Week 7- Introduction to Chemical Energy, Glycolysis

Question 1

Metabolism

Answer 1

• both biosynthesis of complex organic molecules and their breakdown
• Catabolism (exergonic): oxidation reaction and generate energy
• Anabolism (endergonic):
  reduction reaction and require energy

Question 2

Breakdown and Metabolism

Answer 2

• Digested food becomes source of metabolic energy (monomers)
  1. starch to glucose (saliva)
  2. protein to a.a (gastric protease)
  3. Lipid to fatty acid (lipase in pancreas)
• Monomers absorbed by cell through membrane transports
• Metabolism of monomers generate energy for growth and other activities

Question 3

Metabolism and Cofactors

Answer 3

• Catabolism: oxidation and loss of electron
• Anabolism: reduction
• Metabolic cofactors: Q, NAD+ and NADP+
• NAD+ involved in catabolic reactions
• NADP+ involved in anabolic reactions
• Ubiquinone (Q) involved in membrane electron transfer

Question 4

Cofactors and electron transfer

Answer 4

• oxidation-reduction reactions involve transfer of electron
• electron lost during oxidation is accepted by reduction reaction

Question 5

Metabolic pathways

Answer 5

• ATP and NADH
• Glycolysis
• Citric Acid Cycle
• Electron transport
• ATP (chemical energy)

Question 6

Free energy and ATP

Answer 6

• ATP represents chemical energy
• Cleavage of phosphoanhydride bonds releases large amount of energy
• example of energy usage: phosphorylation reaction of glucose

Question 7

Overview of glycolysis

Answer 7

• Glycolysis and fermentation: series of enzymatic reactions to convert 6-carbon glucose to two 3-carbon pyruvate and generate 2 ATPS
• Glucose: breakdown product from carbohydrates and glucose enters cells by membrane transport
• Stages in glycolysis:
  1. energy investment
  2. energy recovery

Question 8

Reactions of glycolysis

Answer 8

• Overview
  Glucose + 2 NAD+ + 2 ADP + 2 Pi = 2 pyruvate + 2 NADH + 2 ATP + 2 H2O + 4 H+
• Fate of pyruvate
  1. aerobic condition: oxidation
  2. anaerobic condition: fermentation

Question 9

Reaction of glycolysis - 1st stage

Answer 9

• Hexokinase: transfer of phosphoryl group from ATP to glucose, to form G6P
• G6P: formed to trap glucose inside cells
• Consumption of 1st ATP: ATP is first consumed, to allow more to be generated
• Fate of G6P:
  1. glycolysis
  2. pentose phosphate pathway
  3. glycogen synthesis
• phosphofructokinase:
  1. phosphorylates F6P to form F-1,6-biphosphate
  2. FBP is not diphosphate
• Consumption of 2nd ATP: second ATP needed to provide phosphoryl group

Question 10

Recap of stage 1

Answer 10

• one molecule of glucose transformed into two molecules of triose
• two molecules of ATP consumed to generate phosphorylated intermediates
• energy investment

Question 11

Reactions of glycolysis - 2nd stage

Answer 11

• Glyceraldehyde-3-phosphate dehydrogenase:
  1. GAPDH catalyzes oxidation of GAP
  2. Transfer of e- to NAD+ results in its reduction to NADH
• GAPDH phosphorylates GAP without using ATP
• phosphoryl group added from inorganic phosphate
• formation of 1st ‘high energy’ intermediate (1,3-BPG), is an acyl phosphate
  -pyruvate kinase: catalyzes transfer of high energy phosphoryl group from PEP to ATP
• result 1: generation of ATP
• result 2: pyruvate formation

Question 12

Recap of 2nd stage

Answer 12

2 C3 units = 4 ATP

Question 13

Product of glycolysis

Answer 13

• ATP: to satisfy cells’ energy needs
• NADH: glucose is oxidized and 2 NAD+ are reduced to 2 NADH
• Pyruvate:
  1. in aerobic conditions, pyruvate will be oxidized completely to CO2 via citric cycle
  2. in anaerobic conditions, pyruvate becomes lactic acid/ ethanol via fermentation

Question 14

Pentose phosphate pathways

Answer 14

• glucose participation in nucleotides synthesis, active in dividing cells
• regenerates NADPH rather than NADH
• NADH involved in catabolism
• NADPH involved in anabolism
• R5P is precursor of ribose unit of nucleotides