Energy Transformation, Cellular Energy & Enzymes (Outline)

• Energy conversions and recycling of matter in the ecosystem. • Forms of energy: potential and kinetic energy • The two laws of thermodynamic and definitions • Chemical reactions and energy transformation • Biochemical metabolic reactions and pathways • Coupling energy consuming biochemical reactions with the energy

releasing reaction of ATP dissociation • Types of cellular work that require energy (ATP) • Role of enzymes in catalyzing biochemical reactions • Biochemical composition of enzymes and the physical and chemical

factors that regulate their activity • Competitive and non-competitive inhibitors of enzymes.

Figure 1.4-0

ENERGY FLOW

Sun

Inflow of light energy

Producers (plants)

Chemical energy in food

Consumers (animals)

Outflow of heat

Leaves take up CO2 from air; roots absorb H2O and minerals from soil

Decomposers such as worms, fungi,

and bacteria return chemicals to soil

Figure 1.4-1

ENERGY FLOW

Sun

Inflow of light energy

Producers (plants)

Chemical energy in food

Consumers (animals)

Outflow of heat

Leaves take up CO2 from air; roots absorb H2O and minerals from soil

Decomposers such as worms, fungi,

and bacteria return chemicals to soil

– Kinetic energy is the energy of motion – Potential energy is stored energy that can be

converted to kinetic energy

• Chemical bonds are a form of potential energy that can be transformed to energize cellular work

Energy is the capacity to do work

The field of study of energy transformations is Thermodynamics • The First Law of Thermodynamics

Energy can not be created or destroyed, it can be transformed from one form to another

• The Second Law of Thermodynamics Energy transformations increase disorder or entropy of the universe, and some energy is lost as heat.

Energy transformation is not 100% efficient

Figure 5.2B

Heat

Chemical reactions

ATP ATP

Glucose +

Oxygen water

Carbon dioxide +

Energy for cellular work

Chemical reactions either store or release energy Endergonic reactions absorb energy and form

products rich in potential energy

Figure 5.3A

Pote

ntia

l ene

rgy

of m

olec

ules

Reactants

Energy required

Products

Amount of energy

required

Exergonic reactions release energy and yield products that contain less potential energy than their reactants

Figure 5.3B

Reactants

Energy released

Products

Amount of energy

released

Pote

ntia

l ene

rgy

of m

olec

ules

Cells carry out thousands of chemical reactions some exergonic and others endergonic

Cellular metabolism is the sum of all chemical

reactions that take place inside the cell

Energy coupling uses exergonic reactions to fuel endergonic reactions

– ATP powers cellular work by shuttling chemical energy

– The energy in an ATP molecule lies in the bonds between its phosphate groups

Phosphate groups

ATP

Energy P P P P P P Hydrolysis Adenine

Ribose

H2O

Adenosine diphosphate Adenosine Triphosphate

+ +

ADP Figure 5.4A

ATP hydrolysis is the main exergonic reaction used in cellular energy coupling

ATP hydrolysis transfers a phosphate group to a

molecule (phosphorylation). A phosphorylated molecule has a higher potential

energy making it possible for the reaction to take place.

ATP

ADP + P

Energy for endergonic reactions

Energy from exergonic reactions

ATP is a renewable resource that cells regenerate

Figure 5.4C

Figure 5.4B

ATP

Chemical work Mechanical work Transport work

P

P

P

P

P

P

P

Molecule formed Protein moved Solute transported

ADP +

Product

Reactants

Motor protein

Membrane protein

Solute

+

Types of Cellular Work

ENZYMES • Proteins that function as catalysts for

biochemical reactions

• Have a conformation (3D shape) that determines their specific binding to reactants (substrates)

• Lower the energy barriers of chemical

reactions

For a chemical reaction to begin reactants must absorb some energy, called the energy of activation

Figure 5.5A

EA barrier

Reactants

Products 1 2 E

nzym

e

A protein catalyst called an enzyme can decrease the energy of activation needed to begin a reaction

Figure 5.5B

Reactants

EA without enzyme

EA with enzyme

Net change in energy

Products

Ene

rgy

Progress of the reaction

Enzymes, as proteins, have unique three-dimensional shapes that determine which chemical reactions occur in a cell

Each enzyme catalyzes a specific cellular

reaction

Figure 5.6

Enzyme (sucrase) Glucose

Fructose

Active site Substrate (sucrose)

H2O

1 Enzyme available with empty active site

2 Substrate binds to enzyme with induced fit

4 Products are released

3 Substrate is converted to products

The catalytic cycle of an enzyme

The cellular environment affects enzyme activity

– Temperature, salt concentration, and pH – Some enzymes require non-protein components Cofactors- metal ions Coenzymes- organic molecules (vitamin

derivatives) – Enzyme inhibitors interfere with an enzyme’s

activity

– A competitive inhibitor takes the place of a substrate in the active site

– A noncompetitive inhibitor alters an enzyme’s function by changing its shape

Figure 5.8

Substrate

Enzyme

Active site

Normal binding of substrate

Enzyme inhibition

Noncompetitive inhibitor

Competitive inhibitor

Many poisons, pesticides, and drugs are enzyme inhibitors