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9.7 The Biochemistry of movement: 10. Sprinting and anaerobic respiration

Extract from Chemistry Stage 6 Syllabus (Amended October 2002) © Board of Studies, NSW.
[Edit:8 Jun 2010]

solve problems and process information from a simplified flow chart of biochemical pathways to summarise the steps in anaerobic glycolysis and analyse the total energy output from this process

• The amount of ATP normally present in muscle cells can support about 5 seconds of intense activity – not quite enough for a 50 m run sprint! Summarise your learning by analysing and processing information to solve the following problems:

• You should be able to see that the oxygen dependent parts of energy released from glucose release ___ times as much ATP as the 2 ATP released in forming two pyruvic acid.

  Answer

• In sprinting, the muscles quickly run down ATP supplies before heavy breathing sets in, indicating heavy supply of oxygen for oxidative decarboxylation and oxidative phosphorylation. A 200 m run sprinter does not breath much during the race but does some heavy breathing and uses aerobic respiration to restore ATP after the race.
  
  
• How does a runner get to the 200m finish if the ATP supply available in the muscles only lasts for about 5 seconds? It takes at least 30 seconds after the start of the race before enough extra oxygen breathed in has reached the muscle cells and enough oxidative decarboxylation and oxidative phosphorylation can occur to replace ATP.
  
  The sprinting muscles use a non-oxygen/non-mitochondrial ATP production method. A method of ATP production that evolved in living things before there were significant levels of oxygen in the earth’s atmosphere.
  
  The muscle cells use anaerobic glycolysis to change pyruvic acid to lactic acid which is carried in the blood away from the muscle cells. This process removes hydrogen from NADH + H⁺ without using oxygen. The muscle cells can continue to change one glucose to two pyruvic acid releasing two ATP per glucose as long as pyruvic acid is removed as lactic acid.
  
  There is a limit to this process as lactic acid concentration increases in the blood but by then sufficient oxygen should have reached the muscle cells for more aerobic release of energy.
  
  
• Anaerobic respiration occurs entirely in the cytoplasm and does not require oxygen to recycle NAD⁺ whereas aerobic respiration relies on oxygen and mostly occurs in the mitochondria.
  
  
• Next time you see an athletic competition involving top athletes, compare the interviews, shortly after the race, of 100m, 200m and 400m sprinters. Which sprinters have the highest level of lactic acid in their blood and are breathing heavily to reverse the pyruvic acid to lactic acid conversion?
  
  
• Running races of 800 m or more largely involve energy released by aerobic respiration.

outline the problems associated with the supply and use of fuels during sprinting and relate this to the sprinting muscles’ reliance on non-oxygen/non-mitochondrial based ATP production

• Sprinting muscles cannot receive oxygen quickly enough and so rely on non-oxygen/non-mitochondrial based systems that produce ATP rapidly. For about the first 5 seconds of sprinting all the existing ATP in the muscle cells is used. Then for about the next 20 seconds creatine phosphate donates its phosphate group to any nearby ADP thus producing about four times as much ATP as was initially present (this is called the alactic acid or ATP-PC system where PC stands for phosphate- creatine). After about 25 seconds the system in which pyruvic acid from glucose, released by glycogen breakdown, changes to lactic acid is important (this is called the anaerobic glycolysis system). This system is limited by buildup of lactic acid in the blood.
  
  
• Outline that since sprinting requires a lot of ATP supplied rapidly for powerful and fast muscle contraction, type 2 muscle fibres are used and these effectively carry out anaerobic respiration, ie glucose to lactic acid.

Note that this is the only reversible reaction shown in the Biochemical Pathways Flowchart:

CH₃ – CO – COOH + NADH + H⁺     CH₃ – CHOH – COOH + NAD⁺

pyruvic acid                                        lactic acid

explain the possible relationship between the production of 2–hydroxypropanoic (lactic) acid during anaerobic respiration and the impairment of muscle contractions by changes in cellular pH

• Recall the experiment you carried out to study the effect of pH on enzymes (subsection 4). Enzymes become less active as pH changes away from the optimal pH and may eventually be denatured by a pH drop.
  
  
• 2–hydroxypropanoic(lactic) acid produced during heavy exercise lowers cellular pH and will impair muscle contractions, possibly causing cramps.

use available evidence and process information from a simplified flow chart of biochemical pathways to trace the path of lactic acid formation and compare this with the process of fermentation

• Use the Internet, text books, CD ROMs and journals to research the reactions called “fermentation” which take place in micro-organisms such as yeast.
  
  
• Compare fermentation to anaerobic glycolyis, noting the common pathway glucose to pyruvic acid, and then distinguishing the two processes by the last step.
  
  
• In micro-organisms, the last step is not a reversible reaction to lactic acid, but an irreversible reaction in which pyruvic acid is converted to ethanol. NADH is oxidised to NAD⁺ in this reaction.

  CH₃ – CO – COOH + NADH + H⁺ → C₂H₅OH + CO₂ + NAD⁺

• The alcohol accumulates and hence this reaction is used in wine and beer making.
  
  
• Like the reaction to lactic acid, fermentation is anaerobic. Also both reactions produce 2 ATP/glucose.
  
  
• Overall equation of fermentation is:

  C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂

process information to discuss the use of multiple naming systems in chemistry using lactic acid (2-hydroxypropanoic acid or 2-hydroxypropionic acid) as an example

• Like pyruvic acid, there is both a trivial name and a systematic name for lactic acid. The systematic name is 2-hydroxypropanoic acid. There is also an old name: 2-hydroxypropionic acid. The trivial name lactic acid is commonly used. An advantages of a trivial name is that it is easier for people to remember the name. A systematic name is given according to the structure. IUPAC rules enable any simple compound to be named as long as the structure is known.

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