MCB 450 1st Edition Lecture 13 Outline of Last Lecture I Catalytic strategies used by enzymes II Inhibition of enzyme activity III Example of an enzyme mechanism a peptide hydrolysis by chymotrypsin Outline of Current Lecture I Enzyme Regulation Allostery II Conformational Changes in Hemoglobin upon O2 binding III Other Ways to Regulate Enzymes Current Lecture Regulation of enzyme activity Allosteric enzymes always catalyze the committed step of metabolic pathways Regulatory step in many biosynthetic pathways is catalyzed by an allosteric enzyme Feedback inhibition is a common means of biochemical regulation Allosteric interactions the concerted model Allosteric constant L0 T R ratio Symmetry rule all must be in the T form or all must be in the R form Heterotropic versus homotropic Heteroptropic regulators Homotropic substrates Allosteric interactions sequential model Enzymes are studied one at a time to gain more information about them Myoglobin vs hemoglobin Hemoglobin carries oxygen from the lungs to the tissues and contributes to the transport of carbon dioxide and hydrogen ions back to the lungs Myoglobin located in muscle and may facilitate the diffusion of oxygen to cellular sites that require oxygen and provide a reserve supply of oxygen in times of need O2 binding by hemoglobin and myoglobin pO2 partial pressure O2 binding by hemoglobin Protoporphyrin organic component in heme made up of four pyrrole rings linked by methine bridges to form a tetrapyrrole ring four methyl groups two vinyl groups and two propionate side chains are attached These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Proximal histidine occupies 5th coordination site on heme Quaternary structure of hemoglobin Globin fold alpha helices that are linked to one another by turns to form a globular structure Conformational changes in hemoglobin 3 D structure of hemoglobin is described as a pair of identical alpha beta dimers that associate to form the hemoglobin tetramer Allosteric Hb is not only regulated by substrate O2 binding but also by allosteric effector molecules that bind Hb 2 3 bisphosphoglycerate BPG allosteric regulator molecule present in red blood cells Fetal Hb binds 2 3 BPG with lower affinity Fetal hemoglobin must bind oxygen when the mother s hemoglobin is releasing oxygen Sickle cell anemia o genetic must be homozygous for gene o heterozygous not usually symptomatic normally just a carrier and is resistant to malaria which is why it is prevalent in Africa
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