1. Chapter 3 Anatomy of Cells

2. Functional Anatomy of Cells The typical cell (Figure 3-4) –Also called composite cell –Varies in size; all are microscopic (Table 3-1) –Varies in structure and function (Table 3-2)

5. Functional Anatomy of Cells Cell structures –Plasma membrane separates the cell from its surrounding environment –Cytoplasm thick gel-like substance inside of the cell composed of numerous organelles suspended in watery cytosol each type of organelle is suited to perform particular functions (Table 3-2) –Nucleus large membranous structure near the center of the cell

6. Cell Membranes Each cell contains a variety of membranes: –Plasma membrane (Figure 3-5) –Membranous organelles sacs and canals made of the same material as the plasma membrane

7. Cell Membranes Fluid mosaic model—theory explaining how cell membranes are constructed –Molecules of the cell membrane are arranged in a sheet –The mosaic of molecules is fluid; that is, the molecules are able to float around slowly –This model illustrates that the molecules of the cell membrane form a continuous sheet

8. Cell Membranes Primary structure of a cell membrane is a double layer of phospholipid molecules (Figure 2-25) –Heads are hydrophilic (water-loving) –Tails are hydrophobic (water-fearing) –Molecules arrange themselves in bilayers in water –Cholesterol molecules are scattered among the phospholipids to allow the membrane to function properly at body temperature –Most of the bilayer is hydrophobic; therefore water or water-soluble molecules do not pass through easily

9. Cell Membranes Membrane proteins (Table 3-3) –A cell controls what moves through the membrane by means of membrane proteins embedded in the phospholipid bilayer –Some membrane proteins have carbohydrates attached to them, forming glycoproteins that act as identification markers –Some membrane proteins are receptors that react to specific chemicals, sometimes permitting a process called signal transduction

10. Structure –Sheet (bilayer) of phospholipids stabilized by cholesterol Function –Maintain wholeness (integrity) of a cell or membranous organelle Cell Membranes

11. Structure –Membrane proteins that act as channels or carriers of molecules Function –Controlled transport of water-soluble molecules from one compartment to another

12. Cell Membranes Structure –Receptor molecules that trigger metabolic changes in membrane Function –Sensitivity to hormones and other regulatory chemicals; involved in signal transduction

13. Cell Membranes Structure –Enzyme molecules that catalyze specific chemical reactions Function –Regulation of metabolic reactions

14. Cell Membranes Structure –Enzyme molecules that catalyze specific chemical reactions Function –Regulation of metabolic reactions

15. Cell Membranes Structure –Membrane proteins that bind to molecules outside the cell Function –Form connections between cells and other structures such as tissue fibers or other cells

16. Cell Membranes Structure –Membrane proteins that bind to support filaments within the cytoplasm Function –Support and maintain the shape of a cell or membranous organelle; cell movement

17. Cell Membranes Structure –Glycoproteins or proteins in the membrane that act as markers Function –Recognition of cells or organelles

19. Cytoplasm and Organelles Cytoplasm –gel-like internal substance of cells –includes many organelles suspended in watery intracellular fluid called cytosol

20. Cytoplasm and Organelles Two major groups of organelles (Table 3-2) –Membranous organelles specialized sacs or canals made of cell membranes –Nonmembranous organelles made of microscopic filaments or other nonmembranous materials

21. Cytoplasm and Organelles Endoplasmic reticulum –made of canals with membranous walls and flat, curving sacs arranged in parallel rows throughout the cytoplasm –extend from the plasma membrane to the nucleus –proteins move through the canals

22. Cytoplasm and Organelles Two types of endoplasmic reticulum: –Rough endoplasmic reticulum Ribosomes dot the outer surface of the membranous walls Ribosomes synthesize proteins, which move toward the Golgi apparatus and then eventually leave the cell Function in protein synthesis and intracellular transportation

23. Cytoplasm and Organelles Two types of endoplasmic reticulum (cont.) –Smooth endoplasmic reticulum No ribosomes border membranous wall Functions are less well established and probably more varied than for rough endoplasmic reticulum Synthesizes certain lipids and carbohydrates and creates membranes for use throughout cell Removes and stores Ca ++ from cell’s interior.

26. Cytoplasm and Organelles Ribosomes (Figure 3-4) –Many are attached to the rough endoplasmic reticulum and many lie free, scattered through the cytoplasm –Each ribosome is a nonmembranous structure made of two pieces, each composed of rRNA large subunit small subunit –Ribosomes in the endoplasmic reticulum make proteins for “export” or to be embedded in the plasma membrane –Free ribosomes make proteins for the cell’s domestic use

28. Cytoplasm and Organelles Golgi apparatus –Membranous organelle consisting of cisternae stacked on one another and located near the nucleus (Figure 3-7) –Processes protein molecules from the endoplasmic reticulum (Figure 3-8) –Processed proteins leave the final cisterna in a vesicle; contents may then be secreted to outside the cell

30. Cytoplasm and Organelles Lysosomes –Made of microscopic membranous sacs that have “pinched off” from Golgi apparatus –The cell’s own digestive system –Enzymes in lysosomes digest the protein structures of defective cell parts plasma membrane proteins particles that have become trapped in the cell

31. Cytoplasm and Organelles Peroxisomes –Small membranous sacs containing enzymes that detoxify harmful substances that enter the cells –Often seen in kidney and liver cells

32. Cytoplasm and Organelles Mitochondria (Figure 3-9) –Made up of microscopic sacs –Wall composed of inner and outer membranes separated by fluid –Thousands of particles make up enzyme molecules attached to both membranes –The “power plants” of cells Mitochondrial enzymes catalyze series of oxidation reactions that provide about 95% of cell’s energy supply –Each mitochondrion has a DNA molecule, allowing it to produce its own enzymes and replicate copies of itself

34. Cytoskeleton The cell’s internal supporting framework –made up of rigid, rodlike pieces –provide support –allow movement –Include mechanisms that can move the cell or its parts (Figure 3-10)

36. Cytoskeleton Cell fibers –Intricately arranged fibers of varying lengths that form a three-dimensional, irregularly shaped lattice –Fibers appear to support the endoplasmic reticulum, mitochondria, and “free” ribosomes

37. Cytoskeleton Cell fibers (cont.) –Smallest cell fibers are microfilaments (Figure 3-11) “Cellular muscles” Made of thin, twisted strands of protein molecules that lie parallel to the long axis of the cell Microfilaments can slide past each other, causing shortening of the cell

38. Cytoskeleton Cell fibers (cont.) –Intermediate filaments twisted protein strands slightly thicker than microfilaments form much of the supporting framework in many types of cells –Microtubules tiny, hollow tubes that are the thickest of the cell fibers made of protein subunits arranged in a spiral fashion function is to move things around in the cell

40. Cytoskeleton Centrosome –An area of the cytoplasm near the nucleus that coordinates the building and breaking of microtubules in the cell –Nonmembranous structure also called the microtubule-organizing center (MTOC) –Plays an important role during cell division –The general location of the centrosome is identified by the centrioles

41. Cytoskeleton Cell extensions –Cytoskeleton forms projections that extend the plasma membrane outward to form tiny, fingerlike processes –Three types (Figure 3-12): Microvilli –found in epithelial cells that line the intestines and other areas where absorption is important –help to increase the surface area manyfold Cilia and flagella –cell processes that have cylinders made of microtubules at their core –cilia are shorter and more numerous than flagella –flagella are found only on human sperm cells

43. Nucleus Definition—spherical body in center of cell; enclosed by an envelope with many pores

44. Nucleus Structure –Nuclear envelope surrounding nucleoplasm –Nuclear pores –DNA Chromatin threads or granules in nondividing cells Chromosomes in early stages of cell division Functions of nucleus are functions of DNA molecules DNA determines both structure and function of cells and heredity

45. Cell Connections Cells are held together by fibrous nets that surround groups of cells (e.g., muscle cells), or cells have direct connections to each other There are three types of direct cell connections (Figure 3-14)

46. Cell Connections Desmosome –Fibers on the outer surface of each desmosome interlock with each other anchored internally by intermediate filaments of the cytoskeleton –Spot desmosomes, connecting adjacent membranes, are like “spot welds” at various points –Belt desmosomes encircle the entire cell like a collar

47. Cell Connections Gap junctions –Membrane channels of adjacent plasma membranes adhere to each other Form gaps or “tunnels” that join the cytoplasm of two cells Fuse two plasma membranes into a single structure

48. Cell Connections Tight junctions –Occur in cells that are joined by “collars” of tightly fused material –Molecules cannot permeate the cracks of tight junctions –Occur in the lining of the intestines and other parts of the body, where it is important to control what gets through a sheet of cells