Chapter 3 Energy, Chemical Reactions, and Cellular Respiration

Formation of Citrate Step 1 Citric Cycle (Krebs Cycle)

Step 1 of the citric acid cycle uses the first enzyme to combine an acetyl CoA molecule produced in the intermediate stage with a molecule of oxaloacetate to form citrate. (Note that the addition of a hydrogen ion to citrate forms citric acid.) The first step of this cycle gives this enzymatic pathway its name.

Thermodynamics

The study of energy transformations

Import Molecules in Chemical Energy Storage

Triglycerides, glucose, ATP

Multienzyme Complex

a group of enzymes that are physically attached to each other through noncovalent bonds to form the complex; work in a sequence reaction

Organic Cofactors (coenzyme)

not attached to the enzyme and have specific functions in assisting the enzyme

Cytosol

semifluid contents of the cell; viscous, syruplike fluid medium with dissolved solutes in the cytoplasm

Biochemists

study the chemical composition/physical principles of living cells/organisms

Products

substances formed from reactants by subsequent chemical reaction; written on right side of equations

Catalysts

substances that accelerate chemical reactions

Inhibitors

substances that bind to an enzyme and turn it off, thus preventing it from catalyzing the reaction; temporarily turns off to prevent overproduction of the product

Chemical Equation

summary of changes to the molecular structure when a chemical reaction occurs; components of equation are called reactants and products; (Ex: A+B->C; Ca^2+ +2Cl- -> CaCl2); the number of elements on one side of the equation is equal to the number of elements on the other side of the equation, in a balanced chemical equation

Laws of Thermodynamics

1) energy can not be created nor destroyed, only transformed/converted from one form to another; 2) each time you convert one form of energy to another, some energy is converted to heat; never 100% conversion of one form to another

Net number of ATP molecules that can be produced from oxidation of a glucose molecule under anaerbonic conditions

2 ATP molecule

Net ATP produced from 1 glucose molecule from cellular respiration

30 ATP

Total ATP produced from 1 glucose molecule

38 ATP

Electron Transport Chain

A sequence of H+ pumps and electron carrier; ATP synthase allows passage of H+ from the outer compartment back into the matrix; during this, kinetic energy from the flow of H+ downs concentration gradient is harnessed to bond Pi to ADP to form ATP;

Exchange Synthesis

Atoms, molecules, ions, or electrons are exchanged between two chemical structures (AB+C -> A+BC)

Ketoacids

Byproduct of fatty acid metabolism

Glucose

C6H12O6; Disassembled during cellular respiration, the chem reaction is: C6H12O6+602-> 6CO2+6H20

Step 6 Citric Cycle (Krebs Cycle)

CoA removed, ATP formed. Step 6 of the citric acid cycle involves the removal of CoA and the formation of ATP through substrate-level phosphorylation.

Mitochondrion

Double-membraned organelle where aerobic cellular respirationoccurs

Activation Energy (Ea)

Energy required to break existing chemical bonds for the chemical reaction to proceed

Induced-Fit Model

Entry of the substrate into the active site induces the conformation (structure) of the enzyme to change slightly, resulting in an even closer fit bet

Chemical reactions can be classified by the relative amounts of chemical energy associate with the reactants and products

Exergonic and endergonic

Step 7 Citric Cycle (Krebs Cycle)

FAD reduced to FADH2. Step 7 of the citric acid cycle occurs through the action of a dehydrogenase that transfers hydrogens to FAD to form FADH2.

Four Stages of Cellular Respiration

Glycolysis, intermediate stage, citric acid cycle, and the electron transport system

Step 9 Citric Cycle (Krebs Cycle)

NAD+ reduced to NADH, oxaloacetate regenerated. Step 9 of the citric acid cycle is catalyzed by a dehydrogenase that transfers hydrogen to NAD+ to form NADH. Oxaloacetate (OAA) is regenerated in this final step.

Steps 4-5 Citric Cycle (Krebs Cycle)

NAD+ reduced to NADH. Steps 4 and 5 of the citric acid cycle occur through two different dehydrogenase enzymes that participate in the transfer of hydrogen to NAD+ to form NADH. CoA is also attached during step 5.

NAD+ (oxidized form of NAD+)

Reduced from NADH because NAD+ has gained H+ and 2 e-

Regulation of Citric Acid Cycle

Regulation of the citric acid cycle occurs primarily at the enzyme in the first step of the citric acid cycle (citrate synthase). The levels of NADH, ATP, and pathway intermediates are the primary regulators of citrate synthase activity. A low level of NADH, ATP, and pathway intermediates indicates that cellular energy demands are high. This results in increased activity of citrate synthase and the citric acid cycle.

Glycolysis Steps 1-5

Steps 1 through 5 of glycolysis involve splitting glucose into two molecules of glyceraldehyde 3-phosphate (G3P) through the action of the first five enzymes. ATP is "invested" when kinase enzymes transfer Pi from ATP to glucose and the breakdown products of glucose (steps 1 and 3). Thus, an investment of 2 ATP molecules occur at these steps

Glycolysis Steps 6-7

Steps 6 and 7 of glycolysis occur twice in oxidation of a glucose molecule. Step 6 involves transferring an unattached Pi to the substrate (so this molecule now has two phosphates), and two hydrogen atoms are released to NAD+ to form an NADH (and H+). This transfer of hydrogen is catalyzed by a dehydrogenase enzyme. In step 7, the original Pi is transferred to ADP to form ATP through substrate-level phosphorylation by a kinase enzyme.

Glycolysis Steps 8-10

Steps 8 through 10 of glycolysis also occur twice. These steps involve converting the molecule produced in step 7 to an isomer (step 8) and then the loss of water molecule. The remaining Pi (on phosphenolpyruvate) is transferred to ADP to form ATP through substrate-level phosphorylation by a kinase enzyme (step 10), forming the final product of pyruvate

Step 2 Citric Cycle (Krebs Cycle)

Water removed from citrate and reattached. Steps 2 and 3 of the citric acid cycle form an isomer by removing a water molecule from citrate and then reattaching it to a different location on the molecule.

Step 8 Citric Cycle (Krebs Cycle)

Water removed. Step 8 of the citric acid cycle is the removal of water.

Allosteric Site/Inhibitor

a specific receptor on the enzyme that is not the active site; binding a noncompetitive inhibitor to the allosteric site induces a conformational change in the enzyme with an accompanying change in the shape of the enzyme's active site

Optimal Temperature

activity of human enzymes increases with a rise in body temperature and continues to rise until 104 F

Metabolism

all chemical reactions taking place in the body, including anabolic and catabolic reactions

Reactants

are substrates or substances that are present prior to the start of the chemical reaction; written on left side of equation

Heat (Kinetic Energy)

associated with random motion of atoms, ions, or molecules; usually considered a unstable form of energy, or waste product that accompanies all changes in energy form; measured as temperature

Inorganic Cofactors

attached to the enzyme and are required for their normal function

Enzymes

biologically active catalysts that facilitate chemical changes in the human body by decreasing the activation energy of millions of chemical changes that occur every second; globular protein with a depressed region that serves as the active site; produced by protein synthesis processes within cells; increases reaction rate

Catabolism (Catabolic Reations)

breakdown of complex molecules into simpler molecules

Pyruvate Dehydrogenase

brings together pyruvate and a molecule of conenzyme A (CoA) to form acetyl CoA (2 carbon molecule with CoA attached)

Decarbonization

carboxyl group (1 carbon atom and two oxygen atoms) release pyruvate as CO2; energy is released during Decarbonization as 2 hydrogen atoms (2 electrons+ 2 hydrogen ions) are transferred to the coenzyme NAD+ to form NADH( and H+); the acetyl CoA then enters the citric cycle

Catalyzed Reaction

chemical reaction with an enzyme

Uncatalyzed Reaction

chemical reaction without an enzyme

ATP Cycling

continous formation/breakdown of ATP; involves (1) ATP formation from ADP and Pi(free phosphate), which is energy requiring (endergonic) reaction (2) ATP splitting into ADP and Pi(phoshate free) which is energy releasing (exergonic) reaction

Citric Cycle (Krebs Cycle)

cyclic metabolic pathway that occurs through the activity of 9 enzymes located in the matrix of the mitochondria; During the citric acid cycle, the acetyl CoA produced in the intermediate stage is converted to two CO2 molecules and a CoA molecule is released. Energy is transferred to form 1 ATP molecule, 3 NADH molecules, and 1 FADH2 molecule during one "turn" of the citric acid cycle; requires oxygen; 2 CO2 molecules produced per turn of cycle; key enzyme in regulation citrate synthetase

Concentration Gradient

difference in the concentration of a substance between two areas

Substrate Level Phosphorylation

direct method of synthesizing ATP

Noncompetitive Inhibitor

doesn't resemble the substrate, functions to inhibit the enzyme by binding to the site on the enzyme other than the active site; not influnced by the concentration of the substrate

ATP Production

each NADH generates 3 ATP and each FADH2 generates 2 ATP; able to calc specific number of ATP molecules produced in breakdown of glucose molecules by knowing: specific number of energy molecules (ATP, NADH, FADH2) that are generated from the glucose breakdown in each stage of cellular respiration; and the specific number at ATP generated by oxidation of each coenzyme in the electron transport system (NADH=3 ATP, FADH=2 ATP)

Metabolic (Biochemical) Pathway

each enzyme catalyzes one progressive change to its specific substrate molecule and then releases the product; the product of one enzyme becomes the substrate of the next enzyme

Radiant Energy (Kinetic Energy)

energy of electromagnetic waves traveling in the universe; pigment: melanin; Ex: gamma rays

Kinetic Energy

energy of motion; can be converted into potential energy

Chemical Energy

energy stored in a molecule's chemical bonds, most important form of energy in the human body; used for the energy requiring processes of movement, synthesis of a molecule, and establishment of concentration gradients;form of potential energy

-ase

enzyme

Denatures

enzyme permanently loses function/weaken the intramolecular bonds that hold enzyme's protein structure when temp is greater than 104 F (40 C); may occur from changes in the pH

Optimal pH

enzymes function most efficiently between pH 6-8

Oxidation-Reduction Reaction (Redox Reaction)

exchange reaction involving transfer of electron from one chemical to another; Ex: nicotinamide adenine dinucleotide (NAD+; reduced form is NADH); Loses Electrons is Oxidized Gains Electrons is Reduced

Most catabolic reactions release energy meaning that they are also

exergonic

Mechanical Energy (Kinetic Energy)

exhibited by an object in motion due to applied forces; Ex; muscle contraction for walking

Beta Oxidation

fatty acids are enzymatically changed two carbon units at a time to form acetyl CoA

Pyruvate

final product of glycolysis; if oxygen is available, pyruvate enters mitochondria to complete aerobic breakdown (carbon dioxide/water); if oxygen is not available, pyruvate is converted into lactate

Glycolysis

first stage of cellular respiration in which glucose is partially catabolized to form pyruvate and transfer energy to form ATP molecule; glucose is boken down in this pathway into two pyruvate molecules with an accompanying energy transfer to form a net production of 2 ATP molecules and 2 NADH molecules; occurs in the cytosol and does NOT require oxygen; requires ATP to continue

Anabolism (Anabolic Reaction)

formation of large, complex molecules from simple molecules

GER

gains electron is reduced

Oxidative Phosphorylation

indirect method of synthesizing ATP; the energy is first released to coenzymes, which transfer the energy to form ATP

Decomposition Reaction

initial large molecule is digested (broken down) into smaller structures (AB-> A+B); all decomp reactions are collectively referred to as catabolism or catabolic reactions; Ex: hydrolysis reaction

Matrix

inner most space of the mitochondria; multienzyme complex of intermediate stage and the enzyme of citric acid cycle metabolic pathway resides inside the matrix

Exergonic Reactions

involve reactants at the start of a reaction that have more potential energy within their chemical bonds than do the products that are formed; energy released during the course of breakdown reactions; decomposition reactions are exergonic; catabolic reations

Endergonic Reactions

involve reactants that have less energy within chemical bonds than do the products; energy must be supplied to proceed; synthesis reaction is endergonic

Irreversible Reaction

involves reactants converted to product at the rate that yields a net loss of reactants and a net gain in product; many actions are irreversible ; A+B->AB or AB-> A+B

Electron Transport System

involves the transfer of electrons (energy) from the coenzymes NADH and FADH2 that are produced during the first 3 stages of cellular respiration. The energy released from these coenzymes is used to form ATP; majority of energy that was originally in the glucose molecule and transferred to coenzymes is now released from the coenzymes and transferred to form the high energy bond bewteen ADP and Pi as ATP is synthesized; final stage; occurs in inner/cristae membrane

Intermediate Stage/Pyruvate Dehydrogenase of Glycolysis

link between metabolic processes of glycolysis (first stage) and citric acid cycle (third stage); this stage is catalyzed by a multienzyme complex called pyruvate dehydrogenase; occurs in the mitochondrion and requires oxygen; involves a multienzyme complex that converts pyruvate to acetyl C0A and 1 CO2; after cycle occurs twice, a total of 2 NADH molecule are formed

Structure of the Electron Transport System

located in the inner folded membrane (cristae) of the mitochondria; molecules embedded in the cristae of mitochondria: H+ (proton) pumps ( proteins that transport H+ from the matrix to the outer membrane; maintains H+ gradient), electron carriers, and ATP synthase enzymes

Triglycerides (Chemical Energy: form of potential energy)

longterm energy storage in adipose connective tissue

LEO

loses electrons is oxidized

Reaction Rate

measure of how quickly a chemical reaction takes place; rate determines the amount of products formed per unit of time; a primary factory that influences the reaction rate is the energy required to break the chemical bonds in a molecule so that new bonds can form products; energy required to break down existing chemical bonds for chemical reactions to proceed is activation energy; chemical reaction occurs when sufficient energy is supplied to overcome the activation energy

Summary of Glycolysis

metabolic process that occurs in the cytosol with/without oxygen; glucose is initial substrate and pyruvate is final product; net transfer of energy is the formation of 2 ATP/2 NADH molecules

Nictotinamide Adenine Dinucleotide (NAD+) Molecule

modified dinucleotide that is linked at the phosphates and contains nicotinamide (nitrogenous base not found in DNA or RNA) and adenine; important in ATP synthesis

Protein

most enzymes are globular; range from small proteins composed of 60 amino acids to large proteins composed of 2500 amino acids

Electrical Energy (Kinetic Energy)

movement of charge particles; Ex: electricity

Cellular Respiration

multistep metabolic pathway whereby organic molecules (glucose, fatty acids, amino acids) are disassembled (broken down) in a controlled manner by a series of enzymes; during disassembly, potential energy stored in the molecule's chemical bonds is released; the energy is used to make new bonds between ADP and Pi(free phosphate) to form ATP;

Cofactor

nonprotein that may be inorganic/organic chemical structure attached to an enzyme that aids in the enzyme function

Reduction

occurs as a molecule, atom, or ion gains an electron and becomes reduced; a hydrogen ion and an electron are added to a structure during a chemical reaction

Oxidation

occurs as a molecule, atom, or ion loses an electron becoming oxidized

Saturation

occurs when so much substrate is present that all enzyme molecules are actively engaged in the chemical reaction, resulting in no further (notable) increase in reaction rate

Sound Energy (Kinetic Energy)

occurs when the compression of molecules move in liquid, solid, or gas is cause by vibrating an object; Ex: vocal cords

Glucose Oxidation

occurs within cells thru cellular respiration and is a step by step enzymatic breakdown of glucose with the accompanying release of energy to synthesize ATP; if oxygen is available, glucose is completely broken down and carbon dioxide and water are formed

Chemical Reaction

process during which chemical bonds of a molecule are broken and new ones are formed

Reversible Reaction

reactants become products at a rate equal to products becoming reactants; no net change in concentration in either reactants or products, and the reaction is in a state equilibrium; A+B->AB, A+B<-AB

Regulation of Glycolysis

regulated thru negative feedback; ATP acts as an allosteric inhibitor to turn off phosphofructokinase (PFK); as ATP levels increase in cell cytosol, ATP binding inhibits PFK, and glycolytic pathway is progressively shut down. In contrast, as ATP decreases, glycolysis increases

NADH (reduced form of NAD+)

release of H+ and 2 e-

When glucose is oxidize, it_________ chemical energy

releases

Dephosphorylation

removal of a phosphate group; enzymes that remove phosphates are called phosphatases

Competitive Inhibitor

resembles the substrate and binds to the active site of the enzyme; influenced by the concentration of substrate

Over time products/reactants are formed at the same rate, the reaction is

reversible

Carbonic Acid Reaction

reversible reaction in the human body that occurs when carbon dioxide and water combine to form carbonic acid; this formed carbonic acid is unstable

Mitochondria

small organelles within the cell

Potential Energy

stored energy; can be converted into kinetic energy

ATP (Chemical Energy: form of potential energy)

stored in all cells in limited amounts and is produced continuously and used immediately for cells' energy requiring processes

Glucose (Chemical Energy: form of potential energy)

stored in the liver/muscle tissue in the form of polymer glycogen

Phosphorylation

the addition of a phosphate group to a molecule; may turn on some enzymes and turn off other; enzymes that add phosphate are generally phosphorlyases/kinases

Energy

the capacity to do work; has no mass and does not take up space

Carbonic Anhydrase

the enzyme that converts carbon dioxide and water into carbonic acid

Active Site of an Enzyme

the region of an enzyme where substrate molecules bind

Kinase Enzymes

transfer phosphate groups, usually from ATP to another molecule

Synthesis Reaction

two or more atoms, ions, or molecules are combined to form a larger chemical structure (A+B-> AB); Ex; dehydration synthesis; anabolism is the collective term for all synthesis reactions in the body