Wassily Kandinsky ( ) Cells

Figure 4.1x Cell Theory: - all organisms are composed of cells - all cells come from other cells

Scanning electron microscope (SEM) Figure 4.1B TEM

Cell size and shape relate to function Minimum Maximum Figure 4.2

A small cell has a greater ratio of surface area to volume than a large cell of the same shape 30 µm10 µm Surface area of one large cube = 5,400 µm 2 Total surface area of 27 small cubes = 16,200 µm 2 Figure 4.3

Prokaryotic cells - “ before nucleus ” - small, relatively simple cells –Single-celled organisms 2 kinds of cells: prokaryotic and eukaryotic

- true nucleus - larger: microns - often multicellular - organelles surrounded by membranes - usually need O2 Eukaryotic cells - functional compartments

What do these have in common? HIV infection Transplanted organs Communication between neurons Drug addiction Cystic fibrosis hypercholesteremia

Plasma membrane Contact between cell and environment Keeps useful materials inside and harmful stuff outside Allows transport, communication in both directions

polar head nonpolar tails P– hydrophobic molecules hydrophilic molecules cytosol 1. Phospholipid bilayer Plasma membrane components

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Fibers of the extracellular matrix Figure 5.12 Glycoprotein Carbohydrate (of glycoprotein) Microfilaments of the cytoskeleton Phospholipid Cholesterol Proteins CYTOPLASM Glycolipid 2. Cholesterol - adds rigidity Fluid mosaic model

3. Membrane Proteins - span entire membrane or lie on either side Structural Support Recognition Communication Transport

How do molecules cross the plasma membrane? Passive transport Active transport Endocytosis and exocytosis

Diffusion and gradients –Diffusion = movement of molecules from region of higher to lower concentration. –Osmosis = diffusion of water across a membrane

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In passive transport, substances diffuse through membranes without work by the cell EQUILIBRIUM Molecule of dye Figure 5.14A & B Membrane EQUILIBRIUM

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings water travels from an area of higher concentration to an area of lower water concentration Osmosis = diffusion of water across a membrane Hypotonic solution Figure 5.15 Solute molecule HYPOTONIC SOLUTION Hypertonic solution Selectively permeable membrane HYPERTONIC SOLUTION Selectively permeable membrane NET FLOW OF WATER Solute molecule with cluster of water molecules Water molecule

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution Water balance between cells and their surroundings is crucial osmoregulation = control of water balance

isotonic solutionhypertonic solutionhypotonic solution 10 microns equal movement of water into and out of cells net water movement out of cells net water movement into cells

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Small nonpolar molecules - simple diffusion Many molecules pass through protein pores by diffusion through channels. Facilitated diffusion Passive transport = diffusion across membranes Figure 5.17 Solute molecule Transport protein

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings against a concentration gradient transport proteins needed requires energy (ATP) Active transport

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Active transport in two solutes across a membrane Na+/K+ pump Protein shape change Figure 5.18 Transport protein 1 FLUID OUTSIDE CELL First solute First solute, inside cell, binds to protein Phosphorylated transport protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell 4 Second solute binds to protein Second solute 5 Phosphate detaches from protein 6 Protein releases second solute into cell

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings exocytosis = vesicle fuses with the membrane and expels its contents Exocytosis and endocytosis transport large molecules Figure 5.19A FLUID OUTSIDE CELL CYTOPLASM

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –or the membrane may fold inward, trapping material from the outside (endocytosis) Figure 5.19B

human immune system ingests whole bacteria

Receptor-mediated endocytosis

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cholesterol can accumulate in the blood if membranes lack cholesterol receptors Figure 5.20 LDL PARTICLE Phospholipid outer layer Protein Cholesterol Plasma membrane CYTOPLASM Receptor protein Vesicle

What do these have in common? HIV infection Transplanted organs Communication between neurons Drug addiction Cystic fibrosis hypercholesteremia