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Transcript
Cells: the building block of all living things Made mostly of C, H, O, N Trace elements are important for cellular function o Ca for blood clotting, Fe for hemoglobin, I for metabolism, Na and K for nerve impulse transmission for muscle contraction. Water takes up about 66% of cells Area between blood and cells is interstitial fluid (saltwater solution) Vary in size, shape and function Anatomy of the cell: There are 3 main parts of the generalized cell: 1. Nucleus (near center) 2. Cell membrane (forms outer membrane) 3. Cytoplasm (semifluid, surrounds organelles) 1) Nucleus: the control center of the cell; contains genes. DNA controls the building of the whole body and more importantly, the instructions for building proteins. o Necessary for reproduction Conforms to the shape of the cell Has 3 parts: 1. Nuclear membrane: double membrane barrier, between which is space or “moat” a. Where the two membranes approach and meet are called nuclear pores (large) b. It is selectively permeable c. Encloses the nucleoplasm, where nucleoli and chromatin are present. 2. Nucleoli: one or more small, dark-staining, round bodies a. Where ribosomes are assembled i. Eventually migrate into cytoplasm (site of protein synthesis) 3. Chromatin: bumpy threads of non replicating DNA combined with protein scattered throughout the nucleus a. At the beginning of replication, the chromatin threads coil and condense to form Chromosomes 2) Plasma membrane: fragile, transparent barrier that contains cell contents and separates from environment Has a core of two lipid fat layers in which proteins and carbohydrates float. Lipid bilayer is formed mostly by phospholipids, but also has a substantial amount of cholesterol (stabilizes and keeps fluidity) Impermeable to most water-soluble molecules. Specialized function is a result of proteins o Some are enzymes, hormone/chemical receptors (binding sites) o Those that span the membrane are usually for transport functions Clusters of proteins form pores for ions, water, and small, watersoluble molecules Others act as carriers that bind to the molecule and bring it into the cell. Some have sugar groups attached to them, called Glycoproteins, which are responsible for determining blood type, receptors that bacteria or viruses can bind to, and for cell-cell interactions. (*step in cancer cell generation) o Specializations such as microvilli and membrane junctions are commonly displayed by epithelial cells (line hollow body organs) Microvilli-increase surface area of the membrane for absorption purposes. Membrane junctions- vary depending on their role 1. Tight junctions: adjacent plasma membranes fuse together like a zipper (leak proof). 2. Desmosomes: anchor cells to prevent cells, such as skin cells from being pulled apart (adjacent cells are connected by protein filaments) 3. Gap junctions: allows communication between cells by having molecules pass from one cell to another. 3) The Cytoplasm: cellular material outside of the nucleus, inside of the plasma membrane Site of most cellular activities, “factory center” Has 3 parts: 1. Cytosol: semitransparent fluid that suspends the other elements Mostly water and dissolved nutrients and solutes 2. Organelles: the metabolic machinery. Each one carries out a specific function 3. Inclusions: chemical substances that may be present, depending on the cell type. Organelles: (compartmentalization of each allows it to do its specific fxn) 1. Ribosomes: tiny, round, dark bodies made of ribosomal RNA and proteins. a) Site of protein synthesis b) Some float free; others are attached to (rough) Endoplasmic Reticulum. 2. Endoplasmic Reticulum: a system of fluid-filled tubules that coil and twist through the cytoplasm. a) ½ of total cell’s membranes b) Network is to carry substances, primarily proteins from one part of the cell to another. c) Rough ER: studded with ribosomes (membrane factory) i. The proteins made on the ribosomes fold into their 3D shape and are then dispatched to the rest of the cell. ii. Size of RER is indicator on the amount of protein the cell makes (large in pancreatic cells) d) Smooth ER: continuation of the RER, but has no role in protein synthesis. 3. 4. 5. 6. i. Functions in cholesterol synthesis and breakdown, fat metabolism, and detox of drugs. (Large in liver cells, and those that produce steroid-based hormones-testes) Golgi Apparatus: a stack of flattened membranous sacs with swarms of vesicles. a) Found close to nucleus and is “traffic director” for cellular proteins b) It modifies and packages proteins received from the RER. i. Proteins “tagged” for export accumulate in the Golgi and cause it to swell. ii. The swollen end pinches off (now called transport vesicles) and travel to the plasma membrane. iii. Fuses w/ the membrane, part ruptures, and the contents are spilled outside of the cell (exocytosis). iv. It also packages proteins and phospholipids to maintain the plasma membrane, and hydrolytic enzyme sacs called lysosomes. Lysosomes: “breakdown bodies” that appear in different sizes, and are bags of powerful digestive enzymes a. These are the cell’s demolition sites b/c they digest worn-out and nonusable cell structures and foreign substances b. Abundant in WBCs c. The enzymes that they contain are formed by ribosomes and “packaged” by the Golgi (bud off of Golgi). Peroxisomes: membranous sacs of oxidase enzymes that use O2 to detoxify a number of harmful or poisonous substances. a. “Disarm” Free Radicals- reactive chemicals with unpaired electrons that can scramble the structure of proteins and nucleic acids. (natural byproduct/dangerous if accumulate) b. Convert free radicals to H2O2 (hydrogen peroxide). Catalase (an enzyme) then turns H2O2 to water. c. Numerous in kidney and liver cells (detoxification) d. Do not pinch off of Golgi like lysosomes, they pinch in half Mitochondria: sausage-shaped organelles that squirm, lengthen, and change shape continuously a. They have a double membrane, equal to two plasma membranes placed side by side i. Outer is smooth, inner has cristae- shelflike protrusions. b. Enzymes in the cristae membrane and within the mitochondria carry out the reactions in which O2 is used to break down food into energy (respiration) c. Much of this energy escapes as heat, but some is used to form ATP molecules (why called the “powerhouse” of the cell) d. “Busy cells” like liver and muscle have hundreds of mitochondria, inactive have just a few 7. Cytoskeleton: elaborate network of protein structures that extend throughout the cytoplasm a. Act as internal framework that determines cell shape, supports other organelles, and provides the machinery needed for cell-cell transport and cellular movements. b. 3 elements of cytoskeleton: 1) Microtubules: Largest and “tube-like”; determine the overall shape of a cell and the distribution of organelles (important in cell division) 2) Intermediate filaments: strong, stable “rope-like” structure; help form desmosomes and provide resistance to pulling forces on the cell 3) Microfilaments: Actin and Myosin; cell motility and produces change in cell shape (**important in muscle cells) 8. Centrioles: pair of rod-shaped bodies that lie close to the nucleus. a. Lie at right angles to each other b. Made of fine Microtubules c. During cell division, they direct the formation of the “mitotic spindle” 9. Others: a. Cilia-whip-like cellular extensions that move substances along the cell surface (respiratory system) i. Where they appear, there are usually many of them. ii. Form when Centrioles multiply and line up beneath the plasma membrane; microtubules then begin to “sprout” from the centrioles and put pressure on the membrane, forming projections b. Flagella- when the projections are substantially longer i. Sperm is the only flagellated cell in the human body **Cilia propel substances, flagella propels the cell itself.