sequence of enzyme-catalyzed reactions that brings about the transformation of substrate to product
major purposes of metabolism?
1) obtain & trap chemical energy from substrates
2) build precursors to macromolecules from substrates
3) assemble precursors into macromolecules like DNA, glycogen, fat
4) degrade macromolecules into simpler molecules (like glycogen to glucose)
catabolism vs. anabolism?
catabolism: oxidative breakdown of large macromolecules into smaller, simpler compounds. accompanied by release of free energy, trapping it as ATP - e.g. glucose -> pyruvate
anabolism: enzymatic synthesis of large macromolecules from smaller, simpler precursors. requires energy input - e.g. pyruvate -> glucose
what are amphibolic pathways?
pathways w/ both cataboilc and anabolic components - so can both breakdown and synthesize
e.g. TCA cycle
what are the major differences in catabolism and anabolism? why?
2) ENERGETICS: ATP made in catabolism, used in anabolism
3) COFACTORS: NAD+->NADH in catabolism and NADPH -> NADP+ in anabolism
4) CELLULAR LOCALIZATION: fatty acid oxidation in th emito, fatty acid synthesis in the cyto
identical pathways would prevent regulation, lead to futile cycling and energy waste
what regulates metabolism?
1) availability and concetration of substrates & cofactors
2) availability and need for energy/ATP
3) regulatory enzymes
4) enzyme characteristics
5) genetic control of amt of enzyme in cell
6) hormonal regulation
what is end product feedback inhibition?
principle that anabolic reations are often inhibited by products of that very anabolic reaction
constituitive vs. adaptive enzymes?
constituitive: enzymes that're always present in constant or near-constant amount; are the more important enzymes
adaptive: enzymes that can increase or diecrease under certain metabolic conditions, in reaction to a substrate, toxin, or drug which changes their amount in response to a signal
chemical messenger produced in a tissue which will modify a specific metabolic reaction in aonther tissue
often acts on regulatory enzymes or activates or represses gene expression
what methods can determine the rate limiting step in a biochemical pathway?
1) assays on relative activites
2) comparisons of the equilibrium constant to the mass action ratio
which enzyme in a pathway is the rate limiting enzyme?
enzyme with the lowest relative activity and enzymes with big discrepancy between their Keq and mass action ratio
what are the rate limiting enzymes of glycolysis?
hexokinase, phosphofructokinase, and pyruvate kinase
what is the effect of an inhibitor on a rate-limiting vs. non-rate-limiting enzyme?
an inhibitor of a rate-limiting enzyme inhibits the overall pathway
an inhibitor of a non-rate-limiting enzyme inhibits the enzyme but likely not the overall pathway
what enzymes are most likely to be regulated?
relatively low active enzymes and enzymes that fail to maintain equilibrium are likely to be regulated
what is the RBC's only form of energy?
glucose. they do not have mitochondria!
what organi is the major controller of our metabolism?
what processes during glycolysis cause the release of ATP?
susbtrate level phosphorylation or oxidative phosphorylation
what kind of energy does ATP hydrolysis yield?
ATP -> ADP + Pi has a deltaG of 7-8 Kcal/mol
ATP is a high energy compound, and yields a middle-amount of energy compared to other compounds
what happens when ATP is hydrolyzed to ADP?
what happens when ATP is hydrolyzed to AMP?
ATP -> ADP + Pi dissipates 1 high energy bond
ATP -> AMP + PiPi dissipates 2 high energy bonds
PiPi, pyrophosphate, is rapidly hydrolyzed to 2 molecules of Pi by pyrophosphatase
what is the structure of NAD+ vs NADH
NAD+ is oxidized, NADH is reduced
what is the difference between FAD and FADH2?
FAD is oxidized, FADH2 is reduced
what hormones regulate glucose/fatty acid metabolism?
insuiln, glucagon, epinephrine (epi)
insulin + epi regulate glucose & fatty acid metabolism in mayn tissues
glucagon acts primarily on the liver & adipose tissue
where is epi produced? when?
in adrenal glands
in response to stress
produced from phenylalanine + tysoine by catacholamine synthesis pathway
where are insulin and glucagon produced? when?
beta (insulin) and alpha (glucagon) cells of the pancrease
in response to glucose levels:
INSULIN in response to HIGH glucose (high carb diet)
GLUCAGON in response to LOW glucose (starvation)
primary function of insulin?
promote use of glucose
primary function of glucagon?
promote production of glucose by the liver
what causes type 1 diabetes?
destruction of the B cells of teh pacnreas largely via autoimmune attack on these cells leads to lack of insulin production
what causes type 2 diabetes?
insulin is produced but its effectiveness in enhancing utilization of glucose is decreased, which means increased resistance to actions of insulin
what do obesity + lack of exercise lead to
type 2 diabetes
what metabolic problems does diabetes cause
build up of high levels of glucose, esp. in the blood, lead to:
1) impaired energy production from glucose
2) fat metabolism's elevated to provide energy, but much fat is oxidized to acidic ketone bodies -> ketosis
3) high circulating glucose levesl react non-enzymatically w/ prteins/enzymes, glycosylate them, form modified proteins w/ altered funtions
4) glucose can be reduced by aldose reducatse to sorbitol which increaes osmotic pressure
what is assay for measuring long-term blood glucose levels?
hemoglobin A1c level - measures that hemoglobin reacts w/ high glucose to form hemoglobin A1c, a glycosylated hemoglobin
high levels of A1c (> 7 mg%) indicate poor glucose control
what are glucagons functions
1) promotes glucose production in the liver by gluconeogenesis and stimulation of glycogen breakdown
2) increases fatty acid release from triglycerides stored in adipose tissue
polymer made of many glucose residues
functions as storage form of glucose
how does glucagon exert its effects?
1) by stimulating the activites of critical enzymes involved in synthesis of glucose & breakdown of glycogen and fat
2) by transcriptionally activating the genes for these critical enzymes
what are insulin's main actions?
promotes utilization of glucose by
1) stimulating glycolysis
2) stimulating glucose uptake in some tissues like muscle & adipose tissue
3) stimulating glycogen formation
4) stimulating fatty acids synthesis from glucose
5) stimulating protein synthesis
how does insulin exert its effects?
1) by increasing critical enzyme activities
2) by increasing synthesis of these enzymes
how do insulin/glucagon work in relation to each other? what pathways does each stimulate/inhibit?
they work in opposite actions - so glucagon does the opposite of everything here
insulin stimulates: glucose-utilizing pathways: glycolysis, glycogen synthesis, fatty acid synthesis
insulin inhibits: gluconeogenesis, glycogen breakdown, fat breakdown
how does insulin exert its effects?
via the insulin receptor on the plasma membrane of all tissues
insulin receptor has 2 alpha + 2 beta subunits. insulin binds alpha subunits, which span membrane, causing tyrosine kinase activity/dimerization of beta subunits, yielding phoshphotyrosine residues
the phosphotyrosine residues of beta subunit phosphorylate proteins IRS-1 and IRS-2
phosphorylated IRS-1 and IRS-2 phosphoryate & activate PI# kinase, which activates AKT
pAKT activates phosphatases, PKC, mTOR, which carry out insulin's actions
take away: insulin binding stimulates activity of protein phosphatases which carry out downstream actions of insulin
what is the structure of glucagon and epi receptors?
glucagon's are in liver, fat tissues; epi's are widely present
both are GPCRs with 7 TM spanning loops
alpha subunit binds GDP in inactive state
activated lgucagon or epi receptor catalyzes exchange of GDP with GTP; follwed by dissociation of beta-gamma subunits to form activate a-GTP G protein
this activates adenylate cyclase to produce cyclic AMP
cAMP activates PKA by binding to and dissociating regulatory subunits of PKA
this frees activte catalytic subunits of PKA
PKA promotes phoshporylation of many enzymes important in metabolism of glucose and fat - these phoshporylations may activate or inhbit the enzyme or txn factor
what is the difference in phosphorylation btwn glucagon/epi and insulin?
glucagon and epi: promote phosphrylation of enzymes by activating cAMP-dependent PKA
insulin: promotes dephosphorylation of enzymes by activating phosphatases eg protein phosphatase 2A
how is the glucagon/epi signal turned off?
alpha-GTP subunit has a GTPase activity; with time, GTP is hydrolyzed to form alpha-GDP subunit
this reassociates w/ the Beta-gamma subunits, reestablishes the inactive GDP-alpha-beta-gamma G protein
eventually, glucagon and epi dissociate from the receptor
also, cAMP is hydrolyzed by phosphodiesterase to AMP; so cAMP-PKA signal is turned off
what does insulin do to phoshpodiesterase?
increases phosphodiesterase activity
phosphodiesterase hydrolyzes cAMP to AMP, turning off the cAMP-PKA signal
this is a way then that insulin counters the actions of glucagon and epi
what is difference in glucagon/insulin re:
-where each is made
-what it activates
-when it is released
why do glucose carriers exist?
glucose is highly polar structure - does not get into cells well, considering all of its OH groups
thus need glucose transporters/carriers to carry glucose from our diet into our cells
how would you prove glucose uptake occurs by a carrier?
1) kinetics: plot energy vs. velocity curve, see that will eventually saturate the carrier
2) specificity: apply inhibitors and show that carriers are specific re: what they uptake
what are the functions of GLUT1 and GLUT3 carriers?
where do they work?
when are they saturated?
work in most all tissue - liver, RBC, brain, pancreas, most cells
do passive carrier-mediate glucose transport
have a low Km/high affinity for glucose (1mM) so catalyze basal glucose uptake
they thus are almost always saturated at normal glucose levels since normal glucose is 4-8 mM
what is GLUT2 carrier function?
where is it present?
what is its function?
high kM, low affinity for glucose (15-20 mM kM)
present in liver and pancreas
senses high glucose levels - for pancreas to produce insulin, and liver to utilize high glucose
does insulin effect rate of glucose uptake by GLUT 1, 2, 3?
where is GLUT4?
muscle, fat cells
is the insulin responsive glucose transporter
insulin elevates number of GLUT4 carriers on plasma membrane of muscle and fat cells so glucose uptake is elevated
does this by translocating GLUT4 from Golgi to PM
this is a way to increase glucose uptake in muscle and fat cells
fat converts glucose -> fat, triglycerides
muscle converts glucose -> glucose, stored as glycogen
GLUT5 function, location?
GI tract and kidney
catalyzes active transport of glucoses
moves molecules against concentration gradient; linked w/ Na+ transport