Flashcards in Maimone and Cross Important Stuff Deck (77):
starch--linear polysaccharide with 100s-1000000s of glucoses in alpha 1,4 linkages
1) starch--branched polysaccharide with 100s-1000000s of glucose residues in alpha 1,4 linkage with alpha 1,6 branches
2) glycogen is basically amylopectin in structure
disaccharide with galactose and glucose in beta 1,4 linkage
1) disaccharide with glucose and fructose in alpha 1,2 linkage
2) non-reducing sugar because the OHs of the 2 anomeric carbons aren't free
1) major component of dietary fiber
2) linear polysaccharide with 100s-1000000s of glucoses in beta 1,4 linkage
3) can't be digested by us since we don't have the right enzyme to cleave linkage
What are the 3 types of enzymes that digest carbs?
1) endoglycosidases (cleave internal bonds)
2) exoglycosidases (cleave external bonds)
3) disaccharides (cleave glycosidic bonds in dimers)
What is alpha amylase and what are the varieties?
2) hydrolyzes interal alpha 1,4 bonds in amylose and amylopectin
3) salivary and pancreatic amylases
What does glucoamylase do?
2) cleaves terminal alpha 1,4 bonds between glucoses
What does maltase do?
cleaves alpha 1,4 bond in maltose and maltotriose to yield glucose and maltose
What does isomaltase do?
cleaves the alpha 1,6 bond in isomaltose and alpha-dextrins to yield glucose and glucose polymers
What does sucrase do?
cleaves alpha 1,2 bond in sucrose to yield glucose and fructose
What does lactase do? (beta-galactosidase)
cleaves beta 1,4 bond in lactose to yield galactose and glucose
Why is ATP energy rich/a good energy carrier?
1) adenosine as a nitrogenous base easy to synthesize
2) charge repulsion stabilized once a/b and b/y bonds broken (resonance!)
3) products interact favorably with H2O
4) soluble, mobile
5) binds with high affinity to enzymes
What are the 3 stores of energy our body uses?
1) ATP--immediate need
2) glycogen--intermediate need
3) fats/proteins--long term need
Describe the common intermediate principle
1) the total deltaG of both rxns not altered by enzyme
2) exergonic rxn coupled to endergonic rxn by the common intermediate of both rxns
What are the rules of ATP generating or utilizing pathways? (think regulation and feedback inhibition)
1) ATP-generating paths limited by high ATP, stimulated by high ADP and/or AMP
2) ATP-using paths limited by high levels of ADP and/or AMP, stimulated by low ATP
Which enzymes help maintain ATP levels under system stress?
1) creatine kinase
2) adenylate kinase, adenylate deaminase
3) they further rxns that create ATP
Which enzymes in glycolysis require ATP?
1) glucose-->glucose-6-P (1st rxn, via hexokinase)
2) F6P-->FBP (via phosphofructokinase, PFK)
3) phosphorylation rxns require energy!
How does the liver's glucokinase compare to hexokinase?
1) it's a less aggressive form of the hexokinase in the liver (much lower affinity)
2) allows the liver to keep a high level of glucose in storage
Which rxn in glycolysis creates 2 NADH (per glucose molecule)?
1) GAP-->1,3 BPG (via GADPH)
2) GADPH uses a cysteine residue for catalysis
Which rxns in glycolysis create ATP (each rxn generates 2 ATP per molecule glucose)?
1) 1,3-BPG-->3PG (via phosphoglycerate kinase, PGK)
2) phosphoenolpyruvate (PEP)-->pyruvate (via pyruvate kinase)
3) both are substrate-level phosphorylation rxns
Which rxn creates lactate (lactic acid)?
1) under anaerobic conditions (but reversible)Ho
2) pyruvate+NADH-->lactate+ NAD+ (via lactate dehydrogenase, LDH)
3) rxn tends to happen when boozing, since NADH/NAD+ ratio is so high
How is fructose metabolized?
1) fructose-->F6P (via separate hexokinase), rxn in liver
2) deficiencies in F1P aldolase (enzyme that helps rxn) cause liver damage and hypoglycemia
How is mannose metabolized?
How is galactose metabolized?
2) deficiency in galactokinase causes galactitol to form, causes cataracts
3) deficiency in UMP transferase causes liver failure/mental retardation (screen babies, remove galactose from diet)
How is glycogen made?
1) G1P condenses with UTP-->UDP-glucose+phosphate (needs pyrophosphatate to make it exergonic rxn)
2) C4 hydroxyl of glucose at end of glycogen joins C1 of UDP-glucose
3) alpha 1,4 glycosidic bond+UDP formed
4) branching enzyme removes 7 fragment from chains of at least 11 residues, forms new alpha 1,6 glycosidic bond with chains from at least 4 residues (other branches)
How is glycogen broken down? (phosphoglycerate mutase is bicurious, rxns go both ways!!)
1) phosphorylase breaks glycosidic bond at end of glycogen chain; adds phosphate to give G1P
2) continues until steric hinderance stops phosphorylase
3) phoshoglucomutase converts G1P-->G1,6P-->G6P-->enters glycolysis (phosphoglucomutase uses Ser-P intermediate, similar to phosphoglycerate mutase but phosphoglycerate mutase uses His-P intermediate)
What are the costs of storing glucose as glycogen?
1) in muscle/liver, 1.1 ATP/G6P (UTP to prime G1P for glycogen synthase, ATP to convert glucose to 1,6 linkages)
2) in liver only, 2 ATP/Glucose (1 ATP to convert glucose to G6P, 1 UTP to prime G1P for glycogen storage)
Where do mitochondria tend to hang out?
in cells with high energy needs--heart (contraction), kidney (transport), liver (biosynthesis)
Where does the TCA cycle occur?
in the mitochondrial matrix; oxidative phosphorylation enzymes are embedded in inner membrane facing the matrix
Describe the traffic in and out of the matrix
1) NO MECHANISM for NADH!!
2) oxygen/CO2 just diffuse through
3) ATP out/ADP in via antiporter system
What's the general redox rxn for NAD+?
1) substrate (SH2, for example) + NAD+--> S (dehydrogenated substrate) and NADH + H+ (substrate hydride attacks sp2 carbon on NAD+)
2) nitrogen on NAD+ has 4 bonds, nitrogen on NADH has 3 bonds
3) other hydrogen leaves product as lone proton
How is acetyl CoA formed?
1) pyruvate + TPP (thiamine, vitamin B)--> hydroxyethyl-TPP (via pyruvate dehydrogenase)
2) rxn is condensation and decarboxylation
3) pyrvuate/TPP complex attack lipoamide-->acetyllipoamide
4) acetyllipoamide + SH-CoA-->acetyl CoA + dihydrolipoamide (both rxns catalyzed by dihydrolipoyl transacetylase, oxidative transfer and transacetylation)
What happens to dihydrolipoamide?
1) dihydrolipoamide + NAD+ + FAD-->lipoamide + NADH + H+ via dihydrolipoyl dehydrogenase
What is the 1st step in the TCA cycle?
1) OAA + acetyl CoA-->citrate + CoA
2) via citrate synthetase
3) condensation and hydrolysis of thioester (acetyl CoA)
What is the 2nd step in the TCA cycle?
1) citrate-->cis aconitate-->isocitrate
2) via aconitase
3) dehydration, then hydration
What is the 3rd step in the TCA cycle?
2) via isocitrate dehydrogenase
3) oxidative decarboxylation (6 carbons-->5 carbons)
4) NADH created
What's the 4th step in the TCA cycle?
1) alpha-ketoglutaric acid+HS-CoA+NAD+-->succinyl CoA+NADH
2) via alpha-ketoglutarate dehydrogenase complex
3) oxidative decarboxylation (5 carbons-->4 carbons) and thioester formation
3) NADH created; same cofactors (NAD+/CoA) and cofactors (TPP/lipoamide/FAD) and products as pyruvate dehydrogenase rxn
What's the 5th step in the TCA cycle?
1) succinyl and GTP formed (GTP will become ATP via NDK enzyme)
2) succinyl CoA synthase catalyzes rxn, substrate-level phosphorylation
3) rxn uses common intermediate principle!!**(exergonic/endergonic rxns coupled by phosphohistidyl)
What's the 6th step in the TCA cycle?
1) succinate-->fumarate + FADH2
2) via succinate dehydrogenase, located in inner mitochondrial membrane
3) oxidation rxn
What's the 7th step in the TCA cycle?
2) via malate dehydrogenase
3) hydration rxn
What's the 8th and final step in the TCA cycle?
1) malate-->oxaloacetate (OAA)
2) via malate dehydrogenase, oxidation rxn
3) oxidation of malate is hard (endergonic), so only a little OAA is in equilibrium with a lot of malate
4) this equil is good, since malate can exit to cytoplasm and do gluconeogenesis in resting state
Where are all the glycolysis and shunt enzymes located?
in da cytosol
What are the steps in the oxidative (non-reversible) phase?
(2 dehydrogenases and a lactonase)
1) G6P + NADP+-->phosphogluconolactone + NADPH (via G6PDH)
2) lactone-->6-phosphogluconate (ring broken by 6-phosphogluconolactonase)
3) 6PG+ NADP+-->ribulose-5-phosphate (Ru5P) + NADPH + CO2 (via 6-phosphogluconoate dehydrogenase)
What happens to Ru5P next? (non-oxidative)
1) Ru5P-->R5P (via ribulose-5-phosphate isomerase)
2) Ru5P-->xyulose-5-phosphate (Xu5P) via ribulose-5-phosphate epimerase
What happens next in the non-oxidative steps?
1) transketolase, epimerase, isomerase, and transaldolase help form F6P, GAP, and E4P
2) 3 Ru5P-->2 F6P + 1 GAP
3) transketolase has TPP as a prosthetic group**
What is produced in the oxidative and non-oxidative steps?
1) oxidative create NADPH
2) non-oxidative create NADH
What are the typical NAD+ and NADP+ ratios?
1) NAD+/NADH about 700, NAD+ (oxidant) kept highly oxidized
2) NADP+/NADPH about 0.01, NADPH (reductant) kept highly reduced
What are the main roles of NADPH?
1) used in detox and biosynthesis
2) used by cytochrome P450 for detox
What's up with NADPH in the RBCs?
1) GSH (glutathione) + peroxide-->GSSG+ ROH (via glutathione peroxidase)
2) GSSG+NADPH-->2 GSH + NADP+ (via glutathione reductase)
3) when NADPH deficient, GSH can't be regenerated to fight ROS
4) G6PDH (1st step of shunt, creates NADPH from G6P) deficiency causes hemolytic anemia (most common human enzyme deficiency)
How are some ways that the body manipulates the shunt according to need?
1) if ribose needed, run non-oxidative portion to end at R5P
2) if NADPH and ribose needed, run the oxidative portion and then convert all the Ru5P to R5P
What are the 3 bypass paths in gluconeogenesis?
1) pyruvate carboxylase/PEPCK (oppose pyrvuate kinase)
2) FBPase (opposes PFK)
3) glucose-6-phosphatase (opposes hexokinase)
4) these bypasses provide thermodynamically favored alternatives!
What's the beginning of the 1st bypass?
1) pyruvate-->oxaloacetate (via pyruvate carboxylase)
2) pyruvate carboxylase only present in mitochondria**, carboxylation rxn (3 C-->4 C)
3) enzyme uses biotin as prosthetic group, needs ATP for activation
4) OAA + GTP-->phosphoenolpyruvate, or PEP (via PEPCK, PEP carboxykinase)
5) PEPCK in mitochondria, PEP transporter exists; no transporter for OAA**
Describe the Cori cycle
1) when ATP demand is greater than ox phos in muscle, lactate produced (also in RBC since they don't have mitochondria)
2) lactate goes to liver, liver converts it back to glucose
3) glucose goes back to muscle via blood
4) process continues as muscle glycogen stores replenished (huffing/puffing after exercise)
What are the flavins and what are they a part of?
1) 2 e- donors/acceptors
2) FMN oxidized form (riboflavin, vitamin B2, needed in diet) in NADH dehydrogenase
3) FAD oxidized form in succinate dehydrogenase
What are the iron-sulfur centers and what do they do?
1) accept e- from flavins and Q; have 2-4 Fe per center, but only one e- donors/acceptors
2) Fe2S2 in complex III (cytochrome bc complex)
3) Fe4S4 in succinate dehydrogenase
4) H2S formed from acidification causes bad egg smell!
What's up with ubiquinone (Q)?
1) 2 e- donor/acceptor and 2H+
2) very hydrophobic and a cofactor, called an "e- buffer", has 10 isoprenoid chains
What and where are the hemes?
1) one e- donor/acceptors (Fe+3-->Fe+2)
2) heme covalently bound to 2 cysteine side chains in cytochromes c and c1
What and where are the copper centers?
1) one e- donor/acceptors in complex IV (cytochrome oxidase)
Describe cytochrome oxidase
1) has 4 redox centers: 2 copper centers, 2 heme irons
2) needed to rapidly give 4e- to oxygen, prevents generation of ROS
3) cytochrome oxidase (complex IV) inhibited by CN-
How is the e- transport chain arranged?
in order of lowest affinity for e- -->greatest affinity for e-, oxygen at end with highest affinity
What controls the rate of respiration?
1) controlled by the availability of ADP
2) when ADP re-enters, H+ comes in too to regenerate ATP
3) however, electrochemical gradient stops e- flow unless H+ are carried back into matrix via ATP-synthase
What do uncouplers do?
1) they 'uncouple' oxidation from phosphorylation
2) they dissipate the H+ gradient by allowing protons to enter the matrix in another way (NOT via ATP-synthase)
3) oxygen consumed during this process, but ATP isn't generated, heat is (when OH- and H+ meet it creates heat)
4) natural uncouplers in brown adipose tissue's mitochondira, allow non-shivering thermogenesis
What do phosphorylation inhibitors do? (oligomycin is a classic example)
1) they block ADP-stimulated respiration but not uncoupler-stimulated respiration (e- transport continues)
2) they don't allow protons to enter ATP synthase
What's the natural phosphorylation inhibitor in heart tissue?
1) during ischemia (no O2), inhibitor protein binds to ATP synthase--prevents ATP hydrolysis
2) once O2 returns, protons leave matrix, inhibitor leaves, and ATP synthesis continues
What does CN- do to ox phos?
1) binds to complex IV instead if O2
2) doesn't accept electrons, so ox phos stops totally
How do Mitchell's loops work?
1) "delocalized electrochemical gradient is required intermediate in coupling exergonic/endergonic rxns in synthesizing ATP"--common intermediate principle
2) Q has to pick up 2 H+ to maintain electroneutrality once it becomes an e- acceptor (from complexes I/II)
3) once Q delivers e-, it dumps 2H+ in inner space to become fully oxidized again
How are ATP/ADP and H+/Pi transported into and out of the matrix?
1) ADP in, ATP out via net exit of one negative charge (electrogenic)
2) One Pi- and one H+ move into matrix from intermembrance space, loss of 1 positive charge from concentration gradient but no change in charge (electroneutral)
How do the bypasses of gluconeogenesis work?
1) the same rate-limiting steps of glycolysis have to be bypassed
2) hexokinase, phosphofructokinase, pyruvate kinase
3) PFK an excellent point to regulate
How does regulation of PFK work?
1) PFK allosterically inhibited by ATP as feedback inhibitor
2) AMP stimulates PFK by competing with ATP at binding site
3) also stimulated by F2, 6BP (b-d-fructose-2,6-bisphosphate)
How does low blood sugar induce gluconeogenesis?
1) glucagon induced, causes increased cAMP
2) increased enzyme phosphorylation
3) PFK inhibited (F2,6P decrease), FBPase-2 activated
4) gluconeogenesis stimulated, glycolysis inhibited
5) increased cAMP is a mechanism used by glucagon, NOT insulin*** (for these paths)
How does high blood sugar induce glycolysis?
1) insulin induced, decreases enzyme phosphorylation
2) increased F2,6P activates PFK, decreases PEPCK
3) glycolysis stimulated, gluconeogenesis inhibited
How are pyruvate kinase and pyruvate carboxylase monitored?
1) pyruvate kinase activated by FBP (earlier glycolysis substrate) and inhibited by acetyl-CoA, ATP, and glucagon-stimulated phosphorylation (feedback inhibition)
2) pyruvate carboxylase activated by acetyl-CoA
How do insulin and glucagon (or norepi) control glycogen formation/breakdown? (in liver)
1) glucagon increases cAMP, activates protein kinase A, which activates phosphorylase kinase, which activates glycogen phosphorylase
2) insulin activates phosphoprotein phosphatase-1, reverses all changes caused by activating protein kinase
3) when glucagon goes up, liver breaks down glycogen
4) when insulin goes up, glycogen synthesized in muscle
How does gluconeogenesis, et al happen in skeletal muscle and fat cells?
1) muscle cells don't have glucagon receptors, since they aren't responsible for keeping blood glucose up***
2) insulin increases glucose uptake into muscle and fat cells by increasing the number of glucose transports on cells (GLUT4 receptors)
3) in fat cells, uptake of glucose causes increased TG synthesis
How does control of phosphorylase control glycogen storage?
1) when blood glucose low, phosphorylase is phosphorylated (active)
2) when blood glucose high, ATP/G6P high, dephosphorylated phosphorylase will be inactive