Cellular Respiration

Which of the following is the best example of potential energy?

A. The energy of a hammer striking the head of a nailB. The energy stored in the chemical bonds of a

gallon of gasolineC. The energy of a baseball bat connecting with a ballD. The energy of a brick hitting the ground after

falling off of a tall buildingE. A rubber band flying across the room toward your

instructors head

Return to Enzymes

• Enzymes are a sub-category of proteins that act as catalysts.

• Enzymes lower the activation energy of a reaction.

Return to Enzymes

• Active Site

• Induced Fit Mechanism

• Enzyme-Substrate Complex

Return to Enzymes

Inhibition of Enzymes• Competitive inhibitors bind with the active site,

preventing substrate binding.– Can be overcome by an excess of substrate

• Non-competitive inhibitors bind at allosteric sites (places on an enzyme other than the active site) causing a conformational change in the enzyme and preventing substrate binding.– Cannot be over-ridden by any [substrate]

Return to ATP• ATP is the energy currency for the body.• A nucleic acid made of a sugar, adenine, and three

phosphate groups• The phosphates have a negative charge causing them to

repel each other. When their bonds break, NRG is released. WHY?

There’s still an NRG barrier, though

How ATP works• When ATP loses a P, the energy that is released

causes the P to attach to another molecule.– This process is called phosphorylation– The “receiving” molecule has been phosphorylated.

• The molecule with the P attached undergoes a conformational change.– Often becomes “activated”

• Phosphorylation is reversible, and is often used as an on/off switch for enzymes.

Which of the following defines an allosteric site on an enzyme?

A. The active site when bound by anything other than a substrate molecule.

B. Site, other than the active site, at which a molecule of substrate can bind without affecting the efficiency of the enzyme.

C. The active site when bound by a substrate molecule.D. A site on the enzyme that is not bound by other molecules.E. Site, other than the active site, at which a molecule can bind

to affect the enzyme’s efficiency.

Aerobic Cellular Respiration

Overview of Cellular Respiration• A series of Red-Ox reactions• Exergonic reactions• Catabolic not anabolicSummary Equation:

ADP +Pi + C6H12O6 + 6O2 6CO2 + 6H20 + ATP

Four Main steps1. Glycolysis2. Oxidation of Pyruvate

(Also known as the transition reaction or Acetyl CoA formation)

3. Kreb’s Cycle4. Electron Transport

System or Chain (Chemiosmosis)

Which of the following about the structure of ATP contributes to the stored energy of the molecule?

A) The nucleotide (adenine) and the sugar (ribose) repel each other.

B) The negatively charged phosphates repel each other.C) The sugar (ribose) repels the negatively phosphates.D) The nucleotide (adenine) repels the phosphate groups.E) The phosphate groups attract each other.

Glycolysis

• This step occurs in the cytoplasm outside of the mitochondria.

• No oxygen is actually required for this step to occur.

• An initial input of 2ATP is required to start breaking down the sugar.

• This step also uses a coenzyme called NAD+. Coenzymes are electron acceptors.

Steps of glycolysis• Using 2ATP, glucose is phosphorylated then broken into

two 3-C molecules called Glyceraldehyde-3-Phosphate.(G-3-P)

Steps of glycolysis• Enzyme catalyzed reactions cause both G-3-P to be

oxidized and 2NAD+ to be reduced to 2NADH + 2H+.• The two G-3-P lose their P groups to become 2

pyruvates.• Substrate level phosphorylation of 4 ADP forms 4 ATP

Oxidation of Pyruvate• If oxygen is present, the pyruvate enters the

mitochondria.• Mitochondria are organelles found in both

plants and animal cells

Oxidation of Pyruvate

• Oxidation of pyruvate occurs in the inter-membrane space.

• Enzyme catalyzed oxidation of the pyruvate kicks off a CO2 from each molecule.

Oxidation of Pyruvate• 2NAD+ are reduced to

2NADH+2H+

• The now 2 C molecules are called acetate.

• Each acetate combines with a molecule called coenzyme A to form two acetyl CoA molecules.

Krebs Cycle (AKA: Citric Acid Cycle)

Krebs Cycle

• This occurs within the matrix of the mitochondria.• This is another series of Red-Ox reactions that

further oxidize the C-containing molecules and reduce coenzymes.

• It’s called a cycle because one of the initial reactants is regenerated.

Steps of the Krebs Cycle1. A dehydration synthesis

reaction joins each acetyl CoA with a 4 C oxaloacetate to form two 6 C molecules called citrate (or citric acid).

2. The two CoA leave to be reused.

3. Further oxidation of citrate ultimately regenerates the oxaloacetate.

Acetyl CoA

CoA—SH

C C

C C C C C C

COO–

CH2

CCH2COO–

COO–HO

CoACS

OCH +

Citrate

1

H2OCitratesynthetase

2A

Steps of the Krebs Cycle

Produced during the Kreb’s cycle:• 6NAD+ are reduced to 6NADH + 6H+ and 2FAD+ to 2

FADH2

• 4CO2 are given off as waste.• 2 ADP + 2P 2 ATP

What is the name of the two carbon molecule which is incorporated into the Krebs cycle?

A) GlucoseB) Pyruvate (pyruvic acid)C) OxaloacetateD) Acetyl CoAE) Citrate (citric acid)

Electron Transport System

Electron Transport System

• Occurs across the inner membrane (cristae).

• Embedded in the membrane are proteins that accept the electrons from the NADH and the FADH.

• In the membrane are H+ pumps that create a steep [H+] electrochemical gradient.

• Oxygen is the final electron acceptor.

Steps of the Electron Transport Chain (Continued)

• The H+ that were pumped out of the matrix create an electrochemical gradient that allows them to diffuse back into the matrix.

• The H+ diffuse through a protein channel called ATP synthase. This drives the synthesis of ATP from ADP and P. (chemiosmosis and substrate level phosphorylation)

ATP Synthase

How Much ATP?

Which of the following lists the correct locations of 1) glycolysis, 2) the Krebs cycle and 3) the electron transport chain respectively?

A) 1) cytosol, 2) mitochondrial matrix, 3) inner membraneB) 1) outer mitochondrial membrane 2) inter-membrane

space 3) mitochondrial matrixC) 1) cytosol 2) intermembrane space 3) mitochondrial

matrixD) 1) mitochondrial matrix 2) intermembrane space 3)

cytosolE) All 3 of these steps occur in the mitochondrial matrix

Catabolism of other MoleculesProteins• The proteins are first broken

down into amino acids.• Deamination process removes

the amine group from each amino acid.

• The remainder of the a.a. is converted to pyruvate or acetyl CoA.

Fats• The fats are broken down into

glycerol and fatty acids.• The fatty acids are broken into

acetyl groups that combine with CoA to form acetyl CoA. (ß-oxidation)

• The glycerol is converted to pyruvate.

Catabolism of other Molecules

Oxidation Without O2

Respiration occurs without O2 via either:

• anaerobic respiration– use of inorganic molecules

(other than O2) as final electron acceptor

• Fermentation– use of organic molecules as

final electron acceptor Saccharomyces cerevisiae

Lactic Acid Fermentation• This occurs in animal cells when

there is no oxygen present.• Glycolysis still occurs the same

as in aerobic respiration.• The pyruvates are converted to

lactic acid.• There is only a net of 2 ATP• The lactic acid causes muscle

fatigue/ache during times of exercise.

Ethanol Fermentation

• Used by yeast (alcohol production)

• Glycolysis occurs the same as in aerobic respiration.

• The 2NADH provide electrons and H+ to convert the pyruvate to ethanol.– Waste CO2 is produced

• Substrate level phosphorylation creates 2 ATP (net).

During ethanol (EtOH) fermentation, pyruvate is converted into EtOH. Pyruvate is a 3 carbon molecule, EtOH is a 2 carbon molecule. What happens to the other carbon?

A) It is incorporated into an acetyl CoA molecule.B) It is released as CO2

C) It is combined with others to form glucose.D) Two of them are joined to make another EtOH

molecule.E) It is incorporated into a lactate molecule.