GLYCOLYSIS & KREBS CYCLE
What is the name of decarboxylated pyruvic acid?
Acetyl (or acetate)
How many of each of the molecules below are produced in the Krebs cycle of every glucose molecule that undergoes cellular respiration? (CO2 ATP NADH FADH2)
CO2: four NADH: six ATP: two FADH2: two
Which molecule in the Krebs cycle has the highest potential energy—citrate, α-ketoglutarate, succinate or oxaloacetate? Provide specific evidence from Model 3 to support your answer.
Citrate, because as the Krebs cycle proceeds, energy is released from citrate through the formation of ATP, NADH, and FADH2 molecules from ADP, NAD+, and FADH molecules, respectively
Has any ATP been used or produced during the link reaction?
No ATP was used or produced during this link reaction
Is oxygen needed as a reactant in the Krebs cycle?
O2/oxygen is not needed as a reactant in the Krebs cycle
Refer to Model 1. Propose an explanation for why the author of this activity put PGAL at the highest point in the Model 1 diagram
PGAL requires an input of energy to produce, and releases energy when it is converted to pyruvate. Since the diagram is organized by increasing potential energy from bottom to top, PGAL is at the highest energy point.
How many carbon atoms are in a glucose molecule
Six carbon atoms
How many carbon atoms are in citrate?
Six carbon atoms are in citrate
Where in the cell does the Krebs cycle take place?
The Krebs cycle takes place in the the mitochondrial matrix
The connection between Coenzyme A and the acetyl group is weak. How is this illustrated in Model 2?
The connection between Coenzyme A and the acetyl group is weak because it is illustrated with a singular dashed line
Where did the missing carbon atom go during the conversion of citrate to α-ketoglutarate?
The missing carbon atom was released in a molecule of CO2
How many carbon atoms are in a pyruvate molecule
Three carbon atoms
How many carbons of the pyruvate molecule remain when is it attached to Coenzyme A?
Two carbon atoms remain
During the link reaction, the pyruvic acid molecule is decarboxylated. What molecule is removed during this process?
A carbon dioxide molecule (CO2) is removed during this process
What is the net production of ATP by glycolysis
+2 ATP
Identify two places in the Krebs cycle where a decrease in free energy is coupled with an increase in free energy.
1. Acetyl-CoA (higher potential energy) being converted to CoA (lower potential energy) is coupled with conversion of oxaloacetate (lower potential energy) to citrate (higher potential energy) 2. Citrate (higher potential energy) is converted to a-ketoglutarate (lower potential energy) while NAD+ (lower potential energy) is converted to NADH (higher potential energy)
Glucose has six carbons. A fat molecule could have ten times that many carbons. Predict how the number of ATP molecules produced would differ between a glucose molecule and a fat molecule.
A glucose molecule would likely produce less ATP than a fat molecule would. This is because although the PGAL molecule made from the fat molecule will produce two pyruvate and thus two acetyl-CoA molecules just like the PGAL from the glucose will, the fatty acids of the fat molecule will produce significantly more acetyl-CoA molecules than a glucose molecule could.
When coenzyme A bonds to the decarboxylated pyruvic acid what molecule is produced?
Acetyl-CoA
What molecule is introduced to the Krebs cycle from the link reaction?
Acetyl-CoA is introduced to the Krebs cycle from the link reaction
How many pyruvate molecules are made from each glucose molecule
Each glucose molecule produces two pyruvate molecules
How many acetyl-CoA, carbon dioxide, and NADH molecules are produced in the link reaction for each glucose molecule that undergoes cellular respiration?
Every one glucose molecule produces two pyruvate molecules, so the link reaction happens twice to produce for each glucose: Acetyl-CoA: 2 NADH: 2 Carbon dioxide: 2
How many carbon atoms are in α-ketoglutarate?
Five carbon atoms
How many carbon atoms are in succinate?
Four carbon atoms
How many carbon atoms are in oxaloacetate?
Four carbon toms are in oxaloacetate
What molecule from food is the primary reactant for glycolysis
Glucose
For each of the products above (excluding urea) identify the phase of cellular respiration where the molecules would enter the cellular respiration process.
Glucose: glycolysis PGAL: glycolysis Pyruvate: link reaction Acetyl-CoA: krebs cycle
Consider where proteins are "stored" in your body. What types of tissues would be affected if your body needed to use protein as an energy source?
Muscle tissues would be impacted when your body needs to use protein as an energy source
What molecule acts as an electron acceptor in glycolysis
NAD+ acts as an electron acceptor during glycolysis (transformed into NADH)
Was oxygen used as a reactant in any of the processes explored in this activity—glycolysis, the link reaction or the Krebs cycle?
No, oxygen was not used for any of the processes explored in this activity
Have any other high potential energy molecules been produced during the link reaction?
One molecule of NADH was produced
Which molecule in the Krebs cycle has the lowest potential energy—citrate, α-ketoglutarate, succinate or oxaloacetate? Provide specific evidence from Model 3 to support your answer.
Oxaloacetate, because as the Krebs cycle proceeds, oxaloacetate is formed as a result of multiple reactions in which energy is released in the form of of NADH, FADH2, and ATP
Does pyruvate have more or less potential energy than glucose? Provide specific evidence from Model 1 to support your answer.
Pyruvate has less potential energy than glucose. The production of pyruvate from PGAL and 1,3 BPG phosphorylates 4 ADP molecules into ATP, while the transformation of glucose to PGAL only requires 2 ATP molecules. Also, the diagram is organized in order of increasing potential energy from bottom to top, and pyruvate is listed below glucose, indicating that it has less potential energy.
Considering your answers to the previous three questions, what can you conclude about the potential energy of the acetyl group that is carried from the link reaction to the Krebs cycle by coenzyme A? Does this group of atoms have a high potential energy or a low potential energy? Explain your reasoning.
The acetyl group must have a high potential energy because it converts the oxaloacetate (low potential energy) into citrate (high potential energy)
In the last steps of glycolysis 4 ATP molecules are produced. Analyze Model 1 to find the source of the four inorganic phosphates (Pi) that are added to the ADP molecules to make the four ATP molecules. Describe the origins of the four inorganic phosphates here.
The four inorganic phosphates (Pi) that are added to the ADP molecules come from 2 molecules of 1,3 BPG
Where did the missing carbon atom go during the conversion of α-ketoglutarate to succinate?
The missing carbon atom was released in a molecule of CO2
Is the pyruvate molecule likely to move across the mitochondrial membranes by diffusion? (Your answer should include a comment about polarity.)
The pyruvate molecule is not likely to move across the membrane by diffusion, unless that diffusion is active transport. This is because the pyruvate molecule is polar, meaning that it would have a difficult time diffusing through the non polar phospholipid bilayer that makes up the mitochondrial membrane
Propose a method by which the pyruvate molecule moves across the mitochondrial membrane.
The pyruvate molecule moves across the mitochondrial membrane with the assistance of a protein carrier
Where did the extra carbon atoms come from to convert oxaloacetate into citrate?
The two carbon atoms come from the Acetyl group that enters the Krebs cycle by means of the link reaction
How many "turns" of the Krebs cycle occur for every glucose molecule (C6H12O6) that undergoes cellular respiration?
There must be two turns of the Krebs cycle for each glucose molecule that undergoes cellular respiration because in glycolysis, each glucose molecule produces two pyruvate molecules, which are converted into two acetyl-CoA molecules, each of which enter into the Krebs cycle
Throughout the Krebs cycle, energy is transferred to other high potential energy molecules. List those molecules and indicate the number produced with one "turn" of the cycle.
Throughout the Krebs cycle, energy is transferred from the high potential energy molecules of NADH, FADH2, and ATP. With one turn of the Krebs cycle, three NADH molecules, one FADH2 molecule, and one ATP molecule are produced.
Does the process of glycolysis require an input of energy?
Yes. In order for glycolysis to occur, 2 ATP molecules must be inputted. These 2 ATP molecules are converted to ADP and power the transformation of one glucose molecule into two PGAL molecules. However, 4 molecules of ATP are phosphorylated from 4 molecules of ADP as the two 1,3-BPG molecules are transformed into two pyruvate molecules. This means that glycolysis nets a total of 2 ATP molecules.
Where in a cell does the link reaction take place
in the mitochondrial matrix