Oxford Tutorial
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 concentration. Diffusion is a type of passive transport, because molecules are always in random motion, and as a result, will naturally balance a difference in concentration, and move from an area of higher concentration to an area of relative lower concentration.
Cell membranes are selectively permeable, which means that it allows some molecules to pass while preventing some molecules from entering. For example, molecules such as amino acids cannot cross the cell membrane without help.
Carrier proteins are saturated throughout the cell membrane, and can facilitate movement by carrying small molecules, such as amino acids, across the cell membrane. Carrier proteins do not require energy because they facilitate movement from an area of high concentration to an area of lower concentration. Many carrier proteins can facilitate movement in both directions, and allow molecules to enter or exit. Direction is based on concentration gradient. For example, if the concentration is higher outside the cell, molecules would naturally move to na area of lower concentration. That is, they would enter the cell.
Once the amino acid has entered the epithelial cell, it must be attached to its tRNA in order to be useful in protein synthesis. tRNA
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 concentration. Diffusion is a type of passive transport, because molecules are always in random motion, and as a result, will naturally balance a difference in concentration, and move from an area of higher concentration to an area of relative lower concentration.
Cell membranes are selectively permeable, which means that it allows some molecules to pass while preventing some molecules from entering. For example, molecules such as amino acids cannot cross the cell membrane without help.
Carrier proteins are saturated throughout the cell membrane, and can facilitate movement by carrying small molecules, such as amino acids, across the cell membrane. Carrier proteins do not require energy because they facilitate movement from an area of high concentration to an area of lower concentration. Many carrier proteins can facilitate movement in both directions, and allow molecules to enter or exit. Direction is based on concentration gradient. For example, if the concentration is higher outside the cell, molecules would naturally move to na area of lower concentration. That is, they would enter the cell.
Once the amino acid has entered the epithelial cell, it must be attached to its tRNA in order to be useful in protein synthesis. tRNA