Lecture 1: Central Metabolism Glycolysis - Exam 4 Flashcards
(36 cards)
What are the three primary central metabolic pathways, what’s happening in them, and when would you expect them to be used (growth on glucose, gluconate, acetate, etc.)?
These three pathways metabolize carbohydrates and carboxylic acids.
1) Embden-Meyerhof-Parnas Pathway (EMP pathway, or glycolysis)
2) Pentose phosphate pathway (PPP)
3) Entner-Duodoroff pathway (ED pathway)
*All of these pathways convert glucose to phosphoglyceraldehyde and then oxidized to pyruvate.
What is the goal of the bacterial cell?
Self-replication
The goal of the bacterial cell is self-replication. What does this take?
This takes energy-generating reactions (dissimilatory) and energy-requiring reactions (assimilatory).
Are all dissimilatory and assimilatory reactions catalyzed in the living bacterial cell by integrated enzyme systems, with the end goal being self-replication?
YES!
What is heterotrophic metabolism?
Biological oxidation of organic compounds, such as glucose, to yield ATP and other simpler organic or inorganic compounds which are needed by the bacterial cell for biosynthetic or assimilatory reactions.
When does respiration take place?
When any organic compound is completely oxidized to CO2 and H2O.
Aerobic respiration yields…?
a theoretical maximum of 38 moles of ATP from 1 mole of glucose.
What is fermentation and what does it yield?
Is an incomplete form of glucose oxidation, less energy is generated. Fermentation yields 2 moles of ATP from 1 mole of glucose.
How do all three pathways differ? How are they similar?
All convert glucose to phosphoglyceraldehyde (with different paths) and all oxidize 3-phosphogylceraldehyde to pyruvate (same paths).
Glycolysis yields 2 ATP, 2 NADH, 2 pyruvate
Entner-Doudoroff yields 1 ATP, 1 NADH, 1 NADPH, & 2 pyruvate
Pentose phosphate yields 1 ATP, & 2 NADPH
What happens to NAD(P)H generated during central metabolism?
It goes to the ETC which drives ATP production via an ETC-generated proton gradient.
Why is glycolysis so important for bacterial cells?
In addition to generating ATP and NADH, glycolysis generates intermediates that are very important in many anabolic pathways.
What are the two phases of glycolysis? Something is converted to something else during glycolysis. What are these things? How many steps does it take?
Preparatory phase (steps 1-5) and the payoff phase (steps 6-10). Glucose is converted to pyruvate in 10 steps by glycolysis.
Describe the preparatory phase.
-This phase is also called glucose activation phase.
-Two molecules of ATP are invested in step 1 & 3.
-Hexose chain is cleaved into two triose phosphates.
-During this, phosphorylation of glucose and its conversion to glyceraldehyde-3-phosphate take place.
Describe the payoff phase.
-This phase is also called the energy extraction phase.
-Glyceraldehyde-3-phosphate is converted to pyruvate.
-ATP is formed and NAD+ is reduced to NADH.
-Because glucose is split to yield two molecules of Glyceraldehyde-3-phosphate, each step in the payoff phase occurs twice per molecule of glucose.
What are the important enzymes? What is different about the steps these enzymes are involved in?
Hexokinase(step 1), Phosphofructokinase (step 3), Pyruvate kinase (step 10)
All of the steps these are involved in are irreversible.
These are also kinases, which attach phosphate groups to a substrate.
ATP is formed in the steps involving these enzymes.
What irreversible enzymes are involved in the preparatory phase?
Hexokinase and phosphofructokinase.
Describe the first step of glycolysis.
Glucose is phosphorylated to form glucose-6-phosphate.
-Glucose forms glucose-6-phosphate through phosphorylation via PEP in the phosphotransfer system or via hexokinase as the catalyst + ATP.
-Hexokinase is the key glycolytic enzyme here. It is a magnesium-dependent enzyme.
-The reaction is IRREVERSIBLE!
Describe the second step of glycolysis.
Glucose-6-phosphate is isomerized to fructose-6-phosphate by phosphohexose isomerase.
-Phosphohexose isomerase is a magnesium dependent enzyme
-The reaction is reversible.
Describe the third step of glycolysis.
Fructose-6-phosphate is further phosphorylated to fructose 1,6-biphosphate.
-The enzyme phosphofructokinase-1 catalyzes the transfer of a phosphate group from ATP to F-6-P.
-The reaction is IRREVERSIBLE.
Describe the fourth step of glycolysis.
The #6 C of fructose 1,6-biphosphate is cleaved into two 3 carbon units:
-One glyceraldehyde-3-phosphate (GAP or G3P) and one molecule of dihydroxy acetone phosphate (DHAP).
-The enzyme which catalyzes the reaction is aldolase.
-The reaction is reversible.
Describe the fifth step of glycolysis.
Glyceraldehyde 3-phosphate (GAP or G3P) is on the direct pathway of glycolysis, whereas DHAP is not.
-DHAP must be converted to G3P by triose-phosphate isomerase. This is necessary because G3P can be used to generate ATP.
-The net result is that glucose is now cleaved into two molecules of glyceraldehyde-3-phosphate (G3P).
-This reaction is rapid and reversible.
Describe the sixth step of glycolysis.
The first step of the payoff stage is glyceraldehyde-3-phosphate oxidized to 1,3-biphosphoglycerate.
-This reaction is catalyzed by glyceraldehyde 3-phosphate dehydrogenase.
***This is an energy-yielding reaction
-During this reaction, NAD+ is reduced to NADH.
-This is a reversible reaction.
Describe the seventh step of glycolysis.
The enzyme phosphoglycerate kinase transfers the high-energy phosphoryl group from the carboxyl group of 1,3-biphosphoglycerate to ADP, forming ATP and 3-phosphoglycerate.
-This is a good example of substrate-level phosphorylation.
-This reaction is reversible.
Describe the eighth step of glycolysis.
3-phosphoglycerate is isomerized to 2-phosphoglycerate by shifting the phosphate group from the 3rd carbon to the 2nd carbon atom.
-The enzyme is phosphoglycerate mutase, which is magnesium dependent.
-Readily reversible reaction.
