☰ Contents · Biology (Cytology and genetics)

Metabolism and energy metabolism

Lessons 30–31 · 2 lessons · A. Zikiryayev, A. To‘xtayev, I. Azimov, N. Sonin. Biology. Basics of Cytology and Genetics, Grade 9, revised and expanded 5th edition. “Yangiyul Poligraph Service”, Tashkent, 2019
31

Energy metabolism

Textbook: pp. 79–80
GoalKnow the essence of energy metabolism, the role of ATP in it and the general equation of glucose oxidation.
New words
dissimilation · dissimilyatsiyaaerobic respiration · aerob nafas olishhigh-energy bond · makroergik bog‘ADP · ADF
Explanation

In energy metabolism the covalent bonds of organic substances are broken and the chemical energy stored in them is released. The general equation of aerobic breakdown with oxygen is C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy; according to the textbook about 2800 kJ is released when 1 mol (180 g) of glucose is fully oxidised. Part of this energy is lost as heat and the rest is stored in the high-energy phosphate bonds of ATP (adenosine triphosphate). Cell processes — division, muscle contraction, active transport, nerve impulses, biosynthesis — are powered directly by ATP energy: ATP → ADP + phosphate + about 40 kJ/mol. The ATP reserve is small (in a muscle it is enough for a few seconds of work), so ATP is constantly resynthesised: ADP + phosphate + energy → ATP; mainly in the mitochondria. In a short fast run the muscle mainly uses its reserve ATP, and afterwards deep breathing restores the ATP reserve.

Worked examples
When 90 g of glucose (0.5 mol) is fully oxidised, 90 × 2800 : 180 = 1400 kJ of energy is released.
Aerobic breakdown of 5 glucose molecules needs 5 × 6 = 30 molecules of O₂ and produces 30 molecules of CO₂.
Class activity

“ATP battery”. Students use “charged” (3 phosphates) and “discharged” (2 phosphates) battery cards to show ATP → ADP: how is the battery recharged after running?

Practice
1
Write the general equation of aerobic oxidation of glucose.
2
How much energy (kJ) is released when 360 g of glucose is fully oxidised? 180 g = 2800 kJ.
3
How many O₂ molecules are used in the aerobic breakdown of 8 glucose molecules?
4
Why does the cell not store much ATP but constantly resynthesises it?