Chapter 6 Energy and Metabolism

You Should Know

•  Examples of endergonic and exergonic reations

•  The key role of ATP in energy coupling

•  Enzymes work by lowering the activation energy

•  The factors that influence enzyme activity

•  Anabolic and catabolic reactions

Energy: The Capacity to do WORK

Kinetic energy (KE): energy associated with motion - Heat (thermal energy) is KE associated with random movement of atoms or molecules

Potential energy (PE): stored energy as a result of its position or structure

- Chemical energy is PE available for release in a chemical reaction

Energy can be converted from one form to another

ex. chemical à mechanical à electrical

Energy: Redox Reactions

Reduction (receiving electrons) couples with

Oxidation (donating electrons)

Reduced form of a molecule has HIGHER level of energy than the oxidized form

Thermodynamics Study of energy transformations that occur in nature

First Law of Thermodynamics Conservation of Energy: Energy cannot be created or destroyed Within living organisms, chemical potential energy stored in some molecules can be transferred to other molecules and stored in different chemical bonds.

During each conversion, energy is dissipated as heat.

Second Law of Thermodynamics Entropy increases: Disorder in the universe is continuously increasing

Disorder is more likely than order.

It takes energy (work) to counteract entropy.

Free Energy (G) The energy available to do work in any system.

Gibbs free energy is EQUAL to the enthalpy (energy contained within a molecule’s chemical bonds) MINUS (entropy TIMES temperature):

As chemical reactions produce changes in free energy, we can use the change in free energy to predict whether the reaction will occur spontaneously:

A cell does three kinds of work: Chemical Transport Mechanical

Cells manage energy resources to do work by energy coupling: using an exergonic process to drive an endergonic one

Activation Energy Before new chemical bonds can form (even less energy intensive ones), existing bonds must be broken. That requires energy…

Catalysts

Adenosine Triphosphate (ATP) -  Cells release and store energy in the bonds of

ATP (currency of energy in the cell) -  Nucleotide:

-  5-c sugar -  (ribose)

-  Nitrogenous base -  (adenine)

-  Phosphate groups ** -  (3 of them)

Adenosine Triphosphate (ATP) When the bonds between the phosphate groups are broken by hydrolysis à energy is released.

This drives endergonic reactions.

The release of energy comes from the chemical change to a state of lower free energy, not in the phosphate bonds themselves

Adenosine Triphosphate (ATP)

Enzymes -  Biological catalysts; most are proteins (some RNA) -  Enzymes facilitate substrates to undergo chemical

reactions

-  Lowers activation energy

-  Not changed or consumed

-  Recycled -  High specificity

Enzymes: Lowers Activation Energy

Enzymes: Active Site

Enzyme Action

Enzyme Action

Enzyme Action

Enzymes Induced Fit: enzyme snugly fits around substrate

Enzymes Occur in Many Forms -  Multi-enzyme complexes (stable assemblies of

more than one enzyme, usually involved in sequential catalytic transformation)

-  Non-protein enzymes (RNA based; ribozymes can act upon themselves or on other molecules)

An enzyme’s activity can be affected by: –  temperature – pH – concentrations – chemicals

Cofactors: non-protein enzyme helpers such as minerals (i.e., Zn, Fe, Cu) Coenzymes: organic cofactors (i.e., vitamins) Competitive inhibitor: binds to the active site of an enzyme, competes with substrate Noncompetitive inhibitor: binds to another part of an enzyme à enzyme changes shape à active site is nonfunctional  

Enzymes: Activators and Inhibitors

Inhibition of Enzyme Activity

To regulate metabolic pathways, the cell switches on/off the genes that encode specific enzymes Allosteric regulation: protein’s function at one site is affected by binding of a regulatory molecule to a separate site (allosteric site)

Activator – stabilizes active site Inhibitor – stabilizes inactive form Cooperativity – one substrate triggers shape change in other active sites à increase catalytic activity

Enzymes: Activators and Inhibitors

The totality of an organism’s chemical reactions Manages the materials and energy resources of a cell

Metabolism

Catabolic pathways release energy by breaking down complex molecules into simpler compounds (ex. digestive enzymes break down food à release energy) Anabolic pathways consume energy to build complex molecules from simpler ones (ex. amino acids link to form muscle protein)

Stepwise fashion:

Metabolism

Feedback inhibition regulates some biochemical pathways:

Chapter 6 Review •  Define metabolism. •  List 3 forms of energy. •  What are the 1st and 2nd Laws of Thermodynamics? •  Is the breakdown of glucose in cellular respiration

‘exergonic’ or ‘endergonic?’ •  What type of factors can affect an enzyme’s activity

on a substrate?