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From CellBiology

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Homework Assignments

Homework assignment 1

In the Cell nuclues lecture i found the process by which the organelles membranes evolved to be very interesting

Homework assignment 2

I had difficulty understanding the process of protein synthesis at the ribosome.

Homework assignment 3

Energy can be used in alot of ways in the cell for example: replication of DNA, In the creation of proteins, in cell movement, to power active transport, to power muscle tissue and to create the digestive enzymes used for the cell to digest things.

Homework assignment 4

There are 4 different "CAMs", L-CAM stands for liver cell adhesion molecule, N-CAM is for nueral cell adhesion molecule, Ng-CAM stands for Nueron-glia cell adhesion molecule and I-CAM is for Intercellular adhesion molecule.

Homework assignment 5

The Stratum spinosum is the name of the layer above the basal layer and below the granulosa layer. The stratum spinosum layer has strong yet flexible properties that are brought about by the abundance of intermediate filament bundles, adhesion junctions and desmosomes.

Homework assignment 6

In the natural B35 cells we saw relatively more stumped, pronged and pygnotic cell types. While in the cells with an over expression of Tm 4 we found that there were for more stringed.

  • Hypothesis: Tm 4 regulates how distally the cytoskeleton extends.

Homework assignment 7

The two main types of confocal microscopes these are the Confocal laser scanning microscope and the spinning-disk confocal microscope.

Homework assignment 8

During the cell cycle the s phase stands for the (DNA) synthesis stage.

Clathrin

Clathrin is a protein that plays an essential role in vesicle formation. It has a triskeleton structure that enables it to form a complex polyhedral (soccer-ball-like) structure that is used to 'basket' compounds for transportation by vesicle and also to add shape the vesicle.

Structure

  • The structure of Clathrin is known as a triskeleion structure with there being three bent legs extending from a central point known as the central trimerization domain. Clathrin is made up of six chains of protein that are braided together in such a way to form to form its distinct shape. Three of these chains are known as heavy chains and form the backbone of Clathrin, they consist of two sub domains a N-terminal zone and a proximal leg domain. A seven bladed β-propeller structure is what the N-terminal domain consists off. While the proximal leg consists of a super Helix (Conner and Schmid, 2002). The other three chains are known as light chains and regulate formation and disassembly of the Clathrin and can be found connected to the proximal portion of the heavy chains. Multiple Clathrin molecules have the ability to form a variety of complex shapes when they interact, they can form 5 or 6 sided rings with the 5 sided kind having a greature curvature and when enough get together they can form a sphere like basket structure (Conner and Schmid, 2002)(Jackson et al., 2003).

Function

  • The main function of Clathrin is to selectively sort cargo and shape vesicles for transport. Clathrin is used when transporting substances between the plasma membrane and golgi, between endosomes and the golgi, and between the plasma membrane and endosomes in vesicle form. Clathrin's job is to coat the surface of forming vesicles this manipulates the shape of the vesicle though bonds between it and proteins found in the vesicle membrane, clathrin also interacts with proteins inside the vesicle. (Lui-Roberts et al., 2005). A diagram showing elements of this process
  • Adaptor proteins are involved in the recruitment of clathrin to areas required, for different areas of the cell different types of adaptor proteins are present. Adaptor proteins are also essential in making the clathrin form correctly by helping them bind to the membrane and by influencing their formation. A good example of an adaptor protein is ap 180, which often plays a major role in the formation of synaptic vesicles. Ap 180 binds clathrin, promotes its formation, binds it to various integral membrane proteins and refines its shape usually into a cage of around 50-100nm in size (Ahle and Ungewickell, 1990) (Lui-Roberts et al., 2005).
  • For the Clathrin coat to form up and start acquiring the right proteins for transportation a number of accessory proteins are involved. There are cargo receptors who's job is to latch onto the substance for transport, mediating the connection between cargo receptor and clathrin are proteins known as adaptins. These accessory proteins are what allows clathrin to play a key role in the sorting of vesicle cargo. A good example of an accessory protein is the AP2 complex that contains multiple sub units including {alpha} and ß2 adaptins. These proteins are known to have a role in membrane targeting and mediating the relation ships between different proteins including clathrin and other important endocytic machinery such as dynamin and auxlin. Their are other processes processes essential to the formation of a clatharin coated vesicle for example GTPase which is recruited by the cytosolic protein amphphysin is essential in the pinching of the vesicle from the membrane once it has formed (Conner and Schmid, 2002).

Clathrin and ap2.gif

  • The Clathrin coat quickly dissassembles after the vesicle has left its place of origin and emerged into the cytoplasm. This process allows for the recycling of clathrin. In Vitro experiments have shown that the coat dissembly of clathrin in clathrin-coated vesicles involves the minimizing of protein-protein interactions between clathrin and proteins in the vesicle membrane. This process requires a range of proteins such as Hsc70 and auxlin (SemerdJieva et al., 2008).

Genetics

Clathrin is encoded by 4 different genes, 2 for the light polypeptides and 2 for the heavy polypeptides (jackson et al., 2003).

Reference

  • Conner, S.D., and S.L. Schmid. 2002. Identification of an adaptor-associated kinase, AAK1, as a regulator of clathrin-mediated endocytosis. J. Cell Biol. 156:921–929.
  • Jackson, A.P, A. Flett, C. Smythe, L. Hufton, F.R. Wettey, and E. Smythe. 2003. Clathrin promotes incorporation of cargo into coated pits by activation of the AP2 adaptor µ2 kinase. J. Cell Biol. 163:231-236.
  • Lui-Roberts, W.W.Y., L.M. Collinson, L.J. Hewlett, G. Michaux, and D.F. Cutler. 2005. An AP-1/clathrin coat plays and essential role in forming the Weibel-Palade bodies of endothelial cells. J. Cell Biol. 170: 627-636.
  • Ahle, S., and E. Ungewickell. 1990. Auxlin, a Newly Identified Clathrin-associated Protein in Coated Vesicle from the Bovine Brain. J. Cell Biol. 111: 19-29.
  • Semerdjieva, S., B. Shortt, E. Maxwell, S. Singh, P. Fonarev, J. Hansen, G. Schiavo, B.D. Grant, and E. Smythe. 2008. Coordinated regulation of AP2 uncoating from Clathrin-coated vesicles by rab5 and hRME-6. J. Cell Biol. 183:499-511.