BIOENERGETICS

By Olena Rodina

Bioenergetics

• Life is an energy intensive process.

• It takes energy to operate muscles, extract wastes, make new cells, heal wounds, even to think.

Bioenergetics

• A discipline within biochemistry dedicated to the study of energy flow within living systems

• What Is Energy?

Question:

Energy

• Capacity to perform work

• Two examples:

1. Kinetic energy

2. Potential energy

Kinetic Energy

• Energy in the process of doing work.

• Energy of motion.

• Examples:

1. Heat

2. Light energySUN

Potential Energy

• Energy that matter occupies because of it’s location, arrangement, or position.

• Energy of position.

• Examples:

1. Water behind a dam

2. Chemical energy (gas) GAS

Thermodynamics

• The study of energy transformations that occur in a collection of matter.

• Two Laws:

1. First Law of Thermodynamics

2. Second Law of Thermodynamics

First Law of Thermodynamics

• Energy cannot be created or destroyed, but only converted to other forms.

• This means that the amount of energy in the universe is constant.

The First Law is not much help...What prevents a melting ice cube from

spontaneously refreezing?

Why doesn’t water flow uphill?

Will L-alanine convert into D-alanine?

The energy of the system and its surrounds won’t

change.

If it does not occur, what is driving force?

The Second Law helps resolve problem

Only those events that result in a net increase in disorder will occur

spontaneously

Second Law of Thermodynamics

• All energy transformations are inefficient because every reaction results in an increase in entropy and the loss of usable energy as heat.

• Entropy: the amount of disorder in a system.

What Can Cells Do with Energy?

Cells use energy for:

–Chemical work

–Mechanical work

–Electrochemical work

What Can Cells Do with Energy?• In some cells, as much as half of a cell’s energy

output is used to transfer molecules across the cell membrane, a process called ‘active transport.’

• Cell movements require energy and thousands of energy-hungry chemical reactions go on in every living cell, every second, every day.

• The kind of energy cells use is chemical bond energy, the shared electrons that holds atoms together in molecules

Endergonic and Exergonic reactions

Endergonic Reactions

• Chemical reaction that requires a net input of energy.

• Example:

1. Photosynthesis

6CO2 + 6H2O C6H12O6

+ 6O2

SUNphotons

LightEnergy

(glucose)

Exergonic Reactions

• Chemical reactions that releases energy.

• Example:

1. Cellular Respiration

C6H12O6 + 6O2 6CO2 + 6H2O + ATP(glucose)

Energy

Cellular MetabolismCells use thousands of different chemical

reactions

this is what is referred to by the term

metabolism

Cellular Metabolism

• In general, metabolism can be split into 2 groups of reactions:

· Catabolism, which breaks down molecules, releasing energy. Some of the energy is captured in the bonds of ATP

· Anabolism, which uses energy from ATP to synthesize large molecules, including macromolecules

Exergonic and Endergonic reactions

Anabolic Pathway

• Metabolic reactions, which consume energy (endergonic), to build complicated molecules from simpler compounds.

• Example:

1. Photosynthesis

6CO2 + 6H2O C6H12O6 + 6O2

SUNlightenergy

(glucose)

Catabolic Pathway

• Metabolic reactions which release energy (exergonic) by breaking down complex molecules in simpler compounds.

• Example:

1. Cellular Respiration

C6H12O6 + 6O2 6CO2 + 6H2O + ATP(glucose)

energy

Question:

• What is ATP?

Answer:• ATP is the universal energy carrier

• Most cell processes use the same energy source, the rechargeable energy carrier,

adenosine-tri-phosphate ATP.

ATP Components

1. adenine: nitrogenous base

2. ribose: five carbon sugar

3. phosphate group: chain of three

ribose

adenine

P P P

phosphate group

• How does ATP work?

Answer:• The phosphate groups are held to each other

by very high energy chemical bonds. • Under certain conditions, the end phosphate

can break away and the energy released to the energy-hungry reactions that keep a cell alive.

Answer:• When the end phosphate is released, what is

left is ADP, adenosine diphosphate. • This change from tri to di is taking place

constantly as ATPs circulate through cells.• The recharging of ADP to ATP requires a

huge energy investment, and that energy comes from the food we eat.

Hydrolysis of ATP• ATP + H2O ADP + P (exergonic)

Hydrolysis(add water)

P P P

Adenosine triphosphate (ATP)

P P P+

Adenosine diphosphate (ADP)

Dehydration of ADPADP + P ATP + H2O (endergonic)

Dehydration synthesis (remove water)

P P P

Adenosine triphosphate (ATP)

P P P+

Adenosine diphosphate (ADP)

Cells Get Most of Their Energy by Oxidizing Carbohydrates, Lipids &

Proteins

Carbohydrates as energy sources

• The storage sugar, glycogen is broken down to glucose when needed

• Almost all cells "burn"glucose (6 carbon sugar) to get energy

• Glucose is metabolized by glycolysis to pyruvate

• The pyruvate can be further metabolized to acetylCoA, which enters the Krebs cycle

Lipids as energy sources

• Storage fats, triglycerides, are broken down into fatty acids & glycerol

• Fatty acids are split into 2 carbon pieces, acetylCoA, which feed into the Krebs cycle

Proteins as energy sources• Proteins are degraded to amino acids• After the amino group is removed different

amino acids feed into both glycolysis and the Krebs cycle

• The nitrogen from the amino group is eliminated as urea

ATPForms

Cellular Work

Energy Releasing Reactions

Energy Requiring Reactions

To maintain your body at rest you need about 2000 Calories/day

• This is called the basal metabolic rate (BMR) • You could get this much energy from 500 grams

of sugar (2000 gm/4 cal/gm = 500 gm) or from 222 gm of fat (2000 gm/9 Cal/gm = 222 gm)

• In the American diet about 65% of our energy comes from sugar and 35% from fat

ATP: Main Energy Carrier

• ATP couples energy inputs and outputs

• ATP/ADP cycle regenerates ATP

energyinput

ADP + Pi

ATP

energy output

How energy is extracted from food molecules and used to synthesize ATP is one of the great discoveries of modern biochemistry.