Topic 3 cells and tissues Flashcards
What are the levels of organisation?
atoms - molecules - Proteins - cells - tissue - organ - organ system - organism
How can the cell interact with it’s surroundings?
With surface proteins such as protein channels, integral proteins etc. They can initiate reactions inside the cells, e.g. polymerization of intracellular filaments.
What 4 different tissue types do we consist of?
Nervous, epithelial, muscle and connective tissue
What is the epithelial tissue?
Usually one tightly packed layer of cells to form a physical barrier (e.g. inside of gut, lining of hollow organs, skin epidermis), these cells are polarized which means that the top and the bottom of the cell is different. Often have a basal membrane consisting of proteins that can attach cells.
What is connective tissue?
Fat, soft padding tissue, bone, blood, tendon and cartilage. Can be dense or not dense (cartilage, have lot of extracellular matrix beneficial for dampening)
How are muscles built up?
Several muscle cells fuse together to one aligned muscle. They have the same direction and the alignment is for the force to be “bigger” when they contract.
Which tissue has a very high density of cells that fuse together with each other?
Muscle tissue
Which tissue is comprised of a tightly-bound layer of polarized cells?
Epithelial cells
Which tissue has a low density of cells?
Connective tissue
How is skin built up?
It’s an organ that consists of 2 tissues - epithelium (dermis, epidermis etc.) and connective tissue (blood vessels, nerves, tissue specific structures and cells, extracellular matrix). Basal lamina between epi. and connective T.
Name 3 cells hanging out in the connective tissue of skin
Tissue macrophage: immune cell that can react on foreign stuff
Fibroblast: produces extracellular matrix
Mast cell - reacts on foreign attack, a type of white blood cell
Which 2 structural fibers are most common in skin?
Elastin and collagen fibers
There are some glycans in the connective tissue and basal lamina of skin, which ones and what are their 2 main categories?
Ground substance (gel): consists of proteoglycans and hyaluronan Matrix glycoproteins: fibronectin and laminin
Describe the basic structure of collagen and what AA is most common
glycine is repeated every 3rd unit. 3 chains are assembled into a triple helix (tropocollagen) bound together by electrostatic bonds. Glycine is the smallest AA which make the chains come close together. The ends of the chain are unorganized.
Briefly explain the collagen synthesis in the cell
Transcription - translation - synthesis of pro-alpha-chain - hydroxylation - glycosylation - self-assebmly into 3 pro-alpha-chains - formation of procollagen triple-helix - secretion - cleavage of propeptides into collagen - collagen fibril.
What mechanical properties do collagen and elastin have?
Collagen is stiff and strong but still a bit elastic. Elastin is highly elastic, low modulus.
Describe the ground substance
Consists of a hyaluronan backbone with attached proteoglycans which have a “bottle brush” morphology. The proteoglycan have a core protein with attached chains sugar molecules called glucoseaminoglycans (GAGs). The GAGs are negatively charged which repel each other and bind water - gel forming.
Name some GAGs
Keratan-, chondroitin-, dermatan- and heparan sulphate. Hyaluranan is also included as well as heparin (most negatively charged molecule in the body)
Why is the gel matrix so important?
It helps transferring signaling molecules and bind growth factors. The GFs can be docked on the GAGs which prevent enzymatic degradation and help present them to cell receptors.
Describe the two matrix glycoproteins
They have multiple bioactive peptides acting as binding sites. They function as a glue between cells and ECM.
What is fibronectin?
A glycoprotein. Have different functional peptides such as heparin binding sites, RGD sequences (cell receptor binding), collagen bind. site also self-association sites. Because of these bind. sites it works as a glue - makes it good to have on biomaterial surfaces!
Describe laminin
Cross-shaped glycoprotein with 3 primary chain. Major component of the basal lamina influencing cell differentiation, migration, and adhesion.Can bind to cells by integrin receptors.
What are integrins
Integrins are transmembrane receptors that facilitate cell-extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle, organization of the intracellular cytoskeleton, and movement of new receptors to the cell membrane.
Which two cellular intefaces are there in tissues?
Cell-Cell contact (tight junctions, desmosomes, gap junctions)
Cell-ECM contact (hemidesmosomes, focal adhesion)
Describe the Cell-ECM interface
The cell membrane integrated integrin can bind to many different ECM proteins such as the glycoproteins to build an inter-connectivity between the ECM and the cells.
How does the integrin receptor work?
Consists of a alpha and a beta, which makes it a heterodimer. They are bound togheter and one end is inside the cell (bind cytoskeleton) and one outside (bind ECM). It needs to have a stand up position to get activated. When activated (from the inside or outside) the two dimers loose contact/gets further apart.
Describe focal adhesion
Clustering of integrin receptors that bind ECM proteins leading to the formation of focal adhesions. The focal adhesion complex works as a physical link between several integrins and actin cytoskeleton. They mediate regulatory signals and mechanical force between the ECM and cell.
What is the difference between proteoglycans and glycoproteins?
Proteoglycans are proteins that are heavily glycosylated (core protein and long chain sugar molecules attached). Glycoproteins are also proteins, they have covalenty bound oligosaccharides to the peptide chain.
What’s the importance of cell attachment?
Highly affect cell fate processes such as viability, protein synthesis, communication, proliferation, migration, activation/differentiation and apoptosis. Biomaterials need to support these functions.
How does cells attach to biomaterial surfaces?
They attach to proteins absorbed at the biomaterial surface by the same mechanism that they attach to tissue ECM, that is through focal adhesion.
Which one of glycoprotein or proteoglycan consists of the highest amount carbohydrates?
Proteoglycans with 50-60% while glycoproteins have 10-15%
