Ch. 3 Cells!

Introduction Cell theory Cells are the smallest living subunit of an organism All cells arise from pre-existing cells Bacteria, amoebas are unicellular and function independently Human cells work interdependently Vary in size, shape, function Mostly microscopic More than 200 kinds

Cell Structure Cell membrane (plasma membrane) Nucleus Cytoplasm Forms outer boundary of cell Nucleus Absent in mature red blood cells Cytoplasm Organelles

Cell Membrane Plasma membrane (PM) Made of phospholipids, cholesterol, proteins (Fig. 3-1) Phospholipid bilayer Permit lipid-soluble materials to enter/leave cell via diffusion Cholesterol makes membrane more stable Proteins Form channels or pores to permit passage of materials Carrier enzymes (transporters) help substances enter cell Antigens identify cells as “self” Receptor sites for hormones

Cell Membrane (cont.) Active, dynamic membrane Selectively permeable Certain substances can pass through, others cannot

Nucleus Within cytoplasm Bounded by 2-layered, porous nuclear membrane Contains 1 or more nucleoli, chromosomes (Fig. 3-2) Nucleolus – small sphere of DNA, RNA, protein Form ribosomal RNA (rRNA); becomes part of ribosomes; involved in protein synthesis

Nucleus (cont.) Control center Contains 46 chromosomes in long threads called chromatin Before cell division, chromatin coils into visible chromosomes (made of DNA, protein) Nucleus contains the same genetic information, but only a small number of genes are active “switched on” Active genes code for proteins

Cytoplasm Watery solution of minerals, gases, organic molecules, organelles Cytosol Water portion of cytoplasm; where many rxns take place

Organelles Intracellular structures, often membrane-bound Have specific functions in cell metabolism (Fig. 3-2) Endoplasmic reticulum (ER) Extensive tubular network extending from nuclear membrane to PM Rough ER has ribosomes on surface, smooth ER does not Passageway for proteins, lipids

Organelles (cont.) Ribosomes Not membrane-bound Very small structures made of protein and rRNA Some on Rough ER, others in cytoplasm Site of protein synthesis

Organelles (cont.) Golgi apparatus (GA) Flat, membranous sacs stacked on top one another Carbohydrate synthesis, packaging for secretion from the cell

Organelles (cont.) Golgi Apparatus Secretion Small sacs of Golgi membrane break off & fuse with PM Substance is released to cell exterior (exocytosis)

Organelles (cont.) Mitochondria Oval or spherical organelles bounded by double membrane Inner membrane has folds (cristae) Site of ATP production Contain own genes in a single DNA molecule Duplicate themselves when cell divides Many mitochondria in muscle cells

Organelles (cont.) Lysosomes Single-membrane digestive structures Have enzymes that digest bacteria, old cell parts and dead cells

Organelles (cont.) Centrioles Cilia Flagella Pair of rod-shaped structures just outside the nucleus Organize spindle fibers during cell division Cilia Short, hair-like structures covering surface of cell Beat in unison and sweep materials across cell’s surface Cilia in fallopian tubes sweep egg toward the uterus Flagella Whip-like tail Provides motility for sperm

Organelles (cont.) Microvilli Table 3-1 Folds of cell membrane on the free surface of a cell Greatly increase surface area of membrane Part of cells lining organs that absorb material Small intestine Kidney tubules Table 3-1

Cellular Transport Mechanisms Enable cells to move materials into or out of cell Diffusion Osmosis Facilitated diffusion Active transport Filtration Phagocytosis Pinocytosis

Diffusion Movement of molecules from an area of high to low concentration along a concentration gradient Oxygen and CO2 move by diffusion (Fig. 3-3)

Osmosis Diffusion of H2O through a selectively permeable membrane Water moves from an area with more to an area with less water Water will move to an area with more solutes If a 2% salt solution and a 6% salt solution are separated by a membrane, allowing only water to pass through, in which direction will water diffuse? See Box 3-1

Facilitated Diffusion Molecules move through a membrane from an area of high to low concentration with assistance Use a carrier enzyme (transporter)

Active Transport Requires ATP to move molecules from a low to high concentration against a concentration gradient Nerve and muscle cells have sodium pumps to move sodium ions out of cells (Fig. 3-3)

Filtration Requires energy of mechanical pressure Water, dissolved materials are forced through a membrane from an area of high to low pressure Formation of tissue fluid; first step in urine formation

Phagocytosis & Pinocytosis Forms of endocytosis Phagocytosis White blood cell engulfs bacteria (Fig. 3-3) Digestion using enzymes in lysosomes Pinocytosis Stationary cells take in small molecules adsorbed or attached to their membranes Kidney tubules reabsorb small proteins (Fig. 3-3) Table 3-2

Cell Division Process by which cell reproduces itself 2 types Mitosis Meiosis

Mitosis One cell with a diploid (2N) # of chromosomes divides into 2 identical cells, each with the diploid number 2N = 46 Interphase DNA replication enables each chromosome (chromatin) to copy itself Resting (non-dividing) stage Stores energy in ATP

Mitosis (cont.) Long, thin, invisible chromatin begins to coil Each looks like a letter X because original DNA molecule & its copy (chromatids) are attached Mitosis stages (PMAT); see Table 3-4; Fig. 3-5 Prophase Metaphase Anaphase Telophase

Mitosis (cont.) Essential to replace damaged or dead cells Occurs constantly in epidermis, stomach lining, red bone marrow Does not occur in most muscle cells & neurons Skeletal muscle cells have limited mitosis Research has found some potential for mitosis in the CNS and heart At present, mitosis does not take place sufficiently enough to replace dead cells

Meiosis More complex Results in gamete (egg, sperm) formation One diploid cell (2N) divides twice to form 4 haploid cells (N) Meiosis takes place in ovaries (oogenesis) and testes (spermatogenesis) “reduction division” During fertilization, the egg joins with the sperm to restore the diploid number of 46 in the fertilized egg (zygote)