😀 EASY

These questions tests some basic knowledge about glycolysis and the metabolism of glucose including locations of the various pathways, the carrier molecules and some simple figures of number of molecules needed or produced, plus a sneaky little short answer question at the end!

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Metabolic pathways

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Question 1
What is the role of hexokinase in glycolysis?
A
Add phosphate to glucose to produce glucose-6-phosphate
B
Remove phosphate from glucose-6-phosphate to produce glucose
C
Remove phosphate from glucose-6-phosphate to produce pyruvate
D
Break down of glycogen in liver to produce glucose-6-phosphate
E
Break down ATP to help transport glucose into the cell
Question 1 Explanation: 
Kinases are typically able to both add or remove phosphate molecules to other molecules, using or producing ATP in the process. However, in glycolysis, the conversion of glucose to glucose-6-phosphate by hexokinase is one directional. The liver is able to reverse this process using a different enzyme called glucose-6-phosphatase.
Question 2
Where would you find glucokinase (tick all that apply)?
A
Brain
B
Liver
C
Blood
D
Muscle
E
Pancreas
Question 2 Explanation: 
Glucokinase is a modified hexokinase that has a slower rate of reaction. It is found in the liver and the insulin-producing beta cells of the pancreas. The reduced reaction rate of glucokinase helps to control the liver's production of glycogen and beta cell's release of insulin, so this activity is proportionate to the amount of glucose.
Question 3
What is the net gain of ATP from the breakdown of glucose via glycolysis?
A
No change
B
1 molecule of ATP gained for each glucose molecule
C
2 molecules of ATP gained for each glucose molecule
D
4 molecules of ATP gained for each glucose molecule
Question 3 Explanation: 
In the first stage of glycolysis, one ATP is used to provide the phosphate to make glucose-6-phosphate. A second ATP is used in the production of fructose-1,6-bisphosphate. Two ATP molecules have been used up. Fructose-1,6-bisphosphate is then broken down into two smaller molecules, each with a phosphate: dihydroxyacetone phosphate (DHAP), and glyceraldehyde-3-phophate (G3P). An isomerase also converts DHAP into G3P. Over the rest of glycolysis, a phosphate group will be added to G3P (but this doesn't come from ATP) and two ATP molecules will be produced. Therefore, each molecule of G3P produces two ATP molecules, meaning four are produced in total. As we have used up two ATPs in the earlier stages, the net production of ATP is 4 - 2 = 2.
Question 4
For each molecule of glucose, how many molecules of NADH are produced during glycolysis?
A
None
B
One
C
Two
D
Three
E
Four
Question 4 Explanation: 
One molecule of NADH is produced from the oxidation of glyceraldehyde-3-phosphate. Glycolysis produces two molecules of G3P and therefore each glucose molecule produces two molecules of NADH.

G3P is produced directly from the breakdown of fructose-1,6-bisphosphate, and indirectly from the conversion (isomerisation) of dihydroxyacetone phosphate (which is the second product from the breakdown of F-1,6-bisP).

Question 5
What is the final product of glycolysis?
A
Dihydroxyacetone phosphate
B
Acetyl-CoA
C
Glyceraldehyde-3-phosphate
D
Pyruvate
E
Ketone bodies
Question 5 Explanation: 
Ketone bodies and acetyl CoA are produced from pyruvate, but pyruvate marks the final product of glycolysis.
Question 6
Where does glycolysis occur?
A
Cell membrane
B
Cytosol
C
Outer mitochondrial membrane
D
Inner mitochondrial membrane
E
Mitochondrial matrix
Question 7
Where does the Kreb’s cycle take place?
A
Cell membrane
B
Cytosol
C
Outer mitochondrial membrane
D
Inner mitochondrial membrane
E
Mitochondrial matrix
Question 7 Explanation: 
The Kreb's cycle is also known as the citric acid cycle and TCA (tricarboxylic acid cycle)
Question 8
Where does beta oxidation occur?
A
Cell membrane
B
Cytosol
C
Outer mitochondrial membrane
D
Inner mitochondrial membrane
E
Mitochondrial matrix
Question 9
Where do you find the electron transport chain (ETC)?
A
Cell membrane
B
Cytosol
C
Outer mitochondrial membrane
D
Inner mitochondrial membrane
E
Mitochondrial matrix
Question 9 Explanation: 
This is quite logical when you think about it: most of the molecules carrying electrons to the ETC are produced by the Kreb's cycle and beta-oxidation, which both take place in the matrix of the mitochondria.
Question 10
What is the Warburg Effect?
A
The uncoupling of the ETC to produce heat
B
The diversion of Kreb’s cycle to produce amino acids
C
Anaerobic metabolism of glucose in cancer cells
D
Increase in cellular NADH levels when cells are under stress
E
None of the above
Question 10 Explanation: 
As anaerobic respiration is very inefficient, cancer cells will have to burn more glucose. Studying the Warburg effect might identify biomarkers to determine cancer prognosis and/or therapeutic targets.
Question 11
Which of the following are products of beta oxidation (tick all that apply)?
A
Acetyl CoA
B
Pyruvate
C
FADH2
D
NADH
E
NADH2
Question 11 Explanation: 
Beta oxidation takes fatty acids and breaks them down two carbons at a time to produce acetyl-CoA. FADH2 and NADH carry electrons produced during beta oxidation to the ETC.
Question 12
Which cycle is involved in the breakdown and excretion of excess amino acids by the body?
A
Citric acid cycle
B
Cori cycle
C
Urea cycle
Question 12 Explanation: 
The breakdown (deamination) of amino acids produces glutamate and ammonia that enter the urea cycle at different stages to produce the less toxic urea which can be excreted in urine.
Question 13
Which by-product of the urea cycle enters the Kreb’s cycle?
A
Citrulline
B
Arginine
C
Fumarate
D
Aspartate
Hint:
Asparatate ENTERS the urea cycle. It is formed by a product of the Kreb's cycle reacting with glutamate from the deamination of amino acids.
E
Malate
Question 14
The proton pumps in the electron transport chain move hydrogen ions in which direction?
A
From the mitochondrial matrix into the intermembranous space
B
From the intermembranous space into the mitochondrial matrix
C
From intermembranous space into the cytoplasm
D
From the cytoplasm into the intermembranous space
Question 14 Explanation: 
The double membrane of the mitochondria helps to maintain a localised high concentration of protons to drive ATP synthase's production of ATP.
Question 15
How many protons must pass through ATP synthase to produce one ATP molecule?
A
One
B
Two
C
Three
D
Four
E
Five
Question 16
Von Gierke’s disease is a potentially fatal genetic disorder of glycogen storage. Which enzyme do these patients lack?
A
Glucose-6-phosphatase
B
Glycogen debranching enzyme
C
Glycogen synthase
D
Glucose phosphatase
E
Hexokinase
Question 16 Explanation: 
Glycogen is stored by the liver until glucose is needed by the body at which point glycogen is broken down, first to glucose-6-phosphate and then to glucose. This causes an enlarged liver as it stores increasing amounts of glycogen. Type III glycogen storage disease is associated with a deficiency in glycogen debranching enzyme. Glycogen synthase is deficient in Type 0 glycogen storage diseases.
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There are 16 questions to complete.
To treat hyperkalaemia, glucose and insulin are often given in combination to reduce the concentration of potassium in the blood stream. Using your knowledge of glucose metabolism and sodium-potassium pumps, explain why this works.

This method exploits the law of mass action. In any (bio)chemical reaction or pathway, the more reactants you have, the more products you produce. In the scenario described, the law of mass action affects the amount of ATP produced, and the activity of the sodium-potassium pump.

First of all, insulin allows glucose to enter the cells. As there is more glucose, there will naturally be more glycolysis, and subsequently more activity in the Kreb’s cycle, and finally more ATP synthesised by the electron transport chain.

As there is more ATP, you will get more sodium pumped out of the cell, and potassium pumped in. This is because the increased concentration of ATP in the cell means there is more ATP available to power the exchanger (and a greater likelihood of an ATP molecule being near the pump when it is needed).

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