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A lysosome (/ ˈ l aɪ s ə ˌ s oʊ m /) is a single membrane-bound organelle found in many animal cells. [1] [2] They are spherical vesicles that contain hydrolytic enzymes that digest many kinds of biomolecules. A lysosome has a specific composition, of both its membrane proteins and its lumenal proteins.
The intracellular degradation of protein may be achieved in two ways—proteolysis in lysosome, or a ubiquitin-dependent process that targets unwanted proteins to proteasome. The autophagy -lysosomal pathway is normally a non-selective process, but it may become selective upon starvation whereby proteins with peptide sequence KFERQ or similar ...
Lysosomal enzymes are synthesised in the rough endoplasmic reticulum along with a range of other secretory proteins. A specific recognition tag has evolved to prevent these harmful lysosomal enzymes from being secreted and to ensure they are targeted to the lysosome. [7] This tag is a mannose 6-phosphate residue.
The enzymes inside of lysosomes are acid hydrolases which require an acidic environment for optimal performance. Lysosomes provide such an environment by maintaining a pH of 5.0 inside of the organelle. [37] If a lysosome were to rupture, the enzymes released would not be very active because of the cytosol's neutral pH.
Protein synthesis is a very similar process for both prokaryotes and eukaryotes but there are some distinct differences. [1] Protein synthesis can be divided broadly into two phases: transcription and translation. During transcription, a section of DNA encoding a protein, known as a gene, is converted into a molecule called messenger RNA (mRNA).
The first chemical synthesis of a lysozyme protein was attempted by Prof. George W. Kenner and his group at the University of Liverpool in England. [41] This was finally achieved in 2007 by Thomas Durek in Steve Kent's lab at the University of Chicago who made a synthetic functional lysozyme molecule. [42]
The fused protein's position within the cell can then be cleanly and efficiently visualized using microscopy. [74] Other methods for elucidating the cellular location of proteins requires the use of known compartmental markers for regions such as the ER, the Golgi, lysosomes or vacuoles, mitochondria, chloroplasts, plasma membrane, etc.
This CMA-targeting motif is recognized by a cytosolic chaperone, heat shock cognate protein of 70 kDa (hsc70) which targets the substrate to the lysosome surface. [5] This substrate protein-chaperone complex binds to lysosome-associated membrane protein type 2A (LAMP-2A), which acts as the receptor for this pathway. [6]