Pathways And Control... Flashcards
Homeostasis
maintenance of a constant
internal state in a changing environment.
Homeostasis ensures
cells can obtain and use energy
- make new cells,
- exchange materials
- eliminate wastes in a changing environment
A series of automatic control systems ensure that the body maintains
constant temperature and steady levels of water, ions and metabolites.
metabolic pathways
Biochemical reactions in human cells are organized into specific sequences
Metabolic pathways are multistep sequences of enzyme-catalyzed reactions where the product of one reaction is used
as the substrate for the next enzyme reaction
Pathways that regenerate a metabolite are called
Cycles
Energy containing nutrients (carbohydrates, fats, proteins)
Ca»ta»bo»lism»
Energy depleted end products
CO2
H2O
NH3
Precursor molecules Amino acid Sugars Fatty acids Nitrogenous bases AN>>ABOL>>ISM
Cell macromolecules (more complex) Proteins Polysaccharides Lipids Nucleic acid
Breakdown complex molecules to give simpler components eg glycolysis
Catabolic
Synthesis of complex molecules from simpler materials
Anabolic
Intermediary pathway that serves both in catabolism and anabolism
Amphibolic
regulation by cell metabolites
Intrinsic regulation
regulation by external factors,
hormones etc.
Extrinsic regulation
Binding of hormone(1st messenger)to its receptor activates
G protein which activates adenylate cyclase
Activated Adenylate cyclase converts
ATP to cAMP
cAMP ( 2nd messenger) activate
Kinases
Activated kinases phosphorylate
Cellular proteins
Millions of phosphorylated proteins cause reactions that
Produce physiological responses
Molecules such as NAD+, NADH, ATP, ADP, AMP are
important allosteric effectors and intrinsic regulators of cellular metabolism
Cellular concentrations of ATP & ADP (AMP) reflect
the energy state of the cell
High [ATP] activates
Anabolic pathways
High [ATP] suppresses
Catabolic pathways
High [ADP] or [AMP] activates
Catabolic
High [ADP] or [AMP] inhibits
Anabolic pathways
If NAD+ is high
The cell needs energy
If NADH is high the cell
Doesn’t need energy
△G
Change in free energy
Free energy
energy available to do work
△G will be zero when reaction reaches
Equilibrium
△G predicts the
Direction of reaction
Negative free energy
Spontaneous
The rate of the reactions depend on the lowering of activation energies by the enzymes that catalyze the reactions.
G values cannot predict rates of reactions
Compounds with “high energy bonds” have high phosphoryl-transfer potential measures energy in acompound Phosphate group can be transferred from ATP to another compound
High energy bonds
Measure of tendency of compound to transfer ~P to H20
Phosphoryl group-transfer potential
ATP can accept ~P from
high- energy compounds
ATP can donate ~P to
Low energy compounds
is a measure of the tendency of a chemical species to acquire electrons or lose electrons, respectively.
Redox potential (oxidation/reduction potential)
is generally associated with catabolic (oxidative) pathways
NAD+/NADH
Serves as an electron donor mainly in anabolic pathways
NADP /NADPH
Catabolic pathways
Oxidative
Anabolic pathways
Reductive pathways
It is a general rule of metabolic regulation that pathways are regulated at
The 1st committed step
The first irreversible reaction unique to the pathway.
Committed step
is the one after which the substrate has only one way to
go.
The committed step
the slowest step in a pathway, which determines how fast the whole pathway can proceed.
The rate limiting step
Irreversible reaction that, once occurs, Leads to the formation of a final substrate with no return
Committed step
phenomenon where the output of a process is used as an input to control the behavior of the process itself, oftentimes limiting the production of more product.
Feedback inhibition
Feed back inhibition advantages
- Fast
- Prevents accumulation of toxic intermediates
- Prevents waste of energy and substrates
When a metabolite produced early in a pathway activates an enzyme that is further down the pathway
Feed-forward activation
Metabolism is composed of
interconnecting reactions and pathways
Thermodynamics (△G) determine the
Direction of the pathway
the universal energy currency
ATP
major source of cellular energy
Oxidation of carbon fuel
Metabolic pathways are
Tightly regulated
Synthetic and degradative pathways differ, they are distinct by
compartmentation or bypass reaction
reactions that proceed with a large negative △G are
bypassed by using different enzymes
Anabolic and catabolic pathways
are never simply the reverse of one another and do not run at the same time
Running corresponding anabolic and catabolic pathways at the same time results in waste of ATP and is named
futile cycle
