Unit 6 - Cellular energetics Flashcards
how do living organisms comply with the 2nd law of thermodynamics?
law states that in every spontaneous RXN, will increase entropy
- life must disorder surroundings more than it disorders self
- 1 visible E –> ~80 IR
what makes ATP’s phosphoric acid anhydride bonds “energy rich”?
the 2 phosphoanhydride bonds are so E-rich b/c:
- charge repulses are relieved upon breaking alpha-beta or beta-gamma bonds
- greater resonance stabilization of products (ADP + Pi or AMP + PPi)
- more favorable interactions with products of water
the phosphoester bond from alpha PO3 to adenosine is not as high E
how are fuels “burned” in controlled steps to extract E in usable form and amount? (energy flow)
electrons on photosynthetic pigments are raiesd to an E level where they can reduce CO2
- E required is provided by absorption of visible photons
- E stored in reduced fuels is converted to ATP by multiple enzyme-controlled steps
- ATP drives work function, returning E to environment as heat (IR photons)
- life disorders its surroundings more than it orders itself by disordering light energy (2nd law thermodynamics)
what 3 work functions do our cells need to perform to stay alive?
mechanical work, transport work, and biosynthetic work
-ATP directly drives all mechanical, and directly/indirectly drives transport and biosynthetic
how is energy storage a 3 tier system?
immediate E needs = ATP
intermediate term = glycogen
long term = fats, PRO
what is the usual flux of ATP in mammals?
turnover is 1 minute
-humans have 2 oz of ATP at any given time, thus go throguh 100 lbs/day
why is ATP well suited for its role as E carrier?
- number of phosphates (b/c sometimes ADP isn’t enough; also ensures RXN can go to completion)
- soluble and mobile (go from exogonic RXN to endergonic RXN)
- high affinity binding to enzymes
- recognition handle
why are ATP’s phosphoric acid anhydride bonds well suited for a role in E transfer?
kinetic stability VS thermodynamic instability
- without an enzyme, requires a lot of activation energy (very few molecules can supply this)
- whether there is an enzyme or not, will give off -7.3 kcal/mol of energy (delta G’)
- an intermediate thermodynamic value is consistent w/ ATPs role as an acceptor and donor of E
how is ATP an acceptor and donor of energy?
ATP accepts P from high energy phosphate compounds
-phosphoenolpyruvate
-1,3-bisphosphoglycerate
-phosphocreatine
ATP donates P to low E phosphate compounds
-glucose-6-phosphate
-glycerol-3-phosphate
how do enzymes employ the common intermediate principle to couple E-releasing RXNs to E-requiring RXNs?
if X –> Y needs -10.3 kcal/mol, and ADP + Pi –> ATP + H20 gives off + 7.3 kcal/mol…
X + E –> EX + Pi –> EP + Y needs -1 kcal/mol
-the “missing” 9.3 kcal/mol is in the EP
ADP + EP –> E + ATP needs -2 kcal/mol
total delta G’ is not altered (always equals 3)
in this case, EP is the common intermediate
how can there be channeling of ~P via NTPs?
exergonic reactions create ATP, which have interconversions via NDK to make…
- UTP –> polysaccharides
- CTP –> lipids
- GTP –> proteins
- all NTPs –> RNAs
- dNTPs –> DNA
what are the advantages of having a central pool of E in the body?
due to nucleoside diphosphatase kinase (NDK), NTP pools can share available energy and avoid rate-limiting steps (like if you flee a predator)
-GTP + ADP GDP + ATP has a free energy change of zero b/c breaking 1 bond and making another
how can levels of ATP, ADP, AMP, and Pi reflect the energy state?
regulatory enzymes have evolved regulatory binding sites that can sense the energy state of the cell by binding adenine nucleotides
- ATP generating pathways are inhibited by high levels of ATP, and stimulated by ADP/AMP
- regulatory enzyme that turns a pathway on/off in response to the E state of the cell usually catalyze an early step of the pathway (feedback inhibition)
how are ATP levels maintained short-term under stressful conditions?
- phosphagens
- in vertebrate muscle and nerves (creatine kinase)
- -phosphocreatine + ADP creatine + ATP - adenylate kinase (ubiquitous)
- 2 ADP ATP + AMP - adenylate deaminase (liver and skeletal muscle)
- AMP + H2O – AD –> IMP + NH3
- -by removing AMP, the AK RXN is pulled forward
what molecule is at a central branch linking numerous pathways?
glucose 6 phosphate (first step is converting glucose to G6P with hexokinase + ATP)
why is glucose-6-phosphate trapped in cells?
there is no transporter for G6P as opposed to glucose
why does liver use glucokinase instead of hexokinase?
liver exports glucose when blood glucose is low, and hexokinase is very aggressive (binds glucose tightly)
-glucokinase is less aggressive (affinity for glucose is 500 fold weaker) so can release it when needed
what does phopshoglucose isomerase do? why?
glucose 6 phosphate to fructose 6 phosphate
-sets the stage for an aldol cleavage between C3/4 (needs carbonyl at C2) to give two equal 3-C fragments after phosphorylation of C1 hydroxyl
