Cell Theory Simple statements, powerful concept: All living organisms are made of cells All Cells come from pre-existing cells The organization of living things The continuity of life

The Size of Cells How big is a cell??? Range from 1µm to 1mm Which cell!!! Range from 1µm to 1mm What limits size? Transport substances into and out of cells Limited by surface area of cell Surface area to volume ratio Decreases as size increases

SA/V Cell radius (r) 1 unit 10 units 3 Surface area (4r2) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. SA/V Cell radius (r) 1 unit 10 units 3 Surface area (4r2) 12.57 units2 1257 units2 0.3 Volume (4/3r3) 4.189 units3 4189 units3

Cell Types At the most basic level, cells come in one of two flavors: Prokaryotic Eukaryotic These are vastly different cell types Simple definition: presence/absence of membrane bound nucleus Later, look at relationship to organization and evolution of life

Prokaryotic Cells Divided into two domains: Tend to be small (1-10 µm) Bacteria (also called eubacteria) Archaea Tend to be small (1-10 µm) Dominant life forms on the planet Biomass Diversity Consider similarities of structure briefly

Prokaryotic Structure No nucleus, but genetic material still compartmentalized: nucleoid Cytoplasm: soluble cytosol and suspended particles Few organelles: ribosomes, the universal organelle Have Cell Wall composed of peptidoglycan (bacteria) Have plasma membrane May be infolded

Fig. 5.5 (TEArt) Pili Nucleoid (DNA) Ribosomes Flagellum Capsule Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 5.5 (TEArt) Pili Nucleoid (DNA) Ribosomes Flagellum Capsule Cell wall Plasma membrane Cytoplasm

Eukaryotic Cells All cells that contain a membrane bound nucleus (genetic material) Animal cells Plant cells Fungal Cells Protists We will consider general features

Compartmentalization The most striking feature of eukaryotic cells is compartmentalization Different compartments perform different functions Usually membrane bound Organelles “Little organs” subcellular components with a specific function Single organism may have many specialized cell types

Fig. 5.8 (TEArt) Golgi apparatus Microvilli Plasma membrane Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 5.8 (TEArt) Golgi apparatus Microvilli Plasma membrane Actin filament Cytoskeleton Microtubule Centriole Intermediate filament Peroxisome Smooth endoplasmic reticulum (SER) Lysosome Ribosomes Nuclear envelope Mitochondrion Nucleolus Rough endoplasmic reticulum (RER) Nucleus Cytoplasm

Nucleus Structure: Function: Nuclear envelope: double membrane (two bilayers) Inner not the same as outer Outer connected to endomembrane system Has pores to control traffic with cytoplasm Function: Houses genetic information Storage of information Expression of genetic information starts here

Fig. 5.10a (TEArt) Nuclear Nucleolus envelope Nuclear pores Nuclear Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 5.10a (TEArt) Nucleolus Nuclear envelope Nuclear pores Nuclear pore Inner membrane Outer membrane Nucleoplasm

Fig. 5.10b

Endomembrane System Internal system of membranes Endoplasmic Reticulum (ER) Smooth (SER): no ribosomes Lipid synthesis, synthesis of new membrane Rough (RER): has ribosomes on surface Protein synthesis, modify proteins Golgi Complex Processing and packaging of proteins Vesicles: small sacs that “bud off” ER

Fig. 5.13a (TEArt) Ribosomes Rough endo- plasmic reticulum Smooth Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fig. 5.13a (TEArt) Ribosomes Rough endo- plasmic reticulum Smooth endo- plasmic reticulum

Fig. 5.13b

Secretory vesicles trans face cis face Transport vesicles Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Secretory vesicles trans face cis face Transport vesicles

Mitochondria/Chloroplasts Involved in energy metabolism Mitochondria is site of respiration Chloroplast is site of photosynthesis Structure related to function Have double membrane Creates internal compartment Both arose by endosymbiosis Once free living Now part of “modern” cell

Back to Phospholipid Structure Phospholipids are amphipathic: they have hydrophobic and hydrophilic regions Hydrophilic regions (phosphate) orient towards water Hydrophobic regions (hydrocarbon) orient away from water Hydrophobic regions orient towards each other Leads to bilayer structure

extracellular fluid cytoplasm

Permeability of Pure Phospholipid Bilayer What kinds of material should be able to pass through phospholipid bilayer? Nonpolar Small polar What kinds of things should not be able to pass through phospholipid bilayer? Large polar Charged

Membrane Permeability nonpolar (hydrophobic) O2, N2 benezene small polar (hydrophilic) H2O, CO2, urea, glycerol large polar (hydrophilic) glucose, sucrose H+, Na+, Ca2+, Mg2+, Cl-, ions (hydrophilic)

What else is in a Membrane? Early physical analysis indicated that membranes contain proteins Now distinguish two kinds of proteins Integral: span the membrane Transmembrane proteins have intra and extracellular domains Peripheral: on one surface of membrane Proteins necessary for function Control traffic across membrane Proteins allow signaling across membrane

Fluid Mosaic Model for Membrane The current view of the plasma membrane was first named the Fluid Mosaic Model Membrane lipids are not fixed, but rather are a fluid structure Integral membrane proteins are floating in this sea of lipids Peripheral proteins are on surface of membrane Dynamic structure

Transmembrane Protein Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Extracellular fluid Cytoplasm Integral Protein Transmembrane Protein Peripheral Protein Microfilament