresProtein synthesis/Transcription (mRNA copies DNA)

RibosomesProtein manufactureFree - cytosol; produce proteins that function in the cellBound – rough endoplasmic reticulum; found on surface membranes; manufacture proteins that are exported from the cellComposed of 2 subunits (rRNA & protein)

Endomembrane System, IEndoplasmic reticulum (ER)Continuous with nuclear envelopeSmooth ER - no ribosomes; synthesis of lipids, metabolism of carbohydrates; detoxification of drugs and poisonsRough ER - with ribosomes; synthesis of secretory proteins (glycoproteins); membrane production

Endomembrane System, IIGolgi apparatus - ER products are modified, stored, and then shippedCisternae: flattened membranous sacs making up Golgitrans face (shipping) & cis face (receiving)Transport vesicles pinch off of ends of Golgi

Endomembrane System, III

Lysosomes - sac of hydrolytic enzymes; digestion of macromoleculesPhagocytosisAutophagy: recycle cell’s own organic materialTay-Sachs disease~ lipid-digestion disorder

Endomembrane system, IVVacuoles -membrane-bound sacs (larger than vesicles)Food Vacuole (phagocytosis)Contractile (pump excess water)Central (storage in plants) •tonoplast membrane