4.5energetics

Bioenergetics

The study of how cells accomplish this is called bioenergetics.

SUN = Living things main source of energy

What is energy?

• The capacity to bring about movement against opposing forces.

• “The capacity to do work”

Forms of energy

• Potential energy —> chemicals stored

• Kinetic energy —> energy in motion

Thermodynamics

Energy cannot be created or destroyed, it can only be transferred.

• First Law of Thermodynamics: energy can not be created or destroyed, only transformed

  • Can be transformed into potential energy, kinetic energy, heat.

• Second Law of Thermodynamics: It states that energy transfer leads to less organization. 

  • That means the universe tends toward disorder (entropy). 

  • In order to power cellular processes, energy input must exceed energy loss to maintain order. 

    • Cellular processes that release energy can be coupled with cellular processes that require an input of energy.

Types of Reactions

• Exergonic reactions→ Catabolic (break down) → releasing energy

  • Those in which the products have less energy than the reactants.

  • The breakdown of a complex carb → simpler sugars

    • Hydrolysis: polymers→monomers = releasing energy → exergonic (downhill)

  • The course of a reaction can be represented by an energy diagram. You’ll notice that energy is represented along the y-axis.

  • (e.g. cellular respiration)

• Endergonic reactions (uphill) → Anabolic (build up)

  • Reactions that require an input of energy are called endergonic reactions. You’ll notice that the products have more energy than the reactants.

  • Energy in living things is stored away in endergonic reactions

  • The linkage of simple sugars to form a complex carb 

    • Reaction cannot happen without an input of energy 

    • needs energy

    • (e.g. photosynthesis)

  • Dehydration reaction: Monomer(more disorder,simple ) → Polymer(more order, complex)

    • To get from disorder → order , needs energy → endergonic (uphill, energy in)

Enzymes

• A catalyst is something that speeds something up.

• Enzymes are biological catalysts that speed up reactions which are by lowering the activation energy and helping the transition state to form.

• Enzymes do NOT change the energy of the starting point or the ending point of the reaction. They only lower the activation energy.

Enzyme Specificity

• Each enzyme catalyzes only one kind of reaction. This is known as enzyme specificity.

• Enzymes are usually named after the molecules they target. In enzymatic reactions, the targeted molecules are known as substrates.

Enzyme-Substrate Complex

• During a reaction, the enzyme’s job is to bring the transition state about by helping the substrate(s) get into position. It accomplishes this through a special region on the enzyme known as an active site.

• The enzyme temporarily binds one or more of the substrates to its active site and forms an enzyme-substrate complex.

• Enzymes Do: increase the rate of a reaction by lowering the reaction’s activation energy form temporary enzyme-substrate complexes remain unaffected by the reaction

• Enzymes Don’t: change the reaction make reactions occur that would otherwise not occur at all

Induced-fit

• Enzymes and substrates don’t fit together quite so seamlessly. Enzymes have to change its shape slightly to accommodate the shape of the substrates. This is called induced-fit.

• Because the fit between the enzyme and the substrate must be perfect, enzymes operate only under a strict set of biological conditions.

Enzymes Don’t Always Work Alone

• Enzymes sometimes need a little help in catalysing a reaction. Those factors are known as cofactors. Cofactors can be either organic molecules called coenzymes or inorganic molecules or ions.

• Inorganic cofactors are usually metal ions (Fe2+, Mg2+).

• Vitamins are examples of organic coenzymes

Factors Affecting Reaction Rates

• Enzymatic reactions can be influenced by a number of factors, such as temperature and pH. The concentrations of enzyme and substrate will also determine the speed of the reaction.

Temperature

• The rate of a reaction increases with increasing temperature.

• An increase in the temperature of a reaction increases the frequency of collisions among the molecules. But too much heat can damage an enzyme and becomes denatured.

• Enzyme denaturation is reversible if the original optimal environmental conditions of the enzyme are restored.

pH

• Enzymes also function best at a particular pH.

• At an incorrect pH, the hydrogen bonds can be disrupted and the structure of the enzyme can be altered

Relative Concentration of Substrates and Products

• The relative concentration of substrates and products can also affect the rate of an enzyme-catalysed reaction.

• An increase in substrate concentration will initially speed up the reaction. However, once all of the enzyme in solution is bound by substrate, the reaction can no longer speed up.

• This concentration of substrate where all of the enzyme in a reaction is bound by substrate is called the saturation point. Additional substrate past this point will no longer increase the speed of the reaction.

Enzyme Regulation

• A cell can control enzymatic activity by regulating the conditions that influence the shape of the enzyme.

• Enzymes can be turned on or off by things that bind to them. Sometimes these things can bind at the active site, and sometimes they bind at other sites, called allosteric sites.

• If the substance has a shape that fits the active site of an enzyme it can compete with the substrate and block the substrate from getting into the active site. This is called competitive inhibition. You can always identify a competitive inhibitor based on what happens when you flood the system with lots of substrate.

• If the inhibitor binds to an allosteric site, it is an allosteric inhibitor and it is noncompetitive inhibition. A noncompetitive inhibitor generally distorts the enzyme shape so that it cannot function. The substrate can still bind at the active site, but the enzyme will not be able to catalyze the reaction.

Reaction Coupling and ATP

• The cell gets its energy through adenosine triphosphate (ATP).

• ATP consists of a molecule of adenosine bonded to three phosphates. Enormous amount of energy is packed into those phosphate bonds.

• When a cell needs energy, it takes one of these potential-packed molecules of ATP and splits off the third phosphate, forming adenosine diphosphate (ADP) and one loose phosphate (Pi ), while releasing energy in the process. ATP → ADP + Pi + energy

• Organisms can use exergonic processes that increase energy, like breaking down ATP, to power endergonic reactions, like building organic macromolecules.

Sources of ATP

• ATP comes from a process called cellular respiration.

• Cellular respiration is a process of breaking down sugar and making ATP.

• In autotrophs, the sugar is made during photosynthesis.

In heterotrophs, glucose comes from the food we eat.