This document summarizes key topics in cell and tissue biology, including the structure and function of different tissue types in plants and animals. It discusses the extracellular matrix, cell junctions, stem cells, and an overview of cancer biology. The main points covered are:
1) Connective tissues provide strength and support through the extracellular matrix composed of collagen, elastin and proteoglycans. Plant cell walls derive strength from cellulose microfibrils.
2) Epithelial tissues form sheets with tight junctions and basal lamina. Cadherin junctions bind cells together.
3) Cancer arises through mutations that alter cell proliferation, survival, invasion and metastasis. Oncogenes and tumor suppressors
2. Most cells in mulitcellular organisms are organized into cooperative assemblies called tissues, such as the nervous, muscle, epithelial, and connective tissues.
3. Cells are made from the EXM , which cells secrete around themselves. – it is the matrix that gives supportive tissues such as bone or wood their strength.
13. Complexes transport sugar monomers across the PM and incorporate them into a set of growing polymer chains at their points of membrane attachment.
14. Each set of chain forms a cellulose microfibril.
15. Under the PM, microtubules are aligned exactly with the cellulose microfibrils just outside the cell, so the MT are thought to act as tracks to guide the movement of the enzyme complexes
16. Cellulose microfibrils are interwoven with other polysaccharides and some structural proteins, all bonded together to form a complex structure that resists compression and tension.
17. Lignin – usually in woody tissue, is deposited within the matrix to make it more rigid and waterproof.
35. According to the type fo tissue, the connective-tissue cells that manufacture and inhabit the matrix go by various names. They make the collagen and other organic components of the matrix
57. Bindong to a molecule on one side of the membrane causes the integrin molecule to stretch out into an extended, activated state so that it can then latch onto another molecule on the opposite side
58. An intracellular signal can activate the integrin causing it to reach out and grab hold of an extracellular structure
59. Binding to an extracellular structure can activate intracellular signaling cascades via protein kinases that associate with the intracellular end of the integrin.
70. Osmotically active, causing large amounts of water to be sucked into the matrix, causing swelling balanced by tension in collagen fibers interwoven with proteoglycans.
86. Rests on some other tissue, usually connective, to which it is attached
87. Supported by a thin, tough sheet of ECMatrix, called the basal lamina, composed of a specialized type of collagen (Type IV) and other macromolecules, one includes laminin, which provides adhesive sites for integrin molecules in the PM of epithelial cells, and thus serves a linking role like that of fibronectin in connective tissues.
88. Absorptive cells, which take up nutrients, and goblet cells, which secrete mucus, in the intestines
89. Tight Junctions Make an Epithelium Leak-Proof and Separate Its Apical and Basal Surfaces
90. Cell junctions – Specialized region of connection between two cells or between a cell and the ECM
92. Seal neighboring cells together so the water-soluble molecules cannot easily leak between them.
93. Formed from claudin and occluding proteins, which are arranged in strands along the lines of junctions to create seals.
94. Without, the pumping activities of apsorptive cells would be futile and the concentration on both sides of the epithelium would be the same
95. The TJs around the apical side of cells prevents diffusion of membrane proteisn within the PM and keep the apical domain of the PM different form the basal domain.
96. TJs are sites of assembly for the complexes of intracellular proteins that fovern apico-basal polarity in the interior of the cell.
106. Each cadherin molecule is tethered inside its cell, via several linker proteins, to actin filaments.
107. Form a continuous adhesion belt, located near the apical end of the cell just below the TJs, around each of the interacting epithelial cells. Actin is therefore connected form cell to cell across the epithelium.
108. By shrinking the apical surface along one axis, the sheet can roll itself up into a tube.
109. Or it can make a cup-shaped concavity and eventually create a vesicle that may pinch off from the rest of the epithelium
118. Gap junction – communicating cell-cell junction that allows ions and small molecules to pass from the cytoplasm of one cell to the cytoplasm of the next.
119. Connexons form the channels across two PMs and allow inorganic ions and small water-soluble molecules to move directly from cytosol to cytosol.
121. GJs in heart muscle cells proved electrical coupling that allows electrical waves of excitation to spread through the tissue.
122. These waves trigger the coordinated contraction of the cells, producing a regular heart beat.
123. Can be opened or closed as needed in response of extracellular signals.
124. Dopamine, a neurotransmitter, reduces GJ communication within a class of neurons in the retina in response to an increase in light intensity.
125. This reduction in GJ permeability changes the pattern of electrical signaling and help the retina switch from using rod photoreceptors, which are good detectors of low light, to cone photoreceptors, which detect color and fine detail in bright light.
158. Signals are from the stem cells themselves, progeny, and surrounding tissues
159. Wnt proteins, a class of signaling molecules, serve to keep the stem cells and precursor cells at the base of each intestinal crypt in a proliferative state: the cells in these regions both secrete Wnt proteins and express the receptors for these proteins; and through positive feedback, stimulate themselves to continue dividing.
164. Problem: if the cells are genetically different, they may be detected and destroyed by the immune system, but therapeutic cloning could prevent this.
167. Therapeutic cloning – ES cells derived in culture, with the aim of generating various cell types that can be used for tissue repair, rather than a whole cloned animal
189. Most human cancer cells not only contain many mutations but also are genetically unstable
190. This genetic instability results from mutations that interfere with the accurate replication and maintenance of the genome and thereby increase the mutation rate itself.
200. Most cancer cells are genetically unstable, with an increased mutation rate
201. Cancer cells are abnormally invasive, mostly due to the lack of cell-adhesion molecules, such as cadherins that hold normal cells in place
202. Cancer cells can often survive and proliferate in foreign tissues to form secondary tumors (metastases), whereas most normal cells die when misplaced.
204. Oncogene – any abnormally activated gene that can make a cell cancerous. Typically a mutant for of a normal gene (proto-oncogene) involved in the control of cell growth or division
206. For cells, the danger lies in mutations that destroy gene function
207. Tumor suppressor gene – a gene that in a normal tissue cell inhibits progress through the cell cycle. Loss or inactivation of both copies of such a gene from a diploid cell can cause it to divide as a cancer cell.
208. Some of these genes code for growth factors, for receptors, like Ras
213. People with a functioning APC gene have been found to have developed two independent somatic mutations which causes them to develop colon cancer.
214. APC encodes an inhibitory protein that normally restricts the activation of the Wnt signaling pathway, which is involved in stimulating cell proliferation in the crypts of the gut lining as described earlier.
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