Overview of Cells Prokaryotic All bacteria Most have cell wall No membrane-bound organelles Biochemical reactions take place in cytoplasm or cell membrane Typically very small Eukaryotic Protist, fungi, plant and animal cells Some have cell walls Possess membrane-bound organelles Biochemical reactions take place in specialized compartments Much larger than bacteria

Prokaryotic Cell Fimbriae Nucleoid Ribosomes Plasma membrane Cell wall Capsule Flagella Bacterial chromosome (a)A typical rod-shaped bacterium (b)A thin section through the bacterium Bacillus coagulans (TEM) 0.5 µm

Animal Cells Surrounded by plasma membrane  Allows certain molecules in or out of the cell  Does not have a cell wall

ENDOPLASMIC RETICULUM (ER) Smooth ERRough ER Flagellum Centrosome CYTOSKELETON: Microfilaments Intermediate filaments Microtubules Microvilli Peroxisome Mitochondrion Lysosome Golgi apparatus Ribosomes Plasma membrane Nuclear envelope Nucleolus Chromatin NUCLEUS

Plant Cells Have plasma membrane and cell wall  Cell wall gives support  Has chloroplasts (contain chlorophyll) and large vacuole

Fig. 6-9b NUCLEUS Nuclear envelope Nucleolus Chromatin Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes Central vacuole Microfilaments Intermediate filaments Microtubules CYTO- SKELETON Chloroplast Plasmodesmata Wall of adjacent cell Cell wall Plasma membrane Peroxisome Mitochondrion Golgi apparatus

Why Small Cells? Cells obtain nutrients (gases, water other molecules) from the environment through the cell membrane High surface area:volume ratios maximizes the amount of cell/environment interaction  Large cells would starve

Cell Membrane Lipid bilayer Integral proteins “float” in fluid  Hydrophobic region of proteins reside in fatty acid layer of membrane  Hydrophilic regions are on cytoplasmic and extracellular surfaces Membrane fluidity may be altered by adjusting fatty acid chains

Fig. 7-3 Phospholipid bilayer Hydrophobic regions of protein Hydrophilic regions of protein

Membranes are complex Membranes are embedded with: Integral proteins Peripheral proteins Glycoproteins Proteoglycans Carbohydrates Membranes are connected to cytoskeleton on the Cytoplasmic surface

Fig. 7-7 Fibers of extracellular matrix (ECM) Glyco- protein Microfilaments of cytoskeleton Cholesterol Peripheral proteins Integral protein CYTOPLASMIC SIDE OF MEMBRANE Glycolipid EXTRACELLULAR SIDE OF MEMBRANE Carbohydrate

Roles of Membranes Gatekeeper of cell  Determines what goes in or out of cell Compartmentalization  Every membrane-bound organelle is isolated Transport  Actively move molecules into cell Signal transduction  Environmental conditions trigger genetic and biochemical changes in cell via receptors Cell-cell communication and interaction

Diffusion Starts with a gradient System will eventually reach equilibrium (even distribution) Happens passively without selective barriers Many small molecules diffuse through cell membrane

Fig Molecules of dye Membrane (cross section) WATER Net diffusion Equilibrium (a) Diffusion of one solute Net diffusion Equilibrium (b) Diffusion of two solutes

Osmosis Requires a gradient and a selectively permeable membrane  Solute is unable to pass through membrane to reach equilibrium  Water will move to area of greater solvent concentration until equilibrium is reached

Lower concentration of solute (sugar) Fig H2OH2O Higher concentration of sugar Selectively permeable membrane Same concentration of sugar Osmosis

Facilitated diffusion An integral protein helps molecules across the membrane Often act as a revolving door (carrier) or tunnel (channel)

Fig EXTRACELLULAR FLUID Channel protein (a) A channel protein Solute CYTOPLASM Solute Carrier protein (b) A carrier protein

Active Transport Cell expends energy to move molecule or atom inside  Often forms gradients to accomplish this

Entry into Cell Summarized Diffusion and Facilitated diffusion are passive transport because no energy is required Facilitated diffusion and active transport can be very selective processes

Membrane Pumps Can be used to remove unwanted molecule from cytoplasm (like sump pump) Can also be used to form a gradient across the membrane which can drive other transports (protomotor force)

Fig Passive transport Diffusion Facilitated diffusion Active transport ATP