GLYCOLYSIS Flashcards
what is the purpose of glycolysis?
- making of energy carrying molecules such as 2 ATP especially for muscle contraction
- making of pyruvate which continues further downstream metabolic pathway such as citric acid cycle
where does glycolysis happen?
it happens in the cytoplasm of the cell and it does not require oxygen
what cells relies predominantly on glucose as energy source?
nerve cells in the brain
what happens after glycolysis?
- in the absence of O2 in the cytoplasm, fermentation occurs producing lactic acid in humans and ethanol is micro-organisms
- in the presence of O2 in the mitochondria, cellular respiration occurs breaking down glucose fully and it is oxidized to CO2 and H2O
how may reactions are involved in glycolysis and what are their significance?
1-5 : STAGE I (INVESTMENT of 2 ATP)
- preparation stage in which hexose glucose is phosphorylated and cleaved to yield 2 molecules of the triose glyceraldehyde-3-phosphate
6-10 : STAGE II (HARVEST ~ 4 ATP)
- 2 molecules of glyceraldehyde-3-phosphate are converted to pyruvate in which it will generate a total of 4 ATP
10 steps of glycolysis?
1 ) glucose is converted to g-6-p with the help of hexokinase and glucokinase by transfer of phosphoryl group from ATP to glucose
2 ) g-6-p is converted to f-6-p with the help of g-6-p isomerase in which it involves molecular changes of g-6-p in the active site of phosphoglucose isomerase
3 ) f-6-p is converted to f1,6-biphosphate with the help of phosphofructose kinase-1 by transfer of 2nd phosphoryl group from ATP to f-6-p
4 ) f1,9-biphosphate is converted to DHAP and G3P with the help of aldose by cleaving the C3-C4 bonds yielding two triose phosphate
5 ) DHAP is converted to G3P with the help of triose phosphate isomerase
6 ) G3P is converted to 1,3bisphosphoglycerate with the help of G3P dehydrogenase in which oxidation and phosphorylation occurs yielding a high energy mixed-acid anhydride - NAD+ & P = NADH & H+
7 ) 1,3biphosphoglycerate is converted to 3-phosphoglycerate with the help of phosphoglycerate kinase in which high energy phosphoryl group is transferred to ADP yielding ATP
8 ) 3-phosphoglycerate is converted to 2-phosphoglycerate with the help of phosphoglycerate mutase involving intramolecular phosphoryl-group transfer
9 ) 2-phosphoglycerate is converted to phosphoenolpyruvate with the help of enolase involving dehydration to an energy-rich enol ester
10 ) phosphoenolpyruvate is converted to pyruvate with the help of pyruvate kinase om which high energy phosphoryl group is transferred to ADP yielding ATP
what is the function of NAD+?
provides oxidizing power for glycolysis to occur in the absence of O2
- NAD+ must continuously be regenerated for glycolysis to continue ~ oxidative phosphorylation or fermentation
what are the regulating enzymes?
1 ) HEXOKINASE
- too much g-6-p = g-6-p will go through feedback inhibition to tell HK
2 ) PHOSPHOFRUCTOSEKINASE-1
- too much ATP will cause inhibition of PFK-1 and PK
- too much AMP will cause activation of PFK-1 by F2,6-biphosphate
3 ) PYRUVATE KINASE
- too much F1,6-biphosphate will feed forward activation to activate PK
can other sugar enter the pathway if they are converted to an intermediate molecule in glycolysis?
yes - fructose, galactose, mannose and glycerol
what are the disease associated with glycolysis defects?
ANEMIA
- deficient levels of HK will result in O2 binding curve to shift left of normal due to insufficient 2,3 BPG so there is not enough to inhibit O2 binding hence, O2 binding to hemoglobin is raised thus tissues cannot get O2 as it is bind too tightly
- deficient levels of PK will result in O2 binding to shift right of normal due to excess 2,3 BPG so it inhibits too much of O2 binding hence, O2 binding to hemoglobin is decreased thus cannot draw enough O2 from lungs as the lungs ties O2 loosely to them
impt notes
- rxn 1 and 3 requires investment of 1 ATP each
- rxn 6 yields NADH and H+
- rxn 7 and 10 yields 1 ATP each
regulating enzymes are HK.PFK-1 and PK
