Metabolism Flashcards
Two Major Purposes of Metabolism
- To obtain usable chemical energy from the environment
- solar energy
- consuming and breaking down nutrient molecules - To make specific molecules that cells need to live and grow
Anabolic Pathways
Use energy to build larger molecules
Generally reductive
Electrons are used to make new bonds
Catabolic Pathways
Release energy
Generally oxidative
Electrons are removed as bonds are broken
Amphibolic Pathways
Operate in both catabolic and anabolic processes
Anapleurotic Reactions
Chemical reactions that form intermediates of a metabolic pathway
Fuel Sources
Polysaccharides Triacylglycerol Proteins Nucleic Acids -first 3 are the most significant
Storage of excess fuels
Carbs are stored as glycogen
Fatty acids are stored as fat in adipocytes
Reactions proceeding forward
When deltaG is negative
Exergonic
Spontaneous
Actual free energy determines if a reaction occurs
When deltaG>0
Reaction will not occur
When deltaG<0
Reaction will occur
When deltaG«0
Reaction is considered irreversible
When deltaG=0
Reaction is considered reversible
Close to equilibrium
Changes in concentration may change the direction of the reaction
Enzyme Regulation
Irreversible steps are usually regulated
Reversible steps are usually not regulated
Rate-Limiting Step in a Pathway
The irreversible, regulated reaction that determines the overall rate of the pathway
Product Inhibition
An enzyme is inhibited by the product of its reaction
Feedback Inhibition
An enzyme is inhibited by a metabolite further down the pathway
Activation
An enzyme may be activated by a metabolite upstream
Ensures that the pathway in functioning in concert
-otherwise intermediates might accumulate
Feed-forward activation
Reciprocal Regulation
Opposing pathways catalyze the reverse of another pathway
The irreversible reactions must be replaced or bypassed
Pathways are regulated to ensure that both do not operate simultaneously
High Energy Intermediates
Compounds that contain usable chemical energy
-energy that can be recovered or used
Types of High Energy Intermediates
Electron carriers: NADH, NADPH, FADH2, FMNH2
Nucleotide triphosphates: ATP, UTP, GTP
Thioesters
Oxidative Reaction
Catabolism
Metabolites are oxidized
Cofactors are reduced
Typically NAD+, FAD
Reductive Reaction
Anabolism
Metabolites are reduced
Cofactors are oxidized
Typically NADPH
Nucleotides that Act as Electron Carriers
NAD+, NADP+, FAD
Reduction Reactions of Cofactors
NAD+ + 2H+ + 2e- = NADH + H+
NADP+ + 2H+ + 2e- = NADPH + H+
FAD + 2H+ + 2e- = FADH2
Which Nucleotides are Typically Cosubstrates (C-O)?
NAD+ and NADP+
Which Nucleotide is Typically a Prosthetic Group (C-C)?
FAD
FAD as a Prosthetic Group
As a prosthetic group, FADH2 must be reoxidized back into FAD for the next enzyme cycle to occur
In CAC, coenzyme Q is used to carry out this reoxidation
What is the high-energy bond in ATP?
Because of phosphoanhydride bonds
Phosphoanhydride Bonds
High energy bonds
deltaG= -32 for hydrolysis
deltaG= +32 for formation
Why is ATP a high-energy molecule?
Decreased electrostatic repulsion
Resonance stabilization
-terminal phosphoryl group of ATP, inorganic phosphate
Solvent effects
-more interactions with water=favourable
These all contribute to free energy change
Thioesters
High Energy Compounds
Similar to esters but with no delocalization
ATP
Energy Currency
-common in multiple systems
-phosphoanhydride bond makes it high energy
Generated by Catabolism
-directly “substrate-level phosphorylation”
-via reoxidation of NADH/FADH2 “oxidative phosphorylation”
Used In
-driving unfavourable reactions (coupling)
-movement
-primary active transport (ion pumping)
Coupling of Free Energies
Free energy changes for reactions are additive
A reaction with an overall unfavourable free energy change can occur when another favourable reaction occurs in concert
The combined reactions must have an overall deltaG<0 to be spontaneous
Phosphate Transfer Potential
Free energies of hydrolysis for phosphate-containing compounds can be referred to as the phosphate transfer potential
