In 1970, [[Günter Blobel]] conducted experiments about the translocation of proteins across membranes. He was awarded the 1999 Nobel prize for his findings. He discovered that many proteins have a [signal sequence]?, a short amino acid sequence at one end, that functions like a [postal code]? for their target organelle. The translation of mRNA into protein by a ribosome takes place within the cytosol. If the synthesized proteins are intended to go to a different organelle, they can do this in two ways, depending on the protein. |
In 1970, [Günter Blobel]? conducted experiments about the translocation of proteins across membranes. He was awarded the 1999 Nobel prize for his findings. He discovered that many proteins have a [signal sequence]?, a short amino acid sequence at one end, that functions like a [postal code]? for their target organelle. The translation of mRNA into protein by a ribosome takes place within the cytosol. If the synthesized proteins are intended to go to a different organelle, they can do this in two ways, depending on the protein. |
Several molecules that attach to special receptors called [coated pit]?s on the outside of cells cause the cell to perform endocytosis, an invagination of the plasma membrane to incorporate the molecule and associated structures. This mechanism is used for three main purposes: |
Several molecules that attach to special receptors called [coated pits]? on the outside of cells cause the cell to perform endocytosis, an invagination of the plasma membrane to incorporate the molecule and associated structures. This mechanism is used for three main purposes: |
# The uptake of some hormones and [growth factor]?s, for example, [epidermal growth factor]? and [nerve growth factor]?. # The uptake of proteins that are to be destroyed, for example, antigens in phagocytotic? cells like macrophage?s. |
# The uptake of some hormones and [growth factors]?, for example, [epidermal growth factor]? and [nerve growth factor]?. # The uptake of proteins that are to be destroyed, for example, antigens in phagocytotic? cells like macrophages?. |
* Some viruses, for example, the [Semliki forest virus]?, get access to the cell through this mechanism. * The poisons/toxin?s of cholera? and diphteria? gain entry to the cell this way. |
* Some viruses, for example, the [Semliki forest virus]?, get access to the cell through this mechanism. * The poisons/toxins? of cholera? and diphteria? gain entry to the cell this way. |
Just like in factories, some proteins are created defective; others are damaged while in use, for example, by oxidative stress. To recycle these damaged proteins, proteins have very different [half life]?s, mainly depending on their N-terminal amino acid residue. The recycling mechanism itself is mediated by ubiquitin (see there). |
Just like in factories, some proteins are created defective; others are damaged while in use, for example, by oxidative stress. To recycle these damaged proteins, proteins have very different [half lifes]?, mainly depending on their N-terminal amino acid residue. The recycling mechanism itself is mediated by ubiquitin (see there). |