18 - Glycolysis Flashcards
What is glycolysis in its simplest terms?
The breakdown of glucose-6-phosphate to pyruvate, along the way ATP is made from ADP and NAD+ is reduced to NADH
What two things are needed for glycolysis?
NAD+ and glucose
What is glycogenolysis?
The conversion of glycogen to glucose-1-phosphate
Whate is isomerization doing after glycogenolysis?
Isomerization occurs to convert glucose-1-phosphate to glucose-6-phosphate. Glucose-6-phosphate is the form of glucose that can undergo glycolysis
What is pyruvate converted to after glycolysis? What does this product do?
Acetyl CoA, enters the TCA cycle and makes CO2 byproduct.
What is the net reaction of glycolysis?
Glucose +2ADP + 2NAD+ + 2Pi = 2 pyruvate + 2 ATP + 2 NADH +2 H+ + 2 H20
What is phase 1 of glycolysis? (energy investment phase)
The energy investment phase where phosphorylation of glucose and conversion to 2 molecules of glyceraldehyde-3-phosphate occurs. 2 ATP are used in this reaction.
what is phase 2 of glycolysis? (ATP production phase)
Conversion of glyceraldehyde-3-phosphate to pyruvate and coupled formation of 4 ATP
What must be regenerated to keep glycolysis going? What three things might happen if regeneration does not occur?
NAD+ must be generated or else there are three possibilites:
REduction of pyruvate to lactate (anaerobic)
Reduction of pyruvate to ethanol (yeast)
Mitochondrial electon trransport chain/oxidative phosphorylation
List the five steps and intermediates in the investment phase of glycolysis (stage 1)
- Phosphorylation of glucose to glucose-6-phosphate
- Isomerization of glucose-6-phosphate to fructose-6-phosphate
- Second phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate
- Aldol cleavage of carbon backbone to form two trioses (glyceraldehyde-3-phosphate and dihydroxyacetone phosphate
- Isomerization of dihydroxyacetone phosphate to glyceraldehyde-3-phosphate
What are the 5 steps and intermediates in the iATP generating phase of glycolysis (stage 2)
- oxidation by dehydrogenase of glyceraldehyde-3-phosphate (NAD+ required) to glyceraldehyde-1,3-bisphosphate
- Substrate level phosphorylation of glycerate-1,3-bisphosphate to glycerate-3-phosphate (2 ATP produced)
- Isomerization of glucose-3-phosphate to glycerate-2-phosphate
- Dehydration of glycerate-2-phosphate to phosphoenolpyruvate
- Substrate level phosphorylation of phosphoenolpyruvate to produce 2 more ATP and a molecule of pyruvate
How does glucose enter cells?
Facilitated transport by GLUT transporters on cell surface. There are several isoforms of GLUT, it is tissue and cell type specific. Different isoforms are regulated differently.
Are GLUT transporters bidirectional?
Yes, in and out.
What happens after hexokinase has its way with glucose?
Glucose is phosphorylated to glucose-6-phosphate shortly after it enters the cell by hexokinase. This prevents it form leaving the cell because GLUT cannot transport glucose-6-phosphate . Therefore phosphorylation retains glucose
What two molecules are required in glucose phosphorylation by hexokinase? Which carbon is phosphorylated?
Mg2+ and ATP. The sixth carbon is phosphorylated, this is the one that sticks out of the 5 carbon ring.
Glucose and fructose are both what type of sugar?
Hexoses, becasue they are both 6 carbon sugars
Describe the phosphorylation of glucose
Glucose nucleophilically attacks a phosphate group on ATP and takes it. Mg2+ acts as a stabilizer between the two phosphates, facilitating the nucleophilic attack of the phosphate
What enzyme isomerizes glucose-6-phosphate to fructose-6-phosphate? What does it do?
phosphoglucose isomerase (PGI). Catalyzes reaction of converting hydrogen on C1 of glucose to CH2OH
What enzyme catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate? What is important about this step? What directionality does this enzyme have and what two other materials are needed?
phosphofructokinase (PFK) with Mg2+. This is the rate-limiting step under many conditions. PFK catalyzes in one direction and requires ATP
What is the rate limiting step in glycolysis?
The isomerization of fructose-6-phosphate to fructose-1,6-bisphosphate by PFK
What enzyme is required for the cleavage of carbon backbone to dihydroxyacetone phosphate and glyceraldehyde-3-phosphate? What are the shortened abbreviations for these two trioses?
Aldolase cleaves backbone of fructose-1,6-bisphosphate to form DHAP and GAP
DHAP and GAP are interconverted by which enzyme?
Triose phosphate isomerase
In the dehydrogenation and addition of inorganic phosphate (Pi = HPO4) of glyceraldehyde-3-phosphate (GAP) to 1,3-bisphosphoglycerate (1,3-BPG), what enzyme is involved? And what two other materials are needed? What is oxidized and what is reduced?
glyceraldehyde-3-phosphate dehydrogenase (GAPDH). NAD+ and a Pi are needed. GAP is oxidized and NAD+ is reduced
What enzyme is used in the dephosphorylation of 1,3-bisphosphoglycerate to 3-phosphoglycerate (3PG) and the first generation of ATP?
Phosphoglycerate kinase (PGK), with the help of a magnesium ion.
Steady state of PGK (phosphoglycerate kinase) action to produce first generation of ATP is influenced by what?
The concentration of ADP/ATP in the cell (ratio). When the cell has a lot of ATP, glycolysis slows down.
What enzyme in glycolysis is an oxidoreductase?
GAPDH (glyceraldehyde-3-phosphate dehydrogenase
What enzyme isomerizes 3-phosphoglycerate to 2-phosphoglycerate (2PG)?
Phosphoglycerate mutase (PGM)
Which enzyme catalyzes generation of phosphoenolpyruvate (PEP) from 2-phosphoglycerate? What is a byproduct?
Enolase with the byproduct water
What enzyme catalyzes the important step of the formation of pyruvate from phosphoenolpyruvate into pyruvate and 2 ATP? In what direction does this enzyme operate?
Pyruvate kinase (PK), only operates in one direction.
NAD+ is generated in what?
Oxidative phosphorylation
PK can only phosphate in one direction, is this the same story for PGK?
PGK (phosphoglycerate kinase) can phosphorylate and dephosphorylate
What is the type of fermentation that makes lactate?
Homolactic fermentation
Is there a change in oxidation state in anaerobic glycolysis? Why?
No, because NAD+ is reduced to NADH by GAPDH phosphorylating glyceraldehyde-3-phosphate to glycerate-1,3-phosphate, but then oxidated back to NAD+ by the conversion of pyruvate to lactate by lactate dehydrogenase (LDH) in homolactic fermentation
Is lactate secreted by the cell? What is the consequence of this?
Yes, this causes acidification of cellular environment.
What are the enzymes and intermediates involved in alcoholic fermentation under anaerobic conditions?
Pyruvate decarboxylase and alcohol dehydrogenase convert pyruvate in a two step mechanism to ethanol.
Pyruvate to acetaldehyde with pyruvate decarboxylase
Acetaldehyde to ethanol with alcohol dehydrogenase
