Unit 2

1. Unit 2 The Cell

2. The cell is: • the most basic structural and functional unit of life. • the smallest structure capable of carrying on all vital life functions.

3. I. Cell Structure and Function A. Plasma (cytoplasmic) membrane • Envelopes the cell • Serves as a barrier between intra- and extra-cellular environments

4. Is usually selectively permeable • Enables the cell to maintain homeostasis by regulating the movement of materials into and out of the cell.

5. Modifications: 1. Microvilli: slender projections created by extensive folding of the free surface Serve to increase the surface area of the cell. Prominent in cells responsible for absorption.

6. 2. Cilia: slender projections containing supportive microtubules. Serve to move (redistribute/relocate) body fluids

7. 3. Flagellum: single “whip like” projection similar in structure to cilia, but longer. Provides the cell with mobility – propulsion. Usually moves the entire cell.

8. B. Cytoplasm • Protoplasmic material contained within the cell by the plasma membrane • Organelles are suspended in the cytoplasm

9. C. Organelles • Distinct structures found in the cytoplasm • They play specific roles in the life process of the cell and, therefore, the organism. • Their abundance is determined by the specific function of each cell.

10. 1. Endoplasmic Reticulum • An extensive system of interconnected tubes and membranes that coil through the cell connecting the cytoplasmic and nuclear membranes

11. a. Smooth ER • Enzymes catalyze reactions involved in: • metabolism and synthesis of lipids, • synthesis of steroid-based hormones, • detoxification of drugs, some pesticides, and carcinogens,

12. breakdown of stored glycogen to form free glucose and • calcium ion storage and release (specific to muscle cells and called sarcoplasmic reticulum).

13. b. Rough ER • The external surface is abundant in ribosomes which are small, dark granules made of proteins and RNA

14. Ribosomes manufacture all proteins that are secreted from cells. • Some ribosomes float free in the cytoplasm…and make soluble proteins that function in the cytoplasm

15. Ribosomes can attach to and detach from the endoplasmic reticulum as necessary.

16. The ribosomes on rER manufactures the proteins and phospholipids that form all cellular membranes (so it is called the “membrane factory”)

17. 2. Golgi Apparatus • Stacked and flattened vesicles • “Traffic director” for cellular proteins… • modifies, concentrates and packages the proteins and lipids made at the rER

18. to aid in their release to the exterior of the cell They also pinch off vesicles that contain lipids and transmembrane proteins to send to the plasma (or other organelle’s) membrane Numerous in cells active in secretion

19. 3. Mitochondria • The energy powerhouse • Contain large amounts of enzymes to break down nutrients providing the cell with energy forming ATP…aerobic cellular respiration

20. They contain their own DNA and RNA making them able to reproduce themselves.

21. An interesting side note (an IFAF): Because mitochondria and mitochondrial DNA are similar to the purple phylum bacteria, it is widely accepted that mitochondria came from bacteria that invaded the ancient ancestors of plant and animal cells!

22. Mitochondria are abundant in cells with high energy needs (muscle cells) and increase in abundance as energy needs increase. The relative density of mitochondria reflects the energy requirements of the cell.

23. 4. Lysosomes • “cellular garbage disposals” • “disintegrator bodies” • Contain enzymes capable of breaking down the components of the cell…worn out or nonfunctional organelles

24. Responsible for the digestion of dead cells Digest ingested bacteria, viruses, and toxins Perform metabolic functions such as the breakdown and release of glycogen

25. Break down nonuseful tissues (i.e.: the webs between fingers and toes during fetal development; the uterine lining during menstruation) Break down bone to release calcium ions into the bloodstream

26. 5. Microtubules Stiff, bendable and hollow tubes made of spherical protein subunits determine the overall shape of the cell and the distribution of cellular organelles.

27. 6. Centrosomes and Centrioles • Centrosomes act as a microtubule organizing center because the microtubules radiate out from here. • Contain paired centrioles

28. Generates microtubules and organizes the mitotic spindle in cell division Centrioles form the bases of cilia and flagella

29. D. The Nucleus • Is surrounded by a nuclear membrane which contains the nucleoplasm

30. Two Vital Functions • Controls and regulates metabolic activities • Essential to the process of cell division

31. Openings in the nuclear membrane connect the nucleus to the ER • The nucleus manufactures nucleic acids needed for protein synthesis

32. The nucleus contains chromatin (a nucleoprotein) which become rod like chromosomes during cell division. • Nucleoproteins are combinations of proteins and nucleic acids.

33. The nucleic acid found in chromatin is deoxyribonucleic acid…DNA! • Inside the nucleus are one or more nucleoli. • Each nucleolus is a cluster of protein, DNA and RNA that are not enclosed by a membrane

34. It is the site where ribosomal subunits are assembled and stored. • It is also where one type of RNA is synthesized.

35. The nucleolus is found in the nuclei of cells that are not undergoing cell division; it disperses and disappears during cell division and reappears when division is complete and new cells are formed.

36. Nucleoli are abundant in cells that synthesize large amounts of proteins such as the liver and muscles cells.

37. II. Cell Transport • Physical processes: • Entails the net movement of ions or molecules through a cell membrane. • This movement occurs across a concentration gradient

38. 1. Diffusion: the scattering of particles…the movement of molecules from a region of high concentration to a region of lower concentration. 2. Osmosis: the diffusion of (primarily) water through a selectively permeable membrane.

39. 3. Active transport: the process by which substances (ions) are moved across the plasma membrane due to the expenditure of energy. A.T. typically occurs from areas of low concentration to high (as opposed to diffusion and osmosis).

40. 4. Transport in vesicles: vesicles are spherical sacs that “bud” off from a membrane. They transport substances from one structure to another within cells; take in from (endocytosis), and/or release substances to (exocytosis), extracellular fluid

41. Cell membranes are not completely permeable to any substance… however, they do allow some substances to pass through with more ease than others.

42. III. Homeostasis And Cells • All of the components of the cell coordinate to maintain homeostasis.

43. A. Homeostatic Imbalances Cystic fibrosis Tay-Sachs Disease Mitochondrial myopathies Progeria Werner Syndrome Cancer (carcinogenesis)

46. Cellular Disorders

47. IV. CELL DIVISION As cells become damaged, diseased or worn out, they are replaced through the process of cell division… the process by which cells reproduce themselves.

48. I. Somatic Cell Division Somatic cell division replaces dead or injured cells and adds new ones for tissue growth.

49. Cells undergo nuclear cell division … called Mitosis and a cytoplasmic division called… cytokinesis

50. The combination of mitosis and cytokinesis results in two identical cells each having the same number and kinds of chromosomes as the original cell.