5 cell metabolism

8/6/2019 5 Cell Metabolism

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� Energy is measured in kilocalories(kcal)

¾ E.g., 1g of carbs ² 4kcal

� Food composed of carbon, hydrogen,O2 & nitrogen (protein only)

Food Adenosine Triphosphate(ATP)



� Our muscles dependence on carbs

during exercise is related to carbs

availability & our muscle·s welldeveloped system for metabolism.

� Carbs are converted to glycogen

�

Glycogen storage¾ 40% liver 60% skeletal muscle



� Our body stores more fat than carbs

� Energy reserve from fat is higher than

carbs¾ 1g fats ² 9 kcal energy

� But fat is less accessible for cellular metabolism.

� Why? It must first reduce from its complexform¾ triglycerides to its basic component: glycerol

& FFA



Gluconeogenesis

AA/glycerol Glucose

Lipogenesis

Protein FA

� Protein supply 5 ² 10% of energy tosustain prolonged exercise

� Basic unit of protein - AA



� ATP ² PCr system

� Glycolytic system

� Oxidative system



� Release of energy is facilitated by

enzyme creatine kinase (CK), which acts

on PCr to separate Pi from creatine� The energy release used to couple Pi to

an ADP forming ATP.

PCr = Phosphocreatine / Creatine Phosphate



� Glycolysis produce pyruvic acid

� When conducted without O2, pyruvic

acid is converted to lactic acid.

� One mole of glucose yields 2 moles ofATP, but one mole of glycogen yields 3

mole of ATP.



� This energy system does not produce largeamounts of ATP.

� The ATP-PCr and Glycolytic systems aremajor contributors during the early minutesof high intensity exercise.

� Limitation:¾ causes accumulation of Lactic Acid.

¾

Acidification of muscle fiber inhibits further glycogen breakdown (impair glycolytic enzymefunction)

¾ Decrease the fiber calcium binding capacity(impede muscle contraction)



� Involves breakdown of fuel with the aid ofO2.

� This system yield more energy

Oxidation of CarbohydrateOxidation of Carbohydrate� Involve 3 process:

¾ Glycolysis¾ Kreb cycle¾ Electron transport chain



� Glycolysis

¾ In the presence of O2, the pyruvic acid is

converted to acetyl co enzyme (acetyl CoA)� Kreb cycle (citric acid cycle)

¾ Once form, acetyl CoA enters the KC

¾ End of cycle ² 2 mole of of ATP, carbon and

hydrogen¾ Remaining carbon then combine with O2 ² CO2

¾ The CO2 transported to the lung via blood to be

expired



� Electron transport chain¾ During glycolysis, hydrogen is released

¾ More hydrogen is released during Kreb cycle.

¾ Hydrogen released by both cycle will combinewith two coenzyme

¾ NAD (nicotinamide adenine dinucleotide) andFAD (flavin adenine dinucleotide)

¾ NAD and FAD will carry the hydrogen atom to

the electron transport chain & split into protons &electron.

¾ End of chain ² H+ combine with O2 to form H2O(prevent acidification)

¾ End result ² H2O, CO2 and 38 or 39 ATP



� Only triglycerides are major energy source

� Triglycerides are stored in fat cell & skeletal muscle fiber.

� To be used as energy, a triglycerides must be broken down into 1glycerol + 3 FA

� This process is call lipolysis (enzyme ² lipase)

ßß OxidationOxidation,, KrebKreb Cycle & ETCCycle & ETC� Fat oxidation begins with ß oxidation of free fatty acids, then

follow the same path as carbohydrate oxidation.

� However the complete combustion of a FFA molecule requiresmore O2 because FFA carries more carbon than glucose ==

� (FFAFFA ² ² CC1616 HH3232 OO00; G C; G C66 HH1212 OO66)

� More carbon in FA - more acetyl CoA - more electron moreenergy

� However, only 40% energy release used to form ATP, 60%- heat



� Some amino acids (BCAA-leusine,isoleusine, valine) can be converted into

glucose(gluconeogenesis)� Our body utilized less protein (5-10% of

total energy expenditure) during restand exercise

� Chemically, protein contain the sameatoms as carbs & lipids ² carbon,hydrogen, oxygen. But protein alsocontain nitrogen.

5 cell metabolism

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