Cellular Respiration

What we will cover

• Adenosine triphosphate ATP is the immediate source of energy for most cellular processes

• ATP breaks down to ADP and releases energy

• ATP is generated in the aerobic breakdown of carbohydrate

• In anaerobic respiration ethanol and lactate are produced and NAD (a coenzyme) is regenerated and can be used to make ATP

CC

C

N

N

N

N

NH2

HCCH

H

O

OH OH

CH2

HH

O O

O O O-

O

O

O- O- O-

PP P

Ribose Phosphates

Adenine

Adenosine Triphosphate

In cells ATP is converted to ADP; energy is released when the bond connecting the phosphates is broken.

ATP to ADP +Pi Releases Energy

Aerobic Respiration

There are three phases to Aerobic Respiration ... they are:

1. Glycolysis (same as the glycolysis of anaerobic respiration)

2. Krebs cycle (AKA - Citric Acid cycle)

3. Oxidative Phosphorylation and The Electron Transport Chain

The Separate Biochemical Steps

• GLYCOLYSIS

• LINK REACTION

• TRICARBOXYLIC ACID OR KREBS CYCLE

• ELECTRON TRANSPORT SYSTEM OR OXIDATIVE PHOSPHORYLATION

Phase One: Glycolysis(takes place in the cytoplasm)

4 ATP Yield = 2 ATP Net Gain

2 NAD+ + 2 e- 2 NADH

Glycolysis

Glucose (6 carbons)

Pyruvic Acid (3C)

Pyruvic Acid (3C)2 ATP’s supply the activation energy

4 ATP’s are produced

The First Stage of Respiration for ALL living organisms, anaerobes or

aerobes, is called Glycolysis

and takes place in the Cytosol.

Glycolysis• glyco means “glucose/sugar”, and • lysis means “to split”. Therefore, • glycolysis means “to split glucose”

• This process was likely used to supply energy for the ancient forms of bacteria.

Glycolysis• Function - to split glucose and produce

NADH, ATP and Pyruvate (pyruvic acid).

• Location - Cytosol

Reactants for Glycolysis • Glucose

• 2 ATP…. As activation energy

• 4 ADP and 4P

• Enzymes• 2 NAD+ (Nicotinamide Adenine Dinucleotide, an

energy carrier)

Glycolysis

Glucose

(6 carbons)

Pyruvic Acid (3 Carbons)

Pyruvic Acid (3 Carbons)2 ATP’s

supply the activation

energy

4 ATP’s are produced

4 ATP Yield = 2 ATP Net Gain

2 NAD+ + 2 e- 2 NADH

Products of Glycolysis

• 2 Pyruvic Acids (a 3C acid)

• 4 ATP

• 2 NADH

Net Result• 2 Pyruvic Acid• 2 ATP per glucose (4 – 2 = 2)• 2 NADH• In summary, glycolysis takes one

glucose and turns it into 2 pyruvates (molecules of pyruvic acid), 2 NADH and a net of 2 ATP.

Cellular Respiration

Recap phase 1 - Glycolysis

Phase 2 – Krebs Cycle

Glycolysis

• Function - Split down the glucose molecules so they are small enough to enter the Mitochondria

• Products:– 2 Pyruvic Acids (a 3 Carbon acid)– 4 ATP– 2 NADH

• ATP – is the immediate source of energy for most cellular processes

• NADH – carries electrons to the Electron Transport Chain

Glycolysis1 molecule of

glucose

6

2 molecules of triose phosphate

3 3

2 molecules of pyruvate

3 3

2ATP

2ADP

4ADP

4ATP

2NAD

Reduced 2NAD

What is the net production of ATP?

phosphorylation

(What you need to know)

The story so far

NADH and FADH

• NAD = Nicotinamide Adenine Dinucleotide

• FAD = Flavin Adenine Dinucleotide

• NADH and FADH are Coenzymes which carry energy in the form of electrons

• NADH = reduced NAD

• FADH = FADH2 = reduced FAD

Oxidation and Reduction

• Oxidation describes the loss of electrons / hydrogen or gain of oxygen (NAD/ FAD)

• Reduction describes the gain of electrons / hydrogen or a loss of oxygen. (NADH/ FADH)

In order for Aerobic Respiration to continue the Pyruvic acid is first converted to Acetic Acid by losing a carbon atom and 2 oxygens as CO2.

The Acetic acid then must

enter the matrix region of the mitochondria. The CO2 produced is the CO2 animals exhale when they breathe.

The Link Reaction

Phase Two: The Krebs Cycle(AKA the Citric Acid Cycle)

Sir Hans Adolf Krebs

Once the Acetic Acid enters the Matrix it combines with Coenzyme A to form a new molecule called Acetyl-CoA.

The Acetyl-CoA then enters the Krebs Cycle.

CoA breaks off to gather more acetic acid. The Acetic acid is

broken down.

Produces most of the cell's energy in the form of NADH and FADH2… not

ATP

Does NOT require O2

Citric Acid Production

The Link reaction

Mitochondrion

Link Reaction pyruvate

3

NAD

Reduced NAD

coenzyme A

Carbondioxide

acetyl coenzyme A

2

NAD

Reduced NAD

The Krebs cycle

Citric Acid Production

 The Krebs Cycle

Mitochondrion

Krebs Cycle acetyl coA

citrateoxaloacetate

ATP Reduced co enzymes 3NADH

1 FADH

2 Carbon dioxide

64

2

SummaryAs a result of one turn of the Krebs cycle the cell makes:

1 FADH2 3 NADH1 ATP

However, each glucose produces two pyruvic acid molecules…. So the

total outcome is:

2 FADH2

6 NADH2 ATP

The key function of the Krebs cycle is to provide electrons for the Electron Transport Chain, the

production of ATP is a bonus.

The story so far

Phase Three:Oxidative Phosphorylation

• Function: Extract energy (in the form of electrons) from NADH and FADH2 in order to add a phosphate group to ADP to make ATP.

• Location: Mitochondria cristae.

Oxidative PhosphorylationRequires

NADH or FADH2

ADP and P

O2

Electron Transport Chain Uses NADH

• During the electrontransport chain, H+ is moved against a gradient.

• The energy needed to do this is supplied by electrons carried by NADH

What happens along the inner membrane of the mitochondria?

• The loss of electrons from NADH result in the addition of energy to protein pumps in the membrane resulting in a H+ being moved from the inside to the outside of the inner membrane

• This happens many times creating an imbalance (gradient) of H+.

Oxygen pulls electrons to keep them moving.

What happens along the inner membrane of the mitochondria?

• ATP is made as H+ ions are allowed back into the matrix of the mitochondria by a different protein (ATP synthase).

• The energy released by the “rush” of H+ is used by this enzyme to make ATP (kind of like a rush of water in a stream being used to turn a water wheel).Ultimately, aerobic respiration

produces ~36 ATP molecules from each individualglucose molecule.

The Electron Transport Chain

Cytochrome c

• Cytochrome c: • is one of the proteins of the electron

transport chain;• exists in all living organisms;• is often used by geneticists to

determine relatedness.

Chemiosmotic Hypothesis• Biologists still don’t know exactly how

ATP is made. • The best theory we have is called the

Chemiosmotic Hypothesis.

The Chemiosmotic Hypothesis

• proposes that the Electron Transport Chain energy is used to move H+ (protons) across the cristae membrane, and

• that ATP is generated as the H+ diffuse back into the matrix through ATP Synthase.

Electron Transport Chain

NAD

Reduced NAD

Carrier 2

ReducedCarrier 2

Carrier 3

ReducedCarrier 3 Carrier 4

ReducedCarrier 4

Water

Oxygen

ATPATP ATP

FAD enters here so 2 ATP produced

ATP Sum

• 10 NADH x 3 = 30 ATPs

• 2 FADH2 x 2 = 4 ATPs

• 2 ATPs (Gly) = 2 ATPs

• 2 ATPs (Krebs) = 2 ATPs

• Max = 38 ATPs per glucose

However...

Some energy (2 ATP’s) is used to shuttle the NADH from Glycolysis into the

mitochondria…..So, some biologists teach there is an actual ATP yield of 36

ATP’s per glucose.

The Final story