Chapter 3 Flashcards
What animals are endothermic?
endothermic= (of an animal) dependent on or capable of the internal generation of heat.
- Mammals and birds
Both ____________ and ______________ cells use ATP
molecules to supply energy for their cellular
work.
prokaryotic, eukaryotic
- . In eukaryotic cells, most of the ATP is produced by mitochondria
Metabolism is
the sum of all chemical reactions in a cell or organism
- anabolic (making bonds) and catabolic (breaking bonds)
Japanese macaques
aka snow monkeys, expend a significant amount of energy to keep warm in their snowy environment. They forage for food to supply this energy
Work is performed when…
energy is used to move an object against an opposing force, such as friction or gravity.
- Ex, it takes energy to link amino acids into a chain to form a protein, or to pump sucrose across a cell membrane
Energy is
is the capacity to do work
- Each form of energy can be converted to other forms of energy
- during the process of photosynthesis, light
energy from the Sun is converted to chemical energy (stored in sugar) by organisms
Most living organisms obtain energy in one of two ways:
1) by obtaining it directly from the Sun through photosynthesis,
2) by consuming energy-rich molecules within food
webs that began with photosynthesis
All energy exists in one of two states: List them
kinetic energy
potential energy
kinetic energy is
the energy of motion –> anything moving like ions are ex of KE
- The KE that is present in movement is useful cuz it can perform work by making other objects move
Potential energy is
the stored energy that an object possesses as a result of its position relative to other objects or to its internal structure
Chemical potential energy
- stored in the electrons & protons that make up atoms & molecules. –> The electrons r often involved in chemical bonds.
- Released or absorbed during chemical reactions.
- stored in food molecules like glucose.–> When food molecules r broken down, usable energy is released to power cellular work.
A bond results when…
electrons are simultaneously experiencing a force of
attraction to protons in the nuclei of two atoms.
Gravitational Potential Energy
Related to an object’s position (e.g., a cyclist at the top of a hill or a diver on a platform).
- Results from Earth’s gravitational pull & the object’s height
When work is done, energy is…
transferred from one body or place to another.
Gravitational Potential Energy to Kinetic Energy: The Diver Example
a diver about to dive from a platform also has PE due to the force of gravity from Earth & her height above the surface of the H2O.
- The diver gains PE as her muscles work to climb the ladder & reach the top of the platform.
- When work is done, energy is transferred from one body or place to another.
- When she dives from the platform, the diver’s speed increases & she gains KE.
- She also loses PE as the distance between her & the water surface decreases
- Thus, as the diver plunges toward the H2O, some of her PE is converted to KE
The First Law of Thermodynamics
- AKA the law of energy conservation
The total amount of energy in any closed system is constant. Energy cannot be created or destroyed; it can only be converted from one form to another. If a physical system gains an amount of energy, another
physical system must experience a loss of energy of the same amount
Plants as Energy Transformers
Green plants convert sunlight into chemical energy through photosynthesis. –> Plants capture light energy from the Sun & convert it into chemical PE.
- This energy is stored in carbohydrates & other energy-rich molecules within plant cells.
- The chemical energy in plants is passed to organisms that eat them.
- Living Organisms: Convert the chemical energy from plants into other forms of energy –> Woodland caribou consume plant material, converting the plant’s chemical energy into mechanical energy to power muscle movement.
Conversion of energy from one form into another depends on…
the breaking & forming of chemical bonds in a chemical reaction.
- During a chem reaction, amount of PE that’s available changes
Potential Energy in Electrons (AKA Chemical PE)
- PE of e- depends on their location with respect to nucleus (+vely charged)
- farther away e- from the nucleus= more PE energy they have
–> The PE of e- increases when they absorb energy, move farther from
the nucleus, and reach an “excited” state. - unlike the diver being pulled by Earth’s gravitational force, there is not just one source of attraction; there r many sources, from many different atomic nuclei varying in their forces of attraction
Making & Breaking Bonds: When is energy absorbed? When is it released?
During chem reaction, some bonds between atoms in reactant molecules must be broken, & new bonds form between atoms in product molecules
- For bonds to break in reactant molecules= energy must be absorbed cuz energy is required to pull an e- away from an atom
- bonds are formed between the atoms of product molecules= energy is released.
–> Ex, combustion involves both the absorbing & releasing of energy
Chemical reactions & change in electron PE
- As bonds break and new bonds form, the positions of some electrons in the atoms
change. –> The change in PE of these electrons accounts for the change in energy during a chem reaction. - Breaking bonds=e- pulled away from nucleus=requires energy but increases the electrons’ PE
- Making bonds= e- move closed to the nucleus of another atom and release energy
- The released energy can be converted to different forms –> light & thermal energy from a burning candle is the result of electrons involved in bond formation.
Bond energy is
measure of the strength or stability of a covalent bond.
-measured in units of kilojoules per mole (kJ/mol) & is equal to the amount of energy absorbed/ mole when the bond between atoms is broken & is equal to the amount of energy released/ mole when the same bonds form.
- The energy needed to break a bond reflects the relative strength of the bond
A mole is
AKA Avogadro’s number,
a standard quantity equal to about 6.022x10^23.
- used in chem when considering # of extremely small particles.
Bond energy values are given as averages bcuz
bcuz actual bond energies vary depending on the other atoms in the molecules
- Ex, the bond energy of the O-H bond will vary depending on what other atoms the O forms a bond with.
The activation energy (Ea) of a reaction is
the min amount of energy needed to break bonds in the reactants and start the chemical reaction.
- All chem reactions involve bonds break in the
reactants and the release of energy as bonds form in the products.–> energy is always required to start a reaction, even if there is an overall release of energy in
the chemical reaction.
- Ex, must be a spark to start the process of combustion. –> may be a small amount of energy, but it’s enough to break the 1st bonds & initiate the chem reaction. Once the reaction begins, it releases enough
energy to break bonds in other reactant molecules and keep the process going.
The transition state of a chemical reaction is
the temporary condition in which bonds in the reactants have reached their breaking point and new bonds are ready to form in the products.
- activation energy= the diff between the PE of the reactants & the PE during the transition state (SEE DIAGRAM ON PAGE 129)
A Exothermic Reaction is
a chemical reaction in which there is a net release of (heat?)energy, leaving the products with less chemical PE than the reactants
- Ex, water freezing
OCCURS IF…
- If the bonds that form in the products are stronger than the bonds in the reactants, the energy released as the product bonds form will be greater than the energy absorbed as the reactant bonds were broken
An Endothermic Reaction is
a chemical reaction in which there is a net absorption of (heat?)energy, giving the products more chemical potential energy than the reactants
- Ex, ice melting
The Second Law of Thermodynamics
In every energy transfer or conversion, some of the useful energy in the system becomes unusable ( unavailable to do work) & increases the entropy of the universe.
- The unusable energy is usually thermal energy, which is the energy associated with random molecular motion.
- is one reason why machines are never 100 % efficient
–> Ex, the engine of a car converts only about 25 % of the PE in gasoline into the KE that makes the car move
- In the process of cellular respiration, cells r able to convert about 40 % of the PE in glucose into a form usable for metabolism; the remainder is lost as thermal energy
Entropy is
a measurement of disorder in a system in the field of thermodynamics
- the overall entropy of the system always increases
- The total entropy of a system and its surroundings increases whenever there is any change, such as a chem reaction –> increase in entropy is thermodynamically favourable, that’s why heat flows from a cup to its surroundings
- Thus, all systems in the universe tend toward disorder –> disorder increases when an orderly arrangement of objects becomes more randomly assorted.
Note: more energy dispersal= more entropy
–> Ex, no matter how much energy you may expend to tidy up your room, it always gets messy again.
At the level of chemical and physical changes, an increase in entropy is
usually associated with a breaking down of large particles into smaller particles, or the spreading out of particles
Examples of Increasing Entropy:
Melting: When ice melts, a structured crystal breaks down into individual molecules.
Evaporation: Liquid water molecules spread out over large distances as water evaporates.
Diffusion: Molecules move from higher to lower concentration, becoming more randomly distributed.
Examples of Increasing Entropy:
Melting: When ice melts, a structured crystal breaks down into individual molecules.
Evaporation: Liquid water molecules spread out over large distances as water evaporates.
Diffusion: Molecules move from higher to lower concentration, becoming more randomly distributed.
In chemical reactions, entropy increases when…
- solids react to form liquids or gases
- liquids react to form gaseous products
- the total number of product molecules is greater than the total number of reactant molecules
One characteristic of all living things is that they are ______________________ structures
highly ordered
- A flower, the compound eye of an insect, & the human brain r all very highly ordered structures
- Living cells have the ability to create order from a
disordered arrangement. –> Ex, individual nucleotide molecules link together 2 synthesize DNA, a highly ordered macromolecular structure
Since cells can create order from disorder, does this mean they do not follow the 2nd law of thermodynamics?
No
- Just as you expend energy to tidy ur room when it becomes disorderly, living cells can, by expending energy, establish & maintain complex & orderly structures & processes
- Essentially, it’s possible to maintain a low level of low entropy in a system but it requires energy
- that’s why even people who don’t have a high
energy demand for movement need to ingest enough food to supply energy, simply to maintain their cells in a highly ordered state
What is the by-product of maintaining order in cells?
1000s of chem reactions that take place to maintain order in a living system release energy in the form of thermal energy & the by-products of metabolism, such as CO2.
- These by-products & released energy increase the entropy of the surroundings, but the living organisms themselves maintain order.
- Thus, entropy of the organism decreases, but the overall entropy of the universe increases.
spontaneous change
a change that will, once begun, continue on its own under a given set of conditions; does not require a
continuous supply of energy
-Ex, a match will not suddenly burst into flame but once it’s lit, it will continue to burn on its own without any continual addition of energy
-Ex, a diver high on a diving board will not begin his dive until he jumps but once he jumps, his falling motion will continue on its own.
A non-spontaneous reaction
cannot occur without a continual input of energy.
- Ex, if you heat a pot of water until it starts boiling and then take it off the heat source, the water will not continue to boil.
Spontaneous Physical Changes & Spontaneous Chemical Changes
- Spontaneous Physical Changes: Can occur at different rates (e.g., ice melts faster at higher temperatures).
- Spontaneous Chemical Changes: Can be slow (e.g., rust forming) or fast (e.g., a match burning).
To determine whether a change will occur
spontaneously, you must take three factors into account: List them
energy changes, entropy, & temperature
Elaborate on Factors Determining Spontaneity:
Exothermic + Increase in Entropy = occur spontaneously because energy is released and entropy increases, both favorable factors. Ex, wood burning
-Endothermic changes + decrease in entropy= not occur spontaneously; neither the change in energy nor the change in entropy is favoured.–> Energy is needed for endothermic changes & for changes that increase order (decrease entropy). Ex, glucose synthesis during photosynthesis
- Exothermic energy change(favoured) + the entropy decreases (not favoured)= spontaneous at low temps; not spontaneous at high temps. Ex, water freezing
- Endothermic energy change (not favoured)+ entropy increases (favoured)= spontaneous at high temps;
not spontaneous at low temps. Ex, sweat evaporating from skin surface
A favourable change means
that it does not require an additional supply of energy.
why is exothermic reactions with an increase in spontaneity favoured in all temps?
- When a process is exothermic, it means that energy is released during the change. This is a good thing because it doesn’t need extra energy to keep going.
- When entropy increases, it means things are becoming more disordered or spread out, which is also a good thing in terms of energy flow. –> To revisit the messy room analogy, you could describe the change from a tidy room to a messy room as a spontaneous change because it can happen “on its own.” –> However, a change from a messy room to
a tidy room is not spontaneous; it will only occur when there is a continual supply of energy from you!
Can ordered structures spontaneously form?
yes they can on a small scale. think of formation of ice.
https://www.youtube.com/watchv=8N1BxHgsoOw
Free energy is
- AKA Gibbs free energy –> represented by symbol G, after Physicist Josiah Willard Gibbs.
Gibbs free energy= the energy that is not lost, or the portion that is still available to do work in the given system —>bond energy changes quantify the total amount of energy released from a reaction, some of this energy is lost and therefore unavailable to do work.
- The concept of free energy applies to both chemical and physical processes.
- all processes in our universe require a source of free energy.
Gibbs Free Energy Equation
The change in free energy (∆G) can be represented by the following equation:∆G= Gfinal state - Ginitial state
∆G–> Represents the usable energy available to do work in a system after accounting for energy lost (usually as thermal energy) = the diff in the free energy of the final state of molecules as compared to the free energy of the initial state
- ΔG<0: The final state has lower free energy than the initial state, meaning the system has released free energy. This makes the process spontaneous, and the reaction will proceed on its own. –> The energy released during a reaction with a -∆G can be used to do work in other reactions that require energy.
-ΔG>0: The final state has higher free energy than the initial state. This means the process requires an input of energy to occur, so the reaction is non-spontaneous. - oxidation (tech combustion) of glucose is an ex of an reaction that releases free energy (-∆G) & thus is spontaneous
- Plants combine CO2 and H2O to create sugars through the process of photosynthesis. This reaction is the opposite of glucose oxidation and is an ex of a chemical reaction that has a +∆G & is not spontaneous: 6CO2 + 6H2O + C6H12O6 + 6O2
exergonic reaction
a chemical reaction that releases free energy (-∆G); the products have less free energy than the reactants
- Exergonic reactions can do work because they act as
a source of free energy. –> Releasing free energy gives cells the ability to do work (to move, to grow, and to reproduce)
- Ex, burning wood releases energy from the glucose molecules in wood.
- Are spontaneous
endergonic reaction
a chemical reaction that absorbs free energy (+∆G) ; the products have more free energy than the reactants
- Ex of an endergonic reaction is the conversion of carbon dioxide and water into glucose and oxygen gas. This reaction requires an input of free energy.
-Are non-spontaneous
energy coupling
the transfer of energy from one reaction to another in order to drive the second reaction
- Cells are able to make endergonic reactions happen by supplying them with the free energy released by an exergonic reaction. –> In other words, cells couple exergonic reactions to endergonic reactions.
- We say that the exothermic reaction is coupled to the endothermic reaction
- When combined, the coupled reactions= net -∆G. –> Free energy is released & both reactions, when coupled, can occur spontaneously. For an endergonic reaction to proceed, it must be coupled with an exergonic reaction that releases more free energy than the endergonic reaction requires. –>In cells, all endergonic reactions are coupled to such exergonic reactions
metabolism is
the sum of all individual reactions
A metabolic pathway is
is a series of sequential reactions in which products of one reaction are used immediately as reactants for the next reaction in the series.
- can consist of a number of individual chemical reactions.
- Some of these reactions may not have the same sign
(positive or negative) for ∆G as the overall pathway - - - Regardless of the
overall ∆G value for an entire pathway, each endergonic step can proceed only if it is
coupled with an exergonic reaction
catabolic pathway
a pathway in which energy is released and complex molecules are broken down into simple molecules
-Ex of a catabolic pathway is cellular respiration, in which energy is extracted from the breakdown of food such as glucose
- overall ∆G of a catabolic pathway is negative.
anabolic pathway is
- AKA a biosynthetic pathway
a pathway in which energy is supplied to build complex molecules from simple molecules - Ex, photosynthesis & the synthesis of macromolecules such as proteins and nucleic acids
- overall ∆G of an anabolic pathway is positive
x
The overall ∆G of an anabolic pathway is positive, whereas the overall ∆G of a catabolic pathway is negative. However…
any one pathway may be made up of a number
of individual chemical reactions.
- Some of these reactions may not have the same sign
(positive or negative) for ∆G as the overall pathway
- Regardless of the overall ∆G value for an entire pathway, each endergonic step can proceed only if it is coupled with an exergonic reaction
All living things perform numerous activities that result in an increase in the ______________ of the products or substances involved—they move, grow, repair & reproduce.
free energy (+∆G)
- These activities need a continuous supply of free energy. Cells need a constant, convenient source to provide this free energy.
- free energy is usually supplied by the energy carrier molecule ATP
Many reactions require the addition of energy for the assembly of complex molecules from simple reactants. These reactions include…
- DNA synthesis, protein synthesis, and the construction of cell walls & other cellular structures.
- Other cell-driven actions—such as muscle contractions in animals, the motion of flagella in bacteria & the movement of sap within a tree—also require a supply of energy
Energy in cells comes in the form of a compound called
adenosine triphosphate (ATP)
- ATP directly supplies the energy that powers nearly every cellular function, and it is considered the universal energy “currency.” The types of work that are carried out by ATP include mechanical, transport, and chemical work
Types of Work Performed by ATP: Mechanical Work
- beating of cilia or movement of flagella
- contraction of muscle fibres
- movement of chromosomes during mitosis/meiosis
Types of Work Performed by ATP: Transport Work
process of pumping substances across membranes against their concentration gradient
Types of Work Performed by ATP: Chemical Work
process of supplying chemical potential energy for non-spontaneous, endergonic reactions, including protein synthesis and DNA replication
Adenosine triphosphate (ATP) consists of three parts:
a nitrogenous base called adenine, which is linked to a five-carbon sugar called ribose, which in turn is linked to a chain of three phosphate groups
ATP & Free energy
ATP contains large amounts of free energy.
–> The energy is high cuz of its 3 negatively charged phosphate groups. –> The phosphate groups crowd together (rmr directly attacched), & their close proximity creates a mutual repulsion of their electrons.
- The mutual repulsion contributes to the weakness of the bond holding the groups together.
-The ATP bonds r easily broken through hydrolysis
https://www.youtube.com/watch?v=23ZzI6WZS28
The hydrolysis of ATP
results in the breaking off of the end (or terminal)
phosphate group and the formation of two products—> adenosine diphosphate (ADP) & an inorganic phosphate (Pi).
- bonds form (releasing free energy) when a —OH group attaches to the phosphorus atom of the phosphate group & when a e- attaches to the oxygen that remains on the ADP.
- Energy is also released as the H+ ion interacts with H2O molecules. The bond rearrangements &
the change in entropy result in an overall free energy change of –30.5 kJ/mol.
-When ATP splits into ADP & Pi in a cell, the phosphate group, rather than remaining
free in solution, often becomes attached to another molecule, which results in a diff bonding arrangement
https://www.youtube.com/watch?v=23ZzI6WZS28
https://www.youtube.com/watch?v=-KE7jTXwNYs
Equation of ATP hydrolysis
ATP + H2O –> ADP + Pi ∆G= –30.5 kJ/mol
- Note that the H+ ion is not normally shown in the chemical equation, since it is understood to be associated with the formation of Pi.
Phosphorylation is
the transfer of a phosphate group, usually from ATP, to another molecule
- It results in the molecule gaining free energy and becoming more reactive
ATP & Energy Coupling
In a process called energy coupling, ATP can be moved into close contact with a reactant molecule of an endergonic reaction. Then, during the reaction, the terminal phosphate group breaks from ATP & transfers to the reactant molecule.
- requires an enzyme to bring the ATP molecule close to the reactant molecule of the endergonic reaction.–> are specific sites on the enzyme that bind both the ATP molecule & the reactant molecule bringing them together
An Ex of energy coupling that is common to most cells is the reaction in which ammonia, NH3, is added to glutamic acid. ELABORATE
- product of this reaction is glutamine, which is an amino acid.
glutamic acid + ammonia –> glutamine + H2O
∆G= +114.2 kJ/mol - glutamine produced takes part in the assembly of proteins during protein synthesis. The + value of ∆G shows that the reaction is endergonic &
cannot proceed spontaneously. - Therefore, the coupling of this reaction with ATP
hydrolysis gives it the necessary energy to proceed. 1) the phosphate group is removed from the ATP & transferred to the glutamic acid molecule, forming glutamyl phosphate
glutamic acid + ATP –> glutamyl phosphate + ADP
∆G < 0 - ∆G, is - for this reaction. This means that the reaction is exergonic & can proceed spontaneously.
2) glutamyl phosphate reacts with ammonia:
glutamyl phosphate + ammonia –> glutamine + Pi (inorganic phosphate) ∆G< 0 - The 2nd step of this reaction also has a - ∆G value, so it also proceeds spontaneously. The overall ∆G value for the two-step reaction is -16.3 kJ/mol
SEE DIAGRAM ON PAGE 143
Do we need to regenerate ATP?
For cells to keep functioning, they must regenerate ATP molecules.
- ATP coupling reactions occur continuously in living cells &, consequently, an enormous number of ATP reactions r required
- If ATP were not formed in the cell from ADP & Pi, the average human would need about 75 kg of ATP per day.
Regeneration of ATP
ATP is regenerated by combining ADP with an inorganic phosphate (Pi). –> an endergonic reaction (requires free energy). –> It’s essentially opposite of the energy coupling.
- Energy for ATP synthesis comes from the exergonic breakdown of complex molecules like carbohydrates, fats, & proteins (from food)
- light energy can also drive ATP synthesis (chptr 5)
- At least 10 million times/second, ATP molecules are hydrolyzed & resynthesized in a typical cell
the ATP cycle is
the cyclic and ongoing breakdown and re-synthesis of ATP
If cells constantly need to use energy from food to reassemble ATP, then why do cells use ATP as their energy currency to begin with? Why Not Use Food Molecules Directly?
- ATP provides a manageable amount of energy and can couple with many different biochemical reactions.
- Its universal use evolved because ATP can easily pair with various endergonic reactions across cells.
- Food molecules release energy, but their availability & the amount of energy they provide are unreliable. –> u can only get glucose from carbs
- Cells can generate ATP from a VARIETY of food sources, ensuring all necessary reactions can occur.
- ATP is immediately accessible, whereas complex food molecules require many steps to release their energy.
ATP is not the only energy carrier in cells. Give another example
There are other phosphate carriers, such as guanosine triphosphate (GTP), that are used specifically as carriers of high-energy electrons.
ATP is the ___________________ of cells & is the ____________ source of energy
energy currency, immediate
Enzymes do not….
-affect where a reaction “begins” or “ends”
-they do not supply energy
- make an endergonic reaction proceed spontaneously
- enzyme does not alter the reactants or the products, thus the change in free energy, ∆G, of the reaction is unaffected by the enzyme
Without the addition of enzymes to cellular reactions, metabolism in living organisms would be _____________
very slow
- The laws of thermodynamics help us determine
whether a reaction will proceed with or without the addition of energy, but not how rapidly it will occur.
–> Just because a reaction is thermodynamically favorable (spontaneous) does not mean it will proceed rapidly; enzymes are needed to increase the speed of reactions. –> just because a reaction CAN proceed on its own DOESN’T mean that it WILL proceed.
Recent research has revealed that some _________________ can also function as enzymes
RNA molecules
A _____________ scientist named ______________ was among the first scientists to shed light on the fundamental role of enzymes
Canadian, Maud Menten –> She developed a mathematical equation to measure the rates of enzyme reactions and explained the basis of enzyme
kinetics
How do enzymes work
- Enzymes briefly combine with reactant molecules, speeding up the reaction, & are released unchanged after the reaction.
- ONLY PURPOSE: lower the activation energy of the transition state, allowing reactants to reach the transition state faster, leading to quicker product formation.
- Each enzyme has specific binding sites that interact with a particular substrate.
- the enzyme binds to the substrate, forming the enzyme-substrate complex, which catalyzes the reaction.
- These catalyzed reactions are reversible.
Naming Enzymes
- Enzyme equations are often written with the name of the enzyme above the reaction arrow
- Enzymes are often named based on the substrate they act on, with names typically ending in -ase. –>Ex, maltase catalyzes the hydrolysis of maltose into glucose
- Other names indicate the type of reaction that
the enzymes catalyze–> enzymes that remove carboxyl functional groups from larger molecules r called decarboxylases.
For the initial bonds to break with the addition of activation energy…..
reactant molecules must be in the correct geometric orientation, & they must collide with enough force for their bonds to break
- It is under these conditions of added activation energy that the transition state of the reaction is reached.
- thus, even though a reaction may be spontaneous
(negative ∆G), like breakdown of sucrose to glucose & fructose, the reaction won’t start until the activation energy is gained by reactants
What provides the activation energy for a chemical reaction?
- Molecules are constantly moving, and sometimes their motion provides enough energy for them to reach the transition state.
- Thermal energy is the primary source of activation energy in most chemical reactions.
–> Ex, in propane combustion, a spark provides the initial energy needed to break bonds. –> The spark creates high temps, increasing kinetic energy, causing bonds to break and new bonds to form (e.g., CO₂ and H₂O), releasing more thermal energy to continue the reaction.
An increase in temperature is one way to speed up a chemical reaction. However, high temperatures are problematic in biology for ___ reasons
2
1) high temps can destroy the structural components of some proteins & DNA so that they lose their ability to function –> can lead to cell death.
2) Raising the thermal energy in cells would speed up all reactions, not just specific ones, making it an ineffective way to regulate reactions.
- thus, even though thermal energy is a great source of activation energy for some chemical reactions, living cells need a more specialized way of controlling chem reactions
- Rather than an increase in temperature, cells use enzymes to speed up chemical reactions
The rate of the reaction is proportional to the number of…
reactant molecules that can overcome the activation barrier to reach the transition state.
- When the enzymes lower the activation energy barrier, more reactant molecules can reach the transition state at a faster rate.
Enzymes function as a catalyst and increase
the number of reactant molecules that reach the transition state. They are able to do this in 3 ways:
1) Enzymes can bring the molecules together. Substrate molecules need to collide with each other to reach the transition state. When BOTH substrate molecules bind to the enzyme, they are in an ideal proximity & orientation for catalysis to occur.
2) Enzymes expose the reactant molecules to altered charged environments that promote catalysis. The active site of some enzymes contains ionic groups with + or - charges that attract and/or repel parts of the substrate. This stresses bonds in a way that favours catalysis
3) Enzymes can change the shape of the substrate. The active site of the enzyme can strain or distort the substrate molecule, weakening its chemical bonds. This reduces the amount of energy required to break the bonds. This mechanism is called the induced-fit model.
In all 3 mechanisms, the substrate molecule (or molecules) binds to the active site, which results in the substrate reaching the transition state. Substrates
may be able to acquire the transition state without enzymes; however, under the conditions that exist within cells, most reactions would proceed extremely slow, if at all
The specific _________ of an enzyme creates its binding sites and allows it to function properly. If an enzyme is heated or chemically altered, it undergoes a process called _________________ and loses ___________.
shape, denaturation, its shape.
- Misshapen enzymes cannot function effectively.
- The temp range in which enzymes retain their shape is tuned to the specific reactions they r specialized to assist.
The one thing that glucose and gasoline have in common that makes them both good fuel molecules is…
an abundance of hydrogen in the form of carbon-hydrogen (C -H) bonds
- As a result of their structure and bond type, there is a great deal of potential energy in both glucose and gasoline
distance from the nucleus & Electron PE
For any atom, an electron that is farther away from the nucleus contains more potential energy than an electron that is more closely held by the nucleus
Electrons in C - H bonds are a good source of energy because…
of their position & proximity to the relatively small atomic nuclei of carbon and hydrogen atoms.
- For any atom, an electron that is farther away from the nucleus contains more potential energy than an electron that is more closely held by the nucleus
- Electrons in C-H bonds are equidistant from two relatively small nuclei (carbon and hydrogen), meaning they have high potential energy because they can be readily pulled closer to larger, more electronegative nuclei —a process that releases energy
Influence of Nucleus Size on Electron Potential Energy:
- Electrons are more strongly attracted to larger nuclei. At the same distance, an electron has more potential energy relative to a larger nucleus than a smaller one.
- An electron releases energy if it moves closer to a large nucleus and must gain energy to be pulled away.
Oxygen’s Electronegativity and Lower Energy:
- Molecules with oxygen have lower potential energy because oxygen’s strong electronegativity pulls bonding electrons close to its nucleus, releasing energy when bonds form.
- It takes the equivalent amount of energy energy to remove these electrons from oxygen once they are in place.
Relevance of Electron PE factors to Everyday Life:
they explain why fat contains more potential energy per unit of weight compared to proteins and carbohydrates –> A fat molecule consists almost entirely of C-H bonds
- When cooking a high-energy food such as bacon, liquefied fat drains from the meat. –> This fat is highly flammable because of its high energy content, & can cause a grease fire in ur kitchen
Redox reactions and energy release
some redox reactions, e- transfer completely, while in others, e- remain shared between 2 atoms. The reaction between methane & O2 shows a redox reaction in which the degree of e- sharing changes
- In methane (CH₄), the e- are shared equally between C & H cuz their electronegativities are similar.
- In the product, CO₂, the e- are drawn closer to the O atoms due to their >electronegativity, causing the carbon atom to partially lose e-, meaning it has been oxidized.
- When O₂ reacts with H from methane, the e- in the resulting H₂O molecule are closer to the O atom because of its >electronegativity. The oxygen has been reduced.
- The redox reaction between CH4 & O2 releases a significant amount of energy. This occurs when the electrons from the C-H bonds in methane move closer to the O atoms in the products, CO₂ and H₂O.
- the same thing can be seen in the oxidation of glucose: C6H12O6 + 6O2 –> 6CO2 + 6H2O
–> The oxidation of fuel molecules, like food, releases potential energy stored in these molecules, which cells use for processes.
rapid oxidation vs. controlled oxidation
RAPID OXIDATION (COMBUSTION):
- During combustion, O₂ does the oxidizing. The oxidation of glucose transfers electrons to O₂, producing completely oxidized CO₂ & H₂O, which contain no more chemical energy.
- A large amount of waste thermal energy is released after a large energy of activation is overcome (e.g., with a spark or flame).
CONTROLLED OXIDATION in Cells:
- This is what happens inside cells, where the energy contained in food molecules is released through controlled oxidation. –> results in same end products, but with a series of steps.
- In cells, controlled oxidation releases energy from glucose through a series of enzyme-catalyzed steps.
- Each step releases a small amount of energy after a small amount of activation energy is absorbed, provided by the thermal energy of the surroundings.
- Energy is transferred to energy-carrying molecules, minimizing thermal energy waste and allowing cells to capture more free energy.
Main similarities & diff between rapid oxidation (combustion) and controlled oxidation
- Thermodynamically, the net energy changes that occur in rapid combustion & controlled oxidation r identical.
- Both r exergonic reactions that have the same overall change in free energy.
- The difference is that, in the rapid combustion reaction, all of the energy is given off at once & can’t be as efficiently harnessed to drive metabolic reactions in the cell
The most important redox reactions in eukaryotic cells is…
when glucose is oxidized by O2 to form CO2 & H2O
Dehydrogenase is
an enzyme that oxidizes a substrate & transfers hydrogen ions to an acceptor
- The oxidation of food molecules often uses dehydrogenases to facilitate the transfer of high-energy e- from food to molecules that act as energy carriers or shuttles.
The most common energy carrier molecule in cells is
a positively charged coenzyme called nicotinamide adenine dinucleotide (NAD+)
Dehydrogenases & NAD+ in cellular respiration
At various points during cellular respiration, dehydrogenases remove two hydrogen atoms from a substrate, transferring two high-energy electrons and one proton (H⁺) to NAD⁺, resulting in the full reduction of NADH.
- The other H+ is released into the cytosol.
- The transfer of energy from food molecules to NAD⁺ is efficient, with minimal loss of thermal energy.
- the potential energy carried in NADH and other reduced molecules facilitates the synthesis of ATP
