You are an amino acid in the lumen of the small intestine of a newborn mammal. You are looking at intestinal epithelial cells that bring important maternal proteins (immunoglobulins) across their apical surfaces by receptor-mediated endocytosis. Your ambition is to be part of a receptor that does that job.
A. beginning from the challenge of entering the cell, until you have been loaded onto an appropriate tRNA.
Amino acids are the building blocks of protein. Within the small intestine is the only site in the digestive tube for absorption of amino acids. Absorption takes place on the surface of small intestinal epithelial cells.
Diffusion is the movement of molecules from an area of higher concentration to an area of lower
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AUG is the start codon. When the stop codon is reached, a release factor, a protein, fills the A site and frees the polypeptide from the ribosome. A protein`s function depends on its shape and a protein`s shape depends on how it folds. Folding begins during elongation and continues as amino acids are being added. Folding is sped up by molecular chaperones. Chaperones bind to the ribosome where the growing polypeptide emerges from the ribosome. Many proteins are modified after they are synthesized by chemical groups added to the protein, or they are altered by enzymes that add or remove phosphate groups. Phosphate groups have negative charges, and adding or removing a phosphate group can cause major changes in the shape and function of the protein. However, all of the information required for the protein to fold into its correct three-dimensional structure is contained in the amino acid sequence of the protein.
But, as the protein is being synthesized on the ribosome there is a danger that the unfinished protein will begin to fold up incorrectly because the rest of the protein has not yet been made. It is also possible that the unfinished protein will interact with other unfinished proteins being made on other ribosomes and form what is called an aggregate: a network of partially folded proteins that have