Glycolysis

Question 1

what is glucose?

Answer 1

the universal fuel for for human cells

Question 2

what is the goal of glycolysis? its products?

Answer 2

to generate ATP and reducing equivalents from glucose; it generates 2 moles NADH and 2 moles APT per mole of glucose

Question 3

what is glycolysis the pathway for?

Answer 3

oxidation of glucose to pyruvate

Question 4

what are some cells that are dependent on glucose as fuel sources for ATP production?

Answer 4

red blood cells: lots of O2, but no mitochondria

brain cells: lots of O2 and mitochondria, but cells lack machinery to use fatty acids for fuel
*** fatty acids don’t cross the blood-brain barrier .

Question 5

glycolysis produces precursors for these other pathways too?

Answer 5

pentose phosphate pathway

amino acid biosynthesis

Glycerol 3-phosphate forms the backbone for triglyceride synthesis

1,3-bisphosphoglycerate can be converted to 2,3-bisphosphoglycerate
which is an allosteric inhibitor of oxygen binding to Hb which
can be dephosphorylated to 3-phosphoglycerate and reenter glycolysis

Question 6

T/F, pyruvate is the a product of glycolysis?if so, what is it a precursor for?

Answer 6

T, fatty acid synthesis

Question 7

*A. Recognize the glycolytic pathway

Answer 7

Net ATP produced independent of TCA cycle (anaerobic ATP production).

NADH produced (reduced cofactor) which leads to ATP production in mito

End of glycolysis is formation of pyruvate

Pyruvate enters TCA cycle leading to Lots of ATP

Question 8

*A. identify the two phases of the pathway

Answer 8

ATP Preparative phase

ATP generating phase

Question 9

*A. define the two phases of the pathway

Answer 9

Glucose → pyruvate (NET 2ATP), 2 moles pyruvate per mole glucose net 2ATP

The Two phases
Preparative phase:
-This one uses 2 ATPs to get glucose phosphorylated on both ends of the molecule
-Activates the glucose molecule
-Cleavage of glucose into two triose phosphates

ATP-generating phase:

• Generates 4 ATP (substrate level phosphorylation) and 2 NADH molecules (glyceraldehyde 3-phosphate oxidation by NAD+ and phosphorylation by Pi)
• Rearrangement of phosphates into high energy bonds

Question 10

where does glycolysis occur?

Answer 10

in the cytosol

Question 11

what is one mole of glucose oxidized too?

Answer 11

one mole of glucose is oxidized to 2 moles of pyruvate

Question 12

glycolysis has an overall net negative ΔGo’, which drives the pathway forward, T/F?

Answer 12

T

Question 13

what happens when you do not have oxidized NAD+ for glycolysis?

Answer 13

glycolysis stops, you won’t have NADH and even ATP if ADP is absent

Glucose + 2 NAD+ (must be present to make ATP) + 2 Pi + 2 ADP ->
2 Pyruvate + 2 NADH + 4 H+ + 2 ATP + 2 H2O

Question 14

*B.Define the role of NAD+/NADH in the glycolytic pathway

Answer 14

NAD+ is the oxidized precursor

NADH is the reduced cofactor

Question 15

describe the total amount of ATP produced from aerobic cellular metabolism?

Answer 15

Pyruvate to Acetyl CoA produces one NADH molecule, and 2 pyruvates are made per one glucose: that contributes 5 ATP molecules. Because 2 acetyl CoA molecules enter the TCA Cycle and we get 9 ATP per single cycle, that’s 18 ATP. 2 net ATP molecules are produced by glycolysis directly. Together, that’s 25 molecules of ATP per single molecule of glucose

Question 16

What is the first committed step of glycolysis?

Answer 16

Use of an ATP to drive reaction costs energy: must not be wasted

Phosphorylated glucose “trapped” in cell: cannot be transported back out

Highly negative ΔGo’ of reaction prevents reverse reaction

glucose 6-phosphate is a common intermediate for pathways that use glucose

key intersection point

allows for regulation of flux of glucose between pathways

Question 17

in liver and pancreatic B cells, what is the enzyme that is used for phosphorylation?

Answer 17

glucokinase which has much lower affinity for glucose…higher Km for glucose

Question 18

*G. Compare and contrast the function of hexokinase and glucokinase, in terms of the tissues where these two enzymes are found.

Answer 18

-Hexokinase and glucokinase (in liver) phosphorylate glucose to glucose 6-phosphate
-Glucokinase has a much lower affinity for glucose and higher Km for glucose
○ Glucose concentration must be much higher in these cells to activate phosphorylation (sigmoidal curve)
-Portal vein carries glucose from small intestine to liver
-High blood glucose drives glucose transport into hepatic cell
-As glucose accumulates in the cell, liver enzyme will start to phosphorylate glucose so the liver cells can use it
-Hexokinase has a greater affinity for oxygen (hyperbolic curve)
-Having just a cracker as a snack, the liver doesn’t care because it’s such a low amount of glucose

Question 19

*E. Identify the glycolysis intermediates that are used by other pathways.

Answer 19

-1,3-bisphosphoglycerate can be converted into 2,3-bisphosphoglycerate
○ Modifies Hb
○ Allosteric inhibitor of oxygen binding to Hb
○ Can be dephosphorylated to 3-phosphoglycerate and reenter glycolysis
-Pyruvate is a precursor to FA synthesis
-Pentose phosphate pathway: ribose 5-phosphate= sugar for nucleotides
-Amino acid biosynthesis: Ser, Gly, Cys, Ala… AA catabolism produces glycolysis intermediates

Question 20

Define the concept of a “committed step” in a pathway, using the conversion of glucose to glucose-6-phosphate as an example.

Answer 20

-A committed step is a step during the pathway where it can not go backward in the pathway
-Very high -deltaG
-Example: PFK-1 commits the pathway to stay in glycolysis by phosphorylating fructose 6-phosphate to fructose 1,6-bisphosphate
-Example: hexokinase phosphorylates glucose to glucose 6-phosphate, which activates glucose and traps it in the cell
○ Glucose 6-phosphate is not committed to glucose and can go to pentose phosphate pathway or glycogen synthesis

Question 21

*H.Recognize why the action of phosphofructose-1 (PFK-1) is considered the committed step in glycolysis.

Answer 21

• PFK-1 phosphorylates fructose 6-phosphate to fructose 1,6-bisphosphate
• Due to the molecule having phosphate on both ends the molecule IS COMMITTED TO GLYCOLYSIS
• Irreversible
• Rate limiting step

this determines how glucose 6 phosphate it used, just because you are G6P does not mean you are committed

Question 22

*M. What is the effect of patients with a PFK-1 deficiency?

Answer 22

In Red Blood Cells: RBCs can’t do glycolysis. As the only means of ATP production, the RBCs can’t survive without PFK-1…hemolytic anemia!

In Skeletal Muscle: Skeletal muscle can’t generate sufficient ATP from glycolysis to meet energy needs. Leads to cramps and muscle weakness.

Question 23

*I.Recognize the effects of AMP versus ATP on PFK-1 activity.

Answer 23

• AMP and fructose 2,6-bisphosphate both activate PFK-1

- ATP inhibits: need ATP to make forward rxn work, when ATP builds up, it shuts down the enzyme negative modulator

Question 24

*J. Define the function of the malate/aspartate and glycerol-3-phosphate shuttles for exchanging NADH / NAD+ reducing equivalents across the inner mitochondrial membrane.

Answer 24

-Glycerol 3-P Shuttle

○ Glucose → pyruvate gives off a NADH + H+
○ An electron is taken from NADH to help oxidize dihydroxyacetone-P → glycerol 3-P
○ Electron from the glycerol 3-P is taken to reduce FAD → FADH2
○ That FADH2 will get put into the ETC via CoQ (complex 1,2,3)
○ Leads to the production of 1.5 ATP per mole of NADH

-Malate-Aspartate Shuttle

○ -deltaG
○ Takes an NADH molecule to help the reaction of oxaloacetate → malate
○ Make NADH in cytosol and regenerate NADH in the mitochondria
○ Players: malare, OAA, aKG (TCA)
○ NADH is regenerated, so 2.5 mol ATP can be produced (1 mol NADH → 2.5 mol ATP in ETC)

Question 25

*K. Identify why some cells favor (or require) conversion of pyruvate to lactate, and likewise, identify conditions in all cells that increase lactate production and increase the risk of lactic acidosis.

Answer 25

-Cells with no mitochondria or limited mitochondrial capacity
○ Mature erythrocytes, skin cells, certain tissues in eyes
-Pyruvate converted to lactate to regenerate NAD+
-Lactate released into blood and picked up by the liver (glucose synthesis) and heart (acetyl CoA production)

Question 26

*L.Define the Cori Cycle and relate why this is crucial for the function of red blood cells.

Answer 26

• The liver makes glucose through gluconeogenesis (uses 6 ATP)
• The glucose enters a RBC and breaks down to 2 lactate (gives off 2 ATP)
• Lactate in the blood can also be picked up by the heart, converted back to pyruvate, then to acetyl CoA for the TCA cycle

Question 27

*N.Define adenylate charge and how it is calculated. In your answer, identify which pathways are stimulated versus inhibited by a high adenylate charge and why.

Answer 27

-Adenylate cyclase 2 ADP → ATP + AMP
-Adenylate charge: energy status of cell controls reactions
○ Catabolic pathways are inhibited by high energy charge
○ Anabolic pathways are stimulated by high energy charge
○ Normal range is 0.8-0.95
■ Below this the catabolic pathways are dominant
■ Above this the anabolic pathways are dominant
○ AC= ATP + ½ ADP / ATP + ADP + AMP

Question 28

*C.Identify the four products that can be formed from pyruvate and recognize the metabolic conditions that favor the production of each of the four products.

Answer 28

• Lactate (reduction)
• Acetyl coA (oxidative decarboxylation)
• Oxaloacetate (carboxylation)
• Alanine (transamination)
• If oxygen and mitochondria are available, pyruvate enters the TCA cycle and is oxidized to CO2
• Without O2 or mitochondria, pyruvate is converted to lactate
• Is also the starting material for fatty acid biosynthesis in liver and adipose tissues

Question 29

*D.Identify which cell types are typically dependent on glucose for energy.

Answer 29

Red blood cells

Brain cells

Question 30

what is significant about Phosphofructokinase 1?

Answer 30

major enzyme, if this is deficient, people are tired, exercise adaptation is a problem and they have issues with glucose metabolism/fasting metabolism; phosphate is added

Question 31

what enzyme of the glycolysis pathway is used for fructo metabolism? what are the products that result in this stage of the pathway?

Answer 31

Aldolase splits the sugar in half, people who are fructo intolerant (fructose metabolism) are missing the adolase enzyme

Remember the products here: dihydroxyacetone phosphate and Glyceraldehyde 3 phosphate: Note that DHAP is important because it is a molecule that adipose tissue makes in large amounts so it can make fat and store triglycerides and liver takes DHAP and makes glucose
Glyceraldehyde 3 phosphate, the aldehyde is more oxidized than glycerol 3-phosphate(starting material for triglycerides) both related by oxidized-reduction reactions

Question 32

what is DHAP converted into?

Answer 32

DHAP is converted to GAP and so you have two GAP

Question 33

what two enzymes are responsible for substrate level phosphorylation?

Answer 33

phosphoglycerate kinase(1,3-BPG to 3-PG) and pyruvate kinase(PEP to Pyruvate)

Question 34

what are the two highest yielding intermediates in the glycolytic pathway?

Answer 34

PEP and 1,3-BPG are high energy molecules

Question 35

During vigorous exercise, the adenylate charge (AC) in skeletal muscle cells decreases from 0.85 to 0.75. Which of the following is most likely responsible this change in AC?

Cellular [ATP]
Cellular [ADP]
Cellular [AMP]

Answer 35

Cellular [AMP]

Question 36

The glycerol-3 phosphate / dihydroxyacetone phosphate shuttle system carries the reducing power of NADH to the inner mitochondrial membrane electron transport chain. What is the fate of the electrons carried by this shuttle?

a. The electrons are transferred to Complex I resulting in the formation of 2.5 ATP per cytoplasmic NADH used.
b. The electrons are transferred to a flavoprotein, resulting in the formation of 1.5 ATP per cytoplasmic NADH used.  
c. The electrons are transferred to Complex III, resulting in the formation of 1.5 ATP per cytoplasmic NADH used.
d. The electrons are transferred by a coupled reaction to the malate-aspartate shuttle system for transfer into the mitochondria.

Answer 36

b. The electrons are transferred to a flavoprotein, resulting in the formation of 1.5 ATP per cytoplasmic NADH used.

Question 37

In the absence of mitochondria or molecular oxygen, what happens to the pyruvate generated by glycolysis?

a. it is phosphorylated to phosphoenolpyruvate to make glucose.
b. it is converted to oxaloacetate to stimulate the TCA cycle.
c. it is reduced to lactate, generating one NAD+  
d. it is oxidized to lactate, generating one NADH

Answer 37

c. it is reduced to lactate, generating one NAD+