BMS2021 Study Guide - Lipoprotein, Ldl Receptor, Familial Hypercholesterolemia
8 Jul 2013
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Document Summary
All proteins have a limited lifetime within a cell. They need to be removed as they can be denatured, damaged by oxidation or mutated and are not in correct tertiary/quaternary structure. There is no enzyme catalysed repair mechanism for proteins. Constitutive enzymes are present in constant concentrations in the cell and have life spans that can range from several days to months. It concentration does not change with changes in metabolic state or environment and are usually enzymes of central metabolic pathways. Some enzymes, such as inducible/repressible enzymes have very short lifespans within a cell, from minutes to hours and are destroyed by proteases. These enzymes are ones that influence the rate of synthesis by specific substances (metabolites, hormones, growth factors). The protein ubiquitin is found free floating within the cytosol of all cells. When a protein is destined for degradation it is marked by a small single ubiquitin protein.
