Chapter 3: Cell Anatomy and Cell Junctions Pages 62-75 © 2015 Pearson Education, Inc.

Anatomy and Physiology of Cells It is important to know the organelles within the cell and to understand the general functions of each Organelles > cell Organs > system Organ systems > human body © 2015 Pearson Education, Inc.

Summary of Organelles and their Functions Nucleus = control center; houses DNA Plasma Membrane = selective; boundary Ribosomes = site of protein synthesis Mitochondria = site of cellular respiration Endoplasmic Reticulum = transportation network Rough = finalizing protein synthesis - folding Smooth = fat metabolism and detoxing Golgi Bodies =protein packaging; become vesicles Vesicles = move products via endocytosis/exocytosis Lysosomes = garbage crew Peroxisomes = detoxification/neutralizers Cytoskeleton = structural organelle Centrioles =direct cell division via mitotic spindle

Figure 3.4 Structure of the generalized cell. Chromatin Smooth endoplasmic reticulum Nuclear envelope Nucleolus Nucleus Plasma membrane Lysosome Mitochondrion Rough endoplasmic reticulum Centrioles Ribosomes Golgi apparatus Secretion being released from cell by exocytosis Peroxisome

“How do cells stick together?” Plasma Membrane Junctions Cells are bound together in three ways: Glycoproteins act as an adhesive or cellular glue Wavy contours of the membranes of adjacent cells fit together in a tongue-and-groove fashion Special membrane junctions are formed, which vary structurally depending on their roles 3 different junctions © 2015 Pearson Education, Inc.

Figure 3.2 Structure of the plasma membrane. Extracellular fluid (watery environment) Glycoprotein Glycolipid Cholesterol Sugar group Polar heads of phospholipid molecules Bimolecular lipid layer containing proteins Channel Nonpolar tails of phospholipid molecules Proteins Filaments of cytoskeleton Cytoplasm (watery environment)

Tight (impermeable) junction Figure 3.3 Cell junctions. Microvilli Tight (impermeable) junction Desmosome (anchoring junction) Plasma membranes of adjacent cells Connexon Underlying basement membrane Extracellular space between cells Gap (communicating) junction

TIGHT JUNCTIONS Tight junctions Impermeable junctions made up of the plasma membrane Bind cells together into leakproof sheets Prevent substances from passing through extracellular space between cells © 2015 Pearson Education, Inc.

DESMOSOMES Desmosomes Anchoring junctions that prevent cells from being pulled as a result of mechanical stress Created by “buttonlike” thickenings of adjacent plasma membranes kind of like the rivets in the pockets of your jeans- they keep the material together © 2015 Pearson Education, Inc.

GAP JUNCTIONS Gap junctions allow direct diffusion of ions and small molecules between adjacent cells Hollow cylinders of proteins (connexons) function like tunnels to send messages Molecules can travel directly from one cell to the next through these channels © 2015 Pearson Education, Inc.

Tight (impermeable) junction Figure 3.3 Cell junctions. Microvilli Tight (impermeable) junction Desmosome (anchoring junction) Plasma membranes of adjacent cells Connexon Underlying basement membrane Extracellular space between cells Gap (communicating) junction

Exocytosis/Endocytosis review Active Transport of bulk materials Endocytosis: Plasma membrane engulfs product from extracellular space to bring into cell Becomes travelling vesicle inside cell Exocytosis: Vesicle from inside the cell fuses with plasma membrane to dump contents outside of cell

Plasma membrane SNARE (t-SNARE) Figure 3.12 Exocytosis. Extracellular fluid Plasma membrane SNARE (t-SNARE) 1 The membrane- bound vesicle migrates to the plasma membrane. Vesicle SNARE (v-SNARE) Molecule to be secreted Secretory vesicle Cytoplasm Fusion pore formed 2 There, v-SNAREs bind with t-SNAREs, the vesicle and plasma membrane fuse, and a pore opens up. Fused SNAREs Vesicle contents are released to the cell exterior. 3 (b) Electron micrograph of a secretory vesicle in exocytosis (190,000×) (a) The process of exocytosis

Figure 3.13a Events and types of endocytosis. Extracellular fluid Cytosol Plasma membrane Vesicle Lysosome Vesicle fusing with lysosome for digestion 1 Release of contents to cytosol 2 Transport to plasma membrane and exocytosis of vesicle contents Detached vesicle Ingested substance 3 Membranes and receptors (if present) recycled to plasma membrane Pit (a)

Cell Extensions Cilia: whiplike extensions Propels substances along passageways Found in respiratory passageways, uterine tubes, kidneys, inner ear Flagella: longer whiplike extensions Propels the cell The sperm is the only flagellated cell in the human Microvilli: extensions of cell membrane Increases cell surface area (often for absorption) Found along entire small intestine; large numbers along the proximal convoluted tubule in the nephron

Figure 14.7 Structural modifications of the small intestine. Blood vessels serving the small intestine Microvilli (brush border) Muscle layers Lumen Circular folds (plicae circulares) Villi Absorptive cells Lacteal (c) Absorptive cells Villus (a) Small intestine Blood capillaries Lymphoid tissue Intestinal crypt Muscularis mucosae Venule Lymphatic vessel Submucosa (b) Villi

Figure 3.8g Cell diversity. Nucleus Flagellum Sperm (g) Cell of reproduction

Cell Diversity Cells can vary in structure and function Variations include: Modified shape More of a particular organelle Modified organelles

Specialized Function of cells Cells are classified based on their structure and function This is known as Histology the study of the structure of cells and their formation into tissues and organs An Histologist can identify abnormalities in tissues obtained from cultures/biopsies

Body Tissues Epithelial Connective Muscular Nervous Secrete and aborb Hold structures together, store nutrients Muscular Movement Nervous communication

Figure 3.8b Cell diversity. EPITHELIAL Nucleus Epithelial cells Intermediate filaments

Figure 3.8c Cell diversity. MUSCULAR Skeletal muscle cell Nuclei Contractile filaments Smooth muscle cells

Figure 3.8a Cell diversity. CONNECTIVE Fibroblasts Rough ER and Golgi apparatus No organelles Nucleus Erythrocytes

Figure 3.8f Cell diversity. NERVOUS Processes Rough ER Nerve cell Nucleus