How Does Energy Behave in the Universe?

• Connection between breathing & life is an ancient one

– Exchange of gases is part of what it means to be alive
– Outward sign of metabolism
– Result of metabolism

• Organic substances are made or converted to other organic molecules
• Energy can take different forms, but it is always conserved

– Before 1807, different forms of energy (light, heat, movement) were studied separately; now energy is the term used to denote anything that can do work

• First Law of Thermodynamics

– Energy may change form, but
– It may neither be created nor destroyed
– There is as much energy in the universe now as there ever was or will be

• Second Law of Thermodynamics

– Changes always occur
– In a direction in which the energy of the universe becomes more disordered

• Entropy – The amount of disorder in universe
• Second Law says

– Entropy will continue to increase until every area of the universe has exactly the same amount of energy, i.e., equilibrium

• In time, entropy will reach its maximum

• • Equilibrium – Condition of maximum entropy
•  Second Law says that
• – Without an infusion of energy from an outside system all systems spontaneously move closer to equilibrium at all times
• – When a system reaches equilibrium no more changes occur unless it gets energy from outside

• Kinetic energy – Energy that is doing work or causing an effect on matter

• Potential energy – Energy that is stored or inactive – Occurs before fuel molecules are oxidized

• Oxidation • Controlled release of energy

Enzymes

• • Metabolism – Highly specific process
• – Specificity & efficiency in metabolism is achieved by enzymes (proteins that catalyze [speed up] metabolic steps)
• • Properties of enzymes & enzyme-catalyzed reactions
• – The Induced Fit Model of the enzyme active site and enzyme action
• – Temperature & enzyme activity
• – pH & enzyme activity
• • Enzyme activity is influenced by pH
• •
• • Metabolic efficiency
• – First hallmark of enzyme-catalyzed reactions
• – Most efficient reaction either captures as much energy as possible from
• • Energy-yielding reactions or
• • Spends as little energy as possible to catalyze a reaction that consumes energy
• • Metabolic specificity
• – Second hallmark of enzyme-catalyzed reactions
• – Given enzyme only binds to a specific kind of molecule (its substrate) - one or few at most

ATP - The Energy Currency of Life

• • Adenosine triphosphate (ATP)
• – Modified ribonucleotide containing three phosphates & adenine
• • Main energy currency molecule in living organisms
• • Adenosine is a combination of
• – Nitrogen-containing base (adenine) & 5-carbon sugar
• • It can connect with 1 phosphate to make Adenosine monophosphate (AMP) or with 2 phosphates (adenosine diphosphate - ADP)
• • 3rd phosphate on ATP can be broken off – easily leaving ADP & 1 phosphate, releasing energy in the process

ATP Cycle
Cellular Respiration

• Cellular respiration is

– The name given to metabolic pathways in which cells harvest the energy from the metabolism of food molecules

• Glucose breakdown is one of the main pathways of cellular respiration and occurs in 3 stages

– Glycolysis
– Krebs cycle
– Electron transport system

Glycolysis

• • Universal energy-harvesting process of life, very primitive
• – Evolved early in life’s history
• – Means “sugar-splitting”
• • 6-C sugar glucose is split in half to make two 3-C compounds
• – Uses no oxygen
• • Sometimes called anaerobic (not requiring oxygen)
• • Pathway of cellular respiration

Krebs Cycle

• • Completes breakdown of glucose to single carbon molecules
• – The process is aerobic (requires oxygen)
• • Completes breakdown of glucose to single carbon molecules
• – Takes derivatives of two 3-C glycolysis products
• – Breaks them apart & strips Cs of their H atoms
• • Leaves behind six CO2 molecules
• • Does not require O2 – prelude to the next cell respiration stage in which O2 is required

Electron Transport System (ETS)

• • Both glycolysis & Krebs cycle
• – Transfer H atoms from Cs of glucose to molecules of NAD+ to make NADH
• • Because the process requires oxygen it is called oxidative phosphorylation

Photosynthesis

• – Uses light energy to make food and is
• – A process by which some organisms can make organic compounds from simple inorganic compounds using energy from the sun
• • First two forms in which light energy is captured are ATP & NADH
• – To make ATP & NADH - light required
• • Absorbed light energy is used to make them
• • Made in the 1st phase of photosynthesis – light-dependent reactions

– Carbohydrates in 2nd phase of photosynthesis which is independent of light

• This 2nd phase is called the light-independent reactions

· • Chloroplasts are the sites of photosynthesis

· – They are large, green, organelles surrounded by 2 membranes (inner & outer)

Return to Syllabus