BISC 220 Week 5 - Energy, Metabolism, Enzymes, Intro to Cellular Respiration

Photosynthesis occurs in what type of cells?

Plant cells

During photosynthesis light energy is used to do what?

Transform CO2 and water into organic molecules (sugars - glucose) and oxygen

The energy released from photosynthesis can be use to produce ATP through what process that occurs in which location?

Cellular respiration in the mitochondria

What is heat?

The energy from random molecular movement, often is the product of metabolic processes (being released)

What is stored/potential energy?

The capacity to do work, this energy is contained within a molecule

What is kinetic energy?

the energy contained within an moving object/molecule

__________ is the kinetic energy of random moving molecules?

heat

What is entropy?

a measure of the degree of disorder in a system

matter usually has an increasing amount of __________ unless energy is used up to keep _______ low

disorder; entropy

Energy transformation occurs when potential energy is converted to kinetic energy (and vice-versa). As the conversion of potential energy to kinetic energy occurs what happens to the entropy of a system?

the degree of entropy increases due to the level of disorder increasing

What is the 2nd Law of Thermodynamics

Whenever there is energy transfer/transformation there is ALWAYS an increase in the overall entropy of the universe

What is free energy?

the amount of energy in a system that is available to do work

Which has a greater amount of free energy: a stable system or an unstable system? Why?

An unstable system will have a greater amount of free energy because it contains excess energy that, when released, can drive the system toward a lower energy and a more stable state

What is the formula for free energy?

deltaG = deltaH - TdeltaS

When free energy (deltaG) is negative the reaction is? What does it mean?

EXERGONIC - meaning free energy is released from the molecule to do work

When free energy (deltaG) is positive the reaction is?

ENDERGONIC - meaning free energy is absorbed the molecule and energy must be added to the system

An exergonic reaction is?

spontaneous

An endergonic reaction is?

NOT spontaneous

What is Spontaneity?

The tendency of a physical or chemical change to proceed spontaneously

Does spontaneity depend on the rate at which the reaction proceeds?

no

What purpose do fuel molecule serve in metabolic processes?

Cells use fuel molecules to perform exergonic reactions that release free energy to do work

What is the relationship between exergonic and endergonic reactions during metabolic processes?

Cells take the energy released from exergonic reactions to drive endergonic reactions

What process is an example of cells taking the energy released from exergonic reactions to drive endergonic reactions

photosynthesis: the splitting of a water molecule drives the conversion of carbon dioxide and water into glucose and oxygen

Exergonic rxn:

• C₆H₁₂O₆ (glucose) + 6O₂ (oxygen) → 6CO₂ (carbon dioxide) + 6H₂O (water)

Endergonic rxn:

• 6CO₂ (carbon dioxide) + 6H₂O (water) → C₆H₁₂O₆ (glucose) + 6O₂ (oxygen)

How many grams is a mole of glucose?

180g

During the conversion of glucose and oxygen to CO₂ and H₂O, approximately how much energy is released?

686 kcal per mol of glucose (deltaG = -686 kcal)

During the conversion of water and carbon dioxide to glucose and oxygen to C₆H₁₂O₆ and O₂, approximately how much energy is gained/absorbed?

686 kcal per mol of glucose (deltaG = +686 kcal)

During the exergonic reaction what occurs in regards to entropy?

Glucose is transformed from a less stable and more complex state (low entropy) to a more stable and less complex state (higher entropy)

In carrying out the photosynthetic endergonic reaction where does energy come from?

sunlight

Photosynthesis releases a lot of energy, if released all at once in the form of heat is this good or bad for the cell and why?

Too much energy released in the form of heat is bad for the cell because it damages critical structures within the cell and can cause protein denaturation

Photosynthesis releases a lot of energy, if released in small steps in the form of heat is this good or bad for the cell and why?

small packets of energy released by the cell are good because these packets can easily be used for other processes with the release of little heat

What molecule links exergonic and endergonic reactions together?

Adenosine Triphosphate (ATP)

Describe the molecular structure of ATP

made up of adenine and a ribose sugar. Has a carbon group attatched to 3 phosphate groups

What is unique about the phosphate group in ATP?

The phosphate group is weak/unstable and contains energy that can be released though hydrolysis and allow the cell to do cellular work

What type of reaction is a hydrolysis reaction? (exer/endergonic)

exergonic

What is the equation for the hydrolysis of ATP

ATP + H₂O → ADP + Pi

In standard laboratory conditions the energy released from the hydrolysis of ATP would be 7.3 kcal/mol (deltaG = -7.3 kcal/mol). However the cell can do this at double the efficiency due to their different concentrations of ATP and water. How much energy is released by the cell then?

13 kcal/mol (deltaG = -13 kcal/mol)

ATP Synthesis (the reverse of hydrolysis) is an endergonic reaction meaning?

it requires energy, specifically 7.3 kcal/mol in standard lab conditions (deltaG = +7/3 kcal/mol)

Where is the energy required for ATP synthesis derived from?

the catabolism (breakdown) of glucose

How specifically do cells take the energy released from exergonic reactions to drive endergonic reactions? What is this process known as?

Cells can transfer the third phosphate bond of ATP to other molecules so that these molecules have a higher free energy, putting them in a state where endergonic reaction occur more easily

• This is known as phosphorylation

The synthesis of glutamine is example of phosphorylation explain how it works?

Glutamine is synthesized from glutamic acid and ammonia ← this is a endergonic reaction (requiring energy) that does not easily occur naturally in cells

So, glutamic acid is phosphorylated by ATP

1. ATP is hydrolyzed

2. The phosphate group is added to the glutamic acid to make a phosphorylated intermediate. ADP is left over and energy is produced

3. The produced energy adds on the ammonia molecule to produce glutamine

What is activation energy?

the energy needed to begin a reaction; the amount required differs depending on the rxn

What does activation energy do specifically to the molecules involved in a reaction

activation energy puts the molecules in into an intermediate and unstable transition-state

• These molecules have have higher free energy that both reactants and products, allowing the reaction to proceed with greater ease

Is adding enough heat to increase the average kinetic energy of the molecules appropriate for starting chemical exergonic in biological system?

NO

What are used in biological systems to increase the average kinetic energy of molecules in a reaction

Enzymes

What are enzymes?

Proteins that act as biological catalysts to decrease activation energy and thus speed up reaction rate. Enzymes bind to specific substrates (reactant molecules)

True or False: Free energy is dependent on enzymes

False

At which area do substrates bind to the enzyme surface?

the active site

RNA polymerase function:

catalyzes formation of RNA

RNA nuclease function:

hydrolyzes RNA polymers

Hexokinase function:

Accelerates the phosphorylation of a hexose monosaccharide (like glucose)

The hydrolysis of sucrose (sucrose → glucose + fructose) is an example of an enzyme catalyzed reaction. What enzyme is involved in this process?

sucrase

What is it called when he enzyme changes shape to ensure that the active site enfolds a bound substrate?

induced fit

Describe the catalytic cycle of an enzyme

1. Substrates bind to active site; induced fit occurs

2. Substrates are held in active site by weak interactions - hydrogen bonds/ionic bonds

3. Active site lowers activation energy (AE)/speeds up rxn

4. Substrates become products and are released

5. Active site is available for two new substrates

List all the ways of how enzymes can alter the activation state of a reaction:

1. Orienting substrates

2. Adding charges to substrates

3. Using covalent catalysis

4. Altering the shape of substrates

List all the conditions that affect enzyme activity

1. Temperature and pH

2. Substrate concentration

3. Cofactors

4. Regulators and inhibitors

What is competitive inhibition?

When a competitive inhibitor interacts with the active site and blocks out the substrate

• Essentially, the competitive inhibitor is competing for the active site with the substrate

What is it called when an enzyme has a second site where a non competitive inhibitor can bind, changing the shape of the enzyme and preventing the substrate from having access to the active site

Noncompetitive inhibition/Allosteric regulation

• NO competition between substrate and inhibitor because they are not competing for the same active site

Describe normal binding of a substrate to an enzyme

The substrates bind to the active site on the enzyme and start the reaction, which will continue to occur as long as there are enough substrates

Define Allosteric

An action at a site OTHER than the active site

Enzymes that are ___________ usually consist of multiple subunits, each with its own active site

allosterically regulated

An allosteric activator does what?

stabilizes the active form of the enzyme

An allosteric inhibitor does what?

stabilizes the inactive form of the enzyme

Enzymes will move between an ____ form and ______ form

active; inactive

Cooperativity occurs when?

When ONE substrate binds to ONE enzyme’s subunit’s active site and stabilizes the entire molecule 

Metabolism is organized into sequences of enzyme-catalyzed reactions called what?

pathways

What is feedback inhibition

When the reaction's end product inhibits or controls the enzyme's function that helped make it.

An example of feedback inhibition is the synthesis of isoleucine, explain how it works

Feedback inhibition occurs when isoleucine (a noncompetitive inhibitor) binds to an allosteric site on threonine deaminase (the enzyme)

1. Threonine deaminase takes the amine group from L-threonine

2. Eventually, threonine is fully converted to isoleucine

3. Then, isoleucine can bind to an allosteric, non-competitive inhibition site on the enzyme threonine deaminase, inhibiting it from making more isoleucine

Metabolic pathways can either be ________ or ________

anabolic (synthesize monomers into polymers); catabolic (breakdown macro/fuel- molecules)

What are the three steps of Glucose Catabolism

1. Glycolysis

2. Citric Acid/Krebs Cycle

3. Electron Transfer Chain/Oxidative Phosphorylation

What are redox reactions?

Reactions that transfer electrons and energy.

• The changes in positions of electrons in covalent bonds cause changes in energy status

Do electrons in covalent bonds between atoms of equal electronegativity have
a greater or lower potential energy than electrons between atoms with unequal electronegativity?

greater

Do covalent C — H bonds have greater or lower potential energy than O — H or C — O bonds? Why?

C —— H bonds have greater PE the electrons are equidistant between C and H

How do you know if a molecule is reduced in a rxn?

The molecule gains one or more electrons or hydrogen atoms

How do you know if a molecule is oxidized in a rxn?

THe molecule loses one or more electrons or hydrogen atoms

What is the oxidizing agent?

The molecule that accepts an electron or a hydrogen atom.

What is the reducing agent?

The molecule that donates an electron or a hydrogen atom.

During the metabolism of glucose, what is the reducing agent and what is the oxidizing agent?

• Glucose is the reducing agent (is oxidized)

• Oxygen is the oxidizing agent (is reduced)

The overall free energy of redox reactions is negative, what does this mean for the system?

that energy is removed from the system so it can be used elsewhere