An Introduction to Metabolism

Metabolism, energy and lifeEnzymesThe control of metabolism

Metabolism

Metabolism- totality of an organism’s chemical reactions

Metabolism

Catabolic pathways- release energy by breaking down complex molecules to simpler compounds

Metabolism

Anabolic pathways- consume energy to build complex molecules from simpler compounds

Energy

Energy- capacity to do work Kinetic energy- the energy of motion Potential energy- the capacity to do work,

energy stored as a result of its location or structure

Chemical energy- form of potential energy- stored in molecules as a result of the arrangement of the atoms

Metabolism, energy, and life

Metabolism = anabolism + catabolism

Metabolic reactions are organized into pathways

Energy: kinetic and potential

Thermodynamics

Thermodynamics- study of energy transformations

The First Law- the energy of the universe is constant

Energy can be transferred and transformed but it cannot be created or destroyed

“principle of conservation of energy”

Thermodynamics

The Second Law- Every energy transfer or transformation increases the entropy of the universe

Entropy- the measure of disorder

Free Energy- the portion of a system that can perform work It is available for work Symbol is G

Exergonic reaction- “energy outward”Proceeds with a net release of free energyOccurs spontaneouslyEndergonic reaction- “energy inward”

absorbs free energy from its surroundingsnonspontaneous

Energy Coupling- the use of an exergonic process to drive an endergonic one

Cells are kept alive with a flow of energyThe products of a reaction become the

reactants of the next reaction.

Rube Goldberg Machine

Cellular Work

1. Mechanical work 2. Transport work 3. Chemical work

ATP

Adenosine Triphosphate Adenine bonded to riboseRNA has one phosphate group attached to riboseATP has three phosphate groups attached to ribose

ATP to ADP

Phosphate bonds- broken by hydrolysis Without 3rd Phosphate Group= Adenosine

Diphosphate (ADP) and inorganic phosphate

ATP + H2O → ADP + Pi

Test tube: Change in G = -7.3 kcal/molCell: Change in G= -13 kcal/mol

ATP to ADP

Is this reaction Exergonic or Endergonic? Exergonic- ADP is more stable than ATP,

energy is released with the loss of Pi

Negative G value

Phosphorylation

Pi is not transferred into solution, given to another compound

Compound receiving the Pi is phosphorylated.

ATP cycle

ATP + H2O → ADP + Pi

Change in G =-7.3 kcal/molADP + Pi → ATP + H2O

Change is G = 7.3 kcal/mol

Enzymes

Catalyst- chemical agent that changes the rate of a reaction without being consumed by the reaction

Enzyme- catalytic protein

Activation Energy or “free energy of activation” – the energy required to break the bonds in the reactants

Symbol- EA

Cellular issue with heat

Induced fit hypothesis

Change in the shape of an enzyme’s active site, which is induced by the substrate.

Enzyme-substrate complex

Substrate held by weak interactions- hydrogen and ionic bonds

R-groups of amino acid chain of the protein catalyze the substrate

Lowering the EA

Active site • Stresses critical bonds that must be broken• Can provide a microenvironment

Ex: Acidic R groups form a pocket of low pH

• Brief bonding- covalent bonding between substrate and R groups

Rate of reaction

Determined by the concentration of substrate and enzyme

Saturation point

Temperature and pH

Optimal TemperatureOptimal pH

Cofactors

Bind to active site permanently or loosely Inorganic Organic- coenzyme

Inhibitors

Competitive inhibitors- block active site Noncompetitive inhibitors- bind to another

part of enzyme Types: poison, antibiotics

When is it useful to inhibit enzymes?

Allosteric regulation

Allosteric site- specific receptor site on enzyme away from active site

Can activate or inhibit

Feedback inhibition

Most commonPathway switch off by its end product

Cooperativity

Substrate induces enzyme to accept more substrates

Multienzyme complex

Team of enzymes assembled together

Ex: Mitochondria in eukaryotic cells- enzymes for respiration are clustered together