Powering Life: An Introduction to Energy

Copyright © 2007 Pearson Prentice Hall, Inc.

Life runs on energy

• Metabolism

• Energy

Fig. 4-2, p. 63

Light energy radiating from the sun reaches Earth. Producers capture some of it by converting it to chemical energy. They and all other organisms use chemical energy to drive cellular work.

ENERGY IN

PRODUCERSplants and other self-

feeding organisms

nutrient cycling

CONSUMERSanimals, most fungi,

many protists, bacteria

ENERGY OUT

With each conversion, there is a one- way flow of a bit of energy back to the environment, mainly in the form of heat.

Biological Energy Transformations

All forms of energy can be placed in two categories:

• Potential energy is stored energy—as chemical bonds, concentration gradient, charge imbalance, etc.

• Kinetic energy is the energy of movement

Energy is Central to Life

• Energy can be converted from one form to another– A peach tree uses light energy to make

sugars• “Photosynthesis”• Solar energy is converted to chemical energy

– We eat a peach and can burn these sugars to release energy

Energy is Central to Life

• Energy released from chemical reactions can be converted into ATP– Adenosine triphosphate– Energy transfer molecule

Laws of energy1. First law of energy

Laws of energy1. First Law of Thermodynamics

• total amount of energy in the universe is constant

• energy can not be created by a cell; it can only be borrowed from someplace else

• energy can be converted from one form

to another

Laws of energy2. Second law of energy

Laws of energy2. Second Law of Thermodynamics• the spontaneous direction of energy

flow is from high energy forms to low energy forms

- entropy is increased

• energy can not change forms with out a loss of unavailable energy (heat)

In a steam engine, energy stored in chemical bonds of coal is transformed into heat

energy and mechanical energy. There is no loss of energy in this process, but energy is transformed from a more-ordered, concentrated form (the chemical bonds of coal) to a

less-ordered, more dispersed form (heat). The amount of disorder-or entropy-increases in the transaction.

Energy is Central to Life

• The Arctic people produce more heat– Aids in staying warm

• This heat production is the result of less efficient energy harvesting– Leaves less energy for other uses

series of energy transformations involved from peach tree photosynthesis to muscle activity

• Some sugars from a peach you eat can be stored for later use

• Sugars can be combined to form glycogen– This reaction “costs” energy- ATP

• Sugars can later be released from glycogen– This release yields energy- ATP

• Cellular respiration

1. ATP2. ADP

Fig. 4-5, p. 65

adenine

three phosphate groups

ribose

adenine AMP ADP ATP

ribose P P P

3. ATP/ ADP cycle

p. 65

ATP forms in energy-requiring reactions

ATP drives energy-requiring reactions

ADP + phosphate

Figure 8.6 Coupling of Reactions

Exergonic and endergonic reactions are coupled.

Active transport of Ca ++ requires energy

The Energy Molecule: ATP

• Energy is stored in the form of ATP for only brief periods of time

• Long-term energy storage is accomplished by glycogen and fat

–These molecules can be broken down and “burned” to generate ATP for immediate use

Enzymes

Fig. 4-1, p. 62

p. 67

p. 67

Enzymes

1. proteins that serve as catalyst

Rate

Enzymes

• Enzymes only accelerate reactions that would occur anyway

–Reactions would occur so slowly without enzymes, that their rate is essentially zero

• Enzymes enable these reactions to occur at a rate sufficient to sustain life

Enzymes

• Enzymes are protein catalysts

–As proteins, the production of enzymes is encoded by units of DNA called genes

•Damaged gene no enzyme produced

Enzymes• Many inherited disorders are caused by the

inability to produce a specific enzyme

• Lactose intolerance- Reduce production of the enzyme lactase after childhood

- Intestinal bacteria eventually break down the lactose– This bacterial breakdown produces gas– Uncomfortable symptoms arise from this gas

production

Enzymes

• Lactase is only one of thousands of enzymes known to exist

• Enzymes facilitate virtually every chemical process that takes place in living things

–Survival depends on enzymes

Enzymes

1. proteins that serve as catalyst

2. lower the energy of activation

Activation Barriers & Enzymes

• For any chemical reactions to occur, an initial input of energy is required– “Activation energy”

• Enzymes function by reducing the required energy input– Reducing the activation energy

Activation Barriers & Enzymes

• Binding to an enzyme makes the substrate molecules more vulnerable to chemical alteration– Substrate molecules become more vulnerable

to chemical alteration– Activation energy is lowered

Enzymes

1. proteins that serve as catalyst

2. lower the energy of activation

3. can be reused

4. their actions are reversible

Enzymes

1. proteins that serve as catalyst

2. lower the energy of activation

3. can be reused

4. their actions are reversible

5. selective and act upon specific substrates

Enzymes

• Enzymes bind to their substrates

–Lock-and-key fit

–Substrate binds to enzymes “active site”

p. 66

Enzymes

• We possess many thousands of enzymes

• Each enzyme facilitates a specific reaction

– Lactase: lactose glucose + galactose

– Sucrase: sucrose glucose + fructose

– RNA polymerase: nucleotides RNA

EnzymesAn example: The enzyme chymotrypsin• Digestive enzyme produced in the pancreas• Works with water to break down proteins in the

small intestine– Breaks bonds between adjacent amino acids

• Chymotrypsin binds to a portion of the protein• Protein shape is distorted• Protein now vulnerable to reaction with water

molecules• Protein chain is clipped• Repeat

Enzymes

• Enzyme helpers/ coenzymes

• Some enzymes require one or more accessory molecules

• Derived from vitamins

Fig. 4-9, p. 68

glucose

++oxygen water

spark

A Glucose and oxygen react (burn) when exposed to a spark. Energy is released all at once as light and heat when CO2 and water form.

carbon dioxide

carbon dioxide

glucose e–

oxygen H+

e–

water

B The same overall reaction occurs in small steps with an electron transfer chain. Energy is released in amounts that cells can harness for cellular work.

1 Energy input splits glucose into carbon dioxide, electrons, and hydrogen ions (H+).

2 Electrons lose energy as they move through an electron transfer chain.

3 Energy released by electrons is harnessed for cellular work.

4 Electrons, hydrogen ions, and oxygen combine to form water.

Stepped Art

Enzymes

• Many activities of living things are multistep processes

– Blood clotting, leaf growth, digestion

• Each step requires a different enzyme

• This series of reactions is termed a metabolic pathway

- reactant product

Animation 6-2

•enzymes

Metabolic pathways

• Metabolism is the sum of all chemical reactions within a cell or larger organism

–Some reactions build things up

–Some reactions break things down

Metabolic pathways

1. reactants

2. end products

p. 64

Reactants End Products

2 H2 (hydrogen)

2 H2O (water)

4 hydrogen atoms + 2 oxygen atoms

4 hydrogen atoms + 2 oxygen atoms

O2 (oxygen)

+

Metabolic pathways

3. biosynthetic pathway

• endergonic reaction

Endergonic Reactions / biosynthetic pathway pathways

Metabolic pathways

4. degradative pathway

• exergonic reaction

Exergonic reaction / degradative pathway

Animation 6-1

•Metabolic pathways

Bioluminescence is an endergonic reaction driven by ATP hydrolysis:

lightPPAMPinoxylucifer

ATPOluciferin

i

luciferase

2

Figure 8.5 ATP (Part 2)