1. 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.

2. 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

3. 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

4. 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

6. 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

9. 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

11. 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

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

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

15. 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

17. 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

19. 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

21. 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

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

25. 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

27. 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

30. 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

32. 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

34. 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

36. 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

38. 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

39. 6 basic cell processes Cell division Cell growth Differentiation
Migration
Apoptosis
Cell connections

40. 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

42. 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

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

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