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Google Answers: Vitamin C and Collagen

Treatment of Deep Cartilage Defects in the Knee with Autologous Chondrocyte Transplantation

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A diagram of a collagen molecule

The cuticle is synthesized at the end of embryogenesis prior to hatching and then prior to molting at the end of each larval stage. During each cuticle synthetic period, the cuticle collagen genes are expressed in a distinct temporal series, the pattern of which is repeated at each synthetic period (). According to their time of expression within this series, the cuticle collagen genes can be described as early, intermediate, or late, corresponding to peaks of mRNA abundance at approximately four hours prior, two hours prior, and concurrent with secretion of each new cuticle, respectively. A comparison of the timing of expression of the early gene and intermediate is given in .

How is it that Vitamin C is so critical to proper collagen synthesis and maintenance?

Collagen biosynthesis is a complex multi-step process in vertebrates (; ). These modifications occur both intra- and extra-cellularly and involve chaperones and numerous modifying, folding and processing enzymes. It is expected that similar steps are involved in nematode collagen biosynthesis (see ) and is supported by the fact that mutations in some of these enzymes result in profound body morphology phenotypes ().

Is Vitamin C required for collagen synthesis?

role in polyamine and collagen synthesis.

The major component of this extracellular matrix (ECM) is collagen, a protein that represents over 80% of the soluble protein released following its extraction in reducing agents. Collagens are ubiquitous structural proteins with a characteristic Glycine-X-Y tripeptide repeat, where X is frequently proline and Y hydroxyproline. The procollagens are synthesised, modified and trimerize in the endoplasmic reticulum (ER). In addition to collagens, a novel highly cross-linked insoluble class of proteins called cuticlins are associated with the cuticle. The outermost layer, the epicuticle is lipid-rich and this in turn is overlaid by a loosely associated glycoprotein-rich surface coat.

Figure 1. The organization and structure of the cuticle. Panel A shows a scanning electron micrograph (SEM) of the surface of a wild type adult stage animal and an accompanying schematic representation. Panel B is a transmission electron micrograph (TEM) depicting a longitudinal cross-section of the adult cuticle highlighting the distinct structural layers and their composition. With the exception of the epicuticle and surface coat, collagens are present in all major layers. Cuticlins are restricted to the cortical layer. The epicuticle contains lipids and is covered by a glycoprotein-rich coat. Panel C depicts the synthesis of a new cuticle and the associated detachment of the old cuticle. The annular pattern of the outer cuticle layer is established by invaginations in the surface of the hypodermal membrane and corresponds to the position of circumferential actin bundles which form early in lethargus. Later in lethargus, the actin bundles dissociate, the invaginations disappear and the non-invaginated inner layers of the cuticle are deposited. Thus the annular pattern is restricted to the outer layer of the cuticle.

Collagen Synthesis, Genetic Diseases, and Scurvy | …

especially, aldosterone promotes collagen synthesis and myocyte hypertrophy in the heart.

During post-embryonic development, is enclosed within an exoskeleton called the cuticle (; ; ; ; ). The cuticle is a collagenous extracellular matrix (ECM) that is synthesized by an underlying ectodermal cell layer termed the hypodermis that surrounds the body of the animal (see ). During synthesis, material is secreted from the apical membranes of the hypodermis, then polymerizes on the outer surface of the membranes where it remains in intimate contact as the mature cuticle.

Figure 5. Developmental timing of collagen expression. Messenger RNA abundance of individual collagen genes display periodic fluctuations associated with cuticle synthesis.

A diagram of younger skin and older skin showing the decrease in collagen in older skin.
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Niacin supplements are available as nicotinamide or nicotinic acid

For the two sets of cuticle collagen genes discussed above, the and genes are all early expressed, whereas the and genes are intermediate expressed. This is consistent with a model where the individual collagen components of the same cuticle sub-structure are synthesized at the same time and different sub-structures may be synthesized at different times.

Integumentary System - InnerBody

The next important step in vertebrate collagen folding, that precedes trimer formation is the correct registration of the monomers. Collagen trimerization can be initiated from either N- or C-terminal directions, and may be set up via PDI catalysed disulfide bond formation. The ER-resident enzyme PDI (see ) may therefore play multiple independent roles in the proper biosynthesis of collagen (see ).

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The final steps in collagen maturation and cuticle synthesis involve the structural cross-linking events. The cuticle collagens and cuticlins are covalently cross-linked via unusual di- and tri- tryrosine cross-links. These non-reducible cross-links impart the characteristic strength and integrity to the cuticle ( ) and differ from the hydroxylysine-derived cross-links of the vertebrate collagens (). The major cuticle cross-linking enzyme is a dual oxidase enzyme encoded by the locus (; ; ). This large enzyme has a signal peptide, a membrane-bound peroxide generating domain and a functionally-active peroxidase domain (). It is proposed that the enzyme functions in a coupled reaction with the NADPH oxidase portion generating the hydrogen peroxide for the cross-linking reaction, which is then catalysed by the peroxidase portion (). The peroxidase domain does however lack residues considered critical for haem-binding and therefore cannot be considered to be "classical" peroxidases. RNAi () or single point mutations () in this enzyme result in worms with weakened cuticles that lack tyrosine cross-links. The resulting adult worms are devoid of cuticle struts and exhibit and phenotypes. This result is consistent with the enzyme having the proposed dual function, but also supports a sole function in generation of hydrogen peroxide that is utilized by an as-yet unidentified Haem peroxidase.

When used as a medication, it is known as hydrocortisone

Collagen biogenesis and ECM function play a critical role in organogenesis and body morphology in all metazoans. Defects in these processes result in a variety of debilitating conditions of humans, including osteogenesis imperfecta, Ehlers-Danlos syndrome, Epidermolysis bullosa, several chondrodysplasias and excessive fibrosis associated with wound healing and liver disease. Additionally, the capacity to control and engineer ECM synthesis will play a critical role in any future attempts at organ culture. Although the cuticle is a highly specialized ECM with distinct and complex features, its biogenesis involves molecules, mechanisms and pathways that are shared with vertebrates. The extreme genetic tractability makes it an excellent experimental system for the dissection of ECM formation.

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