Carbohydrates 2

Question 1

Glycolysis Stage 1

Answer 1

Phosphorylation of glucose to trap it in cell; uses energy to destabilize molecule to make break down easier in stage 2 (2 ATPs used)

Question 2

Glycolysis Stage 2

Answer 2

6C F-1,6-BisP spilts into 2 3C molecules (DHAP and GAP; DHAP CANNOT proceed on in glycolysis pathway, must be converted to GAP or to glycercol for synthesis of storage fat)

Question 3

Glycolysis Stage 3

Answer 3

3C GAP molecule is oxidized in 5 steps to generate pyruvate; energy-yielding phase; 2 molecules of ATP are synthesized by substrate level phosphorylation; 2 ATP’s per 1 GAP so 4 ATP’s per 1 glucose molecule

Question 4

Degradation of Fructose: Liver and Muscle

Answer 4

Liver—Fructose metabolized in liver; converted to F-1-P by fructokinase and then further cleaved into DHAP enters at Stage 2 glycolysis; remember fructose doesn’t trigger insulin release
Muscle—fructose is -P’d by hexokinase, then enters glycolysis

Question 5

Degradation of Galactose

Answer 5

must be converted to glucose; is first -P’d then linked to UDP, UDP-galactose is then transformed into UDP-glucose; in pathway once Galac-1-P is formed it must be degraded–but if accumulated; also the UDP is recycled back in reaction

Question 6

Essential Fructosuria

Answer 6

Deficiency of liver fructokinase, fructose is NOT utilized and excreted in urine; no harmful effects

Question 7

Hereditary Fructose Intolerance

Answer 7

Deficiency in Aldolase B enzyme; fructose-1-P CANNOT be converted to DHAP and then is accumulated in the liver; liver phosphate pools are depleted and then it cannot break down glycogen; enlarged liver, coma, hypoglycemia, jaundice, decrease liver function

Question 8

Galactosemia

Answer 8

failure to utilize galactose in glycolysis; 3 types based on enzyme effected— galactokinase, galactose-1-phosphate uridyltransferase, UDP-galactose epimerase; intellectual disability, vision loss, liver damage, jaundice

Question 9

Regulatory Signals of Glycolysis

Answer 9

Intermediates of energy metabolism (ATP, citrate); Hormones (insulin, glucagon, epinephrine); Fructose-2,6-BisP

Question 10

3 Regulated Steps of Glycolysis

Answer 10

Phosphofructokinase, Hexokinase, pyruvate kinase

Question 11

Regulation of Phosphofructokinase

Answer 11

most important regulated step/rate controlling step; F-6-P –> F-1,6-P
inhibited by ATP, citrate
stimulated by hormones (via F-2,6-BisP), ADP and AMP

Question 12

Regulation of Hexokinase

Answer 12

Glucose –> G-6-P; Stimulated by insulin

Inhibited by end product (G-6-P), acetyl-CoA

Question 13

Regulation of Pyruvate Kinase

Answer 13

PEP –> Pyruvate; stimulated by F-2,6-BisP, insulin

inhibited by ATP

Question 14

Fructose-2,6-Bisphosphate

Answer 14

synthesized from F-6-P; accelerator of glycolysis; regulates PFK1/Fructose bisphosphatase

Question 15

Common Misconception about Glycolysis

Answer 15

glycolysis is NOT performed solely for energy generation; it is also for removal of glucose from circulation and building up long term stores of energy–if glucose is available, glycolysis is very active regardless of cellular energy demands

Question 16

Regulation of Glycolysis in Starvation State

Answer 16

Glucagon activates PKA via cAMP cascade; PKA inhibits PFKII so F-2,6-BisP is no longer made from F-6-P; w/o F-2,6-BisP then gluconeogenesis can proceed uninhibited

Question 17

Regulation of Glycolysis in Well Fed State

Answer 17

Insulin inhibits PKA (cAMP cascade not started); inhibition of PKA leads to active PFKII which produces F-2,6,-BisP; F-2,6-BisP upregulates PFKI and glycolysis proceeds while GNG is shutdown

Question 18

PFKII

Answer 18

F-6-P –> F-2,6-BisP; upregulated by AMP, F-6-P and downregulated by PKA

Question 19

Glycerol Phosphate Shuttle

Answer 19

muscle and brain; gets electrons from NADH in cytosol and puts them on FADH in mito matrix; less efficient than other shuttle; for tissues that utilize a lot of glucose; loss of 1 ATP formation by going from NADH to FADH; glycercol-3-phosphate dehydrogenase

Question 20

Malate-Aspartate Shuttle

Answer 20

Liver/heart tissue; NADH reduces OAA to malate, malate transported across inner mito membrane, inside it is converted back to OAA and NADH is produced; more efficient than other shuttle

Question 21

If O2 is not available–Fermentation

Answer 21

pyruvate must accept electrons from NADH to regenerate NAD+ for glycolysis; pyruvate–> lactate; occurs in RBC’s since they have no mito; lactate taken up by liver; accumulation = lactic acidosis

Question 22

Pyruvate Kinase Deficiency

Answer 22

deprives RBC’s of ATP; leads to lysis of RBC’s b/c membrane potential cannot be maintained; hemolytic anemia;

Question 23

Arsenate Poisoning

Answer 23

Aresnate can micmic phosphate; causes glycolysis to not be able to produce ATP (via substrate level -P); BAD for RBC’s = hemolytic anemia

Question 24

Cori Cycle

Answer 24

RBC’s/muscles convert pyruvate to lactate; lactate enters circulation and is picked up by liver; liver uses GNG to convert lactate–> pyruvate–> glucose; glucose sent back into circulation for RBS’s to utiltize to create ATP