Chapter 16- Glycolysis and Gluconeogenesis Flashcards
What is the main pathway for metabolizing glucose?
Glycolysis
Which pathway is the preferred macronutrient fuel for most cells?
Glycolysis
How many carbons does glucose have and what is it classifies as?
A 6 Carbon sugar
How many carbons does pyruvate have?
3 carbons
What are the 3 stages of metabolism?
Stage 1: digestion and absorption
- happens outside of cells
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What are the 3 stages of glycolysis?
C6 stage: Investment
Another stage: Splitting
C3 stage: Harvesting
What does the splitting stage do in glycolysis?
The conversion of 6 carbons to 3 carbons
What is the C6 stage also called?
The investment stage
What does the C6 stage include in glycolysis?
the hexokinase and the phosphofructokinase-1 (PFK-1) reactions as well as others
what does a kinase do?
transfers a phosphate from one organophosphate onto another
What do hexokinases do?
They transfer a phosphate onto hexoses.
what is the first reaction in glycolysis?
glucose + ATP using a hexokinase to get glucose 6 phosphate and ADP and H+
Is the first reaction in glycolysis heavily favored or not favored?
Yes, it is because ATP -> ADP is highly favored because its unstable. And because ATP is a high energy organophosphate
What type of organophosphates are sugars?
They are low energy organophosphates
What’s the delta G for the hydrolysis of ATP?
7.3 kilocalories/mole
Why is the C6 stage called the investment stage?
Because we spend 2 molecule of ATP.*
Why is the first investment of ATP worthwhile ?
Because the glute transporter is passive.
the glute transporter is an example of
a passive transporter
what does the glute transporter do for glycolysis?
The glucose that leaks into the cell can also leak outside of the cell.
Hexokinase phosphorylating it does what ?
it traps it into the cell because glucose 6 phosphate cant go through the glute transporter
After the 1st investment in glycolysis what is next?
an isomerase reaction
what are isomerases?
enzymes that catalyze the making of one isomer to another
what is the delta G for an isomerization?
near 0
what is the isomerase reaction?
takes glucose 6 phosphate to fructose 6 phosphate using an isomerase
what is the committed step in glycolysis?
fructose 6 phosphat spending a ATP using PFK 1 to get fructose 1,6 bisphosphate and ADP and H
is the committed step a favorable reaction?
yes, because it goes from high energy ATP to 2 low energy phosphoester bonds
is the committed step another investment?
yes you spent the second molecule of ATP
why is the second molecule of ATP worthwhile to invest?
because you cut the 6 carbon into quantity 2 3 carbon compounds
what is the committed step enzyme of glycolysis?
PFK-1
phosphofructoskinase 1
What are the inputs of glycolysis?
What are the outputs of glycolysis?
How is glycolysis regulated?
What are the two parts of the splitting stage of glycolysis?
splitting and interconversion reactions
Explain the splitting stage.
take fructose 1,6 bishophaste and split it into quantity 2 3 carbon sugars dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3 phosphate (GAP)
how are DHAP and GAP related to each other?
they are isomers of each other.
what interconverts DHAP into GAP? and what is the delta g of this reaction?
an isomerase, near zero
how many GAP molecules do you get 1 per glucose molecule?
2 GAP molecules
The last stage of glycolysis is called the what?
c3 stage or harvesting stage
what does the C3 stage include?
the glyceraldehyde 3 phosphate dehydrogenase reaction (GAP DH) producing NADH
is NADH energy currency? if so what is NADH?
no thats ATP but it can be converted into ATP
it is a high energy electron carrier
what is our first yield in glycolysis?
1 NADH in the C3 harvesting stage
what are we harvesting in the C3 stage?
NADH
2 molecules of ATP
how many ATP to we get at the end of glycolysis?
2 ATP
Why is GAPDH so important?
- because what it does is very unique
- and its the first of many similar enzymes (that are in the Rossmann fold family of enzymes)
what makes someone a Rossmann fold family member?
has the saddle (a alpha helix in the center and two binding sites on the side most often adenosine and niacin)
whats the role of NAD? and involved in what kind of reactions?
a high energy electron carrier
redox reactions
almost all rossmann fold family members are what kind of enzymes?
redox enzymes
is redox important in energy metabolism?
yes probably the single most important
why is GAP DH called GAP DH?
its substrate is GAP and a dehydrogenase it takes off a hydrogen (not dehydration, not taking off waters)
redox takes off?
electrons
dehydrogenases are redox _______?
catalysts
What Rossman fold family member is NAD dependent?
GAP DH
Why is GAP DH different from other Rossman fold family members?
It couples two reactions: phosphorylation and oxidation (1/2 reaction the other 1/2 is a reduction)
What does the other 1/2 reaction of the reduction piece do in the NAD DH reaction?
it reduces NAD+ to NADH
what is the first harvest in the glycolysis pathway?
NADH (from the reduction step)
GAP DH is not just a dehydrogenase but it is also a…..
phosphorylase (because it attaches an inorganic phosphate to an organic molecule)
Are thioesters high or low energy?
They are high energy
Is GAP DH a member of the Rossmann fold family?
Yes, it is NAD dependent
What does the GAP DH step do?
makes bisphosphate dehydrogenase
what are the two labels for GAP DH?
dehydrogenase and phosphorylase (because it atatches an inorganic phosphate to an organic molecule
How is GAP DH similar and unique to other enzymes?
similar: rossmann fold family member
unique: it couples two reactions (phosphorylation and the redox reaction) and forms an acyl phosphate (which has a carboxylic ester bond which makes it high energy)
What are the two reactions that GAP DH couple?
phosphorylation of the carboxylic group and a redox reaction which is 1/2 an oxidation and the other 1/2 a reduction from NAD+ to NADH
what is our first harvest?
NADH
Which step does our first NADH come from?
GAP DH specifically the reduction reaction NAD+ to NADH
If the two reactions that are coupled by GAP DH were seperated what would happen?
separated it would not happen spontaneously and the redox reaction is very favorable and the phosphorylation would be unfavorable
what is the importance of the coupling of reactions? why does it happen?
so that it is spontaneous and because the phosphorylation is highly favorable.
what does the C3 stage produce?
ATP and pyruvate
what reaction happens after the GAP DH step? What is the Delta G for the reaction and what does that tell us about the reaction? And what is unique about this reaction?
1,3 bishophoglycerate and ADP gets you 3 phosphoglycerate and ATP
delta G is close to 0 (reversible)
it is done twice, so we break even and get two ATP out of this reaction per glucose molecule
what reaction is after PEP?
PEP and ADP —> pyruvate and ATP using the 2nd kinase in the C3 stage
what are the next two steps after making 3 phosphoglycerate?
3 phosphoglycerate —> 2 phocphoglycerate
2 phosphoglycerate —> phosphoenolpyruvate
What is unique about PEP?
it has the highest energy of any organophosphate
where does the phosphate come from in PEP?
the phosphate comes from the enol bond to take ADP to ATP
what do kinases do?
they take a high energy phospho ester and transfer it to a phosphate on ADP to make ATP
