Energy Flow and Enzymes

What is thermodynamics?

energy changes

What is energy?

the capacity to do work

What are the 2 main types of energy?

kinetic and potential energy

What is kinetic energy?

energy in motion

What is potential energy?

stored energy

What are the different forms that energy can take?

mechanical, heat, sound, electric current, light, and radioactivity

What is a kilocalorie?

the unit of heat most commonly used in biology

How much temperature can 1 kcal raise in 1 g of water?

1°C (joule = physics)

What is sunlight?

ultimately all energy flows into the biological world from the sun

What living things capture a fraction of sunlight energy via photosynthesis?

plants, algae, and some bacteria

Energy absorbed from sunlight is used to do what?

combine small molecules (H₂CO₃ and CO₂) into more complex molecules (sugars)

Energy from the sunlight is stored as what in sugar molecules?

potential energy in the covalent bonds

Energy stored in chemical bonds can be used to make what?

new bonds during chemical reactions; electrons are often passed from 1 atom or molecule to another

What is an oxidation reaction?

the process by which an atom or molecule loses an electron is said to be oxidized because oxygen is the most common electron acceptor in biological systems

What is a reduction reaction?

the process by which an atom or molecule gains an electron is said to be reduced

What does the reduced form of a molecule have a higher level of compared to its oxidized form?

energy

What do oxidation-reduction reactions play a key role in?

the flow of energy through biological systems

What do oxidation and reduction reactions do?

take place together

What is the 1st law of thermodynamics?

energy cannot be created or destroyed, it can only change from 1 form to another (ex. potential or kinetic)

The total amount of energy in the universe remains what?

constant

What is an example of potential energy being transferred from the tissues of 1 to the tissues of another?

animals eating plants or other animals

Within a living organism, what can chemical potential energy stored in some molecules be?

transferred to other molecules to be stored in different chemical bonds or converted into other forms of energy such as kinetic energy, light, or electricity

During each conversion, some energy dissipates into the environment as what?

heat (the random motion of molecules and a measure of kinetic energy)

What is constantly supplying new energy to replace the energy dissipated as heat?

the sun (energy flow through the biological system goes in 1 direction)

What is the 2nd law of thermodynamics?

entropy (the disorder in the universe) is continuously increasing

Disorder is more likely than what?

order

Why do energy transformations proceed spontaneously?

to convert matter from an ordered stable to disordered unstable form

What does every energy change increase?

the amount of entropy

What is free energy?

the energy available to do work in any system

What does it take to break the bonds between the atoms of a molecule?

energy

What makes it easier to pull atoms apart?

heat

What reduces disorder and what increases it?

chemical bonding reduces and heat increases

Free energy is the amount of energy available to do what?

break chemical bonds and form others

What is the equation for free energy and what do each of the variables mean?

G = H - TS; G = free energy, T = temperature, S = entropy, and H = enthalpy

What is enthalpy?

energy contained in a molecule’s chemical bonds

Why does the equation for free energy work for a cell?

volume and pressure within a cell does not change so it does not have to be factored in

What is the equation for free energy for biological reactions?

∆G = ∆H - T∆S

What does a positive ∆G mean?

the products of a reaction contain more free energy than the reactants, therefore less disorder (S) or higher bond energy (H)

Why is a positive ∆G not spontaneous?

it requires an input of energy (endergonic)

What does endergonic mean?

accompanied by or requiring the absorption of energy, the products being of greater free energy than the reactants

What does exergonic mean?

accompanied by the release of energy

What happens if the ∆G is negative?

the products of the reaction contains less free energy than the reactants which means that the bond energy is lower or the disorder is higher

Why is a negative ∆G spontaneous?

releases the excess free energy as heat (exergonic)

What determines chemical reactions to be spontaneous?

if the difference in disorder (T∆S) is greater than the difference in bond energies between reactants and products (∆H)

What does it mean if chemical reactions are reversible?

a reaction that is exergonic in 1 direction will be endergonic in the reverse direction

What must happen before new bonds can be formed?

existing bonds must be broken; this requires energy input

What is activation energy?

the energy needed to destabilize existing chemical bonds and initiate a chemical reaction

Why do chemical reactions take place at different rates?

different activation energies

In what 2 ways are rates of reactions increased?

increasing the energy of reacting molecules and lowering the activation energy

What is a common way to increase the energy of reacting molecules?

heating up the reactants

What does lowering the activation energy require?

the use of a catalyst

What is catalysis?

the process of using catalysts to stress specific chemical bonds to easier break them, thus lowering the activation energy

By reducing the activation energy, what does a catalyst do?

accelerate both forward and reverse reactions by exactly the same amount

Catalysts can do what to reactions?

make them proceed much faster (enzymes in living systems)

What in cells uses ATP?

every energy-requiring process in cells

What is adenosine triphosphate?

a nucleotide composed of ribose, adenine, and a chain of 3 phosphates

What require ATP?

making sugars, supplying activation energy for chemical reactions, active transport of substances across membranes, movement, and growing

What are the PO₄ bonds in ATP?

negatively charged and repel each other

Why does the ATP molecule have a low activation energy and what does it allow?

the PO₄ bonds are unstable, allowing the bonds to be easily broken during hydrolysis

What happens when the PO₄ bonds break during hydrolysis?

a considerable amount of energy can be transferred (a negative ∆G, meaning energy is released to do work)

What is dephosphorylation?

when usually only the outermost PO₄ group is hydrolyzed (ATP — ADP)

ADP can be hydrolyzed to what?

AMP

What is there none of to help drive the 3rd PO₄ away from the molecule