Aerobic Respiration Controls and Related Pathways

Regulation of Aerobic Respiration 

• regulated by → feedback inhibition and product activation loops

1. if citrate (intermediate in krebs) accumulates some will enter the cytoplasm ad inhibit pFK to slow dow gycolysis 

• citrate is used upon its concentration will decrease and the rate of glycolysis will increase 

2. conversion of pyruvate into acetyl-CoA & CO2 

• enzyme pyruvate dehydrogenase is inhibited by excess NADH 

• several krebs cycle enzymes are also inhibited by excess ATP, NADH and acetyl-CoA

Phosphofructokinase (PFK)

• is main control point in glycolysis 

• is an aloestetric enzyme that catalyzes the third reaction in glycolysis 

  • inhibited by ATP → stimulated by ADP 

Controlling Aerobic Respiration → Speed up

• high levels of ADP 

• low level of citrate 

• both act on phosphofructokinase (PFK) 

Controlling Aerobic Respiration → Slow down

• excess ATP (acts on phosphofructokinase) 

• accumulation of citrate (acts on phosphofructokinase) 

• excess NADH (acts on pyruvate dehydrogenase) 

Related Pathways

• carbohydrates → first source of energy 

• proteins, lipids and nucleic acids → when necessary 

• Protein Catabolism 

• Lipids Catabolism

• Anaerobic Pathways

Protein Catabolism

• deamination: first stage of protein metabolism, where amino acids are removed 

•  converts amino group into ammonia, NAh3 → becomes waste product

• amino acids are oxidized 

1. as pyruvate 

2. as acetyl units 

3. as molecules of the krebs cycle 

• the point of enetry on the identify of the amino acid 

  • lecuine → acetyl-CoA 

  • alanine → pyruvate 

  • proline → a-ketoglutarate 

Lipids Catabolism

• 2nd energy source, if carbs are not available 

• triglycerides → glycerol & fatty acids 

• glycerol → G3P and enters glycolysis 

• fatty acids undergo → B-oxidation in the mitochondrial matrix 

  • enzymes remove 2-C acetyl groups 

• groups combine with coenzyme A forming acetyl-CoA → which can be fed into Krebs 

• *Fats produced 2x amount of energy that an equal mass of carbs

Anaerobic Respiration

• Glycolysis → anaerobic 

• NADH produced during glycolysis → no oxygen cannot be converted into NAD+ 

• limited supply of NAD+ 

• NADH can donate its hydrogen atoms to other organic molecules to free themselves up for more glycolysis 

Fermentation: ATP from Glucose, without O2 

• ells live without O2, serving energy from glycolysis and fermentation 

• pathways partly oxdize glucose and generate energy-contatining products 

• Fementation reaction anaerboically oxidize the NADH + H produced in glycolysis 

Ethanol Fermentation 

• Co2 is removed from pyruvate to form acetlaldehyde 

• NADH passes its hydroge atoms to acetalaldehyte → ethanol 

• Ethanol is a waste product 

• carried out by yeast 

• this process is used to bread, wine beer, liquor, soy sauce   

Lactic Acid Fermentation 

• muscle cells respire glycose faster than oxygen can be supplied to the ETC 

• pyruvate acts as an acceptor for the hydrogen atoms form NADH 

• pyruvate → lactate 

• lactate accumulation in muscle tissue → stiffness, soreness and fatigue 

• lactate is oxidized → pyruvate (when O2 is available) 

Oxygen Debt

• extra O2 is required to catbolize lactate to CO2 and H2O through the aerobic pathways 

  • Ex. panting after exercise → “pays” the oxygen debt

Contrasting Energy Yields

• for each molecule of glucose used, fermentation yields 2 molecules of ATP 

• glycolysis + pyruvate oxidation + citric acid cycle + respirator chain → yield 36 ATP 

Metabolic Pathways- Catabolic Pathways

• catbolic pathways feed into the respiratory pathways 

• polysaccharides are broken down into glucose which enters glycolysis 

• glycerol from fats also enter glycolysis and acetyl CoA from fatty acid degradation enters krebs 

• proteins enter glycolysis and the citric acid cycle via amino acids

Metabolic Pathways- Anabolic Pathways

intermediate components of respiratory metabolism synthesizes fats, amino acids, and other essential building block for cellular structure and function

Exercise Physiology

• brach of biology that deals with the bodys biolgocial response to exercis e

• Aerobic fitness 

• ability of the heart, lungs & blodstreem to supply oxygen to cells → during physical activity 

• total physical fitness detemied by factors:

  •  aerobic fitness muscular strength and endurance, flexibility, body composition 

VO2 Max

• Maximum volume of oxygen (mL): cells of the body can remove from the bloodstream in one minute per kilogram of body mass while the body experiences maximal exertion 

• measured with a treadmill exercise test 

• higher VO2 max values→ more physically fit

• Lower VO2 values → less physically fit 

• typically value: 35 mL/kg/min 

• elite athletes: 70 mL/kg/min

Lactate Threshold

• Lactate fermentation occurs continuously as one exercise 

• Lactate threshold (LT): value of exercise intensity at which blood lactate concnetration begins to increase sharply 

• once threshold is reached → exercise may be limited to pain, stiffness and fatigue 

• untrained individuals → LT at 60% VO2 max 

• elite athletes → LT at 80% VO2 max