Carbohydrate Catabolism Flashcards
Glucose, Fatty Acids and most amino acids all converge in catabolism to form which ONE of the following biomolecules?
A) Pyruvate
B) Glycogen
C) Acetyl-CoA
D) Hexokinase
E) Starch
C) Acetyl-CoA
(2C)
- Stage 1 of catabolism
- End product of Glycolysis
Which ONE of the following amounts in the nearest approximation the complete oxidation of glucose in the presence of oxygen?
A) 3000 kJ/mol
B) 30 kJ/mol
C) 3 kJ/mol
D) 3000 kJ/mol
E) 10,000 kJ/mol
A) 3000 kJ/mol
Which ONE of the following pathways is responsible for the major flux of carbon in cells?
A) Citric Acid Cycle
B) Gluconeogenesis
C) Beta-Oxidation
D) Glycolysis
E) None of the above
D) Glycolysis
Which ONE of the following describes the number of enzymes that function in glycolysis and the localisation of these enzymes in cells?
A) 8, Cytosol
B) 5, Cytosol
C) 5, Mitochondria
D) 10, Nucleus
E) 10, Cytosol
E) 10, Cytosol
What is the name of this biomolecule?
A) Acetyl-CoA
B) Glucose
C) Fructose-6-Phosphate
D) Pyruvate
E) Glyceraldehyde 3-Phosphate
D) Pyruvate
Which ONE of the following describes the total amount of energy obtained during glycolysis?
A) 2 NADH and 2 ATP
B) 4 NADH and 2 ATP
C) 2 NADH and 4 ATP
D) 2 NADH and 1 ATP
E) 1 ATP and 2 NADH
A) 2 ATP and 2 NADH
Exergonic pathway
Which ONE of the following enzymes converts phosphoenolpyruvate to pyruvate in glycolysis?
A) Pyruvate kinase
B) Pyruvate carboxylase
C) Phosphoenolpyruvate kinase
D) Pyruvate dehydrogenase
E) None of the above
A) Pyruvate kinase
Which ONE of the following enzymes is the committed step in glycolysis?
A) Hexokinase
B) Phosphofructokinase-1
C) Pyruvate kinase
D) Glyceraldehyde 3-Phosphate Dehydrogenase
E) Glucose 6-Phosphate
B) Phosphofructokinase-1
Which ONE of the following enzymes do vertebrates lack, preventing them from converting pyruvate to ethanol?
A) Pyruvate Decarboxylase
B) Pyruvate Kinase
C) Pyruvate Dehydrogenase
D) Pyruvate Isomerase
E) Pyruvate Mutase
A) Pyruvate Decarboxylase
Which of the following group of 2 enzymes convert pyruvate to ethanol?
A) Pyruvate Carboxylase and Alcohol Dehydrogenase
B) Pyruvate Decarboxylase and Alcohol Dehydrogenase
C) Pyruvate Kinase and Lactate Dehydrogenase
D) Lactate Dehydrogenase and Pyruvate Carboxylase
E) Hexokinase and Phosphofructokinase-1
B) Pyruvate Decarboxylase and Alcohol Dehydrogenase
What are the THREE stages of catabolism in the presence of O2?
- Acetyl-CoA production
- Acetyl-CoA oxidation
- Electron transfer and oxidative phosphorylation
What are the major nutrients used for energy?
- Carbohydrates
- Proteins
- Fats
In what tissue/cell types is glucose the major source of energy?
- Brain
- Erythrocytes
- Renal medulla
- Sperm
What are some of the things E.coli synthesise from glucose?
Carbon skeletons for:
* Amino acids
* Coenzymes
* Fatty acids
What diseases have altered glycolysis?
- Diabetes
- Cancer
- Neurodegeneration
- Immune diseases
- Infection
What are the major pathways of glucose utilisation?
- Synthesis of structural polymers
- Storage
- Oxidation via pentose phosphate pathway
- Oxidation via glycolysis
How was glycolysis discovered?
Through work with yeast and muscle cells
What is the near universal pathway for glucose catabolism called?
Glycolysis
How many Cs does Pyruvate have?
3C
What biochemical processes in the cell were discovered as a result of studies on Glycolysis?
Role of ATP & Phosphorylated compounds
How many enzymes take part in Glycolysis?
10
What is the enzyme that converts Glucose to Glucose 6-phosphate?
Hexokinase
1st enzyme in Glycolysis
What happens in the “Preparatory” phase of Glycolysis?
Phosphorylation of glucose and its conversion to glyceraldehyde 3-phosphate
What happens in the “Pay-Off” phase of Glycolysis?
Oxidative conversion of glyceraldehyde 3-phosphate to pyruvate and the coupled formation of ATP and NADH
What occurs in the “Preparatory” phase of Glycolysis in terms of energy?
Energy is invested in the form of 2 ATP
Steps 1 and 3
What occurs in the “Pay-Off” phase of Glycolysis in terms of energy?
Energy is produced in the form of 4 ATP and 2 NADH
- NADH - Step 6
- ATP - Steps 7 and 10
What happens in Step 1 of Glycolysis?
- Glucose is phosphorylated on position 6
- ATP donates the phosphate
Which enzyme is involved in Step 1 of Glycolysis?
Hexokinase
Why does Hexokinase need Mg2+ to add a phosphate group to glucose in Step 1 of Glycolysis?
Mg2+ shields the terminal phosphate of ATP from hydrolysis by H2O to enable nucleophilic attack by OH on C6 of glucose
What happens in Step 3 of Glycolysis?
Fructose 6-phosphate is phosphorylated to Fructose 1-6-bisphosphate
- Committed step in Glycolysis
- ATP donates a phosphate
Which enzyme is involved in Step 3 of Glycolysis?
Phosphofructokinase-1
Major regulatory enzyme for Glycolysis
What happens in Step 6 of Glycolysis?
2x Glyceraldehyde 3-phosphates are oxidased and phosphorylated to 1,3-bisphosphoglycerate
How is energy produced in Step 6 of Glycolysis and how much energy is produced?
Oxidation transfers electrons from 2x Glyceraldehyde 3-phosphate to 2NAD –> 2NADH
What enzyme is involved in Step 6 of Glycolysis?
Glyceraldehyde 3-phosphate dehydrogenase
Removes H+
What happens in Step 10 of Glycolysis?
2x Phosphoenolpyruvate is dephosphorylated to yield 2x Pyruvate & 2ATP
Which enzyme is involved in Step 10 of Glycolysis?
Pyruvate Kinase
What does a kinase enzyme do?
Add phosphoryl groups to substrates
What is a substrate level phosphorylation?
A reaction that results in the production of ATP by the transfer of a phosphate group from a substrate
What are the regulatory enzymes in Glycolysis?
- Hexokinase
- Phosphofructokinase
- Pyruvate kinase
Does Glycolysis need oxygen?
No
What are the THREE possible fates of Pyruvate?
- 2x Ethanol + 2CO2
- 2x Acetyl-CoA
- 2x Lactate
What is Pyruvate converted into in the presence of O2?
2x Pyruvate decarboxylated to 2x Acetyl-CoA
What TWO molecules are Pyruvate converted to in the absence of O2?
- Lactate
- Ethanol
Is Pyruvate oxidised or reduced when converted to lactate / ethanol?
Reduced
Does NAD+ get regenerated for Step 6 of Glycolysis in the conversion of Pyruvate to lactate / ethanol?
Yes. Allows continuous Glycolysis to occur in absence of O2
What organsims convert Pyruvate to ethanol?
Yeast
What are the TWO enzymes called that convert Pyruvate to enthanol?
- Pyruvate decarboxylase
- Alcohol dehydrogenase
Describe the reaction of converting Pyruvate to ethanol
- Pyruvate is decarboxylated
- Forms Acetaldehyde
- Hydrogen atoms from NADH + H+ convert Acetaldehyde to Ethanol
What can’t vertebrates and lactic acid bacteria make ethanol from Pyruvate?
Pyruvate Decarboxylase is absent
What is the enzyme called that produces Lactate from Pyruvate?
Lactate Dehydrogenase
Describe the reaction of coverting Pyruvate to Lactate
- Lactate Dehydrogenase removes NADH + H+ make NAD+
- Pyruvate is converted lactate
Describe what happens during anaerobic respiration in muscle during a sprint
- O2 can’t get to muscle fast enough
- Muscle switches to anaerobic glycolysis
- Breaks down muscle glycogen stores to lactate for energy
- Lactate enters the blood and goes to the liver
- Lactate synthesises glucose in the liver
- Glucose goes from the liver –> blood –> muscle to replenish glycogen
Describe the potential importance of anaerobic respiration in cancer cells
- Increased levels of glycolytic enzymes occur in cancer cells
- Pyruvate kinase (PKM2) has reduced catalytic activity compared to PKM1
- Allows cancer cells to keep using anaerobic glycolysis for energy, promoting proliferation
Describe the potential importance of anaerobic respiration in immune cells
Immune cells “rewire” metabolism to use anaerobic glycolysis (Glucose to Lactate) even when O2 is present
Where in the cells is Pyruvate converted to Acetyl-CoA?
Mitochondria
