Glycolysis Flashcards
(361) What is the universal fuel for cells?
Glucose (which makes ATP later)
What is the principal pathway by which cells generate ATP from glucose?
Glycolysis (literall: sugar breakdown)
What does oxidation of glucose yield via glycolysis (net?)
2 ATP, 2 NADH
Does glycolysis occur in both aerobic and anaerobic conditions?
Yes
(365) Where does glycolysis take place?
Cytosol, located in all tissues
(367) Describe the preparatory phase
Glucose broken down into Glyceraldehyde 3 phosphate and DHAP, uses 2 ATP (net negative 2 ATP in this phase)
Describe ATP-generative phase
G3P converted to pyruvate, 4 ATP made, 2 NADH made
What enzyme phosphorylates glucose in the first rxn of glycolysis?
Hexokinase (remember from earlier we have 4 different isozymes depending on tissue)
Which step produces NADH?
The reaction of G3P to 1,3 BPG via G3P dehydrogenase
What steps generate ATP ?
Pyruvate kinase step, and phosphoglycerate kinase step
How many molecules of pyruvate are formed?
Two (remember we had two 3 carbon products of prepatory phase which each go into a phase of payoff to generate ATP,NADH)
(373) What is the commited step of glycolysis?
PFK-1
(375) During strenuous exercise in anaerobic glycolysis what is produced?
Lactic acid via lactate dehydrogenase (reduces pyruvate to lactate and replenishes depleted stores of NAD+ in tissues rapidly performing glycolysis)
(376) Under aerobic conditions what happens to pyruvate?
Completely oxideized via TCA and ETC to carbon dioxide and water
What is the cori cycle?
Lactate secreted into blood is taken up by liver and oxidized back to pyruvate, pyruvate goes back to liver for gluconeogenesis
What is the glycerol 3 phosphate shuttle?
(378) Cytosolic G3P DH takes electrons from NADH and makes G3P from DHAP, G3P enters mitochondria and transfers electrons to FADH2 for transport to ETC via CoQ
What is the malate shuttle?
NADH gives electrons to oxaloacetate to produce malate which can be transferred to mitochondria, in mitochondria malate is transferred back to oxaloacetate regenerating mitochondrial NADH, in the mitochondria oxaloacetate is converted to aspartate and alphaketoglutarate by a transaminase that takes amino groups off glutamate and forms alpha ketoglutarate and aspartate Aspartate freely moves into cytosol via glutamate/aspartate transporter Aspartate is then deaminated again in the cytosol to convert back to oxaloacetate
Does glucagon activate glycolysis?
Yes (means we need glucose)
What are 5 sites of regulation in glycolysis?
HK, PFK1, Pyruvate kinase, PDH complex, glucose entry
What inhibits PFK-1? Activates it?
Inhibits: ATP,citrate Activates: F-2,6-BP, AMP
What inhibits hexokinase?
G6P
Describe the mechanism of F26BP allosteric control of PFK-1.
F26bisphosphate is usually formed from F16bisphosphate (same substrate for PFK-1 rxn) by a separate enzyme, PFK-2. This lets PFK1 know that there is still plenty of F16bisphosphate around and we should continue glycolysis. When blood sugars are low glucagon causes cAMP mediated cascade that results in phosphorylation of PFK2 and inactivation of its kinase domain that produces F26bisphosphate. Therefore we have no more F26bisphosphate around and PFK1 is no longer activated. Furthermore, the glucagon mediated cascade activates a separate domain on PFK2 that acts as F16bisphosphatase in gluconeogenesis (therefore increasing glucose in response to glucagon signal).
What inhibits pyruvate kinase? Activates?
ATP and F26BP/AMP , respectively
Does muscle pyruvate kinase have these allosteric sites for regulation?
No, not involved in glycolysis regulation, only wants to break down glycogen to give glucose to skeletal tissue that needs it
(366) what are the two phases of glycolysis?
Preparatory, payoff (energy required in preparatory, energy made in payoff)
(374) What are the three regulated enzymes in glycolysis?
Hexokinase, PFK-1, pyruvate kinase
Under what type of conditions are pyruvate and NADH used to form lactate? What rxn is used? What is the significance of this rxn?
anaerobic conditions
pyruvate and NADH form lactate via LDH rxn
-significance of LDH rxn is that NAD+ is regenerated for glycolysis
Under aerobic conditions, what are used to transfer electrons from glycolytic formed NADH into mitochondria? which is used for the reverse direction of gluconeogenesis and NAD+ is reformed?
malate shuttle and glycerol phosphate shuttle
malate shuttle
In anaerobic conditions, what reversibly reduces pyruvate to lactate? what is the result of this?
lactate dehydrogenase
regeneration of NAD+
Describe the energy utilizing phase of glycolysis: characters, setting, requirements, result
phosphorylation of glucose by
characters: HK or GK and PFK-1
setting: in cytosol
requirements: 2 mol of ATP
result: formation of fructose-1,6-biphosphate
Describe the energy generating phase of glycolysis: characters, setting, requirements, result
cleavage by aldolase, oxidation by glyceraldehyde-3-phosphate dehydrogenase
setting: cytosol
result: 1. synthesis of 4 mol of ATP/ glucose from 2 substrate-level phosphorylation rxns
What are some other substrates for glycolysis other than glucose?
fructose, galactose, mannose, pentose sugars, glycerol
Which regulator of the glycolytic pathway has a low Km for glucose? Which works near Vmax even at fasting blood glucose?
HK, HK
Which regulator is inhibited by G-6-P and non specific so it can phosphorylate other sugars?
HK (hexokinase)
Which regulator is found in the liver with a high Km for glucose?
GK
Which is most active after a meal? Least active during fasting?
GK, GK
Which regulator is induced by insulin?
GK (Glucokinase)
Which has a high specificity for glucose and not inhibited by G-6-P at physiologic conditions?
GK
What are the regulators of the glycolytic pathway?
HK, GK, PFK-1, pyruvate kinase
What inhibits PFK-1? activates it?
inhibited by ATP and citrate
activated by AMP and Fru-2-6-bisphosphate
What is an important regulator of both glycolysis and gluconeogenesis? Describe its [ ] in fed and fasting state
Fructose-2,6-bisphosphate
fed state=> high
fasting=> low
Describe the relationship between glucagon, cAMP, fruc-2,6-bisphosphate and the results involving glycolysis/gluconeogenesis
Glucagon acts through cAMP to lower the concentration of fru-2,6-bispho
decreases glycolysis and increases gluconeogenesis
What inhibits pyruvate kinase? activates it?
inhibited by ATP and alanine
activated by F-1,6-P2
Describe the relationship of glucagon, PKA and pyruvate kinase => what is the result?
Glucagon via PKA phosphorylates and inactivates pyruvate kinase => promotion of gluconeogenesis
What will promote gluconeogenesis in relation to pyruvate kinase?
- inactivation of pyruvate kinase
2. alanine inhibition of hepatic PK
How many moles of ATP are formed for each mole of oxidized NADH? FADH2?
- 5 mol of ATP/ 1 mol of NADH
1. 5 mol of ATP / 1 mol of FADH2
Describe glycolysis in RBCs wrt to hemoglobin affinity. What molecule is found in high [ ] in RBC?
1, 3-BPG can be converted to 2,3-BPG which decreases affinity of hemoglobin for O2
2,3 BPG
What molecule in glycolysis of RBCs allows 2,3 BPG to renter the glycolytic pathway?
3-phosphoglycerate
Describe the relationship of ATP to 2,3-BPG and its result
1 ATP is lost when 2,3 BPG is synthesized which helps control oxygenation of the tissue
What is the creation of a high energy phosphate bond in a metabolite by a mechanism other than electron flow in the mitochondria membrane? Is O2 or the ETC necessary?
substrate level phosphorylation
-No
When collecting blood for glucose analysis, what should it be collected in? Why?
Gray top vaccum tube containing fluoride which is an inhibitor of glycolysis
What is an intracellular enzyme involved in amino acid and carbohydrate metabolism?
Aspartate aminotransferase
What is the end product of anaerobic glycolysis? What produces the molecule? Where is it metabolized?
lactate
- produced by erythrocytes and skeletal muscle after exercise
- metabolized by liver and other tissues
What is the result of lactate production through increased levels of NADH levels? What type of lactate acidosis is this?
tissue hypoxia (cardiac arrest) -Type A lactic acidosis
T/F Lactate accumulation in blood will result if lactate metabolism decreases even in absence of tissue hypoxia
True (type B lactic acidosis)
Drinking alcohol leads to formation of lactate-how?
increases NADH levesl => conversion of pyruvate to lactate
What deficiency is common in alcoholics that decreases activity of pyruvate dehdrogenase complex (pyruvate to acetylCoA
thiamine deficiency
What is the anion gap? Why is it useful?
difference between the commonly measured serum anioins and cations generally around 12-18 mEq/L
- diagnostic tool where a large anion gap indicates the presence of an anion which we have not measured usually lactate or ketones
ALL RBC glycolytic deficiencies result in what?
deficiency of ATP and reducing equivalents in the RBC resulting in insufficient ATP membrane transport resulting in shrinking thus causing anemia
What does pyruvate dehydrogenase deficiency cause?
accumulation of pyruvate and lactate resulting in lactic acidosis
A deficiency in what is classified as a glycogen storage disease?
PFK-1 deficiency
What are 5 vitamins and coenzymes in glycolysis?
thiamine, riboflavin, niacin, pantothenic acid, pyridoxine, pyridoxal phosphate
In the preparative phase what enzyme commits glucose to the glycolytic pathway? does it require energy?
PFK and it requires ATP
-Fru-6-P => PFK-1 => Fru-1,6-BiPhos
In the ATP-generating phase, what is the oxidation step? and what must be oxidized?
NADH must be oxidized at the high energy acyl phosphate which results in 1,3 BiPhosph
T/F phosphoglycerate kinase requires O2 or ETC of mitochondria
False, phosphoglycerate kinase
What is the reaction of the ATP generating step? What is yielded?
gly-3-P + Pi => 1,3-BPG + NADH
DHAP => Gly-3 => 1,3 BPG + NADH
-2 NADH, 4 ATP, 2 pyruvate generated from 1 glucose
NET YIELD => 2ATPS FROM 1 GLUCOSE
IN anaerobic glycolysis, what is re-oxidized in cytosol by LDH?
NADH re-oxidized to convert pyruvate to lactate
T/F anaerobic glycolysis is completely dependent on the mitochondria for energy production
True
How is ATP formed in aerobic glycolysis?
pyruvate is oxidied to CO2 in mitochondria which forms ATP via O2 dependent oxidative phosphorylation
What occurs if NAD+ is not present or cannot be oxidized?
additional rounds of glycolysis cannot continue
Under anaerobic conditions, where does the oxidation of NADH to NAD+ occur? How?
cytosol
LDH converts pyruvate to lactate oxidizing NADH to NAD+
In aerobic glycolysis, oxidation of NADH back to NAD+ occurs where? How?
mitochondria via ETC
Describe the Cori cycle
Lactate accumulates in tissue of anaerobic respiration => lactate released into blood and taken by blood into gluconeogenesis pathway =>released into blood by G-6-P to undergo more rounds of glycolysis
How does cytosolic NADH enter mitochondria?
Mitochondria inner membrane is impermeable to NADH so shuttles must be used (glycerol 3-phosphate shuttle and malate-aspartate shuttle)
Describe the glycerol-3-phosphate shuttle
a. cytosolic DHAP reduced to G-3-P by NADH
b. G-3-P reacts with FAD linked dehydrogenase in inner mitochondrial membrane where DHAP regenerates and re-enters cytosol
c. 2 ATP produced via oxidative phosphorylation
d. 4 mol ATP PRODUCED VIA THIS SHUTTLE
Describe the malate asparate shuttle
a. cytosolic oxaloacetate reduced to malate by NADH which is catalyzed by cytosolic malate dehydrogenase
b. malate enters mitochondria and re-oxidized to oxaloacetate by Mt malate dehydrogenase (NADH generated in matrix)
c. oxaloacetate transaminated to aspartate to be transported out
d. 6 ATP PRODUCED
What is the rate limiting enzyme of glycolysis which controls the rate of glucose entry to glycolsis?
PFK-1
What are the 2 sites for substrates for PFK-1 regulation?
F-6-P and Mg-ATP
Describe the response of pyruvate kinase in the liver and muscle
Liver: responds to changes in ATP and F-1,6-Bisphos
Muscle: no allosteric sites (no regulation of glycolysis)
What molecule is is regulated by the rate of ATP utilization?
pyruvate dehydrogenase
