1. PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 3 Cells: The Living Units: Part A

2. Copyright © 2010 Pearson Education, Inc. Cell Theory The cell is the smallest structural and functional living unit Organismal functions depend on individual and collective cell functions Biochemical activities of cells are dictated by their specific subcellular structures Continuity of life has a cellular basis

3. Copyright © 2010 Pearson Education, Inc. Developmental Aspects of Cells All cells of the body contain the same DNA but are not identical Chemical signals in the embryo channel cells into specific developmental pathways by turning some genes off Development of specific and distinctive features in cells is called cell differentiation Elimination of excess, injured, or aged cells occurs through programmed rapid cell death (apoptosis) followed by phagocytosis

4. Copyright © 2010 Pearson Education, Inc. Theories of Cell Aging Wear and tear theory: Little chemical insults and free radicals have cumulative effects Immune system disorders: Autoimmune responses and progressive weakening of the immune response Genetic theory: Cessation of mitosis and cell aging are programmed into genes. Telomeres (strings of nucleotides on the ends of chromosomes) may determine the number of times a cell can divide.

5. Copyright © 2010 Pearson Education, Inc. Generalized Cell All cells have some common structures and functions Human cells have three basic parts: Plasma membrane—flexible outer boundary Cytoplasm—intracellular fluid containing organelles Nucleus—control center

6. Copyright © 2010 Pearson Education, Inc. Figure 3.2 Secretion being released from cell by exocytosis Peroxisome Ribosomes Rough endoplasmic reticulum Nucleus Nuclear envelope Chromatin Golgi apparatus Nucleolus Smooth endoplasmic reticulum Cytosol Lysosome Mitochondrion Centrioles Centrosome matrix Cytoskeletal elements Microtubule Intermediate filaments Plasma membrane

7. Copyright © 2010 Pearson Education, Inc. Plasma Membrane Bimolecular layer of lipids and proteins in a constantly changing fluid mosaic Plays a dynamic role in cellular activity Separates intracellular fluid (ICF) from extracellular fluid (ECF) Interstitial fluid (IF) = ECF that surrounds cells

8. Copyright © 2010 Pearson Education, Inc. Extracellular Materials Body fluids (interstitial fluid, blood plasma, and cerebrospinal fluid) Cellular secretions (intestinal and gastric fluids, saliva, mucus, and serous fluids) Extracellular matrix (abundant jellylike mesh containing proteins and polysaccharides in contact with cells)

9. Copyright © 2010 Pearson Education, Inc. Figure 3.3 Integral proteins Extracellular fluid (watery environment) Cytoplasm (watery environment) Polar head of phospholipid molecule Glycolipid Cholesterol Peripheral proteins Bimolecular lipid layer containing proteins Inward-facing layer of phospholipids Outward- facing layer of phospholipids Carbohydrate of glycocalyx Glycoprotein Filament of cytoskeleton Nonpolar tail of phospholipid molecule

10. Copyright © 2010 Pearson Education, Inc. Membrane Lipids 75% phospholipids (lipid bilayer) Phosphate heads: polar and hydrophilic Fatty acid tails: nonpolar and hydrophobic (Review Fig. 2.16b) 5% glycolipids Lipids with polar sugar groups on outer membrane surface 20% cholesterol Increases membrane stability and fluidity

11. Copyright © 2010 Pearson Education, Inc. Functions of Membrane Proteins 1.Transport 2.Receptors for signal transduction 3.Attachment to cytoskeleton and extracellular matrix

12. Copyright © 2010 Pearson Education, Inc. Figure 3.4a A protein (left) that spans the membrane may provide a hydrophilic channel across the membrane that is selective for a particular solute. Some transport proteins (right) hydrolyze ATP as an energy source to actively pump substances across the membrane. (a) Transport

13. Copyright © 2010 Pearson Education, Inc. Figure 3.4b A membrane protein exposed to the outside of the cell may have a binding site with a specific shape that fits the shape of a chemical messenger, such as a hormone. The external signal may cause a change in shape in the protein that initiates a chain of chemical reactions in the cell. (b) Receptors for signal transduction Signal Receptor

14. Copyright © 2010 Pearson Education, Inc. Figure 3.4c Elements of the cytoskeleton (cell’s internal supports) and the extracellular matrix (fibers and other substances outside the cell) may be anchored to membrane proteins, which help maintain cell shape and fix the location of certain membrane proteins. Others play a role in cell movement or bind adjacent cells together. (c) Attachment to the cytoskeleton and extracellular matrix (ECM)

15. Copyright © 2010 Pearson Education, Inc. Functions of Membrane Proteins 4.Enzymatic activity 5.Intercellular joining 6.Cell-cell recognition

16. Copyright © 2010 Pearson Education, Inc. Figure 3.4d A protein built into the membrane may be an enzyme with its active site exposed to substances in the adjacent solution. In some cases, several enzymes in a membrane act as a team that catalyzes sequential steps of a metabolic pathway as indicated (left to right) here. (d) Enzymatic activity Enzymes

17. Copyright © 2010 Pearson Education, Inc. Figure 3.4e Membrane proteins of adjacent cells may be hooked together in various kinds of intercellular junctions. Some membrane proteins (CAMs) of this group provide temporary binding sites that guide cell migration and other cell-to-cell interactions. CAMs (e) Intercellular joining

18. Copyright © 2010 Pearson Education, Inc. Figure 3.4f Some glycoproteins (proteins bonded to short chains of sugars) serve as identification tags that are specifically recognized by other cells. (f) Cell-cell recognition Glycoprotein

19. Copyright © 2010 Pearson Education, Inc. Membrane Transport Plasma membranes are selectively permeable Some molecules easily pass through the membrane; others do not

20. Copyright © 2010 Pearson Education, Inc. Types of Membrane Transport Passive processes No cellular energy (ATP) required Substance moves down its concentration gradient Active processes Energy (ATP) required Occurs only in living cell membranes

21. Copyright © 2010 Pearson Education, Inc. Passive Processes What determines whether or not a substance can passively permeate a membrane? 1.Lipid solubility of substance 2.Channels of appropriate size 3.Carrier proteins PLAY Animation: Membrane Permeability

22. Copyright © 2010 Pearson Education, Inc. Passive Processes Simple diffusion Carrier-mediated facilitated diffusion Channel-mediated facilitated diffusion Osmosis

23. Copyright © 2010 Pearson Education, Inc. Passive Processes: Simple Diffusion Nonpolar lipid-soluble (hydrophobic) substances diffuse directly through the phospholipid bilayer PLAY Animation: Diffusion

24. Copyright © 2010 Pearson Education, Inc. Figure 3.7a Extracellular fluid Lipid- soluble solutes Cytoplasm (a) Simple diffusion of fat-soluble molecules directly through the phospholipid bilayer

25. Copyright © 2010 Pearson Education, Inc. Passive Processes: Facilitated Diffusion Certain lipophobic molecules (e.g., glucose, amino acids, and ions) use carrier proteins or channel proteins, both of which: Exhibit specificity (selectivity) Are saturable; rate is determined by number of carriers or channels Can be regulated in terms of activity and quantity

26. Copyright © 2010 Pearson Education, Inc. Facilitated Diffusion Using Carrier Proteins Transmembrane integral proteins transport specific polar molecules (e.g., sugars and amino acids) Binding of substrate causes shape change in carrier

27. Copyright © 2010 Pearson Education, Inc. Figure 3.7b Lipid-insoluble solutes (such as sugars or amino acids) (b) Carrier-mediated facilitated diffusion via a protein carrier specific for one chemical; binding of substrate causes shape change in transport protein

28. Copyright © 2010 Pearson Education, Inc. Facilitated Diffusion Using Channel Proteins Aqueous channels formed by transmembrane proteins selectively transport ions or water Two types: Leakage channels Always open Gated channels Controlled by chemical or electrical signals

29. Copyright © 2010 Pearson Education, Inc. Figure 3.7c Small lipid- insoluble solutes (c) Channel-mediated facilitated diffusion through a channel protein; mostly ions selected on basis of size and charge

30. Copyright © 2010 Pearson Education, Inc. Passive Processes: Osmosis Movement of solvent (water) across a selectively permeable membrane Water diffuses through plasma membranes: Through the lipid bilayer Through water channels called aquaporins (AQPs)

31. Copyright © 2010 Pearson Education, Inc. Figure 3.7d Water molecules Lipid billayer Aquaporin (d) Osmosis, diffusion of a solvent such as water through a specific channel protein (aquaporin) or through the lipid bilayer

32. Copyright © 2010 Pearson Education, Inc. Passive Processes: Osmosis Water concentration is determined by solute concentration because solute particles displace water molecules Osmolarity: The measure of total concentration of solute particles When solutions of different osmolarity are separated by a membrane, osmosis occurs until equilibrium is reached

33. Copyright © 2010 Pearson Education, Inc. Figure 3.8a (a) Membrane permeable to both solutes and water Solute and water molecules move down their concentration gradients in opposite directions. Fluid volume remains the same in both compartments. Left compartment: Solution with lower osmolarity Right compartment: Solution with greater osmolarity Membrane H2OH2O Solute molecules (sugar) Both solutions have the same osmolarity: volume unchanged

34. Copyright © 2010 Pearson Education, Inc. Figure 3.8b (b) Membrane permeable to water, impermeable to solutes Both solutions have identical osmolarity, but volume of the solution on the right is greater because only water is free to move Solute molecules are prevented from moving but water moves by osmosis. Volume increases in the compartment with the higher osmolarity. Left compartment Right compartment Membrane Solute molecules (sugar) H2OH2O

35. Copyright © 2010 Pearson Education, Inc. Importance of Osmosis When osmosis occurs, water enters or leaves a cell Change in cell volume disrupts cell function PLAY Animation: Osmosis

36. Copyright © 2010 Pearson Education, Inc. Tonicity Tonicity: The ability of a solution to cause a cell to shrink or swell Isotonic: A solution with the same solute concentration as that of the cytosol Hypertonic: A solution having greater solute concentration than that of the cytosol Hypotonic: A solution having lesser solute concentration than that of the cytosol

37. Copyright © 2010 Pearson Education, Inc. Figure 3.9 Cells retain their normal size and shape in isotonic solutions (same solute/water concentration as inside cells; water moves in and out). Cells lose water by osmosis and shrink in a hypertonic solution (contains a higher concentration of solutes than are present inside the cells). (a) Isotonic solutions (b) Hypertonic solutions (c) Hypotonic solutions Cells take on water by osmosis until they become bloated and burst (lyse) in a hypotonic solution (contains a lower concentration of solutes than are present in cells).

38. Copyright © 2010 Pearson Education, Inc. Summary of Passive Processes Also see Table 3.1 ProcessEnergy Source Example Simple diffusion Kinetic energy Movement of O 2 through phospholipid bilayer Facilitated diffusion Kinetic energy Movement of glucose into cells OsmosisKinetic energy Movement of H 2 O through phospholipid bilayer or AQPs