5.7.2(Glycolysis)

What is meant by the term glycolysis

• Glycolysis is the first stage of respiration, it is a dehydrogenation reaction which involes breaking down glucose into pyruvate

Name the enzymes used in glycolysis

• dehydrogenase

Outline the 3 stages of glycolysis

1. phosphorylation of glucose to hexose

   1-6 bisphosphate

2. Splitting of hexose1-6 bisphosphate into 2 triose phosphate molecules

3. Oxidation of triose phosphate into pyruvate

Name the coenzyme involved in glycolysis

• NAD

Describe the function of NAD

• NAD is a hydrogen accepting co enzyme which accepts 2 hydrogen during oxidation - dehydrogenase enzymes

Describe the first stage of glycolysis

1. Phosphorylation

   • 2 ATP molecules are hydrolysed to release a phosphate group which are added to carbon 1 and 6 on the glucose molecule

   • This produced Hexose1-6bisphosphate

   • This molecule is unstable

Describe the second stage of glycolysis

1. Splitting the hexose bisphosphate

   • The Hexose bisphosphate molecule splits into 2 three-carbon molecules named: triose phosphate, each with a phosphate attached

Describe the final stage of glycolysis

1. Oxidation of triose phosphate

   • Dehydrogenase enzymes, aided by NAD, remove 2 hydrogens from triose phosphate

   • The NAD molecules accept the 2 hydrogens and become reduced NAD

   • During this process, the phosphate groups also break off from each triose phosphate, they combine with an ADP molecule to form 2 ATP molecules

   • The final product is a pyruvate, 4 APT molecules and 2 reduced NAD moelcules

Explain why phosphorylation occurs

• Glucose needs to be activated before it can split into 2 three carbon molecules

What occurs after glycolysis in anaerobic conditions in animals and plants

• Animals:

  • Lactate fermentation

• Plants:

  • Ethanol fermentation

Describe the process of lactate fermentation

• Reduced NAD from glycolysis transfers its hydrogens to pyruvate to form lactate and NAD

• The enzyme Lactate deghyrodgenase catalyses this reaction

• The regenerated NAD can then be used again in glycolysis

Describe the process of Ethanol fermentation

• The enzyme Pyruvate decarboxylase removes CO2 from pyruvate to form ethanal

• Reduced NAD from glycolysis transfers hydrogens to ethanal to form ethanol. which is catalysed by ethanol dehydrogenase

Compare Lactate fermentation and ethanol fermentation(8 comparisons)

• Lactate fermentation:

  1. hydrogen acceptor: Pyruvate

  2. produce CO2: No

  3. produce ATP: No

  4. End products: Lactate and NAD

  5. Enzymes: Lactate dehydrogenase

  6. NAD reoxidised: Yes

  7. Site of pathway: cytoplasm

  8. Reversible: Yes

• Ethanol:

  1. hydrogen acceptor: Ethanol

  2. produce CO2: yes

  3. produce ATP: No

  4. End products: Ethanol, CO2 and NAD

  5. Enzymes: Ethanol dehydrogenase and pyruvate decarboxylase

  6. NAD reoxidised: Yes

  7. Site of pathway: cytoplasm

  8. Reversible: No

Explain why Lactate fragmentation is a reversible reaction when ethanol fermentation isn’t

• This is because CO2 is produced during ethanol fermentation which is gas that escapes the reaction environment and so therefore cannot be added back to the reaction