1. Chapter 3 Cells: The Living Units

2. Cell Theory 1. The cell is the basic structural and functional unit of life 2. Organismal activity depends on individual and collective activity of cells 3. Biochemical activities of cells are dictated by subcellular structure 4. Continuity of life has a cellular basis

3. 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 Microtubule Microvilli Microfilament Intermediate filaments Plasma membrane

4. Plasma Membrane Separates intracellular fluids from extracellular fluids Separates intracellular fluids from extracellular fluids Plays a dynamic role in cellular activity Plays a dynamic role in cellular activity Glycocalyx – “fingerprint” of the cell Glycocalyx – “fingerprint” of the cell

5. Fluid Mosaic Model Double bilayer of lipids with imbedded proteins Double bilayer of lipids with imbedded proteins Bilayer consists of phospholipids, cholesterol, and glycolipids Bilayer consists of phospholipids, cholesterol, and glycolipids Glycolipids are lipids with bound carbohydrate Glycolipids are lipids with bound carbohydrate Phospholipids have hydrophobic and hydrophilic poles Phospholipids have hydrophobic and hydrophilic poles

6. Fluid Mosaic Model Figure 3.3

7. Functions of Membrane Proteins Transport Transport Enzymatic activity Enzymatic activity Receptors for signal transduction Receptors for signal transduction Figure 3.4.1

8. Functions of Membrane Proteins Intercellular adhesion Intercellular adhesion Cell-cell recognition Cell-cell recognition Attachment to cytoskeleton and extracellular matrix Attachment to cytoskeleton and extracellular matrix Figure 3.4.2

9. Membrane Junctions Tight junction – impermeable junction that joins cells Tight junction – impermeable junction that joins cells Desmosome – anchoring junction scattered along the sides of cells Desmosome – anchoring junction scattered along the sides of cells Gap junction – allows chemical substances to pass between cells for communication Gap junction – allows chemical substances to pass between cells for communication

10. Membrane Junctions: Tight Junction Figure 3.5a

11. Membrane Junctions: Desmosome Figure 3.5b

12. Membrane Junctions: Gap Junction Figure 3.5c

13. Passive Membrane Transport: Diffusion Diffusion is movement of substances from high to low concentrations Diffusion is movement of substances from high to low concentrations Diffusion occurs along a concentration gradient Diffusion occurs along a concentration gradient

14. Passive Membrane Transport: Simple Diffusion Simple diffusion – nonpolar and lipid-soluble substances Simple diffusion – nonpolar and lipid-soluble substances Diffuse directly through the lipid bilayer Diffuse directly through the lipid bilayer Diffuse through channel proteins Diffuse through channel proteins Nonpolar, lipid-soluble, and hydrophobic are synonyms Nonpolar, lipid-soluble, and hydrophobic are synonyms

15. Passive Membrane Transport: Facilitated Diffusion Facilitated diffusion Facilitated diffusion Transport of glucose, amino acids, and ions Transport of glucose, amino acids, and ions Transported substances bind carrier proteins or pass through protein channels Transported substances bind carrier proteins or pass through protein channels Carrier proteins are transmembrane and are specific for certain polar molecules Carrier proteins are transmembrane and are specific for certain polar molecules Polar, lipid-insoluble, and hydrophilic are synonyms Polar, lipid-insoluble, and hydrophilic are synonyms

16. Diffusion Through the Plasma Membrane Figure 3.7 Extracellular fluid Cytoplasm Lipid- soluble solutes Lipid bilayer Lipid-insoluble solutes Water molecules Small lipid- insoluble solutes (a) Simple diffusion directly through the phospholipid bilayer (c) Channel-mediated facilitated diffusion through a channel protein; mostly ions selected on basis of size and charge (b) Carrier-mediated facilitated diffusion via protein carrier specific for one chemical; binding of substrate causes shape change in transport protein (d) Osmosis, diffusion through a specific channel protein (aquaporin) or through the lipid bilayer

17. Passive Membrane Transport: Osmosis Diffusion of water across a semipermeable membrane due to differences in concentration of a solvent across the membrane Diffusion of water across a semipermeable membrane due to differences in concentration of a solvent across the membrane Osmolarity – total concentration of solute particles in a solution Osmolarity – total concentration of solute particles in a solution Tonicity – how a solution affects cell volume Tonicity – how a solution affects cell volume

18. Effect of Membrane Permeability on Diffusion and Osmosis Figure 3.8a

19. Effect of Membrane Permeability on Diffusion and Osmosis Figure 3.8b

20. Effects of Solutions of Varying Tonicity Isotonic – solutions with the same solute concentration as that of the cytosol Isotonic – solutions with the same solute concentration as that of the cytosol Hypertonic – solutions having greater solute concentration than that of the cytosol Hypertonic – solutions having greater solute concentration than that of the cytosol Hypotonic – solutions having lesser solute concentration than that of the cytosol Hypotonic – solutions having lesser solute concentration than that of the cytosol

21. Passive Membrane Transport: Filtration The passage of water and solutes through a membrane by hydrostatic pressure The passage of water and solutes through a membrane by hydrostatic pressure Pressure gradient pushes solute-containing fluid from high to low pressure Pressure gradient pushes solute-containing fluid from high to low pressure

22. Active Transport Uses ATP to move solutes across a membrane Uses ATP to move solutes across a membrane Requires carrier proteins Requires carrier proteins

23. Figure 3.10 Cytoplasm Extracellular fluid K + is released and Na + sites are ready to bind Na + again; the cycle repeats. Cell ADP Phosphorylation causes the protein to change its shape. Concentration gradients of K + and Na + The shape change expels Na + to the outside, and extracellular K + binds. Loss of phosphate restores the original conformation of the pump protein. K + binding triggers release of the phosphate group. Binding of cytoplasmic Na + to the pump protein stimulates phosphorylation by ATP. Na + K+K+ K+K+ K+K+ K+K+ ATP P P Na + K+K+ K+K+ P PiPi K+K+ K+K+

24. Types of Active Transport Symport system – two substances are moved across a membrane in the same direction Symport system – two substances are moved across a membrane in the same direction Antiport system – two substances are moved across a membrane in opposite directions Antiport system – two substances are moved across a membrane in opposite directions

25. Types of Active Transport Primary active transport – hydrolysis of ATP phosphorylates the transport protein causing movement of solutes Primary active transport – hydrolysis of ATP phosphorylates the transport protein causing movement of solutes Secondary active transport – indirect use of a primary pump to drive the transport of other solutes through a second channel Secondary active transport – indirect use of a primary pump to drive the transport of other solutes through a second channel

26. Types of Active Transport Figure 3.11

27. Active Transport: Vesicular Transport Transcytosis – moving substances into, across, and then out of a cell Transcytosis – moving substances into, across, and then out of a cell Vesicular trafficking – moving substances from one area in the cell to another Vesicular trafficking – moving substances from one area in the cell to another Phagocytosis – pseudopods engulf foreign objects and bring them into the cell Phagocytosis – pseudopods engulf foreign objects and bring them into the cell

28. Active Transport: Vesicular Transport Fluid-phase endocytosis – the plasma membrane brings extracellular fluid and solutes into the cell Fluid-phase endocytosis – the plasma membrane brings extracellular fluid and solutes into the cell Receptor-mediated endocytosis – a ligand binds to a receptor on the cell membrane, and the complex is brought into the cell Receptor-mediated endocytosis – a ligand binds to a receptor on the cell membrane, and the complex is brought into the cell Exocytosis – release of a substance from a cell through a vesicle Exocytosis – release of a substance from a cell through a vesicle Transcytosis, receptor-mediated endocytosis, and phagocytosis all use clathrin-coated pits Transcytosis, receptor-mediated endocytosis, and phagocytosis all use clathrin-coated pits

29. Exocytosis Figure 3.12a

30. Clathrin-Mediated Endocytosis Figure 3.13a Recycling of membrane and receptors (if present) to plasma membrane Cytoplasm Extracellular fluid Extracellular fluid Plasma membrane Detachment of clathrin- coated vesicle Clathrin- coated vesicle Uncoating Uncoated vesicle Uncoated vesicle fusing with endosome To lysosome for digestion and release of contents Transcytosis Endosome Exocytosis of vesicle contents Clathrin- coated pit Plasma membrane Ingested substance Clathrin protein (a) Clathrin-mediated endocytosis 2 1 3

31. Phagocytosis Figure 3.13b

32. Receptor Mediated Endocytosis Figure 3.13c

33. Passive Membrane Transport – Review Process Energy Source Example Simple diffusion Kinetic energy Movement of O 2 through membrane Facilitated diffusion Kinetic energy Movement of glucose into cells Osmosis Kinetic energy Movement of H 2 O in & out of cells Filtration Hydrostatic pressure Formation of kidney filtrate

34. Active Membrane Transport – Review Process Energy Source Example Active transport of solutes ATP Movement of ions across membranes ExocytosisATP Neurotransmitter secretion EndocytosisATP White blood cell phagocytosis Fluid-phase endocytosis ATP Absorption by intestinal cells Receptor-mediated endocytosis ATP Hormone and cholesterol uptake

35. Membrane Potential Voltage across a membrane Voltage across a membrane Resting membrane potential Resting membrane potential Ranges from –20 to –200 mV Ranges from –20 to –200 mV Results from Na + and K + concentration gradients across the membrane Results from Na + and K + concentration gradients across the membrane Steady state – potential maintained by active transport of ions (sodium-potassium pump) Steady state – potential maintained by active transport of ions (sodium-potassium pump)

36. Generation and Maintenance of Resting Membrane Potential Potassium leak channels allow K+ to exit the cell Potassium leak channels allow K+ to exit the cell Negatively charged proteins are trapped within the cell Negatively charged proteins are trapped within the cell The sodium-potassium pump ejects 3 positive charges for every 2 positive charges that it brings into the cell The sodium-potassium pump ejects 3 positive charges for every 2 positive charges that it brings into the cell

37. Roles of Membrane Receptors Contact signaling – important in normal development and immunity Contact signaling – important in normal development and immunity Electrical signaling – voltage-regulated “ion gates” in nerve and muscle tissue Electrical signaling – voltage-regulated “ion gates” in nerve and muscle tissue Chemical signaling – neurotransmitters bind to chemically gated receptors in nerve and muscle tissue Chemical signaling – neurotransmitters bind to chemically gated receptors in nerve and muscle tissue G protein-linked receptors – ligands bind to a receptor which activates a G protein, causing the release of a second messenger G protein-linked receptors – ligands bind to a receptor which activates a G protein, causing the release of a second messenger

38. Operation of a G Protein An extracellular ligand (first messenger), binds to a specific receptor An extracellular ligand (first messenger), binds to a specific receptor The receptor activates a G protein that relays the message to an effector protein The receptor activates a G protein that relays the message to an effector protein

39. Operation of a G Protein The effector is an enzyme that produces a second messenger inside the cell The effector is an enzyme that produces a second messenger inside the cell The second messenger activates a kinase The second messenger activates a kinase The activated kinase can trigger a variety of cellular responses The activated kinase can trigger a variety of cellular responses This pathway is important for amplification of a signal This pathway is important for amplification of a signal

40. Operation of a G Protein Figure 3.16 Extracellular fluid Cytoplasm Inactive second messenger Cascade of cellular responses (metabolic and structural changes) Effector (e.g., enzyme) Activated (phosphorylated) kinases First messenger (ligand) Active second messenger (e.g., cyclic AMP) Membrane receptor G protein 1 2 3 4 5 6

41. Cytoplasm Cytoplasm – material between plasma membrane and the nucleus Cytoplasm – material between plasma membrane and the nucleus Cytosol – largely water with dissolved protein, salts, sugars, and other solutes Cytosol – largely water with dissolved protein, salts, sugars, and other solutes Cytoplasmic organelles – metabolic machinery of the cell Cytoplasmic organelles – metabolic machinery of the cell

42. Cytoplasmic Organelles Specialized cellular compartments Specialized cellular compartments Membranous Membranous Mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus Mitochondria, peroxisomes, lysosomes, endoplasmic reticulum, and Golgi apparatus Nonmembranous Nonmembranous Cytoskeleton, centrioles, and ribosomes Cytoskeleton, centrioles, and ribosomes

43. Mitochondria Double membrane structure with shelf-like cristae Double membrane structure with shelf-like cristae Provide most of the cell’s ATP via aerobic cellular respiration Provide most of the cell’s ATP via aerobic cellular respiration Contain their own DNA and RNA Contain their own DNA and RNA

44. Mitochondria Figure 3.17a, b

45. Ribosomes Granules containing protein and rRNA Granules containing protein and rRNA Site of protein synthesis Site of protein synthesis Free ribosomes synthesize soluble proteins Free ribosomes synthesize soluble proteins Membrane-bound ribosomes synthesize proteins to be incorporated into membranes Membrane-bound ribosomes synthesize proteins to be incorporated into membranes

46. Endoplasmic Reticulum (ER) Interconnected tubes and parallel membranes enclosing cisternae Interconnected tubes and parallel membranes enclosing cisternae Continuous with the nuclear membrane Continuous with the nuclear membrane Two varieties – rough ER and smooth ER Two varieties – rough ER and smooth ER

47. Endoplasmic Reticulum (ER) Figure 3.18a, c

48. Rough ER External surface studded with ribosomes External surface studded with ribosomes Manufactures all secreted proteins Manufactures all secreted proteins Responsible for the synthesis of integral membrane proteins and phospholipids for cell membranes Responsible for the synthesis of integral membrane proteins and phospholipids for cell membranes

49. Signal Mechanism of Protein Synthesis mRNA – ribosome complex attaches to rough ER at a signal-recognition particle (SRP) mRNA – ribosome complex attaches to rough ER at a signal-recognition particle (SRP) SRP is released and polypeptide grows into cisternae SRP is released and polypeptide grows into cisternae The protein is released into the cisternae and sugar groups are added The protein is released into the cisternae and sugar groups are added

50. Signal Mechanism of Protein Synthesis The protein folds into a three-dimensional conformation The protein folds into a three-dimensional conformation The protein is transported to the Golgi apparatus The protein is transported to the Golgi apparatus

51. Signal Mechanism of Protein Synthesis Figure 3.19 Cytosol Ribosomes mRNA Coatomer- coated transport vesicle Transport vesicle budding off Released glycoprotein ER cisterna ER membrane Signal- recognition particle (SRP) Signal sequence Receptor site Sugar group Signal sequence removed Growing polypeptide 1 2 3 4 5

52. Smooth ER Tubules arranged in a looping network Tubules arranged in a looping network Catalyzes the following reactions Catalyzes the following reactions In the liver – lipid and cholesterol metabolism, breakdown of glycogen, and detoxification of drugs In the liver – lipid and cholesterol metabolism, breakdown of glycogen, and detoxification of drugs In the testes – synthesis of steroid-based hormones In the testes – synthesis of steroid-based hormones In the intestinal cells – absorption, synthesis, and transport of fats In the intestinal cells – absorption, synthesis, and transport of fats In skeletal and cardiac muscle – storage and release of calcium In skeletal and cardiac muscle – storage and release of calcium