Cells Wassily Kandinsky 1866 1944 Cell Theory all

Cells Wassily Kandinsky (1866 -1944)

Cell Theory: - all organisms are composed of cells - all cells come from other cells Figure 4. 1 x

• Scanning electron microscope (SEM) TEM Figure 4. 1 B

• 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 µm Figure 4. 3 Surface area of one large cube = 5, 400 µm 2 10 µm Total surface area of 27 small cubes = 16, 200 µm 2

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

Eukaryotic cells - functional compartments - true nucleus - larger: 10 -100 microns - often multicellular - organelles surrounded by membranes - usually need O 2

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

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

• 2. Cholesterol - adds rigidity Fluid mosaic model Glycoprotein Carbohydrate (of glycoprotein) Fibers of the extracellular matrix Glycolipid Phospholipid Cholesterol Microfilaments of the cytoskeleton Proteins CYTOPLASM Figure 5. 12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• 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

• In passive transport, substances diffuse through membranes without work by the cell Molecule of dye Membrane EQUILIBRIUM Figure 5. 14 A & B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Osmosis = diffusion of water across a membrane • water travels from an area of higher concentration to an area of lower water concentration Hypotonic solution Hypertonic solution Selectively permeable membrane Solute molecule HYPOTONIC SOLUTION HYPERTONIC SOLUTION Water molecule Selectively permeable membrane Solute molecule with cluster of water molecules NET FLOW OF WATER Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 5. 15

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

10 microns isotonic solution equal movement of water into and out of cells hypertonic solution net water movement out of cells hypotonic solution net water movement into cells

Passive transport = diffusion across membranes • Small nonpolar molecules - simple diffusion • Many molecules pass through protein pores by diffusion through channels. • Facilitated diffusion Solute molecule Figure 5. 17 Transport protein Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

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

• Active transport in two solutes across a membrane FLUID OUTSIDE CELL Transport protein First solute 1 • Na+/K+ pump Phosphorylated transport protein First solute, inside cell, binds to protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell 5 Phosphate detaches from protein 6 Protein releases second solute into cell Second solute • Protein shape change 4 Second solute binds to protein Figure 5. 18 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Exocytosis and endocytosis transport large molecules exocytosis = vesicle fuses with the membrane and expels its contents FLUID OUTSIDE CELL Figure 5. 19 A CYTOPLASM Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

– or the membrane may fold inward, trapping material from the outside (endocytosis) Figure 5. 19 B Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

human immune system ingests whole bacteria

Receptor-mediated endocytosis

• Cholesterol can accumulate in the blood if membranes lack cholesterol receptors LDL PARTICLE Phospholipid outer layer Receptor protein Protein Cholesterol Plasma membrane CYTOPLASM Figure 5. 20 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Vesicle

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