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BIOL 130
Heidi Engelhardt

Oxford Tutorial PART A 1 When a person eats food is absorbed and broken down into its components When the food reaches the small intestine it is already an amino acid An amino acid is a simple organic compound which contains a carboxyl an amino group a hydrogen and a side chain specific to each amino acid They are the building blocks of proteins 2 The small intestine is the primary site of amino acid and glucose absorption into the blood It is critical for this to happen since the supply of amino acids must be reached to all tissues3 Most of the internal and external body surfaces such as the intestines are covered with epithelial cells called epithelium Many epithelial cells transport ions or small molecules from one side of the epithelium to the other The epithelium lining the small intestine transport products of digestion such as glucose and amino acids into the blood These epithelial sheets are connected by specialized regions of the plasma membrane called cell junctions These provide strength and rigidity to the tissue and prevent the watersoluble material on one side of the sheet from moving across to the other side Amino acid is POLAR and TOO BIG thats why it cannot go directly through the membrane The epithelial cell is polarized because one side differs in function and structure from the other 4 The plasma membrane has 2 regions each with different sets of transporter proteins In epithelial cells that line the intestineportion of the plasma membrane facing the intestine the apical surface is specialized for absorption the rest of the plasma membrane the lateral and basal surfaces often referred to as the basolateral surface mediates transport of nutrients from the cell to the surrounding fluids which lead to the blood 5 The apical surface of the intestinal epithelial cells have fingerlike projections called microvilli The microvilli increase surface area for absorptionIncrease in apical surface causes an increase in transport proteins it can contain Apical surface makes direct contact with lumen 6 To enter the epithelial cell the amino acid in the gut lumen has to pass through the membrane transport proteins 7 The amino acid passes through an import Naamino acid symport on the apical surface in microvillar membrane It functions by active transport therefore energy is needed imported against its concentration gradient This symporter couples the energetically unfavorable inward movement of oneamino acid to the energetically favorable inward transport of Na ions The Naamino acid symport is coupled with NaK ATPase antiport This is found on the basolateral surface of plasma membrane Pumps 2K in and 3Na out It maintains internal concentration of Na used to drive uptake of amino acids It is coupled to ATP hydrolysis and Pi changes shape
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