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Metabolic regulation

Uni of Notts, Signalling & Metabolic Regulation, Year 2, Topic 4

TermDefinition
Three main ways to regulate carbohydrate metabolism Changing enzyme amount (transcription, degradation, epigenetics) Changing catalytic activity (allosteric, covalent, hormonal, isoforms) Changing substrate availability (altering membrane permeability with transporters)
How cells change the amount of an enzyme By increasing or decreasing transcription, altering mRNA stability, & degrading enzymes faster; epigenetic tags & metabolic intermediates modulate transcription
How epigenetic tags & glycolytic intermediates influence enzyme expression Metabolites (e.g., glycolytic intermediates) act as signals that recruit or modify epigenetic enzymes (e.g., histone acetyltransferases, deacetylases), changing chromatin structure & thus transcription of metabolic genes
Hormonal regulation timescale compared to allosteric & covalent regulation Hormonal regulation (e.g., insulin, glucagon) often changes gene expression, enzyme levels, or long‑term phosphorylation states, acting over hours to days, whereas allosteric & covalent changes act in seconds to minutes
Isoenzymes (isoforms) & why they're useful in metabolism Different molecular forms of the same enzyme that catalyse the same reaction but have different kinetic properties, allowing tissue‑specific tuning of metabolism for their energy needs
substrate accessibility regulation in carbohydrate metabolism Control of glucose entry via transporters (e.g., GLUT4) & hormones (insulin increases transporter insertion; glucagon promotes glucose output), thereby regulating flux through pathways
(Adenylate) energy charge ratio of ATP, ADP, & AMP; high energy charge activates biosynthetic (anabolic) pathways & inhibits catabolic ones, while low energy charge does the opposite
How negative feedback via allosteric control prevents overproduction of metabolites End product of a pathway binds an early enzyme allosterically & inhibits it, reducing flux when product is abundant, stabilising metabolite levels
In CTP feedback inhibition, how enough product is still produced despite inhibition *Example: don't need to memorise* Graded, not absolute: at low CTP, the enzyme is active; as CTP rises, activity decreases but rarely reaches zero, basal flux continues to maintain necessary levels despite NTP instability
How the laws of thermodynamics apply to metabolic pathways overall First law: Energy conserved: metabolism converts energy between forms Second law: Total entropy increases: cells couple exergonic reactions to endergonic ones so that the overall ΔG is negative
How phosphorylation regulates enzyme activity at the structural level Adding a phosphate introduces negative charge & H-bonding capacity, which can cause conformational changes or create new binding sites for regulatory proteins
How insulin promotes glucose utilisation at the cellular level Insulin triggers signalling (e.g., MAP kinase), increases glucose transporter translocation to the membrane & upregulates glycolytic & lipogenic enzymes, enhancing glucose uptake & storage
How glucagon opposes insulin in carbohydrate metabolism Glucagon activates cAMP/PKA signalling, promoting glycogen breakdown & gluconeogenesis, while inhibiting glycolysis in the liver, increasing blood glucose
Why lactate dehydrogenase (LDH) is considered near‑equilibrium & reversible Small redox potential difference between substrates & products, ΔG is close to zero; direction depends mainly on substrate & product concentrations
How LDH isoforms support tissue‑specific metabolism *Example: don't need to memorise* LDH1: higher substrate affinity, favours pyruvate → CO₂ pathways, suited to aerobic tissues (e.g., heart) LDH5: higher Vmax, favours pyruvate → lactate, suited to anaerobic conditions (e.g., fast‑twitch muscle)
Created by: Denny12
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