Lecture 3: Out in the Cytosol

What is the conservation of energy?

Energy cannot be created nor destroyed, rather, it can only be transferred from one form to another

What are the three ways energy is used for within the muscle?

- Chemical work

-Mechanical work

-Transport work

What is Chemical work?

synthesis of cellular molecules (forming ATP)

What is Mechanical Work?

muscle contraction (crossbridge power stroke)

What is Transport Work?

pump substances against concentration gradient to maintain concentrations (action potentials, Ca+ reuptake to SR)

What is metabolism? What are the two types?

Metabolism: describes the sum of cellular processes

• Anabolism

• Catabolism

What is Anabolism?

smaller molecules are combined to make larger molecules

• Requires energy in

• Forms or repairs tissues

• "Storage" of energy as bonds

What is Catabolism?

larger molecules are broken down to make smaller molecules

• Releases energy

• Involves breakdown of tissues and fuels

• Liberates energy from bonds

Why are muscle demanding energy?

• Activity (and movement) requires energy to power crossbridge powerstrokes for muscles to produce force and/or movement

• Adenosine Triphosphate (ATP) is the energy currency of the body

• Muscular ATP storage is low (~6mmol/kg of muscle)- Lasts 1-3 seconds

What is ATP?

Adenosine Triphosphate (ATP) breakdown provides energy required for muscle cell function

What does the breakdown of ATP cause?

Breakdown of ATP into ADP and Pi referred to as "hydrolysis" as chemical bond is broken through addition of water

Breaking of chemical bonds.....

releases energy

1 ATP=

1 crossbridge formation

Within the muscle what are the three ways that ATP is used?

• Crossbridge power stroke (Myosin ATPase) (~70%)

• Re-sequester Calcium to SR (Ca2+ ATPase) (25-30%)

• Restore membrane resting Na+ and K+ balance (Na+ /K+ ATPase (<5%)

What are the two limiting factors for metabolic processes?

• Substrate (fuel) availability

• Enzyme availability

What is Substrate (fuel) availability?

• Mass Action:

• More substate results in faster rate (more reactions)

• Less substrate results in slower rate (fewer reactions)

What is Enzyme availability?

• Enzymes ("-ase"s) lower activation energy • More enzymes results in more reactions

What are the 4 energy sources that we use?

• Stored ATP

• Stored Phosphocreatine

• Glycolysis

• Oxidative (Aerobic) Phosphorylation

What energy sources are anaerobic?

(doesn't require oxygen) Occurs in cytosol

1. Stored ATP

2.Stored Phosphocreatine 3. Glycolysis

What energy sources are aerobic?

Aerobic (Requires oxygen) Occurs in mitochondria

1. Oxidative (Aerobic) Phosphorylation

For stored ATP- Energy Source, Fuels, Timeframe, By-products and Activity Examples

Fuels -ATP

Timeframe- <2s

Byproducts- none

Activity- Single Jump and Standing up

For Phophocreatine - Energy Source, Fuels, Timeframe, By-products and Activity Examples

Fuels- CP

Timeframe- 0-20s

By-products- Cr and ATP

Activity- 100m sprint, Jumping and Power lifting

For Glycolytic - Energy Source, Fuels, Timeframe, By-products and Activity Examples

Fuels- CHO

Timeframe- 15-120s By-products- Lactic acid, ATP and CO2 Activites- 200m sprint, 800m sprint and Resistance training

For Aerobic - Energy Source, Fuels, Timeframe, By-products and Activity Examples

Fuels- CHO, Fats and Protein

TimeFrame- 120s-several hours

By-Products ATP and CO2

Activities- Distance running 1500m and Marathon

ATP is...

available (fast fast fast) but in a VERY limited in supply

What is glycolysis?

Partial breakdown of glucose through series of enzyme-driven fermentation reactions

What is glycgenolysis?

Partial breakdown of glycogen through series of enzyme-driven fermentation reactions

The process of Glycolysis and Glycogenolysis requires __________ to begin?

glucose-6-phosphate

• Conversion of Glucose costs 1ATP

• Conversion of glycogen costs 0ATP(free)

What are the two possible outcomes of Glycolysis and Glycogenolysis?

• Pyruvate as end-product - results in continued CHO breakdown

• Pyruvate converted to lactate, lactate as end-product Glucose Time M

What is lactate formation?

• Without anywhere for pyruvate or NADH to go, they accumulate:

• Limited NAD+ prevents glycolysis

• Accumulation of Pyruvate inhibits glycolysis (mass action)

• Conversion of Pyruvate to Lactate solves both problems

- Conversion of Pyruvate to Lactate enables continued glycolysis