Anaerobic Metabolism

Anaerobic metabolism requires energy NOW,

avoids using O2 —> aerobic metabolism is too slow

happens in cytosol at high intensity (>60-80% of VO_2max)

Range of VO_2max intensity for anaerobic metabolism varies based on

training, fiber type, and genetics

Glycolysis ends with pyruvate, with oxygen pyruvate turns into

acetyl CoA
**aerobic metabolism

Glycolysis ends with pyruvate, without oxygen pyruvate turns into

lactic acid
** anaerobic metabolism

Lactic acid dissociates into

1. lactate = can be used for energy (particularly good for cardiac cells)

2. H⁺ ions = cause fatigue, acidosis of the blood impairs enzymes

ATP-PCr system

skeletal muscle energy stores

small ATP stores — rel. large stores of phosphocreatine

technically anaerobic

molecular battery - you pay as you go after initial depletion

PCr concentrations depend on…

fiber type, training, dietary intake

Energy substrate for glycolysis

carbs only
glucose—>pyruvate

“Anaerobic glycolysis”

pyruvate—>lactate

“aerobic glycolysis”

pyruvate —> Acetyl CoA

When lipids (FFA) and protein (amino acids) enter aerobic pathway, they aid glycolysis via

gluconeogenesis

Glycolysis is regulated by

exercise intensity level

during exercise carb in-take

carb depletion state in blood glucose and muscle/liver glycogen

Metabolic stimulators

tell cell it needs energy
ex: ADP, P_i, AMP, increased pH, (NH₄⁺)

Metabolic inhibitors

tell cell it does not need energy — relax

ex: ATP, CP, citrate; ATP, CP; Glucose-6-phosphate, ATP

Key enzymes in controlling glycolysis

phosphofructokinase

pyruvate kinase

hexokinase

lactic dehydrogenase

Glycolysis step 1

glucose —> glucose-6-phosphate via hexokinase
requires ATP, releases ADP (irreversible)
**already completed when starting from glycogen

Glycolysis step 2

glucose-6-phosphate <—> fructose-6-phosphate via phosphoglucose isomerase

does not req. ATP

glycolysis step 3

fructose-6-phosphate —> fructose-1,6-phosphate via PFK enzyme

requires ATP, releases ADP
highly regulated step

Step 4 glycolysis

splitting of fructose-1,6- biphosphate into

a. glyceraldehyde 3-phosphate

b. dihydroxyacetone phosphate

uses aldolase enzyme

Step 5 glycolysis

all dihydroxyacetone phosphate molecules must be converted into glyceraldehyde-3-phosphate before entering phase II

conversion to G3P is done with triosephosphate isomerase

step 6 glycolysis

have 2 glyceraldehyde-3-phosphate → 1,3-biphosphoglycerate (2)

via glyceraldehyde-3-phosphate dehydrogenase

uses 2NAD⁺+ P_i

releases 2NADH + 2H⁺

step 7 glycolysis

1,3-biphosphoglycerate (2) —> 3-phosphoglycerate (2) via phosphoglycerate kinase
uses 2 ADP, releases 2 ATP

step 8 glycolysis

3-phosphoglycerate (2) to 2-phosphoglycerate (2) via phosphoglyceromutase
no atp used

step 9 glycolysis

2-phosphoglycerate (2) ←→ phosphoenolpyruvate (2) via enolase
releases 2 H₂O

step 10 glycolysis

phosphoenolpyruvate (2) —> pyruvate (2) via pyruvate kinase

uses 2 ADP, produces 2 ATP

2nd most regulated glycolysis step

Benefits of producing lactate in anaerobic glycolysis

Under aerobic conditions, NADH is re-oxidized back to NAD⁺ in the mitochondria via ETC but ETC can’t keep up in anaerobic conditions

Pyruvate is reduced to lactate via lactate dehydrogenase (LDH).

• NADH donates electrons and is converted back to NAD⁺.

• The regenerated NAD⁺ is recycled back into glycolysis, allowing the pathway to continue producing ATP without oxygen

Aerobic training substrate adaptations

increases use of FFA during moderate intensity
spares glycogen
untrained aerobic metabolism = ~60% VO_2max
trained aerobic metabolism = ~80% VO_2max

Anaerobic energy substrate adaptations

increased glycogen storage
increased exercise intensity
increased buffering capacity of H⁺

Normal, hyperglycemic, and hypoglycemic blood glucose values

normal: 90-110 mg/dL
hyperglycemic: >130 mg/dL
hypoglycemic: <45 mg/dL

catabolism of amino acids

gluconeogenesis

catabolism of triacylglycerides

lipolysis

catabolism of glycogen

glycogenolysis

Glucose transporters (GLUT)

give glucose access into cell
many are tissue specific

GLUT-4

increased by insulin

in muscle, cardiac, and adipose tissue

GLUT-1

basal glucose uptake
almost every cell has GLUT-1