Thom2/3-Glycolysis, TCA, ETC, PPP

Question 1

What are the properties of hexokinase and glucokinase?

Answer 1

• Hexokinase: in most tissues; low Km (high affinity glucose transporter), high Vm; inhibition by glucose-6-P
• Glucokinase: in liver and beta-cells; high Km (low affinity for glucose), high Vm (can easily take up glucose from blood when needed), no inhibition by-glucose 6-P
• Both catalyze conversion of glucose into Glucose-6-P

Question 2

What is the effect of phosphorylating intermediates in a metabolic pathways?

Answer 2

1) Net negative charge traps molecule inside cell (ionized at pH7)
2) Conserves energy from breaking “high energy” phosphate bonds in fromation of phosphate esters
3) Sets up for further metabolism; committed

Question 3

How is the liver uptake of glucose different compared to other organs?

Answer 3

Liver only takes glucose when there is an excess for storage. That is because the liver first make sure that all organs have glucose and even makes some if needed.

Question 4

How is the cAMP cascade activated?

Answer 4

A) When receptor is unoccupied, it is bound to G protein, which is bound to GDP. It is inactive

B) When bound by a hormone, G protein releases GDP to bind GTP. G protein then interacts with Adenylyl cyclase, which can convert ATP to cAMP.

Question 5

What is metabolic acidosis?

Answer 5

-When blood pH is lower than it should be. not enough oxygen consumption, decreased oxygen. Make less ATP and more lactate (lactic acidosis).

Question 6

What can pyruvate be converted into?

Answer 6

–>Oxaloacetate (plus CO2)

–> Acetyl CoA (makes NADH)

–> Lactate (makes NAD+)

–> Acetaldehyde –> ethanol (makes NAD+)

Question 7

What are the cofactors required for pyruvate dehydrogenase?

Answer 7

• COA
• TPP
• Lipoic acid
• FAD
• NAD+

Question 8

How does glucagon inhibit glycolysis?

Answer 8

1) Glucagon binds ot receptor in membrane
2) G-protein binds GTP and interacts with Adenylyl cyclase
3) Adenylyl cyclase converts ATP into cAMP
4) cAMP bind PKA and activates it
5) PKA phosphorylated PHK2 (inactivating it)
6) F-6-P is not converted to F-2,6-bP –> no glycolysis

Question 9

How does insulin oppose the cAMP cascade?

Answer 9

• Insulin multi-subunit receptor phosphorylates itself & downstream proteins, which reverses glucagon’s actions
• Other effects: induction and repression of genes, stimulation of general protein synthesis, stimulation of glucose transport glut4, reversal of glucagon-stimulated phosphorylation, phosphorylation of more proteins

Question 10

What are the 3 irreversible steps in glycolysis?

Answer 10

Hexokinase (step 1)

PFK1 (committed step, step 3)

Pyruvate kinase (step 9)

Question 11

What can be converted into AcetylCoA?

Answer 11

–> glucose (pyruvate)

–> Ketone bodies

–> AAs , acetate, FAs

Question 12

What are the Energy-yielding products of TCA?

Answer 12

• 3 NADH
• 1 FADH
• 1 GTP

Question 13

What is the irreversible & most highly regulated step in TCA cycle?

Answer 13

• > Isocitrate dehydrogenase step (isocitrate is converted to a-ketogluatrate)
• > Oxidative decarboxylation
• > Produces NADH and CO2

Question 14

What is the importance of the citric acid cycle?

Answer 14

-It is the source of biosynthetic precursors

–Anepleurotic (“fill up”) reactions replenish depleted cycle intermediates

Question 15

What are the 3 irrveersible steps of TCA cycle?

Answer 15

1) Citrate synthase (inhibited by citrate)
2) Isocitrate dehydrogenase (inhibited by ATP & NADH, promoted by ADP & Ca2+)
3) a-ketoglutarate dehydrogenase (inhibited by NADH & succinyl CoA, promoted by Ca2+)

Question 16

What is the net gain from glycolysis?

Answer 16

• 2 ATPs /glucose
• 2 NADHs/ glucose

Question 17

How does pyruvate enter the TCA cycle?

Answer 17

• Pyruvate is decarboxylated and converted into AcetylCoA by pyruvate dehydrogenase in the mitochondria matrix
• Enzyme inhibited by NADH and AcetylCoA
• NADH and CO2 are produced
• Enzyme is regulated by phosphorylation (P-inactive)

Question 18

How can ETC and ATP production be stopped?

Answer 18

1) Uncoupling proteins create a “protein leak,” allowing protons to reenter the matrix w/o capturing any energy as ATP

Ex. Thermogenin generates heat instead of ATP in brown adipose tissue

2) Chemical inhibitors stop e-flow from substrate to oxygen bc the reactions of the ETC are tightly coupled

Ex. Amytal rotenone, antimycin-A, CN-, CO, Sodium azide

Question 19

What are the two shuttle cycles?

Answer 19

Glycerol phosphate (as FADH) & Malate aspartate (as NADH)

–> Shuttle reducing equivalents from NADH generated in glycolysis from cytosol to mitochondria

Question 20

What is the E-yield from the complete oxidation of 1 acetyl-CoA to CO2 in ATP equivalents?

Answer 20

–> 3 NADH (x3) = 9

–> 1 FADH (x2) = 2

–> 1 GTP (x1) = 1

12

Question 21

What is the E-yield from one glucose molecule in ATP equivalents?

Answer 21

• Glycolysis: 2 NADH (x3) = 6ATPs, 2ATPs
• Pyruvate to Acetyl-CoA: [1NADH (x3) = 3ATPs] x2 = 6 ATPs
• TCA: [3 NADH, 1 FADH, 1 GTP = 12 ATPs] x2 = 24 ATPs

—–> 38 ATPs total

Question 22

What are reactive oxygen species & what is oxidative stress?

Answer 22

1) ROS: hydroxyl OH*, superoxide O2-, hydrogen peroxide; created from O2

2) Oxidative stress: occurs when ROs are produced faster than they can be removed by antioxidant vitamins & enzymes

Question 23

What are the cells’ endogenous defenses to convert free radicals into non-toxic species?

Answer 23

-> Enzymatic defenses. Highest activity of antioxidant scavenging enzymes are in the liver, adrenal gland, & kidney, where mitochondria, perixisomes, & cytP450 are abundant.

2O₂^- —-Superoxide dismutase—-> H₂O₂ —-catalase or glutathione peroxidase—-> 2 H₂O

_{<em>*glutathione reductase regenerates cofactors for glutathione peroxidase</em>}

Question 24

What is ALS?

Answer 24

• Amyotrophic lateral sclerosis is a motor neurone disease characterized by rapidly progressive weakness, muscle atrophy, dyspnea, & difficulty speaking & swallowig
• Some cases of familial ALS are associated with a defect in SUPEROXIDE MUTASE.

Question 25

What is the role of the pentose phosphate pathway?

Answer 25

• Oxidizes glucose-6-P to intermediates of the glycolytic pathway, generating NADPH & ribose-5-P for nucleotide synthesis
• NADPH is used for reductive pathways:

FA synthesis, detoxification by monooxygenases, glutathione defense against ROS, cholesterol synthesis, neurotransmitter synthesis, nucleotide synthesis, respiratory burst during phagocytosis, & NO production.

Question 26

What are the tissues with most active Pentose Phosphate pathway?

Answer 26

• Adrenal gland, ovary, testes (steroid synthesis)
• Liver, testes, adipose tissue, mammary gland (FA synthesis)
• RBCs (maintenance of reduced glutathione)

Question 27

What are the functions of transketolase and transaldolase?

Answer 27

1) Transketolase: transfers two carbons; requires TPP
2) Transaldolase: transfers three carbons

–> Used in pentose phosphate pathway

Question 28

What is the effect of Glucose-6-P dehydrogenase defficiency?

Answer 28

-> Impairs ability of RBCs to form NADPH,

–> Glutathione reductase cannot regenerate GSH cofactor

—-> Glutathione peroxidase is no longer able to convert H₂O₂ into H₂O

——> ROS accumulation causes hemolysis (protective effect against malaria)