Biochemistry - Glycolysis

Question 1

Input of Glycolysis

Answer 1

• 1 Glucose
• 2 NAD+
• 2 Pi
• 2 ADP
• 2 ATP

Question 2

Output of Glycolysis

Answer 2

• 2 Pyruvate
• 2 NADH
• 2 ATP
• 2 H+
• 2 H2O

Question 3

Glycolysis Step 1

Answer 3

Trapping and Investment

• Hexokinase or Glucokinase
• Use of 1 ATP
• Produces Glucose 6-Phosphate
• Tagged, cannot leave the cell by adding phosphate

Question 4

Hexokinase vs Glucokinase

Answer 4

• Glucokinase is only present in the liver kidney and pancreatic B-Cells - has low affinity (high Km) binding to glucose
• Hexokinase is present in most tissue and has high affinity (low Km) binding to Glucose
• Hexokinase is inhibited by Glucose 6-Phosphate

Question 5

Glycolysis Step 2

Answer 5

Rearrangement

• Phosphoglucose Isomerase
• Isomer - Fructose 6-Phosphate

Question 6

Glycolysis Step 3

Answer 6

Commitment and Investment

• Phosphofructokinase
• Use of 1 ATP
• Produce Fructose - 1,6 -bisphosphate
• Permanently tagged for metabolism by adding a second phosphate

Question 7

Inhibitors and Activators of Phosphofructokinase

Answer 7

Inhibitors

• High ATP levels
• Citrate (CAC is saturated)
• Decreased pH

Activators
- High levels of AMP (not enough ATP)

Question 8

Glycolysis Step 4

Answer 8

Rearrangment

• Adolase
• Breaks molecule into two different 3 C molecules
• DHAP and Glyceraldehyde 3-phosphate (moves straight to step 5)

Question 9

Glycolysis Step 5

Answer 9

Rearrangement

• Triose phosphate isomerase
• Converts DHAP to Glyceraldehyde 3-Phosphate
• Fast

Question 10

Glycolysis Step 6

Answer 10

Oxidation

• Glyceraldehyde 3-Phosphate Dehydrogenase
• 2 x Glyceraldehyde 3-Phosphate are oxidised and then phosphorylated
• Produced 1,3-Bisphosphoglycerate
• 2 NADH produced

Question 11

Glycolysis Step 7

Answer 11

Harvest

• Phosphoglycerate Kinase
• Substrate phosphorylation - 2 ATP made
• Produces 2x 3-Phosphoglycerate

Question 12

Glycolysis Step 8

Answer 12

Rearrangement

• Phosphoglycerate Mutase
• Make molecule more reactive by moving phosphate to another O group
• Produced 2x 2-Phosphoglycerate

Question 13

Glycolysis Step 9

Answer 13

Rearrangment

• Enolase
• Removal of 2 H2O (1 from each molecule)
• Greater ability to donate phosphate
• Produces 2x Phosphoenolpyruvate

Question 14

Glycolysis Step 10

Answer 14

Harvest

• Pyruvate Kinase
• 2x ATP produced
• 2x Pyruvate produced

Question 15

Reproduction of NAD+

Answer 15

• NADH must be re-oxidised to NAD+ so it can accept electrons in step 6 of glycolysis
• Under anaerobic conditions this can happen by lactate dehydrogenase reducing pyruvate to lactate and oxidising NADH to NAD+
• Under aerobic conditions this can happen by oxidative phosphorylation in the mitochondria via Malate Aspartate shuttle or G3PD Shuttle

Question 16

The Cori Cycle

Answer 16

• The transfer of glucose from the liver to skeletal muscle and lactate from the skeletal muscle to the liver is known as the Cori Cycle
• Heart muscles of vertebrates have different iso forms for lactate dehydrogenase which can convert blood lactate to pyruvate
  e. g. yeast and goldfish can produce school and CO2 under fermentation

Question 17

Malate Aspartate Shuttle

- In cardiac and liver cells

Answer 17

• Cytosolic Malate Dehydrogenase reduces oxaloacetate into malate which is able to enter the mitochondria matrix
• This oxidises NADH to NAD+ which can now be reused in Glycolysis
• Inside the matrix Malate is oxidised to oxaloacetate and mitochondrial NAD+ is reduced to NADH

Question 18

G3PD Shuttle

- In skeletal muscle

Answer 18

• Cytoplasmic Glycerol 2-Phosphate Dehydrogenase reduces DHAP to G3P and oxides NADH to NAD+ allowing it to be reused in glycolysis
• G3P moves into the IMS which it is oxidised to DHAP and transfers 2e- and 2H+ to FAD reducing it to FADH
• FADH2 can no reduce Ubiquinone forming Ubiquinol which can be fed into complex 3
• This pathway bypasses complex 1 and so will produce 1.5 ATP per molecule of NADH
• NADH produced in the CAC will produce 2.5 ATP per molecule of NADH