Lecture Outline Cell Structure and Function 3 Chapter Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

3.1 Cellular Organization 3 main parts of a cell Plasma membrane Nucleus Cytoplasm Organelles are scattered throughout the cytoplasm and have various functions The cytoskeleton maintains cell shape and allows the cell and its content to move

Cellular Organization Plasma Membrane Separates the inside of the cell (cytoplasm) from the outside Phospholipid bilayer Attached peripheral and integral proteins Receptors Channels Carriers Cholesterol molecules stabilize the membrane Glycoproteins and glycolipids attached to outer surface of some protein and lipid molecules mark cells as belonging to a particular individual

Cellular Organization The Nucleus Stores genetic information Chromatin Contains DNA, protein, and some RNA Coils into rodlike structures called chromosomes before the cell divides Nucleoli Contains rRNA Site where ribosomes are formed Nuclear envelope separates nucleus from cytoplasm

Cellular Organization Ribosomes Composed of subunits containing proteins and rRNA Can be found free within the cytoplasm sometimes in groups called polysomes Also found attached to the endoplasmic reticulum Produce proteins that carry out various functions within the cell

Cellular Organization Endomembrane System Nuclear envelope Endoplasmic reticulum (ER) Continuous with the outer membrane of the nuclear envelope Rough ER Has attached ribosomes Processes proteins produced by attached ribosomes Smooth ER synthesizes phospholipids

Cellular Organization Endomembrane System Golgi apparatus Processes, packages, and secretes various substances Receives protein and/or lipid-filled vesicles from ER Contains enzymes that modify proteins and lipids Produces lysosomes

Cellular Organization Endomembrane System Lysosomes Contain hydrolytic digestive enzymes Autodigestion responsible for cell rejuvenation and development Vesicles – tiny membranous sacs

Cellular Organization Peroxisomes and Vacuoles Peroxisomes Enzyme-containing vesicles, similar to lysosomes Detoxify drugs, alcohol, and other toxins Large numbers found in liver and kidney Break down fatty acids from fats Vacuoles isolate substances captured inside the cell

Cellular Organization Mitochondria Bound by a double membrane Site of ATP production Undergo cellular respiration (use up oxygen and release carbon dioxide) The Cytoskeleton Helps maintain the cell’s shape and anchors or assists the movement of organelles Includes microtubules, intermediate filaments, and actin filaments

Cellular Organization Centrioles Composed of microtubules A pair of centrioles are found near the nucleus of every cell Involved in cell division Form basal body (anchor point) for each cilium or flagellum Cilia and flagella are projections of cells Allow for movement of cell or movement of material along the cell surface

3.2 Crossing the Plasma Membrane Simple Diffusion Movement of atoms or molecules from an area of higher concentration to an area of lower concentration Movement of atoms or molecules occur until they are equally distributed Only certain types of molecules can enter and exit a cell by simple diffusion No cellular energy is required

Crossing the Plasma Membrane Osmosis Diffusion of water across a plasma membrane Occurs when there is an unequal distribution of water on either side of a selectively permeable membrane Osmotic pressure – force exerted on a selectively permeable membrane

Crossing the Plasma Membrane Tonicity – concentration of solute versus the concentration of water Isotonic – equal concentration of solutes (dissolved substances) and solvent (water) inside and outside cell; cell shape is maintained Hypotonic – higher concentration of water (lower concentration of solutes) outside cell; water moves into cell causing it to swell and eventually lyse Hypertonic – lower concentration of water (higher concentration of solutes) outside cell; water moves out of cell causing it to shrink or crenate

Crossing the Plasma Membrane Filtration is the movement of liquid from high pressure to low pressure Transport by Carriers Facilitated diffusion Solutes are transported by means of a protein carrier Movement from area of higher concentration to area of lower concentration (no energy required)

Crossing the Plasma Membrane Transport by Carriers Active transport Solutes move up their concentration gradient Requires a protein carrier (often called pumps) Requires the use of cellular energy

Crossing the Plasma Membrane Endocytosis and Exocytosis In endocytosis the plasma membrane envelopes a substance and forms an intracellular vesicle Phagocytosis (“cell eating”) – cell ingests solid particles Pinocytosis (“cell drinking”) – cell consumes solutions In exocytosis a vesicle fuses with the plasma membrane as secretion occurs

3.3 The Cell Cycle Set of stages that take place between the time a cell divides and the time the daughter cell divides Apoptosis (cell death) occurs at the restriction checkpoint if the cell did not complete mitosis and is abnormal Some specialized cells no longer go through the cell cycle Muscle cells Nerve cells

The Cell Cycle Cell Cycle Stages Interphase Cell is not dividing, but is preparing to divide The cell carries on regular activities Three phases G1 phase – cell doubles number of organelles and accumulates materials used for DNA synthesis S phase – “synthesis” phase; DNA replication occurs G2 phase – cell synthesizes proteins that will assist cell division

The Cell Cycle Major events during interphase Replication of DNA Before replication, the two strands of DNA are hydrogen bonded together Parental DNA strands unwind (hydrogen bonds are broken) New complimentary nucleotides pair with nucleotides in the parental DNA strands and DNA polymerase joins the new nucleotides When replication is complete, two identical double helix molecules have been formed Each strand of this double helix is equivalent to a chromatid

The Cell Cycle Protein synthesis DNA also serves as a template for RNA formation and protein construction Two steps involved in protein synthesis are: Transcription – formation of mRNA Translation – involves mRNA, tRNA, and rRNA; specifies the order of amino acids in a polypeptide

The Cell Cycle Mitotic stage Mitosis – cell division stage divided into 4 phases Prophase The centrioles near nucleus begin moving towards opposite ends of nucleus Spindle fibers appear Nuclear envelope begins to fragment Nucleolus begins to disappear Metaphase Spindle is fully formed Chromosomes are aligned at the equator

The Cell Cycle Cytokinesis – division of the cytoplasm and organelles Anaphase Sister chromatids separate (now called chromosomes) Chromosomes move toward opposite poles of the spindle Telophase Chromosomes become chromatin Spindle disappears and nucleoli appear Nuclear envelope reassembles and two daughter cell nuclei can be observed Cytokinesis – division of the cytoplasm and organelles

The Cell Cycle Importance of Mitosis Meiosis: Reduction-Division Each cell in our body is genetically identical Important to the growth and repair of multicellular organisms Meiosis: Reduction-Division Produces gametes (sex cells) Stages of mitoses are repeated twice Gametes (sperm or ova) that results have half the normal number of chromosomes