Biology Cellular Respiration

Rate of cellular respiration 

• due to supply and demand 

  • High demand when working/ low when resting 

• Basal Metabolic rate

  • Amount of energy expended per unit time at rest

  • Measured in oxygen consumption

BMR

the minimum energy your body needs to stay alive at rest.

Measured in oxygen consumption

• Cellular respiration consumes oxygen in the ETC during oxidative phosphorylation.

• The more ATP the body needs, the more oxygen your cells consume.

• So oxygen consumption is a way to measure the rate of cellular respiration.

Regulating cellular respiration

Key idea: Feedback control of enzymes

• Many enzymes in cellular respiration are controlled by feedback.

• Feedback inhibition: When there’s enough product (ATP), the enzyme slows down → prevents making too much ATP.

• Feedforward activation: When there’s more substrate or need (ADP), the enzyme speeds up → makes more ATP.

• Phosphofructokinase (PFK) — the most important regulator

  • PFK is a key enzyme in glycolysis (converts fructose-6-phosphate → fructose-1,6-bisphosphate).

  • Often called the rate-limiting step because it controls the overall pace of glycolysis

  • How PFK is regulated

    1. Buildup of ATP inhibits PFK ✅

       • High ATP → cell has plenty of energy → glycolysis slows

       • This prevents waste of glucose when energy is already sufficient

    2. Increase in ADP (or AMP) activates PFK ✅

       • Low ATP → high ADP → cell needs energy → glycolysis speeds up

       • Ensures more glucose is broken down to make ATP

    3. Decrease in citrate activates PFK ✅

       • Citrate is a Krebs cycle intermediate

       • Low citrate → Krebs cycle is not overloaded → glycolysis can speed up

       • High citrate → Krebs cycle is backed up → slows glycolysis

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