1. Chapter 3 The Cellular Level of Organization

2. A Generalized Cell: Animal Model 1. Plasma membrane 2. Cytoplasm 3. Nucleus Copyright 2009 John Wiley & Sons, Inc. 12/31/082

3. Copyright 2009 John Wiley & Sons, Inc. A Generalized Cell 1. Plasma membrane  forms the cell’s outer boundary  separates the cell’s internal environment from the outside environment  is a selective barrier  plays a role in cellular communication 12/31/083

4. Copyright 2009 John Wiley & Sons, Inc. A Generalized Cell 2. Cytoplasm  all the cellular contents between the plasma membrane and the nucleus  cytosol: the fluid portion, mostly water  organelles: sub-cellular structures having characteristic shapes and specific functions 12/31/084

5. Copyright 2009 John Wiley & Sons, Inc. A Generalized Cell 3. Nucleus  large organelle that contains DNA  contains chromosomes, each of which consists of a single molecule of DNA and associated proteins  a chromosome contains thousands of hereditary units called genes 12/31/085

6. Copyright 2009 John Wiley & Sons, Inc. Plasma Membrane Flexible yet sturdy barrier The fluid mosaic model - the arrangement of molecules within the membrane resembles a sea of lipids containing many types of proteins  Fluid inside of bilayer consistency of olive oil  Mosaic of proteins The lipids act as a selective barrier to certain substances The proteins act as “gatekeepers” to certain molecules and ions 12/31/086

7. Copyright 2009 John Wiley & Sons, Inc. Structure of a Membrane Consists of a lipid bilayer – made up of phospholipids (amphipathic), cholesterol and glycolipids Integral/transmembrane proteins – extend into or through the lipid bilayer; most integral proteins, span the entire lipid bilayer Peripheral proteins - attached to the inner or outer surface of the membrane, do not extend through it 12/31/087

8. Copyright 2009 John Wiley & Sons, Inc. Structure of a Membrane Glycoproteins – membrane proteins with a carbohydrate group attached that protrudes into the extracellular fluid Glycocalyx – the “sugary coating” surrounding the membrane made up of the carbohydrate portions of the glycolipids and glycoproteins  Self recognition  Immune response - foreign antigens  Adherence  Protection  Hydrophilic – attracting water 12/31/088

9. Copyright 2009 John Wiley & Sons, Inc. Structure of the Plasma Membrane 12/31/089

10. Copyright 2009 John Wiley & Sons, Inc. Functions of Membrane Proteins Some integral proteins are ion channels Transporters – selectively move substances through the membrane Receptors – for cellular recognition; a ligand is a molecule that binds with a receptor Enzymes - catalyze chemical reactions Others act as cell-identity markers (blood groups ABO) Attachment to neighboring cells 12/31/0810

11. Copyright 2009 John Wiley & Sons, Inc. Selective Membrane Permeability The cell’s membrane is either permeable or impermeable to certain substances The lipid bilayer is permeable to oxygen, carbon dioxide, water and steroids, but impermeable to glucose Transmembrane proteins act as channels and transporters to assist the entrance of certain substances, for example, glucose and ions 12/31/0811

12. Copyright 2009 John Wiley & Sons, Inc. Passive vs. Active Processes Passive: 1. substances move across cell membranes without the input of any energy 2. with or down the gradient 3. lipid soluble Active: 1. energy usually from hydrolysis of ATP 2. carrier protein 3. gradient independent usually against a concentration gradient 12/31/0812

13. 03_table_01

14. Copyright 2009 John Wiley & Sons, Inc. Diffusion Factors affecting diffusion: Steepness of concentration gradient Temperature Mass of diffusing substance Surface area Diffusion distance Can substance readily cross membrane? 12/31/0814

15. Copyright 2009 John Wiley & Sons, Inc. Simple Diffusion 12/31/0815

16. Copyright 2009 John Wiley & Sons, Inc. Osmosis Net movement of water through a selectively permeable membrane from an area of high concentration of water (lower concentration of solutes) to one of lower concentration of water Water can pass through plasma membrane in 2 ways: 1. through lipid bilayer by simple diffusion 2. through aquaporins, integral membrane proteins 12/31/0816

17. Copyright 2009 John Wiley & Sons, Inc. 12/31/0817

18. Copyright 2009 John Wiley & Sons, Inc. Tonicity 12/31/0818

19. Active Transport Solutes are transported across plasma membranes with the use of energy Gradient independent: from an area of lower concentration to an area of higher concentration Carrier molecule / protein Example: sodium – potassium pump Copyright 2009 John Wiley & Sons, Inc. 12/31/0819

20. Copyright 2009 John Wiley & Sons, Inc. Transport in Vesicles Vesicle - a small spherical sac formed by budding off from a membrane Endocytosis - materials move into a cell in a vesicle formed from the plasma membrane 1. receptor-mediated endocytosis 2. Phagocytosis 3. bulk-phase endocytosis (pinocytosis) Exocytosis - vesicles fuse with the plasma membrane, releasing their contents into the extracellular fluid Transcytosis - a combination of endocytosis and exocytosis 12/31/0820

21. Copyright 2009 John Wiley & Sons, Inc. Organelles Ribosomes - sites of protein synthesis Endoplasmic reticulum - network of membranes in the shape of flattened sacs or tubules  Rough ER – connected to the nuclear envelope, a series of flattened sacs, surface is studded with ribosomes, produces various proteins  Smooth ER – a network of membrane bound tubules without ribosomes, synthesizes fatty acids and steroids, detoxifies certain drugs, and stores calcium 12/31/0821

22. Copyright 2009 John Wiley & Sons, Inc. Endoplasmic Reticulum 12/31/0822

23. Copyright 2009 John Wiley & Sons, Inc. Organelles Golgi complex - consists of 3-20 flattened, membranous sacs called cisternae - modify, sort, and package proteins for transport to different destinations - proteins are transported by various vesicles  Lysosomes - vesicles that form from the Golgi complex, contain powerful digestive enzymes 12/31/0823

24. Copyright 2009 John Wiley & Sons, Inc. Golgi Complex 12/31/0824

25. Copyright 2009 John Wiley & Sons, Inc. Organelles Mitochondria - the “powerhouses” of the cell  Generate ATP  More prevalent in physiologically active cells: muscles, liver and kidneys  Inner and outer mitochondrial membranes  Cristae - the series of folds of the inner membrane  Matrix - the large central fluid-filled cavity  Self-replicate during times of increased cellular demand or before cell division 12/31/0825

26. Copyright 2009 John Wiley & Sons, Inc. Mitochondria 12/31/0826

27. Copyright 2009 John Wiley & Sons, Inc. Organelles Nucleus  Spherical or oval shaped structure  Usually most prominent feature of a cell  Nuclear envelope – a double membrane that separates the nucleus from the cytoplasm  Nuclear pores – numerous openings in the nuclear envelope, control movement of substances between nucleus and cytoplasm  Nucleolus – spherical body that produces ribosomes  Genes – are the cell’s hereditary units, control activities and structure of the cell  Chromosomes – long molecules of DNA combined with protein molecules 12/31/0827

28. Copyright 2009 John Wiley & Sons, Inc. 12/31/0828

29. Copyright 2009 John Wiley & Sons, Inc. End of Chapter 3 Copyright 2009 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein. 12/31/0829