cells can obtain and use energy - make new cells, - exchange materials - eliminate wastes in a changing environment

Pathways And Control... Flashcards by Sara xx

Homeostasis

maintenance of a constant

internal state in a changing environment.

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Homeostasis ensures

cells can obtain and use energy

make new cells,
exchange materials
eliminate wastes in a changing environment

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A series of automatic control systems ensure that the body maintains

constant temperature and steady levels of water, ions and metabolites.

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metabolic pathways

Biochemical reactions in human cells are organized into specific sequences

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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

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Pathways that regenerate a metabolite are called

Cycles

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Energy containing nutrients (carbohydrates, fats, proteins)

Ca»ta»bo»lism»

Energy depleted end products
CO2
H2O
NH3

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Precursor molecules 
Amino acid 
Sugars 
Fatty acids 
Nitrogenous bases
AN>>ABOL>>ISM

Cell macromolecules (more complex)
Proteins 
Polysaccharides 
Lipids 
Nucleic acid

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Breakdown complex molecules to give simpler components eg glycolysis

Catabolic

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Synthesis of complex molecules from simpler materials

Anabolic

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Intermediary pathway that serves both in catabolism and anabolism

Amphibolic

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regulation by cell metabolites

Intrinsic regulation

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regulation by external factors,

hormones etc.

Extrinsic regulation

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Binding of hormone(1st messenger)to its receptor activates

G protein which activates adenylate cyclase

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Activated Adenylate cyclase converts

ATP to cAMP

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cAMP ( 2nd messenger) activate

Kinases

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Activated kinases phosphorylate

Cellular proteins

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Millions of phosphorylated proteins cause reactions that

Produce physiological responses

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Molecules such as NAD+, NADH, ATP, ADP, AMP are

important allosteric effectors and intrinsic regulators of cellular metabolism

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Cellular concentrations of ATP & ADP (AMP) reflect

the energy state of the cell

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High [ATP] activates

Anabolic pathways

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High [ATP] suppresses

Catabolic pathways

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High [ADP] or [AMP] activates

Catabolic

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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