Cellular Energy: ATP & Enzymes. What is it? Where do we get it? How do we use it?

Cellular Energy: ATP & Enzymes What is it? Where do we get it? How do we use it? Energy • The capacity to perform work; ability to rearrange matter ...
Author: Duane Hunt
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Cellular Energy: ATP & Enzymes What is it? Where do we get it? How do we use it?

Energy • The capacity to perform work; ability to rearrange matter • Energy is required to drive reactions • 2 forms: – Potential Energy (PE): stored energy, due to position of structure – Kinetic Energy (KE): Energy of motion • Heat is KE associated with the movement of molecules/atoms within matter

Energy is just transformed • Total amount of Energy in Universe is constant (1st Law) – Nothing created or destroyed, only transformed

• One result of ALL energy transfers is the production of heat (2nd Law) – Heat = disordered, unharnessed KE. This KE is LOST; cannot be used to perform work

Energy is lost during rxns

Chemical Reactions • Endergonic (energy input): Store Energy – products have higher energy than reactants; Anabolic • Exergonic (energy output): Release Energy – products have lower energy; Catabolic

Endergonic/Anabolic • Photosynthesis: – Reactants = CO2 & H2O + light energy – Products = sugar molecules

Exergonic/Catabolic • Bonfire – Reactants: Cellulose (glucose), O2 – Products: light, heat, CO2, H2O

• Cellular respiration “burns” glucose to harness energy for work

Anabolic and Catabolic Reactions ANABOLIC REACTIONS Glycogen

Uses energy

Uses energy







Uses energy +

Fatty acids

Amino acids + Amino acids



Yields energy



Yields energy


Fatty acids

Yields energy

Amino acids

Yields energy

Cellular metabolism • The sum of all cellular endergonic and exergonic rxns. • Energy coupling (transfer) = use of released energy to run cellular processes • ATP provides coupling mechanism


• High energy bonds join negatively charged phosphate groups – Energy in bonds + energy of magnetic repulsion (high PE!)

• Hydrolysis rxn frees trapped energy

ATP • Some freed energy is lost as heat • The rest is transferred via the phosphate group when it binds to another molecule (phosphorylation)

ATP fuels ALL cellular work

ATP is continually regenerated

Enzymes are also required to drive reactions

Enzymes lower Activation Energy • Some energy (EA) must be applied to begin a rxn – Sometimes the energy barrier is prohibitively large – Enzymes reduce that barrier, allowing rxn to proceed with LESS energy input

Enzyme cycle 1. Available enzyme w/ active site 2. Substrate binds 3. Conversion to products 4. Products released

Enzymes possess: • Ideal temperature regimes • Ideal pH ranges • Cofactors (inorganic molecules & ions) and coenzymes (organic molecules)

What fuels our bodies? 1. 2. 3. 4.

Adenosine triphosphate (ATP) Creatine Phosphate (CP) Glucose Fats

What fuels our bodies? • Adenosine triphosphate (ATP) – THE energy carrying molecule in the body • Muscles store only enough ATP for 1 – 3 seconds of activity – ATP must be generated continuously • Usually via carbohydrate metabolism with or without O2

ATP structure

Alternative Fuels • After depleting ATP stores, muscles turn to other sources: – Creatine phosphate (CP) stores energy that is used to make ATP – Creatine phosphate stores enough energy for 3 to 15 seconds of maximal physical effort

CP transfers P to make ATP

Glucose • After CP, Glucose is the next source of energy for production of ATP • Metabolism of glucose – Anaerobic breakdown of glucose yields 2 ATP molecules (no O2) – Aerobic breakdown of glucose yields 36 – 38 molecules of ATP (with O2)

Glucose metabolism

In cytoplasm

In mitochondria

Fat as fuel • Stored triglycerides can be metabolized to generate ATP – For low intensity exercise – For exercise of long duration • Ex: 10 hr. car-to-car approach + climb

– Abundant energy source. – Provides 2x more energy per gram as carbohydrate

Carbs. or Fats • Use BOTH as energy sources for production of ATP – Carbohydrates - high intensity activity – Fats - low intensity exercise

• Proteins (amino acids) rarely used as a fuel source for exercise

Distribution • Short duration, max. int. (0-3 sec) • Short duration, high int. (1012 sec) • Short-Mid duration, high int. (4-6 min) • Mid duration, moderate int. (32-40 min) • Long duration, moderate int. (2.5-3 hr) • Extended duration, low-mod int. (5.5-7 hr)

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