CHAPTER 10 MULTICELLULARITY Brenda Leady, University of Toledo Prepared by Brenda Leady, University of Toledo Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Multicellular Single organism composed of more than one cell Main benefit from the division of labor Larger genomes = larger proteomes Additional proteins for Cell communication Arrangement and attachment of cells Cell specialization

Extracellular matrix (ECM) Network of material secreted from the cells forming a complex meshwork outside of cells Major component of certain parts of plants and animals Bone and cartilage of animals Woody parts of plants

Major macromolecules of ECM are proteins and polysaccharides Proteins form large fibers Polysaccharides give a gel-like character Important roles such as strength, structural support, organization, and cell signaling

Proteins of ECM Adhesive Structural Fibronectin and laminin Help cells adhere to ECM Structural Collagen provides tensile strength Main protein found in bone, cartilage, tendon, skin Elastin provides elasticity Needed in areas that expand and return to original shape

Collagens are a family of proteins that give animal cells a variety of ECM properties At least 27 different types of collagens in humans Many different genes Collagens all have a common triple helix structure Similar yet distinct amino acid sequence affects structure and function of collagen fibers Differential gene regulation controls which types of collagens are made Wrinkling a symptom of decreasing collagen synthesis with age

Polysaccharides in animal ECM In vertebrates, the most abundant are glycosaminoglycans (GAGs) Long, unbranched polysaccharides with a repeating disaccharide unit Highly negatively charge attracts ions and water Majority linked to core proteins to form proteoglycans

GAGs and proteoglycans resist compression Abundant in joints Chitin important ECM in invertebrates Exoskeleton

Plant cell walls Protective ECM outside the plasma membrane Usually stronger, thicker and more rigid than animal ECM

Primary cell wall Secondary cell wall Develops between newly made cells Flexible and allows for size increase Main macromolecule is cellulose Secondary cell wall Layers of cellulose and other components More variable structure than primary cell wall

Cell junctions Adhere cells to each other and to the ECM Animals cells have a more varied group of junctions In plants, cellular organization is different because of the rigid cell wall

Anchoring junctions Attach cells to each other and to the ECM Rely on cell adhesion molecules (CAM) Cadherin and integrin 4 main categories Adherins junctions Desmosomes Local adhesions Hemidesmosomes

Cadherins CAMs that create cell-to-cell junctions Dimer of identical subunits Extracellular domain of two cadherin dimers, each in adjacent cells, bind to each other to promote cell-to-cell adhesion Inside the cell, linker proteins connect cadherins to the cytoskeleton Major CAMs of vertebrates By expressing only certain types of cadherins, each cell will only bind to other expressing same type

Integrins Group of cell-surface receptor proteins Extracellular domain for binding cell to ECM Intracellular domain for binding to cytoskeleton

CAMs and cell signaling CAMs originally thought to be only mechanical Recent evidence points to role in cell signaling When junctions are formed or broken, signaling pathways are affected Signaling pathways can also affect CAM Integrins are capable of both outside-in and inside-out signaling

Tight junctions Or occluding junctions Forms tight seal between adjacent cells Prevents ECM from leaking between cells Tight junctions Made by occludin and claudin Bind to each to form tight seal Not mechanically strong, not bound to cytoskeleton

Gap junctions Small gap between plasma membranes of cells at junction Six connexin proteins in one cell align with six connexin proteins in an adjacent cell to form a connexon Connexon allows passage of ions and small molecules Allow adjacent cell to share metabolites and directly signal each other

Loewenstein and colleagues followed the transfer of fluorescent dyes to determine the size of gap-junction channels Gap junctions allow passage of small molecules up to about 1,000 Daltons Determined by experiments using fluorescent dyes Monolayer of rat liver cells injected with fluorescent dyes of different masses Dyes up to 901 Daltons moved from cell to cell

Middle lamella Plants don’t form cell-to-cell connections Additional component of ECM First layer to form when cells dividing Cement cell walls of adjacent cells together Middle lamella rich in pectins Ripening fruit secrete pectinases such that ripe fruit is less firm than unripe fruit

Plasmodesmata Functionally similar to gap junctions Allow passage of ions, water, signaling molecules between cells Different in that they are open channels where the cell membrane of one cell is continuous with adjacent cell membrane Desmotubule connects ER membrane of adjacent cells

Tissues and organs Tissue Organ Group of cells having a similar structure or function Organ Collection of two or more tissues that perform a specific function or set of functions

6 basic cell processes Cell division Cell growth Differentiation Migration Apoptosis Cell connections

4 general types of animal tissue Epithelial tissue Cells joined together forming continuous sheets to cover and line body surfaces Connective tissue Support body or connect tissues Muscle tissue Facilitates movement Nervous tissue Receives, generates and conducts electrical signals

3 types of plant tissue Dermal tissue Ground tissue Vascular tissue Covering on various plant parts Ground tissue Most of plant’s body with variety of functions Parenchyma, collenchyma, sclerenchyma Vascular tissue From interconnected conducting vessels for water and nutrients

Compare plant and animal tissues Certain tissues show intriguing similarities Epithelial and dermal tissues Both form layers of cells Both tightly woven together

Compare plant and animal tissues Connective and ground tissues Both provide structural support and are rich in ECM