homeostasis
-a stable biochemical environment
-is maintained by careful regulation of biochemical processes
-three regulatory control are especially prominent:
1. the amount of enzyme present- depends on both its rate of synthesis and its rate of degradation. the lev
quantity of enzyme
-regulated by gene transcription
catalytic activity
-regulated allosterically or by covalent modification
-hormones coordinate metabolic activity, often by instigating the covalent modification of allosteric enzymes
-kinases phosphorylate other molecules to turn them on of off
energy status
-an important regulator of enzyme activity
-tow common means are used to assess this: energy charge and phosphorylation potential
compartmentalization
-opposing reactions, such as fatty acid synthesis and degradation, may occur in different cellular compartments
-regulating the flux of substrates between compartments is used to regulate metabolism
generation of energy
-from the oxidation of food takes place in three stages
1. large molecules in food are broken down into smaller units- digestion- protein are hydrolyzed to the 20 amino acids, ppolusaccharides are hydrolyzed to simple sugars and fats are hydrolyzed to fat
Track in metabolism
1. energy- give or require energy (delta G)
2. metabolites (basic building blocks)- what goes in and what comes out
3. electrons- how do you know you're getting electrons? electrons carriers are required to reduce or oxidize the molecules
energy sources
fats, polysaccharides and protiens
fats are more efficient
-they are more reduced so you get more electrons pre cleavage
continual input of free energy
-need this for 3 major purposes:
1. the performance of mechanical work in muscle contraction and cellular movement
2. the active transport of molecules and ions
3. the synthesis of macromolecules and other biomolecules from simple precursors
phototrophs
-obtain free energy by trapping sunlight in a chemical form
chemotrophs
-humans
-obtain energy through the oxidation of carbon fuels
Principles that govern energy manipulation
1. fuels are degraded and large molecules are constructed step by step in a series of linked reactions called metabolic pathways
2. an energy currency common to all life forms, ATP, links energy releasing pathways with energy requiring pathways
3. the oxi
Metabolism
-a linked series of chemical reaction that begins with a particular biomolecule and converts it into some other required biomolecules in a carefully defined fashion
-process a biomolecule from a starting point to an end point without the generation of was
intermediary metabolism
-entire set of cellular metabolic reactions
-consists of a collection of defined pathways that process a biochemical from starting point to an end point without the generation of wasteful or harmful side products.
-the pathways are interdependent- a bioch
pyruvate
-has a lower energy than glucose so the 10 steps harness the energy difference
2 classes of metabolic pathways
1. those that convert energy from fuels into biologically useful forms such as ATP or ion gradients- catabolic
2. those that required input of energy to proceed - anabolic
catabolic
-transform fuels into cellular energy
Fuel (carbohydrates, fats) -> CO2 + H2O + useful energy
anabolic
-reactions that require energy
-the useful forms of energy that are produced are employed to generate complex structure from simple ones, or energy rich states from energy poor ones
useful energy + simple precursors -> complex molecules
amphibolic pathways
-pathways that can be either anabolic or catabolic, depending on the energy conditions in the cell
two criteria for a metabolic pathway
1. the individual reaction must be specific- will yield only one particular product or set of products from its reactants- it is facilitated by enzymes which are highly specific catalysts
2. the entire set of reactions that constitute the pathway myst be
thermodynamically unfavorable reaction
-can be driven by a thermodynamically favorable reaction to which it is coupled
-metabolic pathways are formed by coupling of enzyme catalyzed reactions such that the overall free energy of the pathways is negative
ATP
-free energy donor in most energy requiring processes such as motion, active transport or biosynthesis
-consists of adenine, a ribose and a triphosphate unit
-in considering its role as an energy carrier, we can focus on its triphosphate moiety
-it is an
ATP hydrolysis
-exergonic reaction becuase the triphosphate unit contains two phosphoanhydride bonds that are unstable - ATP is very unstable, but its products are extremely stable
-the energy release on _______ is used to power a host of cellular functions
Products:
-A
Coupling
-an otherwise unfavorable reaction can be made possible by ______ to ATP hydrolysis
-endergonic chemical reactions, which could not occur without an input of free energy and have a positive delta G , are required for biosynthetic pathways
energy coupling agent
-ATP
-because of its thermodynamic essence
-the hydrolysis of an ATP molecule in a coupled reaction changed the equilibrium ratio of products to reactants by a very large factor
-a thermodynamically unfavorable reaction sequence can be converted into a fa
standard free energy of hydrolysis
-a common means of comparing the tendency of an organic compound bearing a phosphoryl group to transfer the phosphoryl group to an acceptor molecule is determined by the amount to energy released when the phosphorylated compound transfers the phosphoryl g
what makes ATP and efficient energy currency
-the tendency of it to transfer the phosphoryl group to an acceptor molecule
phosphoryl-transfer potential
-something has a higher ______ if the delta G is more negative
-the higher _____ of ATP can be explained by the features of the ATPs structure
1. electrostatic/charge repulsion: at pH 7, the triphosphate unit of ATP carries about 4 negative charges. These
ATP's phosphoanhydride bonds
-are referred to as high energy bonds
-they are high energy bonds in the sense that much free energy is released when they are hydrolyzed
intermediate position
-ATP is not the only compound with a high phosphoryl-transfer potential.
-some compounds in biological system have a higher phosphoryl-transfer potential such as PEP and 1,3-BPG and creatine. PEP can transfer its phospohoryl group to ADP to form ATP.
-ATP
Creatine phosphate
-a high phosphoryl-tranfer protein molecule in vertebrate muscle, serves as a reservoir of high-potential-phosphoryl groups that can be readily transferred to ADP
-catalyzed by creatine kinase
-because of its abundance and high phosphoryl transfer potenti
phosphate and its esters
-have several characteristics that render it useful for biochemical systems:
1. phosphate esters have the important property of being thermodynamically unstable while being kinetically stable - Phosphate esters are molecules whose energy release can be ma
immediate donor of free energy
-ATP serves as the principal _______ in biological systems rather than as a long term storage form of free energy
-the turnover of this small quantity of ATP is very high
-Motion, active transport, signal amplification and biosynthesis can take place only
oxidation reactions
-all _____ include the loss of electrons from carbon molecules and the gain of those electrons by some other molecule
redox reactions
-the coupling of oxidation and reduction reactions
aerobic organisms
-the ultimate electron acceptor in the oxidation of carbon is O2 and the oxidation product is CO2
-the more reduced a carbon is to begin with, the more free energy is released by its oxidation - fats are more efficient food source than glucose because fat
oxidation
-when a field is oxidized, the oxidation take place on one carbon at a time
-the carbon-oxidation energy is used in some cases to create a compound with high phosphoryl-transfer potential and in other cases to create an ion gradient- it either case, the e
carbon atoms in fuels
-are oxidized to yield CO2 and the electrons are ultimately accepted by oxygen to form H20
Fats
-more efficient food source than glucose because fats are more reduced
activated carriers
2 common characteristics:
1. the carriers are kinetically stable in the absence of specific catalysts
2. the metabolism of activated groups is accomplish with a small number of carriers
-ATP is an ___________ of phosphoryl groups because phosphoryl transf
Activated carriers of electrons for fuel oxidation
-in aerobic organisms, the ultimate electron acceptor in the oxidation of fuel molecules is O2. however, electrons are not transferred directly to O2. Instead, fuel molecules reduce or transfer electrons to special carriers, which are either pyridine nucl
NAD+ (nicotinamide adenine dinucleotide)
-a pyridine nucleotide
-major electron carrier in the oxidation of fuel molecules
-the reactive part is its nicotinamide ring, a pyridine derivative
-in the oxidation of a substrate, the nicotinamide ring of ____ accepts a hydrogen ion and two electrons w
dehydrogenation
-redox reaction is often referred to as this because protons accompany the electrons
-one proton and two electrons of the substrate are directly transferred to NAD+, where as the other proton appears in the solvent as a proton
FAD (flavin adenine dinucleotide)
-electron acceptor
-the reactive part is its isoalloxazine ring
-can accept two electrons, but also takes up two protons.
activated carriers of electrons for the synthesis of biomolecules
-high potential electrons are required for anabolic reactions
-the precursors are more oxidized than the products and reducing power is needed in addition to ATP- this process is called reductive biosynthesis
reductive biosynthesis
-when the precursors are more oxidized than the products and reducing power is needed in addition to ATP
-the electron donor in most reductive biosyntheses is NADPH, the reduced form of NADP+
NADPH
-differes from NADH in that the 2'-hydroxyl group of its adenosine moiety is esterfied with phosphate
-its used almost exclusively for reductive biosynthesis, where NADH is used primarily for the generation of ATP
-the extra phosphryl group is a tag that
NADP+
-an activated carrier of electrons for reductive biosyntheses because the extra phosphoric group is a tag that enable enzymes to distinguish between high potential electrons used in anabolism and those to be used in catabolism
An activated carrier of two carbon fragments
-coenzyme A is a carrier of acyl groups
-the terminal sulfhydryl group of CoA is the reactive site. Acyl groups are linked to the sulfhydryl group of CoA by thirster bonds
0the resulting derivative called an acyl CoA. An acyl group often linked to CoA is
CoA
-an activated carrier of acyl groups such as the acetyl group
-the transfer of the acyl group is exergonic because the thioester is unstable
activated carriers
-responsible for two keep aspects of metabolism
1. NADH, NADPH, and FADH2 react slowly with O2 in the absence of a catalyst. ATP and acetyl CoA are hydrolyzed slowly in the absence of a catalyst. The kinetic stability of these molecules in the absence of
Pantothenate kinase associated degeneration
-also called Hallervorden-Spatz syndrome
-neruodegeneration and iron accumulation in the brain
-all patients with classic form of this lack the enzyme pantothenate kinase- an important regulatory enzyme in the biosynthetic pathway for CoA by activating th
Pantothenate
-component of coenzyme A and a cofactor required for fatty acid synthesis.
-it is plentiful in many foods, with egg yolk being a rich source
Carries electrons
-NADH, NADPH, FADH, FMNH2
carries phosphoryl groups
-ATP
Carries acyl groups
-Coenzyme A
B vitamins
-function as coenzyme
vitamins
-organic molecules need in small amounts in the diets of many higher animals
-almost all activated carriers that act as coenzymes are derived form these
-must be modified before it can serve its function
-it is biologically more efficient to ingest ____ t