1. Cells: The Living Units PART 1

2. Introduction to Cells  Cells – the smallest living units in our bodies  An average adult has 70 trillion cells!  Our bodies are composed of cells, and products of cells…only!  Cells produce matrix such as bone, tendons, ligaments, cartilage etc. Organelles – “little organs” – carry on essential functions of cells Enzymes – direct chemical reactions in cells Metabolism – the sum of all chemical reactions in the cell

3. Introduction to Cells  Cells have three main components Plasma membrane Cytoplasm Nucleus

4. Cell basics... Plasma membrane Nucleus Organelles Cytosol Cytoplasm

5. Cytoskeleton fibers adsorb water and crosslink to each other, giving the cytoplasm the consistency of gelatin (without the strawberry flavor)

6. Structure of a Generalized Cell Figure 2.1

7. The Plasma Membrane  Plasma membrane defines the extent of the cell-it is the nervous system of the cell  Structure of membrane Fluid mosaic model (phospholipid bilayer) Types of membrane proteins  Integral proteins – firmly imbedded in, or attached to lipid bilayer  Peripheral proteins – attach to membrane surface  Membrane proteins facilitate information into and out of the cell

8. The Plasma Membrane Figure 2.2a

9. The Plasma Membrane Monday  Functions – relates to location at the interface of cell’s exterior and interior Provides barrier against substances outside cell Some plasma membranes act as receptors

10. The Plasma Membrane  Determines which substances enter or leave the cell Membrane is selectively permeable  Diffusion – molecules move from a region where they are more concentrated to an area where they are less concentrated  Osmosis – the diffusion of water across a membrane

11. Endocytosis  Endocytosis Mechanism by which particles enter cells  Phagocytosis – “cell eating”  Pinocytosis – “cell drinking”  NOTE: Clathrin is a protein that causes bending of the cell membrane in order for a molecule to be captured by endocytosis

12. Receptor-mediated Endocytosis  Receptor-mediated endocytosis Plasma proteins bind to certain molecules  Invaginates and forms a coated pit Pinches off to become a coated vesicle  NOTE: This is the method by which insulin and cholesterol enter cells!

13. Two Types of Endocytosis Figure 2.3

14. Exocytosis  Exocytosis – a mechanism that moves substances out of the cell Substance is enclosed in a vesicle-such as a hormone The vesicle migrates to the plasma membrane Proteins from the vesicles (v-SNAREs) bind with membrane proteins (t-SNAREs) The lipid layers from both membranes bind, and the vesicle releases its contents to the outside of the cell

15. Exocytosis Figure 2.4

16. The Cytoplasm  Cytoplasm – lies internal to plasma membrane Consists of cytosol, organelles, and inclusions  Cytosol (cytoplasmic matrix) Jelly-like fluid in which other cellular elements are suspended Consists of water, ions, and enzymes

17. Cytoplasmic Organelles  Ribosomes – constructed of proteins and ribosomal RNA Site of protein synthesis NOTE: Most antibiotics work by blocking bacterial protein synthesis. The antibiotic works on one of the subunits to prevent bacteria from multiplying!

18. Structure of a Generalized Cell Figure 2.1

19. Cytoplasmic Organelles  Endoplasmic reticulum – “network within the cytoplasm” Rough ER – ribosomes stud the external surfaces Smooth ER – consists of tubules in a branching network  No ribosomes are attached; therefore no protein synthesis

20. The Endoplasmic Reticulum and Ribosomes Figure 2.5

21. Figure 2.6 Assembly of Proteins at the Rough Endoplasmic Reticulum It works just like a factory assembly line where the “frame” which comes from the nucleus starts on the assembly line. The parts (amino acids) are on the inside of the membrane of the RER and build up the protein

22. Cytoplasmic Organelles  Golgi apparatus – a stack of three to 10 disk- shaped envelopes Sorts products of rough ER and sends them to proper destination Products of rough ER move through the Golgi from the convex (cis) to the concave (trans) side

23. Role of the Golgi Apparatus in Packaging Products of Rough ER Figure 2.8

24. Cytoplasmic Organelles  Lysosomes – membrane-walled sacs containing digestive enzymes Digest unwanted substances  Peroxisomes – membrane-walled sacs of oxidase enzymes Enzymes neutralize free radicals and break down poisons Break down long chains of fatty acids Are numerous in the liver and kidneys

25. Mitochondria  Mitochondria – generate most of the cell’s energy; most complex organelle  More abundant in energy-requiring cells, like muscle cells and sperm Figure 2.10

26. Cytoplasmic Organelles  Cytoskeleton – “cell skeleton” – an elaborate network of rods Contains three types of rods  Microtubules – cylindrical structures made of proteins  Microfilaments – filaments of contractile protein actin  Intermediate filaments – protein fibers

27. Cytoskeleton: Microtubule Figure 2.11a

28. Cytoskeleton: Microfilament Figure 2.11b

29. Cytoskeleton: Intermediate Filament Figure 2.11c

30. Cytoplasmic Organelles  Centrosomes and centrioles Centrosome – a spherical structure in the cytoplasm  Composed of centrosome matrix and centrioles Centrioles – paired cylindrical bodies  Consists of 27 short microtubules  Act in forming cilia  Necessary for karyokinesis (nuclear division)

31. Cytoplasmic Inclusions  Temporary structures Not present in all cell types  May consist of pigments, crystals of protein, and food stores Lipid droplets – found in liver cell and fat cells Glycosomes – store sugar in the form of glycogen

32. The Nucleus  The nucleus – “central core” or “kernel” – control center of cell DNA directs the cell’s activities Nucleus is approximate 5µm in diameter

33. The Nucleus Figure 2.13

34. The Nucleus  Nuclear envelope – two parallel membranes separated by fluid-filled space  Chromatin – composed of DNA and histone proteins Condensed chromatin – contains tightly coiled strands of DNA

35. The Nucleus  Chromatin – composed of DNA and histone proteins Extended chromatin – contains uncoiled strands of DNA  DNA’s genetic code is copied onto mRNA (transcription) while in “extended chromatin” form  Chromosomes – highest level of organization of chromatin Contains a long molecule of DNA

36. The Nucleus  Nucleolus – “little nucleus” – in the center of the nucleus Contains parts of several chromosomes Site of ribosome subunit manufacture

37. Cellular Diversity  Specialized functions of cells relates to Shape of cell Arrangement of organelles

38. Cellular Diversity  Cells that connect body parts or cover organs Fibroblast – makes and secretes protein component of fibers Erythrocyte – concave shape provides surface area for uptake of the respiratory gases Epithelial cell – hexagonal shape allows maximum number of epithelial cells to pack together

39. Cells that Connect Body Parts or Cover Organs Figure 2.16, step 1

40. Cellular Diversity  Cells that move organs and body parts Skeletal and smooth muscle cells  Elongated and filled with actin and myosin  Contract forcefully

41. Cells that Move Organs and Body Parts Figure 2.16, step 2

42. Cellular Diversity  Cells that store nutrients Fat cell – shape is produced by large fat droplet in its cytoplasm  Cells that fight disease Macrophage – moves through tissue to reach infection sites

43. Cells that Store Nutrients and Cells that Fight Disease Figure 2.16, steps 3–4

44. Cellular Diversity  Cells that gather information Neuron – has long processes for receiving and transmitting messages Figure 2.16, step 5

45. Cellular Diversity  Cells of reproduction Oocyte (female) – largest cell in the body  Contains many copies of organelles for distribution to daughter cells Sperm (male) – possesses long tail for swimming to the egg for fertilization Figure 2.16, step 6