1.Components of connective tissue 2. Collagen synthesis and organization 3.Glyco
ID: 85978 • Letter: 1
Question
1.Components of connective tissue 2. Collagen synthesis and organization 3.Glycosaminoglycans: types, structure and function 4. Types of epithelial 5. Types of epithelial cell- cell junctions: their components, location and function1.Components of connective tissue 2. Collagen synthesis and organization 3.Glycosaminoglycans: types, structure and function 4. Types of epithelial 5. Types of epithelial cell- cell junctions: their components, location and function
2. Collagen synthesis and organization 3.Glycosaminoglycans: types, structure and function 4. Types of epithelial 5. Types of epithelial cell- cell junctions: their components, location and function
Explanation / Answer
1.There are three main components of connective tissues-
Fibres which are of 2 types- elastic and collagen fibres, cells and ground substance
2. Procollagen is assembled which is a three dimensional structure. Proline and lysine are the amino acids which form important place in collagen. The transition from procollage to collagen starts with the hydroxylation of these amino acids.Hydroxylation is needed for tripple helix of collagen.Two enzymes are needed fro hydroxylations- prolyl 4 hydroxylase and lysyl hydroxylase. Vitamin C acts as a cofactor in these reactions. Thus a deficiency of vitamin C leads to scurvy where there is impaired collagen synthesis.
About 34 genes are required for collagen synthesis.Each codes specifically for mRNA sequence.When the final mRNA is formed it exits the nucleus and with the help of ribosome assist in the formation of collagen by translation.The initial few peptides form a signal sequence which is recognized by the signal recognition particle in endoplasmic reticulum and is send in for posttranscriptional modification. Now this is known as pre pro collagen.
Pre pro collagen converts into pro collagen by hydroxylations and glycosylation. Signal peptide on N terminal gets dissolved.Once these modifications have taken place, three of the hydroxylated and glycosylated propeptides twist into a triple helix forming procollagen.
Now it enters into golgi apparatus where last post transcriptional modification takes place. In this step oligosaccharides are added . "Collagen peptidases" present outside the cell remove the "loose ends" of the procollagen molecule. Now tropocollagen is formed. Lysyl oxidase acts on lysines and hydroxylysines producing aldehyde groups, which will eventually undergo covalent bonding between tropocollagen molecules. This polymer of tropocollogen is known as a collagen fibril.This is the final step in the synthesis of collagen.
3.On the basis of their structure units and linkage between disaccharide units; they can be classified in two types.
There are disaccharides repeating regions in glycosaminoglycans chains which are composed of uronic acid like D-glucoronic acid or L-iduronic acid and amino sugar like D-galactosamine or D-glucosamine. All these glycosaminoglycans are differing in the type of hexosamine, hexose or hexuronic acid unit as well as geometry of the glycosidic linkage between these units.
Functions-Hyaluronic acid shows many important functions in signalling activity during embryonic morphogenesis, wound healing and pulmonary and vascular diseases. It also acts as lubrication of synovial joints and helps in joint movement as well as space filler, wetting agent and flow barrier within the synovium. It also influences on cancer progression and protector of cartilage surfaces.The anti-coagulation property of sulphated GAGs is because of its capacity to prolong the process of blood clotting which is due to the potentiating interaction of GAGs with the natural inhibitor of thrombin, antithrombin III , with only about one-third of all heparin chains possessing the structures required for AT binding.
4.There are three principal cell shapes associated with epithelial cells: squamous epithelium, cuboidal epithelium, and columnar epithelium.
5.Cell junctions- are of following types-
Plasmodesmata- specialized junctions are called plasmodesmata places where a hole is punched in the cell wall to allow direct cytoplasmic exchange between two cells.
gap junctions-they are channels between neighboring cells that allow for the transport of ions, water, and other substances.gap junctions develop when a set of six membrane proteins called connexins form an elongated, donut-like structure called a connexon. Gap junctions are particularly important in cardiac muscle: the electrical signal to contract spreads rapidly between heart muscle cells as ions pass through gap junctions.
tight junctions -create a watertight seal between two adjacent animal cells.These proteins are called as claudind which form tight junctions.The purpose of tight junctions is to keep liquid from escaping between cells, allowing a layer of cells to act as an impermeable barrier.
Desomsomes- These are formed by certain proteins which are formed by proteins like cadherins.
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